184,787 results
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2. A novel thermodynamic and heat and mass transfer model for the multicylinder dryer section of a paper machine
- Author
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Ali Anjomshoaa and Mazyar Salmanzadeh
- Subjects
Materials science ,business.product_category ,General Chemical Engineering ,Papermaking ,Evaporation rate ,04 agricultural and veterinary sciences ,02 engineering and technology ,Mechanics ,040401 food science ,Water consumption ,0404 agricultural biotechnology ,Paper machine ,020401 chemical engineering ,Section (archaeology) ,Mass transfer ,Heat transfer ,0204 chemical engineering ,Physical and Theoretical Chemistry ,business - Abstract
Modeling of the dryer section of a paper machine is of high importance in both designing and operation points of view. In this research, a novel thermodynamic and heat and mass transfer model has b...
- Published
- 2021
3. Numerical calculation of transient electric field considering space charge in oil-paper insulation of converter transformers
- Author
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Hongwei Cai, Jingxuan He, Zhiye Du, Liancheng Xiu, Fan Yi, and Yu Tian
- Subjects
Materials science ,Computer simulation ,Field (physics) ,Applied Mathematics ,Mechanics ,Space charge ,Finite element method ,Computer Science Applications ,law.invention ,Computational Theory and Mathematics ,law ,Electric field ,Transient (oscillation) ,Electrical and Electronic Engineering ,Transformer ,Voltage - Abstract
Purpose The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation. Design/methodology/approach The main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field. Findings A numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified. Originality/value A variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.
- Published
- 2021
4. Effect of multi‐factors on heterocharges for oil‐impregnated paper in converter transformer using modified charge transport model
- Author
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Heng Zhang, Jiefeng Liu, Shen Yan, Xianhao Fan, Yiyi Zhang, and Mingchen Shi
- Subjects
TK1001-1841 ,Materials science ,Computer simulation ,Distribution or transmission of electric power ,Energy Engineering and Power Technology ,Mechanics ,TK3001-3521 ,Conductivity ,Space charge ,law.invention ,Dynamic simulation ,Temperature gradient ,Production of electric energy or power. Powerplants. Central stations ,Control and Systems Engineering ,law ,Insulation system ,Electric field ,Electrical and Electronic Engineering ,Transformer - Abstract
The heterocharge accumulated in the oil‐paper insulation system of the converter transformer will enhance the local electric field and cause insulation deterioration. Numerical simulation is an effective method to analyze heterocharge. Currently, the numerical simulation of heterocharge is mainly based on the bipolar charge transport (BCT) model and the impurity ion transport (IIT) model. However, the effects of temperature, conductivity, and thickness of oil‐impregnated paper on charge transport have not been considered in these models. In view of this, a modified charge transport (MCT) model by introducing the Maxwell–Wagner model and heat conduction equation is proposed in this paper based on the BCT model and IIT model. Then, the influence of multi‐factors (temperature gradient, moisture content, and oil‐impregnated paper thickness) on heterocharge accumulation is investigated by using the MCT model. The simulation results obtained by the MCT model are more consistent with the experimental results than the BCT model, which proves the accuracy and superiority of the MCT model. Moreover, the increase in temperature gradient, moisture content, and oil‐impregnated paper thickness will enlarge the ion dissociation rate, conductivity, and trap density, and thus promote the generation of heterocharge. In that respect, the MCT model is expected to optimize the insulation design and provide a reference for space charge dynamic simulation.
- Published
- 2021
5. Comprehensive model of electromigrative transport in microfluidic paper based analytical devices
- Author
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Federico Schaumburg, Pablo A. Kler, and Claudio Luis Alberto Berli
- Subjects
Electrophoresis ,Paper ,Materials science ,Otras Ingenierías y Tecnologías ,Differential equation ,Capillary action ,Clinical Biochemistry ,Microfluidics ,INGENIERÍAS Y TECNOLOGÍAS ,02 engineering and technology ,ELECTROPHORESIS ,01 natural sciences ,Biochemistry ,Electromigration ,Analytical Chemistry ,Diffusion ,ELECTROOSMOTIC FLOW ,PAPER-BASED MICROFLUIDICS ,Diffusion (business) ,010401 analytical chemistry ,Electric Conductivity ,TRANSPORT PHENOMENA ,Mechanics ,Microfluidic Analytical Techniques ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Models, Chemical ,MATHEMATICAL MODELING ,Electric potential ,0210 nano-technology ,Transport phenomena ,Porous medium - Abstract
A complete mathematical model for electromigration in paper-based analytical devices is derived, based on differential equations describing the motion of fluids by pressure sources and EOF, the transport of charged chemical species, and the electric potential distribution. The porous medium created by the cellulose fibers is considered like a network of tortuous capillaries and represented by macroscopic parameters following an effective medium approach. The equations are obtained starting from their open-channel counterparts, applying scaling laws and, where necessary, including additional terms. With this approach, effective parameters are derived, describing diffusion, mobility, and conductivity for porous media. While the foundations of these phenomena can be found in previous reports, here, all the contributions are analyzed systematically and provided in a comprehensive way. Moreover, a novel electrophoretically driven dispersive transport mechanism in porous materials is proposed. Results of the numerical implementation of the mathematical model are compared with experimental data, showing good agreement and supporting the validity of the proposed model. Finally, the model succeeds in simulating a challenging case of free-flow electrophoresis in paper, involving capillary flow and electrophoretic transport developed in a 2D geometry. Fil: Schaumburg, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Kler, Pablo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Berli, Claudio Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina
- Published
- 2020
6. Liquid Wicking in a Paper Strip: An Experimental and Numerical Study
- Author
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Subhashis Patari and Pallab Sinha Mahapatra
- Subjects
Work (thermodynamics) ,Filter paper ,Capillary action ,General Chemical Engineering ,Microfluidics ,Evaporation ,General Chemistry ,Mechanics ,Article ,Chemistry ,Porous medium ,Water content ,Scaling ,QD1-999 - Abstract
In this decade, paper-based microfluidics has gained more interest in the research due to the vast applications in medical diagnosis, environmental monitoring, food safety analysis, etc. In this work, we presented a set of experiments to understand the physics of the capillary flow phenomenon through paper strips. Here, using the wicking phenomenon of the liquid in porous media, experimentally, we find out the capillary height of the liquid in filter paper at different time intervals. It was found that the Lucas-Washburn (L-W) model, as well as the evaporation model, fails to predict the capillary rise accurately. However, the detailed numerical solution shows a better similarity with the experimental results. We have also shown the different regimes of the wicking phenomenon using scaling analysis of the modified L-W model. The capillary rise method was applied to detect the added water content in milk. We used milk as a liquid food and found the added water content from the change in the capillary height at different concentrations of milk. Finally, results obtained from the paper-based device were verified with the commercially available lactometer data.
- Published
- 2020
7. The Study of Paper Capillarity with a Simple Technique
- Author
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Septia Ardiani, Handika Dany Rahmayanti, and Nurul Akmalia
- Subjects
Absorption of water ,Materials science ,Absorption time ,Capillary action ,Simple (abstract algebra) ,visual_art ,visual_art.visual_art_medium ,cardboard ,Mechanics ,Absorption (electromagnetic radiation) ,Tissue paper ,Physical quantity - Abstract
The study of water absorption by capillarity on paper with a simple technique is simple but important to do to inform the public about the characteristics of paper and for the development of research on the absorption of different types of paper. In this study, five types of paper were used, namely HVS paper, cardboard, tissue paper, concord paper and buffalo paper. In the capillary water absorption test on paper, the physical quantities analyzed are the water absorption, the absorption time and the water absorption rate. The capillarity of the paper is a comparison of the rate of water absorption by the paper which is analyzed using the straight line movement approach. The value of water absorption is estimated using the ratio between the height of water absorption and the time absorption. Based on the results of the capillary test on paper, it was found that the water absorption height for the five types of paper increases with increasing absorption time. The highest water absorption capacity is tissue paper, which is 7.4 ± 0.2 cm every 180 seconds. While the lowest water absorption capillarity is HVS paper which is 0.5 ± 0.1 cm at the 180th second. Cardstock and buffalo paper have almost the same water absorption value and are higher than HVS paper and match. The absorption speed which is almost the same between cardboard and buffalo paper is due to the fact that both belong to the same type of paper, namely printing paper.
- Published
- 2020
8. Modeling the effect of creep in paper fibres under the influence of external loading and changes in moisture
- Author
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P. Samantray, Marc G.D. Geers, Ron H. J. Peerlings, Thierry Massart, Mechanics of Materials, Group Peerlings, and EAISI Foundational
- Subjects
Paper ,Work (thermodynamics) ,Résistance et comportement des matériaux ,Materials science ,Moisture ,Scale (ratio) ,Hygro-mechanics ,Mechanics ,Creep ,Microstructure ,Sciences de l'ingénieur ,Power law ,Technologie matières ligneuses ,Mechanics of Materials ,Fibrous network ,Stress relaxation ,Connaissance des matériaux ,Relaxation (physics) ,Déformation, rupture matériaux ,General Materials Science ,Instrumentation - Abstract
Paper is a material exhibiting a complex microstructure that is composed of a network of fibres at the micro-level. When subjected to external loading or variations in moisture conditions over different time scales, changes in strain that are non-linear with respect to time are observed at the sheet level (macro-scale). In order to investigate this time-dependent behavior of paper, a creep power law model is implemented within a finite element approach at the level of single fibres. This rate-dependent model is found to capture experimental results available in literature for single fibres with a good agreement (both quantitatively and qualitatively). Based on the identified model at the level of single fibres, the time-dependent hygro-mechanical response is upscaled towards the network scale. To this end, random model networks of ribbon shaped fibres are generated and their response is simulated. The network-scale response, emerging from the rate-dependent fibre model, demonstrates the ability to predict the response of networks subjected to relaxation at a constant moisture level. The developed numerical model predicts lower values of overall stress response in single fibres as compared to networks. Also, stress relaxation predicted by the rate-dependent model in the cross-direction of the networks is in agreement with the experimental observations. Therefore, one of the remarkable findings of the present work is that the developed rate-dependent model is robust enough to capture the sheet scale response also qualitatively. Based on the study of these computational results, a better understanding is achieved regarding the influence of mechanical and rate-dependent properties of single fibres on the hygro-expansion of complete fibre networks, and in particular of paper sheets., info:eu-repo/semantics/published
- Published
- 2021
9. Numerical Simulation of Condensation Heat Transfer and Structural Optimization in Dryer of Paper Machine
- Author
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Mingliang Zheng
- Subjects
Materials science ,Paper machine ,business.product_category ,Computer simulation ,Condensation heat transfer ,Media Technology ,General Materials Science ,General Chemistry ,Mechanics ,business - Published
- 2020
10. Application of Cole–Cole model to transformer oil‐paper insulation considering distributed dielectric relaxation
- Author
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Sivaji Chakravorti, Biswendu Chatterjee, S. K. Ojha, and Prithwiraj Purkait
- Subjects
transformer oil-paper insulation ,dielectric testing techniques ,Materials science ,Transformer oil ,power transformer insulation ,lcsh:QC501-721 ,Energy Engineering and Power Technology ,Dielectric ,dielectric relaxation ,frequency domain ,Dielectric withstand test ,cable insulating oil ,law.invention ,ionic liquids ,oil-paper insulated transformers ,law ,elementary Debye relaxation properties ,lcsh:Electricity ,Cole–Cole diagram ,Time domain ,Electrical and Electronic Engineering ,time domain dielectric response ,Transformer ,transformer oil ,distributed dielectric relaxation ,paper ,dielectric mixtures ,Mechanics ,distribution density functions ,many-body interaction process ,Cole–Cole model ,polar liquids ,Nonlinear Sciences::Exactly Solvable and Integrable Systems ,Frequency domain ,dielectric materials ,insulation condition assessment ,Cole–Cole plots ,lcsh:Electrical engineering. Electronics. Nuclear engineering ,lcsh:TK1-9971 ,Cole–Cole equation ,Test data - Abstract
Researchers have been exploring dielectric testing techniques both in time and frequency domain for insulation condition assessment of oil-paper insulated transformers. In a practical dielectric system, dipoles are found to behave according to a distribution of elementary Debye relaxation properties. Suitable distribution density functions have been proposed to characterise such many-body interaction processes. Cole–Cole diagrams can be one of the methods for studying the nature of frequency dependency of dielectric materials of complex structure. Cole–Cole plots are commonly used for characterising different materials such as dielectric mixtures, ionic liquids, cable insulating oil, polar liquids etc. The scope of its application for assessing transformer oil-paper insulation considering distributed relaxation process has not been explored yet. The present contribution discusses mathematical formulations used for transforming the experimentally obtained time domain dielectric response test data to distribution domain and further to frequency domain for obtaining the Cole–Cole plots. Findings about the influence of various operating conditions and insulation status on the Cole–Cole diagram have been reported in this contribution. Results of tests on field transformers are also presented. This paper attempts to employ the features of Cole–Cole diagrams as potential indicators for analysing condition of the oil-paper insulation considering distributed relaxation process.
- Published
- 2019
11. Description of space charge transport in oil‐paper insulation using adaptive time‐stepping transient upstream finite element method
- Author
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Jiefeng Liu, Yiyi Zhang, Wei Zhang, Bing Gao, Mingchen Shi, and Shuo Liang
- Subjects
QC501-721 ,Materials science ,Electricity ,Time stepping ,Energy Engineering and Power Technology ,Upstream (networking) ,Electrical engineering. Electronics. Nuclear engineering ,Mechanics ,Transient (oscillation) ,Electrical and Electronic Engineering ,Space charge ,Finite element method ,TK1-9971 - Abstract
The charge transport and accumulation in oil–paper can cause the insulation degradation. So far, the most widely used model to simulate space charge transport and accumulation is the bipolar charge transport (BCT) model, which can well simulate the space charge dynamics. However, there are two shortcomings in the algorithms for solving the BCT model. One is that there is almost no use of vectorisation technology, which may increase the complexity of the algorithm, the other is the usage of fixed step size which might bring extra computation cost. In view of this, an adaptive time‐stepping transient upstream finite element method (FEM) is developed to solve the BCT model considering trapping/detrapping, as well as the recombination phenomenon under DC condition in this article. Then, a vectorisation technology is used in the method to optimise the algorithm. Moreover, the adaptive time‐stepping method is introduced in simulation to reduce computation time and calculation amount. Simulation results are obtained by programing and later presented, which are basically consistent with the corresponding experimental results. Therefore, the proposed method is expected to promote the optimization design of the oil–paper insulation system.
- Published
- 2021
12. Discussion on the Paper 'Combined Effects of Thermal Radiation and Magnetohydrodynamic on Peristaltic Flow of Nanofluids: Applications to Radiotherapy and Thermotherapy of Cancer' by Wahed Hasona et al
- Author
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A. Elogail Mostafa
- Subjects
Cancer Research ,Materials science ,Peristaltic flow ,medicine.medical_treatment ,Cancer ,Mechanics ,medicine.disease ,Radiation therapy ,Nanofluid ,Oncology ,Thermal radiation ,medicine ,Molecular Medicine ,Magnetohydrodynamic drive - Abstract
Recently, Hasona et al. Aimed to investigate the influence of thermal radiation and magnetic field on the peristaltic flow of Carreau nanofluid in a vertical asymmetric channel. The authors have considered the Joule heating, viscous dissipation, chemical reaction, Brownian motion, thermophoresis, Soret, and Dufour effects in their study. Several mistakes and typos were discovered in the study mentioned above, which would affect the obtained results. This report outlines some of these mistakes with suggested corrections to attract the readers' attention through a more in-depth insight into analyzing and exposing these defects.
- Published
- 2021
13. Experimental study on the friction stability of paper-based clutches concerning groove patterns
- Author
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Jikai Liu, Man Chen, He Yan Li, Biao Ma, and Liang Yu
- Subjects
Automatic transmission fluid ,Variable coefficient ,Materials science ,Mechanical Engineering ,02 engineering and technology ,Paper based ,Mechanics ,021001 nanoscience & nanotechnology ,Stability (probability) ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,General Energy ,0203 mechanical engineering ,Clutch ,Temperature difference ,0210 nano-technology ,Friction torque ,Groove (music) - Abstract
Purpose This paper aims to study and compare the friction stability of wet paper-based clutches with regard to the radial grooves (RG) and waffle grooves (WG). Design/methodology/approach This paper presents an experimental study of a wet clutch concerning the effect of groove patterns on the friction torque and surface temperature. The friction stabilities of RG and WG are investigated with the applied pressure, rotating speed and automatic transmission fluid (ATF) temperature taken into consideration. Findings The friction torque and surface temperature of WG are larger than those of RG under the same operating condition. The friction torque difference between RG and WG grows with the increase of applied pressure and narrows with the increase of ATF temperature. Additionally, their temperature difference expands via increasing the rotating speed and ATF temperature or reducing the applied pressure; in this way, not only the variable coefficient difference between RG and WG can be narrowed, but also the friction stability of the clutch can be improved dramatically. Originality/value This paper explains the thermodynamic differences between RG and WG; moreover, it is verified experimentally that WG has a better friction stability than RG.
- Published
- 2019
14. IMPROVING THE QUALITY OF MONITORING OF CIRCULATING AND WASTE WATERS OF PULP AND PAPER PRODUCTION
- Author
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Михаил (Mikhail) Семенович (Semenovich) Лурье (Lur'e), Юрий (Iuriy) Давыдович (Davydovich) Алашкевич (Alashkevich), Александр (Aleksandr) Владимирович (Vladimirovich) Смородько (Smorod'ko), and Ольга (Ol'ga) Михайловна (Mikhaylovna) Лурье (Lur'e)
- Subjects
погрешности монтажа ,Materials science ,installation errors ,Plant Science ,engineering.material ,vortex flowmeters ,Flow measurement ,sewage and circulating water ,Biomaterials ,symbols.namesake ,вихревые расходомеры ,Deflection (engineering) ,численное моделирование ,Measurement method ,Pulp (paper) ,Organic Chemistry ,flow body ,Paper production ,Mechanics ,Frequency spectrum ,Volumetric flow rate ,сточные и оборотные воды ,numerical simulation ,тело обтекания ,engineering ,symbols ,Strouhal number - Abstract
The issue of operation of submersible vortex flowmeters used in the systems of monitoring of circulating and waste waters of pulp and paper production is considered. It is shown that in the event of an error in the installation of these instruments, an additional error appears due to the angle between the axis of the flow body (TO) of the flowmeter and the axis of the pipeline. This error is related to the measurement method, which in turn leads to a change in the Strouhal number (Sh). The influence of this error leads to a change in the geometry of the flow part of the submerged flowmeter (the appearance of the angle β), which in turn leads to a change in the vortex formation process. Variants of finding this error are considered, from which the method of numerical modeling of hydrodynamic processes with subsequent processing by the method of experiment planning was chosen. For each investigated velocity of the fiber suspension and the angle of deflection of the TO axis, a graph of the frequency spectrum of the vortex formation process was obtained. Which was later used to find the number Sh. The dependence of the installation error ΔSh,% is presented. in the form of a response surface. It is revealed that the error in the installation of the TO, which is estimated by the angle β, is relatively small and varies linearly with increasing β. If the angle β = ± 3 ° is accepted as an allowable value, then the error in measuring the flow rate of the suspension will not exceed 0.25% over the entire range of velocities under consideration., Рассматривается вопрос особенностей эксплуатации погружных вихревых расходомеров, применяемых в системах мониторинга оборотных и сточных вод целлюлозно-бумажного производства. Показано, что при ошибке монтажа данных приборов может появляться дополнительная погрешность, появляющаяся вследствие угла между осью тело обтекания (ТО) расходомера и осью трубопровода. Данная погрешность связана с методом измерения, которая в свою очередь ведет к изменению числа Струхаля (Sh). Влияние данной погрешности приводит к изменению геометрии проточной части погружного расходомера (появление угла β), что способствует изменению процесса вихреобразования. Рассмотрены варианты нахождения данной погрешности из которых был выбран метод численного моделирования гидродинамических процессов с последующей обработкой методом планирования эксперимента. Для каждой исследуемой скорости волокнистой суспензии и угле отклонения оси ТО был получен график частотного спектра процесса вихреобразования на ТО, который впоследствии использовался для нахождения числа Sh. Представлена зависимость погрешности монтажа ΔSh,% в виде поверхности отклика. Выявлено, что погрешность монтажа ТО, которая оценивается углом β, является относительно небольшой иизменяется сувеличением β линейно. Если принять в качестве допустимой величины угла β=±3°, то погрешность измерения расхода суспензии не будет превосходить 0,25% во всем диапазоне рассматриваемых скоростей.
- Published
- 2018
15. Crack growth and energy dissipation in paper
- Author
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Juha Koivisto, Tero Mäkinen, Mikko J. Alava, Markus Ovaska, Maryam Hanifpour, Complex Systems and Materials, Department of Applied Physics, Aalto-yliopisto, and Aalto University
- Subjects
Digital image correlation ,Multidisciplinary ,Materials science ,Nonlinear phenomena ,lcsh:R ,lcsh:Medicine ,Hot spot (veterinary medicine) ,02 engineering and technology ,Mechanics ,Dissipation ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,law.invention ,law ,Intermittency ,0103 physical sciences ,Paper sample ,lcsh:Q ,Fracture process ,010306 general physics ,0210 nano-technology ,lcsh:Science - Abstract
Here, we follow the stable propagation of a roughening crack using simultaneously Digital Image Correlation and Infra-Red imaging. In a quasi-two-dimensional paper sample, the crack tip and ahead of that the fracture process zone follow the slowly, diffusively moving “hot spot” ahead of the tip. This also holds when the crack starts to roughen during propagation. The well-established intermittency of the crack advancement and the roughening of the crack in paper are thus subject to the dissipation and decohesion in the hot spot zone. They are therefore not only a result of the depinning of the crack in a heterogeneous material.
- Published
- 2018
16. Nonlinear Dielectric Response Characteristics of Damp Oil-Paper Insulation and Application of H-W Model in Time-Frequency Conversion
- Author
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Lijun Yang, Zhen Qin, Wei Li, Xingjun Guo, Yingxin Deng, Wei Nie, and Ruijin Liao
- Subjects
010302 applied physics ,Work (thermodynamics) ,Materials science ,Mechanics ,01 natural sciences ,Domain (software engineering) ,Time–frequency analysis ,symbols.namesake ,Nonlinear system ,Fourier transform ,Frequency domain ,0103 physical sciences ,symbols ,Time domain ,Electrical and Electronic Engineering ,Debye model - Abstract
In this work, the extended Debye model or Fourier transform is adopted to convert the polarization and depolarization current test results from the time domain into the frequency domain at low frequencies, thereby shortening the test time but producing large errors when the oil-paper insulation exhibits nonlinear characteristics. The voltage-current response characteristics of samples with three different moisture contents are tested to study the influence of moisture on the nonlinear characteristics. Hammerstein-Wiener (H-W) equivalent mathematical model is proposed for time-frequency domain conversion, and the results from this model and two formal methods are compared. The findings show that the errors of the two conventional methods increase with nonlinearity. The H-W model accurately depicts the nonlinear dielectric response of oil-paper insulation and thus can provide high-precision time-frequency domain conversion data.
- Published
- 2020
17. Liquid film thickness of two‐phase slug flows in capillary microchannels: A review paper
- Author
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Yuri S. Muzychka, Amin Etminan, and Kevin Pope
- Subjects
Liquid film ,Microchannel ,Materials science ,biology ,Capillary action ,Slug ,General Chemical Engineering ,Phase (matter) ,Two-phase flow ,Mechanics ,Slug flow ,biology.organism_classification - Published
- 2021
18. Pressure as a Motivator: A Conceptual Paper on the Physics of Stress and Flow
- Author
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Michael G. Frino, Matthew Toppin, and Katie P. Desiderio
- Subjects
Stress (mechanics) ,Physics ,Flow (mathematics) ,General Medicine ,Mechanics - Published
- 2021
19. Numerical and experimental studies on the characteristics of friction torque based on wet paper-based clutches
- Author
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Man Chen, Liang Yu, Jikai Liu, Liangjie Zheng, Biao Ma, and Heyan Li
- Subjects
Materials science ,Mechanical Engineering ,02 engineering and technology ,Surfaces and Interfaces ,Paper based ,Mechanics ,Growth model ,021001 nanoscience & nanotechnology ,Stability (probability) ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Heat transfer ,Torque ,Clutch ,0210 nano-technology ,Friction torque - Abstract
A coupled numerical multi-physics model is developed to study the generation and variation mechanisms of friction torque, including fluid lubricating, micro-contact, sliding and heat transfer among the friction components. The engagement experiment is conducted to verify the accuracy of numerical model and investigate the stability of friction torque. The results show that the most significant operating factor affecting the friction stability is the applied pressure, followed by the rotating speed and the ATF temperature. Simultaneously, the operating factors have great influence on the torque response, engagement time and temperature rise. Moreover, the growth model of friction torque can be divided into two categories: one is increasing linearly and the other is concave parabolic rising.
- Published
- 2019
20. Charging and Discharging Current Measurements and Impact of Polarization Dynamics on Electric Field Modeling in HVDC Paper-Insulated Cables
- Author
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Pasquale Cambareri, Carlo De Falco, Luca Di Rienzo, Paolo Seri, Gian Carlo Montanari, Cambareri P., De Falco C., Di Rienzo L., Seri P., and Montanari G.C.
- Subjects
Permittivity ,Electric fields ,Materials science ,General Computer Science ,Field (physics) ,020209 energy ,02 engineering and technology ,Dielectric ,HVDC transmission ,01 natural sciences ,Electric fields, Transient analysis, Current measurement, HVDC transmission, Permittivity, Mathematical model, Dielectrics ,Transient analysis ,Mathematical model ,electric field transient ,dielectric polarization ,Insulation system ,Electric field ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,General Materials Science ,Polarization (electrochemistry) ,010302 applied physics ,General Engineering ,Mechanics ,Current measurement ,HVDC cables ,Dielectrics ,electrical insulation ,lcsh:Electrical engineering. Electronics. Nuclear engineering ,Transient (oscillation) ,lcsh:TK1-9971 ,Voltage - Abstract
Accurate modeling and simulation of electric field transients in HVDC cables is an important support to optimize insulation system design and to evaluate the influence of voltage transients and steady-state conditions on accelerated ageing mechanisms and insulation reliability. Traditionally, field models considering time-independent permittivity and conductivity are used, but this approach neglects polarization mechanisms and charge trapping-detrapping phenomena. This article includes polarization dynamics in the field model and shows that its impact on transient electric field simulations in HVDC paper-insulated cables can be significant. A method is presented to infer the model parameters from experimental polarization and depolarization current measurements.
- Published
- 2021
21. FLUID FLOW BODIES FOR THE PULP AND PAPER INDUSTRY
- Author
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Yuriy Davidovich Alashkevich, Ol'ga Mikhaylovna Lur’e, Mikhail Semenovich Lur’e, and Aleksandr Sergeyevich Frolov
- Subjects
Physics ,010405 organic chemistry ,Organic Chemistry ,Flow (psychology) ,Plant Science ,Mechanics ,Vortex generator ,01 natural sciences ,Noise (electronics) ,0104 chemical sciences ,Working range ,Volumetric flow rate ,Biomaterials ,010404 medicinal & biomolecular chemistry ,symbols.namesake ,Flow velocity ,symbols ,Strouhal number ,Suspension (vehicle) - Abstract
The question of the use of vortex flowmeters with different versions of the flow body (TO) under operating conditions on the technological lines of pulp and paper production is considered. It is shown that when using different TO in vortex flowmeters, an error occurs in the working range of speeds (flow rates). The observed error arises due to a change in the Strouhal number (Sh) and is associated with the measurement method. In this case, the Strouhal number begins to depend not only on the TO used as a vortex generator, but also on the flow velocity and the concentration of the fibrous suspension. As the main comparative factor for the investigated TOs, the force action on the sensitive element (flexible electrode) located inside the TO was taken. The study was carried out in several stages using numerical modeling and experimental design method. According to the results of a numerical study, the dependence of the Strouhal number (Sh) on the flow rate (V) and the concentration of the suspension (c) is presented. In a comparative analysis of the deviation of the Strouhal number from the average values, it was revealed that MOT No. 1 has a minimal effect on the concentration of the suspension in the working range of flow rates (± 0.5%). This circumstance makes it possible to verify and test flow meters with such maintenance in conventional pouring installations. The analysis of the maintenance with respect to the signal-to-noise ratio shows that the purest signal is generated by the cylindrical maintenance (maintenance No. 3), and maintenance No. 2 and No. 1 have noticeably large noise. The differences are explained by the absence on the surface of a cylindrical TO of extra protrusions, faces, which leads to a smoother flow of a suspension around its surface, as well as to a decrease in internal spurious noise.
- Published
- 2020
22. BREAKDOWN VOLTAGE OF MICRON RANGE AIR INCLUSIONS IN CAPACITOR PAPER
- Author
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O. O. Palchykov
- Subjects
Permittivity ,Materials science ,электрический пробой ,модель конденсаторной бумаги ,микронный промежуток ,электростатическое поле ,метод конечных элементов ,finite element method ,Electrical breakdown ,electrostatic field ,Mechanics ,Finite element method ,TK1-9971 ,law.invention ,electrical breakdown ,model of capacitor paper ,micron gap ,Capacitor ,Volume (thermodynamics) ,law ,621.3.048.8 ,Electric field ,Breakdown voltage ,Electrical engineering. Electronics. Nuclear engineering ,Intensity (heat transfer) - Abstract
Purpose. To substantiate the breakdown mechanism of capacitor paper on the basis of numerical-field models with segmented cross-sections of cylindrical volumes of air and water, and also use the proposed models to determine the breakdown strength of air in micron-sized gaps under normal conditions. Methodology. The model bases on a finite element solution to an electrostatic problem in a volume of capacitor paper consisting of cellulose and pores with air and water. First, the possible scenarios for the growth of breakdown in capacitor paper are analyzed and to the conclusion is made, that complete breakdown developed from a partial breakdown in the air cavity. A brand of capacitor paper is chosen in such a way that when its thickness changed, the breakdown strength of the electric field changed over a wide range. Then, for the paper with the lowest average electric field intensity the possibility of explaining the complete breakdown by the breakdown of air segments on the basis of the Paschen dependence is checked. Further points of the obtained dependence by constructing models of papers of the same brand and a different thickness under the assumption of the similarity of electrostatic fields are determined. As such a criterion, the constancy of the equivalent effective permittivity are taken. Results. The dependence of the breakdown strength of the air in the range of 1.36...5.54 μm under normal conditions is determined. The obtained relationship is between the Peschot and Taev curves. Originality. For the first time, the possibility of indirectly estimation the breakdown strength of an insulating material using an electrostatic field model is indicated. Practical value. The proposed method for the numerical calculation of the breakdown voltage of air inclusions in the presence of water inclusions in the thickness of solid insulation can be applied to other types of solid thin-layer insulation., Полученная в работе зависимость напряженности электрического поля воздуха от длины разрядного промежутка удовлетворительно объясняет значения пробивных напряжений образцов конденсаторной бумаги при изменении их марок и толщины. Построена зависимость пробивной напряженности воздуха при нормальных условиях в диапазоне 1,36…5,54 мкм на основании расчета электростатических полей в моделях конденсаторной бумаги с сегментными поперечными сечениями цилиндрических объемов воздуха и воды. Проведено сопоставление полученной зависимости с известными экспериментальными данными. Полученные данные в диапазоне 2…5,54 мкм наиболее близки экспериментальным данным Пешо.
- Published
- 2020
23. Comment on the paper 'MHD slip flow of a dissipative Casson fluid over a moving geometry with heat source/sink: A numerical study, C.S.K. Raju, N. Sandeep, Acta Astronautica 133 (2017) 436–443'
- Author
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Asterios Pantokratoras
- Subjects
Source sink ,Physics ,Slip flow ,Dissipative system ,Aerospace Engineering ,Casson fluid ,Mechanics ,Magnetohydrodynamics - Published
- 2021
24. [Paper] Droplet Formulation Method for Viscous Fluid Injection Considering the Effect of Liquid-Liquid Two-Phase Flow
- Author
-
Nobuhiko Mukai, Masamichi Oishi, Takuya Natsume, and Marie Oshima
- Subjects
Surface tension ,Fluid simulation ,Computer science ,Signal Processing ,Media Technology ,Particle method ,Liquid liquid ,Two-phase flow ,Mechanics ,Viscous liquid ,Computer Graphics and Computer-Aided Design - Published
- 2021
25. Aging of oil-impregnated paper at different frequencies
- Author
-
Weichuan Zhao and Mohamad Ghaffarian Niasar
- Subjects
Work (thermodynamics) ,Materials science ,Computer Science::Neural and Evolutionary Computation ,aging ,Oil-impregnated paper ,Mechanics ,Time–frequency analysis ,breakdown voltage ,high frequency electric stress ,Breakdown strength ,lifetime curve ,Waveform ,Breakdown voltage ,Peak value ,Voltage ,Weibull distribution - Abstract
In this work, breakdown strength and lifetime curve of oil-impregnated paper (OIP) are compared at 50Hz and 1500 Hz. For the ramp breakdown tests, sinusoidal voltage ramp of 1 kVp/s is used. The ramp breakdown experiments is conducted on OIP samples made of single and double sheets of OIP. Weibull plots and interpretation of the results are presented. In order to obtain lifetime curves, a step sinusoidal voltage waveform whose peak value is close to the minimum OIP ramp breakdown voltage is applied on single sheet of OIP samples. Time to breakdown is measured, and each experiment is repeated between 20-30 times to obtain good statistical results. The experiments were focused on four different voltage levels and the lifetime curves are plotted for those two target frequencies. Parameters of the lifetime curves are extracted and the interpretation is given.
- Published
- 2021
26. Application of Paper Folding Technique to Three-Dimensional Space Sound Absorber with Permeable Membrane: Case Studies of Trial Productions
- Author
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Kimihiro Sakagami, Hirotaka Suzuki, Masahiro Toyoda, Takeshi Okuzono, and Nao Koyanagi
- Subjects
Materials science ,Semipermeable membrane ,Mechanics ,Folding (DSP implementation) ,Sound Absorber ,Three-dimensional space - Abstract
The authors propose a space sound absorber made of a permeable membrane (PM), including woven or non-woven fabrics in three-dimensional shapes, e.g., cylinder, rectangle, etc. The proposed absorbers are examined by experimental measurements and boundary element analyses, and it is found that they can be effectively used especially for middle and high frequencies. In order to develop these absorbers for wider applications, it would be desirable to give them additional values and functions, particularly to elaborate on their design. Supposing that they could also be used for lighting equipment, such as lampshades as one of the applications, pilot studies on pseudo-cylindrical, and pseudo-spherical PM space absorbers with uneven surfaces produced by paper-folding (origami technique) are carried out. The pseudo-cylindrical concave curves (PCCC) shell shape has been proven as a suitable form for a lampshade, and the pseudo-spherical concave curves (PSCC) shell shape is an application of PCCC. In this paper, PCCC and PSCC shell shapes are applied to three-dimensional PM space absorbers, and trials are conducted using PMs selected by flow resistance measurements and preliminary simulations. The sound absorptivity of the specimens is measured in a reverberation chamber, and their absorptivity is 0.6 (PCCC case) and 0.4 (PSCC case) at mid-high frequencies.
- Published
- 2020
27. Radial Wicking of Biological Fluids in Paper
- Author
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Rico F. Tabor, Michael J. Hertaeg, Joseph D. Berry, and Gil Garnier
- Subjects
Capillary action ,Drop (liquid) ,02 engineering and technology ,Surfaces and Interfaces ,Mechanics ,Plasma ,Penetration (firestop) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Physics::Fluid Dynamics ,Surface tension ,Contact angle ,13. Climate action ,Electrochemistry ,General Materials Science ,Wetting ,Dewetting ,0210 nano-technology ,Spectroscopy - Abstract
In this study, we analyze stain growth kinetics from droplets of biological fluids such as blood, plasma, and protein solutions on paper both experimentally and numerically. The primary difference of biological fluids from a simple fluid is a significant wetting/dewetting hysteresis in paper. This becomes important in later stages of droplet wicking, after the droplet has been completely absorbed into paper. This is shown by anomalous power dependence of area with time in the later stages of radial wicking. At early stages, current numerical wicking models can predict stain growth of biological fluids. However, at later stages, the introduction of hysteresis complicates modeling significantly. We show that the cause of the observed hysteresis is due to contact angle effects and that this is the dominant mechanism that leads to the anomalous stain growth kinetics measured uniquely in biological fluids. Results presented will streamline the design process of paper-based diagnostics, allowing a modeling approach instead of a trial and error method.
- Published
- 2020
28. Multiphysics simulation of paper curl due to moisture transport
- Author
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Seungjun Lee, Taehan Kim, Gil Ho Yoon, Junseong Woo, Byoungho Yoo, and Woon Kyung Kim
- Subjects
Curl (mathematics) ,0209 industrial biotechnology ,Materials science ,Moisture ,Viscoplasticity ,Mechanical Engineering ,Multiphysics ,02 engineering and technology ,Mechanics ,Physics::Classical Physics ,Curvature ,Finite element method ,Computer Science::Other ,Curling ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,0203 mechanical engineering ,Mechanics of Materials ,Material properties ,Physics::Atmospheric and Oceanic Physics - Abstract
The moisture transport at the fuser nip of printers is postulated to be the main reason for paper curls. However, the fundamental mechanisms of paper curling remain unclear. Observing the moisture transport inside a sheet of paper through experiments is difficult because moisture transport rapidly occurs in a micro-scale thickness. Therefore, developing a theoretical model is crucial to understand the mechanisms of paper curling and to control the curls. In this study, we proposed a multiphysics model that includes the moisture and heat transport and mechanical deformation. The elasticity, plasticity, viscosity, and expansion caused by moisture were considered in the mechanical model to describe the complex material characteristics of paper. The curvature of curls was calculated using an effective two-spring model. The mechanisms of curling in printers and the direction of curls were understood through finite element simulations. The proposed model can qualitatively predict the paper curls observed in experiments. The temperature- and moisture-dependent material properties of paper will be studied in the future to improve the proposed model.
- Published
- 2020
29. Breakdown and streamer behavior in double-layer oil-paper insulation under impulses of varying front time
- Author
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Qiaogen Zhang, Heli Ni, Chong Guo, and Tao Wen
- Subjects
010302 applied physics ,Imagination ,Materials science ,Impulse testing ,Dielectric strength ,Physics::Instrumentation and Detectors ,media_common.quotation_subject ,Mechanics ,Impulse (physics) ,01 natural sciences ,Space charge ,Voltage amplitude ,Physics::Plasma Physics ,0103 physical sciences ,Breakdown voltage ,Electrical and Electronic Engineering ,media_common ,Voltage - Abstract
The breakdown and streamer behavior in double-layer oil-paper insulation under impulses of varying front time were investigated in this study to determine the prebreakdown process in oil-paper insulation. The relationships between front times and breakdown characteristics were investigated and impulse-polarity-dependent variations were observed. The complete impulse breakdown process and precise role of front time were assessed as per streamer initiation and streamer propagation based on emitted light signals and shadow images. The re-initiation of streamers in non-first oil gaps was determined to be the key factor in breakdown as-dominated by applied voltage and space charge accumulation. The initiation and propagation times of streamers were observed to find that the streamers tend to propagate at phases with higher voltage amplitude as front time increases, which facilitates streamer re-initiation and thus decreases the breakdown voltage. Equivalent applied voltages during streamer propagation were further calculated to quantitatively investigate the effect of front time on streamer propagation.
- Published
- 2020
30. Comments on the paper 'Thermal radiation and variable electrical conductivity effects on MHD peristaltic motion of Carreau nanofluids: Radiotherapy and thermotherapy of oncology treatment'
- Author
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M. A. Elogail
- Subjects
Fluid Flow and Transfer Processes ,Radiation therapy ,Nanofluid ,Materials science ,Thermal radiation ,Electrical resistivity and conductivity ,medicine.medical_treatment ,medicine ,Mechanics ,Magnetohydrodynamics ,Condensed Matter Physics ,Peristalsis - Published
- 2020
31. Investigation of Two-Phase Rimming Flow and Heat Transfer Inside Rotational Paper Cylinder Dryers Using Three Multiphase Computational Models
- Author
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Chris Kononchek, Victor Barboza Pereira, Ting Wang, Joseph V. D'Amico, and Hamed Abdul Majeed
- Subjects
Fluid Flow and Transfer Processes ,Computational model ,Materials science ,Flow (mathematics) ,Phase (matter) ,Heat transfer ,General Engineering ,Cylinder ,General Materials Science ,Mechanics ,Condensed Matter Physics - Abstract
The paper industry uses rotating cylinder dryers that employ steam to heat the paper web moving over the cylinder outer walls. As steam condenses, the condensate is accumulated inside the dryers and evacuated using siphons. The form of condensate motion occurring inside a rotating dryer consists of three modes: puddling, cascading, or rimming. To help improve the drying performance, it is important to understand the fundamental thermal-fluid physics in the rotational dryer. Thus, the objectives of this study are to (a) investigate the dynamic two-phase flow and heat transfer behavior inside the rotational dryer at different rotational speeds; (b) employ three different multiphase computational models, the Volume of Fluid (VOF) model, the Mixture model, and the Eulerian–Eulerian (E–E) model; and compare their results. The results show that the E–E model better captures the physics of condensate behavior inside the dryer. It also predicts very well the rimming speed in comparison with the empirical correlation although it takes longer computational time than the VOF model. The mixture model does not adequately capture the cascade and rimming physics due to excessive liquid dispersion. Based on the results, the categorization of the thermal-flow behavior of the liquid layer is expanded from the traditional three phases to five phases: puddling, transitional cascading, cascading, transitional rimming, and steady rimming. Generally, the heat transfer increases during the initial puddling period, followed by oscillatory attenuation during the cascade period, and finally reaches the steady-state after rimming is achieved.
- Published
- 2022
32. Heat and Mass Transfer on Free Path Portions in Drying Paper in Multicylinder Contact-Convective Units
- Author
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A. G. Nikolaeva, V. Yu. Lakomkin, and E. N. Gromova
- Subjects
Convection ,Imagination ,Chemical substance ,Materials science ,Convective heat transfer ,media_common.quotation_subject ,General Engineering ,Mechanics ,Condensed Matter Physics ,Physics::Fluid Dynamics ,Mass transfer ,Path (graph theory) ,Water content ,Physics::Atmospheric and Oceanic Physics ,media_common - Abstract
Convective heat- and mass-transfer processes are considered that occur on free surfaces of a wet paper web in an air medium with a single-row arrangement of drying cylinders. Calculated dependences are determined making it possible to predict the duration of the process of drying the paper web in multicylinder contact-convective units.
- Published
- 2019
33. Mechanism and numerical model of bubble effect in oil-paper insulation based on microtubule model
- Author
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Chenhao Jia, Tao Zhao, Yixin Tong, Liu Yunpeng, and Nijie Chao
- Subjects
010302 applied physics ,Pressboard ,Materials science ,Bubble ,Mechanics ,Microstructure ,01 natural sciences ,Ideal gas ,law.invention ,Physics::Fluid Dynamics ,law ,0103 physical sciences ,Growth rate ,Electrical and Electronic Engineering ,Transformer ,Porosity ,Physical quantity - Abstract
In this paper, a numerical model of bubble evolution is established by studying the microstructure of pressboard and the physical process of bubble generation. In the model, the porous structure of fibers is equivalent to microtubules, the gases in the bubbles are classified into two categories, and the ideal gas state equation is used to describe the bubble state. Then the pressure conditions at the bubble boundary and the evaporation rate of water are taken as solution conditions to solve the physical quantities in the state equation. The numerical model provides a new way to calculate the initial temperature of bubble escape (ITBE). And the bubble evolution inside the pressboard is obtained which is hard to be observed in experiment. After that, the influences of moisture content of pressboard and cellulose aging on ITBE in the numerical model are discussed. The model results show that the expansion rate of bubble is not uniform. Bubble growth is slow in the early stage of temperature rise, when the temperature reaches a certain threshold the growth rate of bubble radius increases significantly, which is of great significance to the temperature limit on oil-immersed power transformers.
- Published
- 2020
34. A flow chemiluminescence paper-based microfluidic device for detection of chromium (III) in water
- Author
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Huijie Li, Chunsun Zhang, Rui Liu, Peng Zhang, and Qiuping Shang
- Subjects
Work (thermodynamics) ,Gravity (chemistry) ,Materials science ,Capillary action ,paper-based microfluidics ,Microfluidics ,Biomedical Engineering ,Medicine (miscellaneous) ,chemistry.chemical_element ,02 engineering and technology ,lcsh:Technology ,01 natural sciences ,law.invention ,Chromium ,law ,gravity flow ,lcsh:QC350-467 ,Chemiluminescence ,capillary flow ,lcsh:T ,010401 analytical chemistry ,detection of chromium (iii) ,Mechanics ,Paper based ,021001 nanoscience & nanotechnology ,chemiluminescence ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,chemistry ,Flow (mathematics) ,0210 nano-technology ,wax screen-printing ,lcsh:Optics. Light - Abstract
In this work, a solely gravity and capillary force-driven flow chemiluminescence (GCF-CL) paper-based microfluidic device has been proved for the first time as a new platform for inexpensive, usable, minimally-instrumented dynamic chemiluminescence (CL) detection of chromium (III) [Cr(III)], where an appropriate angle of inclination between the loading and detection zones on the paper produces a rapid flow of CL prompt solution through the paper channel. For this study, we use a cost-effective paper device that is manufactured by a simple wax screen-printing method, while the signal generated from the Cr(III)-catalyzed oxidation of luminol by H2O2 is recorded by a low-cost and luggable CCD camera. A series of GCF-CL affecting factors have been evaluated carefully. At optimal conditions, two linear relationships between GCF-CL intensities and the logarithms of Cr(III) concentrations are obtained in the concentration ranges of 0.025–35[Formula: see text]mg/L and 50–500[Formula: see text]mg/L separately, with the detection limit of 0.0245[Formula: see text]mg/L for a less than 30[Formula: see text]s assay, and relative standard deviations (RSDs) of 3.8%, 4.5% and 2.3% for 0.75, 5 and 50[Formula: see text]mg/L of Cr(III) ([Formula: see text]). The above results indicate that the GCF-CL paper-based microfluidic device possesses a receivable sensitivity, dynamic range, storage stability and reproducibility. Finally, the developed GCF-CL is utilized for Cr(III) detection in real water samples.
- Published
- 2019
35. Vibration analysis of paper machine’s asymmetric tube roll supported by spherical roller bearings
- Author
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Behnam Ghalamchi, Aki Mikkola, Janne Heikkinen, Jussi Sopanen, Jari Juhanko, Petri Kuosmanen, Raine Viitala, LUT University, Department of Mechanical Engineering, Aalto-yliopisto, and Aalto University
- Subjects
Timoshenko beam theory ,Materials science ,Spherical roller bearings ,Spherical roller bearing ,Aerospace Engineering ,02 engineering and technology ,01 natural sciences ,law.invention ,Physics::Fluid Dynamics ,Paper machine bearing defect ,0203 mechanical engineering ,law ,0103 physical sciences ,010301 acoustics ,Asymmetric rotor ,Civil and Structural Engineering ,Bearing (mechanical) ,ta214 ,Waviness ,Rotor (electric) ,Mechanical Engineering ,Mechanics ,Computer Science Applications ,Vibration ,Bearing waviness ,020303 mechanical engineering & transports ,Control and Systems Engineering ,Rolling-element bearing ,Signal Processing ,Subcritical vibrations ,Paper machine roll ,Beam (structure) - Abstract
This paper presents a simulation method that is used to study subcritical vibrations of a tube roll in a paper machine. This study employs asymmetric 3D beam elements based on the Timoshenko beam theory. An asymmetric beam model accounts for varying stiffness and mass distributions. Additionally, a detailed rolling element bearing model defines the excitations arising from the set of spherical roller bearings at both ends of the rotor. The results obtained from the simulation model are compared against the results from the measurements. The results indicate that the waviness of the bearing rolling surfaces contributes significantly to the subcritical vibrations while the asymmetric properties of the tube roll have only a fractional effect on the studied vibrations.
- Published
- 2018
36. Axisymmetric acoustophoresis for paper pulp concentration
- Author
-
Pierre Gelinas, Maxime Bilodeau, Romain Le Magueresse, Robert Schiavi, Tamara Krpic, and Nicolas Quaegebeur
- Subjects
Materials science ,Acoustics and Ultrasonics ,QC221-246 ,02 engineering and technology ,engineering.material ,Acoustic levitation ,01 natural sciences ,Inorganic Chemistry ,Paper pulp concentration ,symbols.namesake ,stomatognathic system ,Pulp flow simulation ,Stokes' law ,Acoustophoresis ,Chemical Engineering (miscellaneous) ,Environmental Chemistry ,Radiology, Nuclear Medicine and imaging ,Original Research Article ,Acoustic radiation force ,QD1-999 ,Turbulence ,Pulp (paper) ,Papermaking ,010401 analytical chemistry ,Organic Chemistry ,Acoustics. Sound ,Mechanics ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Chemistry ,stomatognathic diseases ,Fiber suspension flow ,symbols ,engineering ,Particle ,Particle size ,0210 nano-technology - Abstract
Highlights • Numerical simulations of acoustophoresis in pulp flow is conducted. • Parametric study of fiber characteristics, pulp flow regimes and acoustic parameters are conducted. • A feasibility study of industrial acoustophoresis for pulp concentration is performed. • A potential concentration gain of 15% is obtained experimentally., In pulp and paper mills, mechanical processes such as screening and washing are commonly used to remove accumulated solid suspensions and concentrate the pulp. For environmental reasons and to optimize paper production, an emerging challenge is to develop alternative methods to concentrate paper pulp between 3 % and 6 % consistency for which the mixed pulp-water flow is complex. Among the proposed solutions in the literature, solutions based on acoustic levitation, also referred as acoustophoresis, of low-consistency pulp have been demonstrated as a potential solution for efficient pulp concentration and water recirculation. However, no sensitivity analysis on the ultrasound and physical parameters was proposed, limiting the extension to a realistic application. Thus, this paper presents a numerical modeling of acoustophoresis for pulp flow concentration in a pipe. For this purpose, the pulp flow is defined as a pseudo-homogenous fluid with a turbulent Low Re k- ∊ formalism, and the pulp particles are considered spherical and deflected by two acoustic forces, namely the acoustic radiation force and the Stokes drag force, both induced by an ultrasound wave generated along the walls of a circular pipe. The combined action of these two forces in the pulp flow enables to concentrate the particles at the center of the pipe. The influences of particle size and mechanical properties, fluid properties and ultrasound parameters are analyzed within a parametric study to optimize the particle deflection and the pulp concentration. The experimental feasibility of the industrial use of acoustophoresis for the concentration of paper pulp is demonstrated with a concentration gain up to 15 %.
- Published
- 2021
37. Wicking in Paper Strips under Consideration of Liquid Absorption Capacity
- Author
-
Surasak Kasetsirikul, Nam-Trung Nguyen, and Muhammad J. A. Shiddiky
- Subjects
Materials science ,Capillary action ,paper-based microfluidics ,Flow (psychology) ,02 engineering and technology ,STRIPS ,absorption capacity ,01 natural sciences ,Capacitance ,Analytical Chemistry ,law.invention ,Physics::Fluid Dynamics ,lcsh:Biochemistry ,law ,wicking ,lcsh:QD415-436 ,Physical and Theoretical Chemistry ,Absorption (electromagnetic radiation) ,Electronic circuit ,ComputingMethodologies_COMPUTERGRAPHICS ,010401 analytical chemistry ,Mechanics ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Electrical network ,electrical circuit analogy ,Current (fluid) ,0210 nano-technology - Abstract
Paper-based microfluidic devices have the potential of being a low-cost platform for diagnostic devices. Electrical circuit analogy (ECA) model has been used to model the wicking process in paper-based microfluidic devices. However, material characteristics such as absorption capacity cannot be included in the previous ECA models. This paper proposes a new model to describe the wicking process with liquid absorption in a paper strip. We observed that the fluid continues to flow in a paper strip, even after the fluid reservoir has been removed. This phenomenon is caused by the ability of the paper to store liquid in its matrix. The model presented in this paper is derived from the analogy to the current response of an electric circuit with a capacitance. All coefficients in the model are fitted with data of capillary rise experiments and compared with direct measurement of the absorption capacity. The theoretical data of the model agrees well with experimental data and the conventional Washburn model. Considering liquid absorption capacity as a capacitance helps to explain the relationship between material characteristics and the wicking mechanism.
- Published
- 2020
38. Study of the Dynamics of Insulating Paper Electrical Breakdown
- Author
-
Nataliya M. Zhuravleva, Denis A. Trubin, Dmitry Kiesewetter, and Alexandr S. Reznik
- Subjects
Materials science ,Electric breakdown ,Electrical breakdown ,Electrical insulation paper ,Breakdown voltage ,Mechanics ,Total energy ,Voltage - Abstract
The dynamics of electric breakdown of insulating paper with different technical characteristics is investigated. In addition to the value of the breakdown voltage the following parameters: the rate of change of the total energy released in the discharge gap during one half-cycle of industrial frequency voltage, changing the voltage of the occurrence of electrical discharges in each half-cycle in the process of the breakdown development, as well as the statistical characteristics of breakdown were measured. The voltampere characteristics of the discharge within one half-cycle at different stages of development of electric breakdown are presented. The difference between the dynamics of electric breakdown of dry insulating paper and paper-impregnated insulation is demonstrated. On the basis of the obtained data, an assumption about the possibility of determining some parameters of the structure of the insulating paper is annonced.
- Published
- 2020
39. ROTATIONAL PAPER PULP VISCOMETER WITH MEASUREMENT AT TWO SHEAR SPEEDS
- Author
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O. V. Kril, O. M. Romaniuk, В. A. Kril, and H. B. Krykh
- Subjects
rotational viscometer ,Materials science ,Pulp (paper) ,Viscometer ,flow behavior index ,Mechanics ,Repeatability ,engineering.material ,paper pulp consistency measurement ,Power law ,Non-Newtonian fluid ,non-newtonian fluids ,effective viscosity ,consistency ratio ,Flow velocity ,engineering ,lcsh:SD1-669.5 ,General Earth and Planetary Sciences ,Torque ,lcsh:Forestry ,Friction torque ,General Environmental Science - Abstract
Maintaining of the proper predetermined paper pulp consistency on the different stages of the paper or cardboard manufacturing process significantly affects on quality and self cost of manufactured articles. The improvement of precision and repeatability of the paper pulp viscosity and consistency measurements is relevant to paper industry. Objective of the work is to improve the industrial-type paper pulp rotational consistometer. A new method for measurement of paper pulp concentration by means of a rotational viscometer was suggested which enables determining the flow consistency index K and flow behavior index n in the Ostwald-de Waele power law. The influence of the following torques on the measurement results is eliminated thanks to the new method: the friction torque in the seal of the sensitive element, the friction torque in the bearings of the shaft and the torque created under the influence of the flow with distorted flow speed profile. This is achieved by measuring the torque which acts on the sensitive element approaching the selected frequencies of sensitive element rotation both from the lower and higher frequencies. The mean torque value is calculated based on the obtained values. The measurements are conducted for two sensitive element rotation frequencies adjusted in advance. The frequency of sensitive element rotation is changed by means of a frequency converter. It is shown that by using two different rotation frequencies of the sensitive element of a rotational viscometer it is possible to define the flow consistency index and the flow behavior index. Paper pulp viscosity and consistency is defined on the basis of these two indexes. It is also suggested to average the results of viscous friction torque measurement approaching the rotation frequency of the viscometer sensitive element to the working frequency chosen for measurement from the lower and higher frequency ranges. By averaging the results of such measurement the friction torques in sealing and bearings supporting the sensitive element shaft are compensated. By changing the rotation direction of the sensitive element and by further averaging the obtained results it is possible to eliminate the influence of the asymmetrical distribution of paper pulp flow speed in the pipeline. This improves accuracy of the paper pulp consistency measurement.
- Published
- 2017
40. Partial Discharge Simulation of Air Gap Defects in Oil-Paper Insulation Paperboard of Converter Transformer under Different Ratios of AC–DC Combined Voltage
- Author
-
Licheng Li, Jia Lei, Tingting Wang, Dong Dai, Luo Bing, and Jian Wang
- Subjects
Technology ,Pressboard ,Control and Optimization ,Materials science ,surface charge density ,Renewable Energy, Sustainability and the Environment ,partial discharge ,combined voltage ,space charge ,Energy Engineering and Power Technology ,Mechanics ,Space charge ,law.invention ,law ,Partial discharge ,Electrical and Electronic Engineering ,Transformer ,Air gap (plumbing) ,Engineering (miscellaneous) ,Polarity (mutual inductance) ,Energy (miscellaneous) ,Voltage ,DC bias - Abstract
A converter transformer is important primary equipment in a DC transmission project. The voltage on the valve side winding is complex when the equipment is running, including DC, AC, and AC–DC combined voltage. The insulation structure of the valve side winding of a converter transformer is an oil-paper insulation structure, which may have a variety of defects in the manufacturing stage and daily use, resulting in partial discharge. Therefore, it is the key to studying the partial discharge characteristics and mechanism of oil-paper insulation under AC–DC combined voltage. In this paper, we build a two-dimensional air gap model of oil-paper-insulated pressboard considering the actual particles and actual reaction based on the fluid model. The characteristics and evolution mechanism of partial discharge (PD) in pressboard under different AC/DC combined voltages are studied by numerical simulation. The results show that when the DC component increases, the polarity effect of partial discharge is more obvious, while the potential and discharge intensity in the air gap decrease. Further analysis revealed that the DC component in the combined voltage accumulated a large number of surface charges on the surface of the air gap, and the space charge distribution was more uniform and dispersed, which generated an electric field with opposite polarity to the DC component in the air gap and, then, inhibited the development of local discharge in the paperboard. The results of the simulation are consistent with the previous experimental phenomena, and the mechanism analysis of the simulation results also verifies the previous analysis on the mechanism of experimental phenomena. This will lay a theoretical foundation for the further study of partial discharge phenomenon of oil-paper insulation structures in practical operation in the future.
- Published
- 2021
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41. Preface to special issue of selected papers from the 13th International Symposium on Numerical Analysis of Fluid Flow, Heat and Mass Transfer — Numerical Fluids 2018
- Author
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Eric Goncalves, Dia Zeidan, T. E. Simos, Ashoke De, and Charis Harley
- Subjects
Computational Mathematics ,Computational Theory and Mathematics ,Modeling and Simulation ,Mass transfer ,Numerical analysis ,Fluid dynamics ,Mechanics ,Mathematics - Published
- 2021
42. Studying droplet adhesion to fibers using the magnetic field: a review paper
- Author
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Hooman Vahedi Tafreshi and M. Jamali
- Subjects
Fluid Flow and Transfer Processes ,Coalescence (physics) ,endocrine system ,Materials science ,technology, industry, and agriculture ,Computational Mechanics ,General Physics and Astronomy ,Context (language use) ,Adhesion ,Mechanics ,engineering.material ,complex mixtures ,eye diseases ,law.invention ,Magnetic field ,Physics::Fluid Dynamics ,Coating ,Mechanics of Materials ,law ,Physics::Atomic and Molecular Clusters ,engineering ,Liquid flow ,A fibers ,Filtration - Abstract
This paper presents a brief overview of the use of magnetic field in studying droplet adhesion to a fiber or a fibrous surface. The paper starts by discussing ways to quantify the force required to detach a droplet from a fiber for its applications in coalescence filtration, i.e., removal of dispersed droplets from a gaseous or liquid flow using a fibrous filter. It then continues to discuss droplet detachment from a fibrous surface or penetrating into a thin fibrous coating. The emphasis is put on a recently develop magnetic approach for measuring force of detachment and on its novel simplicity and non-intrusive nature in the context of existing droplet detachment methods. Our review also includes a discussion on force of detachment for multiphase droplets comprised of two immiscible liquids, i.e., compound droplets. Atomistic- and continuum-level numerical simulations pertaining to droplet detachment are also discussed throughout the paper when appropriate.
- Published
- 2021
43. Simulation for the Partial Discharge of Wedge-Shaped Oil-paper Insulated under DC Electric Field
- Author
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Caipeng Yue, Qingquan Li, Wenwei Zhu, Dongxin He, Qingjing Zang, and Wenjie Gong
- Subjects
Pressboard ,Electron mobility ,Materials science ,law ,Electric field ,Partial discharge ,Direct current ,Arc flash ,Mechanics ,Transformer ,law.invention ,Voltage - Abstract
The converter transformer is a kernel equipment in ultra-high voltage direct current(UHVDC), and some partial discharge(PD) occurs under wedge-shaped electrode of the converter transformer. For researching PD mechanism of oilpaper insulation at wedged electrode, a model based on the fluid dynamics theory and the bipolar charge transport theory was built. Microscopic images including PD and charge distribution obtained by this simulation were analyzed. Besides, the influence of parameters such as voltage amplitude and charge mobility on PD characteristics were discussed. Through the simulation, we can get the conclusion that the partial discharge process under DC stress at the wedged electrode can be broadly classified into the following parts: ionization and polarization in oil, the surface discharge at the oil-paper interface, the deep discharge in pressboard, and surface flashover. During the discharge process, the voltage plays a facilitating role in the discharge. And the effect of charge mobility especially of pressboard on discharge is twofold, the flashover voltage reaches the maximum when the electron and hole mobility is 10-13 m2V−1s−1, when the longitudinal trend of discharge is the strongest. The longitudinal trend inhibits the development of transverse discharge and increases the flashover voltage. The results of this paper have theoretical value for studying the partial discharge mechanism of converter transformer.
- Published
- 2021
44. Once again on the Gatchina discharge and ball lightning: (comments on G D Shabanov’s paper 'On the possibility of making natural ball lightning using a new pulse discharge type in the laboratory' [Phys. Usp. 62 92 (2019); Usp. Fiz. Nauk 189 95 (2019)])
- Author
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Mikhail L. Shmatov
- Subjects
Physics ,Pulse discharge ,Ball (bearing) ,General Physics and Astronomy ,Ball lightning ,Mechanics - Abstract
We show that a recent paper by Shabanov [Phys. Usp. 62 92 (2019); Usp. Fiz. Nauk 189 95 (2019)] contains several important unsubstantiated and erroneous statements. In particular, the estimate of the average ball lightning charge presented in that paper corresponds to an impossible situation with an approximately 100-fold excess of the electric field strength near the outer boundary of the ball lightning over the air breakdown field under nearly standard conditions.
- Published
- 2020
45. On the functioning of coalescence filters with a drainage layer – A comment on several papers by Chang et al
- Author
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Gerhard Kasper and Eckhard Kolb
- Subjects
Coalescence (physics) ,Pressure drop ,Materials science ,Capillary action ,Oil distribution ,Filtration and Separation ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Analytical Chemistry ,020401 chemical engineering ,Mechanical compression ,Wetting ,0204 chemical engineering ,Drainage ,0210 nano-technology - Abstract
This comment jointly addresses experimental observations related to the functioning of coalescence filters with or without added drainage layer and their interpretation, put forth in the following papers by Chang, C., Ji, Z. and Liu, J.:. The effect of a drainage layer on filtration performance of coalescing filters. Separation and Purification Technology 170, 370-376, 2016 The effect of a drainage layer on the saturation of coalescing filters in the filtration process. Chemical Engineering Science 160, 354-361, 2017 Pressure drop and saturation of non-wettable coalescing filters at different loading rates. AIChE Journal 64, 180-185, 2018 The effect of a drainage layer on saturation and liquid distribution of oleophobic coalescence filters. Separation and Purification Technology 194, 355-361, 2018 These papers concluded that the addition of a drainage layer alters the behavior of a coalescence filter in terms of pressure drop evolution, saturation profile, as well as internal oil distribution pattern, in ways that necessitates significant modifications to the “Film-and-Channel-Model”. Notably, the jump-Δp is supposed to be reduced in presence of a drainage layer. We were able to reproduce most of these experimental observations and find that the observed phenomena (especially those related to the shape of the Δp curve during loading) can be explained within the realm of capillary effects in fibrous media and without recourse to modifications of the Film-and-Channel-Model. Certain other data (e.g. those related to unusual oil distribution patterns) appear to have been impacted by experimental artifacts. We also show in this context that the mechanical compression of non-wettable coalescence media can lead to significant changes in apparent wettability.
- Published
- 2019
46. Multiscale simulation of ink seepage into paper: A mesoscopic variational model
- Author
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David Vidal, Mohamed Cheriet, Sébastien Leclaire, Athmane Bakhta, and François Bertrand
- Subjects
Work (thermodynamics) ,Mesoscopic physics ,Finite volume method ,Scale (ratio) ,Discretization ,Computer science ,Monte Carlo method ,Lattice Boltzmann methods ,General Physics and Astronomy ,Mechanics ,01 natural sciences ,010305 fluids & plasmas ,Physics::Popular Physics ,Hardware and Architecture ,0103 physical sciences ,Deposition (phase transition) ,010306 general physics - Abstract
This work focuses on the study of ink seepage and spreading into paper to ease the deciphering of digitized ancient documents and therefore make them legible and researchable. A three-dimensional model is proposed for the simulation of ink seepage into paper at the fiber level. The model takes into account a finite volume of ink and describes the system state through gravity, cohesion and adhesion force interactions. At the mesoscopic scale, the writing paper is modeled using a discretized fiber structure generated using a numerical deposition procedure. A modified Monte Carlo method is introduced for the simulation of the ink dynamics. Finally a multiphase lattice Boltzmann method is suggested to fine-tune the mesoscopic variational model parameters and it is shown that the ink seepage behaviors predicted by the proposed model can resemble those predicted by a method relying on first principles .
- Published
- 2019
47. Extraction of nonlinear elastic parameters of paper from the amplitude-dependent frequency response of cantilever beams
- Author
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Isaias Cueva-Perez, Roque Alfredo Osornio-Rios, Ion Stiharu, and Angel Perez-Cruz
- Subjects
Frequency response ,Materials science ,Cantilever ,Applied Mathematics ,Mechanical Engineering ,Linear elasticity ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Vibration ,Mechanical system ,Nonlinear system ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Dynamic loading ,Nonlinear resonance ,0210 nano-technology - Abstract
In recent years, paper has been used as an alternative to traditional substrate materials in the development of strain sensors and accelerometers due to its flexibility, disposability due to environment low footprint and low cost. A lack of knowledge about the sources of nonlinearity in the mechanical behavior of paper makes difficult to consistently predict its performance. The characterization procedures available in the literature are based on both static and dynamic loading as a first attempt to describe the elastic behavior of paper in sensing applications. However, these procedures do not reveal the necessary information to describe the elastic behavior of paper under dynamic excitation. In this work, the nonlinear dynamic response of a harmonically excited paper-based cantilever beam is studied. A lumped model with a quadratic nonlinearity is adopted to describe the nonlinear response of paper-based cantilever beams. The obtained results show that the nonlinear resonance frequency response is dependent on the intrinsic properties of paper when discarding hygrothermal variations of paper as the main source of nonlinear behavior. It was found that the estimation of two nonlinear elastic parameters, α p (hysteresis nonlinear parameter) and E 0 (linear elastic modulus) could yield an improved description of the elastic behavior of paper subjected to vibrations. It was concluded that the existing paper characterization standards should be adapted to better predict the dynamic behavior of paper-based mechanical systems. Different types of paper materials were analyzed to study the influence of the intrinsic characteristics of paper on the nonlinear parameters.
- Published
- 2019
48. Dynamics of stain growth from sessile droplets on paper
- Author
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Joseph D. Berry, Gil Garnier, Michael J. Hertaeg, and Rico F. Tabor
- Subjects
Materials science ,Capillary action ,Kinetics ,02 engineering and technology ,Mechanics ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Stain ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Surface tension ,Colloid and Surface Chemistry ,Sessile droplet ,Growth rate ,Boundary value problem ,Wetting ,0210 nano-technology - Abstract
Hypothesis The rate of stain growth of a sessile droplet deposited on paper has been previously studied (Kissa, 1981; Danino and Marmur, 1994; Kawase et al., 1986; Borhan and Rungta, 1993) but is not fully understood. In particular, the mechanism by which the abrupt decrease in growth rate occurs is unknown. This process is expected to follow a model where the disappearance of the droplet is represented by a change to the boundary condition at the droplet-paper interface when the volume of the fluid inside the paper is equal to the volume of the simulated droplet. Experiments The stain size of sessile droplets on paper was monitored against time. A series of fluids varying in surface tension and viscosity was studied. The kinetics of stain growth was modelled and compared with experiments and existing models of stain growth. Findings The measured stain area formed by a sessile droplet deposited on paper follows a two regime mechanism (Danino and Marmur, 1994). In the initial regime, the dynamics are governed by the filling of pores. However, in the later stage, the process is influenced by the emptying/redistribution of fluid. Simulations show that experimental results are well described by a model that identifies the change in boundary conditions after the droplet is no longer present above the paper, coupled with the change to a redistribution dominated mechanism.
- Published
- 2019
49. Simulating the hygroexpansion of paper using a 3D beam network model and concurrent multiscale approach
- Author
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Artem Kulachenko and Hamid Reza Motamedian
- Subjects
Pointwise ,Deformation (mechanics) ,Computer science ,Applied Mathematics ,Mechanical Engineering ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermal expansion ,Stress (mechanics) ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Modeling and Simulation ,General Materials Science ,Fiber ,0210 nano-technology ,Microscale chemistry ,Beam (structure) ,Network model - Abstract
A number of problems associated with dimensional stability of paper products have to do with hygroexpansion in response to changes in humidity or moisture content. The main underlying mechanism of hygroexpansion in paper is the effect of the change of fiber cross-sections transferred through fiber bonds. In fact, the transverse expansion of fibers can be an order of magnitude greater than the longitudinal expansion. Addressing such problems using modeling on the microscale is associated with large computational costs since both the bonds and the fibers need to be resolved. We present a method for modeling the hygro or thermal expansion of interconnected fiber networks modeled with beam elements and connected through beam-to-beam contact. Being a line structure, beams can only support pointwise contact, which poses a challenge for modeling the force transfer induced by the deformation of the cross-sections at the contact point. The idea of implementing the stress transfer is to use a concurrent multiscale approach in which the bond level is resolved in detail using the configuration of the fibers and the computed strains are passed over to the beam elements. We verify and prove the applicability of this approach by comparing it with continuum models. We demonstrate the advantage of using this approach in terms of its tremendous saving in time. The use of beam models for modeling the hygro- or thermal expansion of fiber networks enables considering relevant sizes in the problems involving dimensional stability, in particular those associated with embedded inhomogeneities. We will show the applicability of the model by providing insights into published experimental observations on the hygroexpansion properties of paper products. Finally, we will demonstrate that the use of a 2D model to simulate the inter-fiber bonds in a network, not only leads to underestimation of out-of-plane deformations, but also to overestimation of the contribution of the transverse deformation of fibers to the in-plane dimensional change of the network.
- Published
- 2019
50. Experimental investigation on the smoldering limit of scraps of paper initiated by a cylindrical rod heater
- Author
-
Osamu Fujita and Hui Yan
- Subjects
Packed bed ,Materials science ,Mechanical Engineering ,General Chemical Engineering ,Airflow ,Autoignition temperature ,Mechanics ,Critical value ,Bulk density ,law.invention ,Physics::Fluid Dynamics ,Ignition system ,law ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Combustion chamber ,Electric current - Abstract
The ignition temperature for smoldering in scraps of paper has been determined experimentally for several bulk densities under different external air flows. Beds of compressed scraps of paper were packed into a vertical combustion chamber to achieve different bulk densities and the temperature of an electrically set rod-heater was heated to temperatures between 350 and 450 °C. Once the rod-heater had reached the set temperature, the electric current supply was then turned off and the heater was embedded into the middle of the vertical combustion chamber filled with a packed bed of paper scraps. We obtained the ignition limit of the scraps of paper for different bulk densities under different external air flows by recording the temperature evolution at different positions in the combustion chamber. Results show that without external air flow, the ignition temperature first decreased with an increase in bulk density, then after a critical value, an increase in bulk density led to an increase in the ignition temperature. Furthermore, we found that even under a quiescent case (without external air flow), for the cases where ignition occurred, the smoldering front first reached the bottom side of the combustion chamber, then propagated to the upper side. As for cases with external air flows, again the propagations of the smoldering front towards the bottom side of the combustion chamber were observed in the cases where ignition happened, and external air flows played different roles in ignition limit of paper scraps bed with low bulk density, medium bulk density and high bulk density regime, respectively.
- Published
- 2019
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