134 results on '"Liou, T.M."'
Search Results
2. Effect of rib orientation on thermal and fluid-flow features in a two-pass parallelogram channel with abrupt entrance
- Author
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Liou, T.M., Chang, S.W., and Chan, S.P.
- Published
- 2018
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3. Influence of entrance geometry on flow field and heat transfer performance in stationary two-pass smooth parallelogram channels
- Author
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Liou, T.M., Chang, S.W., Chan, S.P., and Lin, A.
- Published
- 2017
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4. Particle image velocimetry and infrared thermography measurements in a two-pass 90-deg ribbed parallelogram channel
- Author
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Liou, T.M., Chang, S.W., Huang, C.Y., Chan, S.P., and Lan, Y.A.
- Published
- 2016
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5. Prediction of confined three-dimensional impinging flows with various turbulence models
- Author
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Liou, T.M., Hwang, Y.H., and Chen, L.
- Subjects
Turbulence -- Research ,Flow visualization -- Research ,Equations -- Analysis ,Engineering and manufacturing industries ,Science and technology - Abstract
This paper deals with three-dimensional, turbulent, confined impinging flows. Various turbulence models are examined with reported laser-Doppler velocimetry data and flow-visualization photographs. The turbulence models considered are the k - [epsilon] k - [epsilon] with the Richardson number correction for swirling and recirculating flows (k - [epsilon] w/scm), algebraic Reynolds stress (k - [epsilon] - A), and modified k - kl models. The k - [epsilon] and k - [epsilon] - A models are found to be superior to the k - [epsilon] w/scm and modified k - kl models in predicting the main flow characteristics. The k - [epsilon] - A model provides a better quantitative agreement with the experimental data than can be achieved with the k - [epsilon] model, however, less computational effort is spent with the k - [epsilon] model than with the k - [epsilon] - A model. Also, the effect of the inlet velocity profile on the characteristics of the confined impinging flows is addressed in this study.
- Published
- 1992
6. Heat transfer in a smooth-walled reciprocating anti-gravity open thermosyphon
- Author
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Chang, S.W., Su, L.M., Morris, W.D., and Liou, T.M.
- Published
- 2003
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7. Downward flame spread over a thick PMMA slab in an opposed flow environment: experiment and modeling
- Author
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Wu, K.K., Fan, W.F., Chen, C.H., Liou, T.M., and Pan, I.J.
- Published
- 2003
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8. THREE-DIMENSIONAL SIMULATIONS OF THE DROPLET FORMATION DURING THE INKJET PRINTING PROCESS
- Author
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Liou, T.M., Shih, K.C., Chau, S.W., and Chen, S.C.
- Published
- 2002
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9. High rotation number heat transfer of a 45° rib-roughened rectangular duct with two channel orientations
- Author
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Liou, T.M., primary, Chang, S.W., additional, Hung, J.H., additional, and Chiou, S.F., additional
- Published
- 2007
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10. The fluid property dependency on micro-fluidic characteristics in the deposition process for microfabrication
- Author
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Chau, S.W., primary, Hsu, K.L., additional, Chen, S.C., additional, Liou, T.M., additional, and Shih, K.C., additional
- Published
- 2004
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11. Large-eddy simulations of turbulent reacting flows in a chamber with gaseous ethylene injecting through the porous wall
- Author
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Liou, T.M., primary, Lien, W.Y., additional, and Hwang, P.W., additional
- Published
- 1994
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12. Effects of momentum ratio on turbulent nonreacting and reacting flows in a ducted rocket combustor
- Author
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Liou, T.M., primary, Chen, L., additional, and Wu, Y.Y., additional
- Published
- 1993
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13. Mechanistic Insights into Effects of Perforation Direction on Thermal Hydraulic Performance of Ribs in a Rectangular Cooling Channel.
- Author
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Qian, Weijia, Shuai, Ruiyang, Meng, Qingkun, Roy, Subhajit, Yao, Songbai, and Wang, Ping
- Subjects
HEAT transfer in turbulent flow ,REYNOLDS number ,HEAT transfer ,LIQUID crystals ,INDUCTIVE effect - Abstract
This study investigates the turbulent flow characteristics and heat transfer performance within a rectangular cooling channel with an aspect ratio of 5:3 and featuring perforated ribs, then explores the effects of the rib perforation directions on its thermal hydraulic performance. Through experimental tests (transient thermographic liquid crystal technique) and numerical simulations, it is demonstrated that horizontal perforated ribs can effectively reduce pressure loss at a high Reynolds number while maintaining notable heat transfer enhancement. Additionally, changing the rib perforation directions results in diverse effects on flow field and heat transfer. Our results show that horizontal perforated ribs can compress the recirculation vortex behind ribs, enhancing heat transfer by flow scouring, whereas upward-tilted perforated ribs increase flow friction and weaken heat transfer due to coupling of the airflow with the separation vortices behind the ribs. Downward-tilted ribs enhance local heat transfer by directing airflow behind the rib, and can also cause detachment of vortices and reduced friction. Our results indicate that introducing horizontal perforated ribs into a rectangular internal cooling channel can decrease pressure loss without significantly compromising heat transfer performance. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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14. Numerical Study on the Influence of Separation Time Sequence on the Initial Thermal Separation.
- Author
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Ma, Chenhui, Wang, Sihang, and Yu, Jianyang
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ROCKETS (Aeronautics) ,FLOW separation ,NOZZLES ,TURBULENCE ,COMPRESSIBILITY ,JET engines - Abstract
The process of separating stages is crucial for multistage rockets, directly influencing the success of the launch plan. Different separation timing methods alter the flow field structure within the interlevel zone at separation, influencing the separation of the two-stage rockets. This paper employs the SST k-ω turbulence model to investigate the structure of the flow field and its aerodynamic and motion characteristics under different nozzle baffle opening and separation times, taking into account variable properties, supersonic compressibility, and the upstream–downstream interference. First, we examined the standard flow field structure, considering the engine jet, the lateral jet between stages, and the disturbance from the external supersonic inflow. Then, we discussed the displacement characteristics and axial force coefficient curves of the first and second steps of the separation process. Finally, we explored the impact of baffle opening and separation times on the flow field structure and axial force coefficients of the two stages at the onset of separation. For the flow field structure, a delay in the baffle opening and separation moment led to a gradual increase in downstream and separation regions until they stabilized after a certain range. However, the axial force coefficients displayed different behavior before and after the design point. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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15. Investigations of Flow Boiling in Mini-Channels: Heat Transfer Calculations with Temperature Uncertainty Analyses.
- Author
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Piasecka, Magdalena, Maciejewska, Beata, Michalski, Dariusz, Dadas, Norbert, and Piasecki, Artur
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HEAT transfer ,HEAT transfer fluids ,HEAT transfer coefficient ,MONTE Carlo method ,EBULLITION ,TWO-phase flow - Abstract
The article aims to explore boiling heat transfer in mini-channels with a rectangular cross-section using various fluids (HFE-649, HFE-7000, HFE-7100, and HFE-7200). Temperature measurements were conducted using infrared thermography for the heated wall and K-type thermocouples for the working fluid. The 2D mathematical model for heat transfer in the test section was proposed. Local heat transfer coefficients between the heated wall and the working fluid were determined from the Robin condition. The problem was solved by means of the finite element method (FEM) with Trefftz functions. The values of the heat transfer coefficient that were obtained were compared with the results calculated from Newton's law of cooling. The average relative differences between the obtained results did not exceed 4%. The study included uncertainty analyses for temperature measurements with K- and T-type thermocouples. Expanded uncertainties were calculated using the uncertainty propagation and Monte Carlo methods. Precisely determining the uncertainties in contact temperature measurements is crucial to ensure accurate temperature data for subsequent heat transfer calculations. The results of the heat transfer investigations were compared in terms of fluid temperature, heat transfer coefficients, and boiling curves. HFE-7200 consistently exhibited the highest fluid temperature and temperature differences at boiling incipience, while HFE-7000 demonstrated the highest heat transfer coefficients. HFE-649 showed the lowest heat transfer coefficients. The boiling curves exhibited a typical shape, with a notable occurrence of 'nucleation hysteresis phenomena'. Upon the analysis of two-phase flow patterns, bubbly and bubbly-slug structures were observed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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16. Optically Transparent Honeycomb Mesh Antenna Integrated into OLED Light Source.
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El Halaoui, Mustapha, Dupuis, Pascal, Pigaglio, Olivier, Asselman, Adel, Zissis, Georges, and Canale, Laurent
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ANTENNAS (Electronics) ,LIGHT sources ,ENERGY consumption of lighting ,HONEYCOMB structures ,COPPER films ,ORGANIC light emitting diodes - Abstract
The co-integration of antennas with lighting sources appears as an effective way to distribute broadband networks closer to users, lowering interference and transmitted power, as well as to reduce energy consumption in future lighting systems. We here present an original contribution to the implementation of transparent and invisible antennas with OLED light sources. To validate the proposed approach, the honeycomb mesh technique was used, and an optical transparency of 75.4% was reached. The transparent mesh antenna was compared with the non-transparent full-metal antenna in terms of radio-electrical parameters. Our prototype was designed using copper films deposited on a glass substrate. The simulation results of the S-parameters and the radiation patterns were validated against measurements performed in an anechoic chamber. The directivity and gain obtained were 6.67 dBi and 4.86 dBi at 5.16 G Hz , respectively. To study the effect of antenna integration with OLEDs, optical and photometric characterizations with and without the antenna were measured, and the colorimetric parameters were then treated using the IES TM-30-18 standard. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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17. Fluid Flow in Helically Coiled Pipes.
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Sigalotti, Leonardo Di G., Alvarado-Rodríguez, Carlos E., and Rendón, Otto
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FLUID flow ,PIPE flow ,NUSSELT number ,MULTIPHASE flow ,TURBULENT flow ,REYNOLDS number - Abstract
Helically coiled pipes are widely used in many industrial and engineering applications because of their compactness, larger heat transfer area per unit volume and higher efficiency in heat and mass transfer compared to other pipe geometries. They are commonly encountered in heat exchangers, steam generators in power plants and chemical reactors. The most notable feature of flow in helical pipes is the secondary flow (i.e., the cross-sectional circulatory motion) caused by centrifugal forces due to the curvature. Other important features are the stabilization effects of turbulent flow and the higher Reynolds number at which the transition from a laminar to a turbulent state occurs compared to straight pipes. A survey of the open literature on helical pipe flows shows that a good deal of experimental and theoretical work has been conducted to derive appropriate correlations to predict frictional pressure losses under laminar and turbulent conditions as well as to study the dependence of the flow characteristics and heat transfer capabilities on the Reynolds number, the Nusselt number and the geometrical parameters of the helical pipe. Despite the progress made so far in understanding the flow and heat transfer characteristics of helical pipe flow, there is still much work to be completed to address the more complex problem of multiphase flows and the impact of pipe deformation and corrugation on single- and multiphase flow. The aim of this paper is to provide a review on the state-of-the-art experimental and theoretical research concerning the flow in helically coiled pipes. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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18. Aptamer-Based Immune Drug Systems (AptIDCs) Potentiating Cancer Immunotherapy.
- Author
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Xiong, Hongjie, Liu, Liu, Liu, Xiaohui, Jiang, Hui, and Wang, Xuemei
- Subjects
IMMUNE system ,BISPECIFIC antibodies ,IMMUNE checkpoint proteins ,KILLER cells ,CELL communication ,IMMUNE response ,PROGRAMMED cell death 1 receptors - Abstract
Aptamers are artificial oligonucleotides with excellent molecule-targeting ability. Compared with monoclonal antibodies, aptamers have the advantages of low cost, no batch effect, and negligible immunogenicity, making them promising candidates for cancer immunotherapy. To date, a series of aptamer agonists/antagonists have been discovered and directly used to activate immune response, such as immune checkpoint blockade, immune costimulation, and cytokine regulation. By incorporating both tumor- and immune cell-targeting aptamers, multivalent bispecific aptamers were designed to pursue high tumor affinity and enhanced immune efficacy. More importantly, benefiting from feasible chemical modification and programmability, aptamers can be engineered with diverse nanomaterials (e.g., liposomes, hydrogels) and even living immune cells (e.g., NK cells, T cells). These aptamer-based assemblies exhibit powerful capabilities in targeted cargo delivery, regulation of cell–cell interactions, tumor immunogenicity activation, tumor microenvironment remodeling, etc., holding huge potential in boosting immunotherapeutic efficacy. In this review, we focus on the recent advances in aptamer-based immune drug systems (AptIDCs) and highlight their advantages in cancer immunotherapy. The current challenges and future prospects of this field are also pointed out in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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19. Thermal Convection in a Heated-Block Duct with Periodic Boundary Conditions by Element-by-Element Treatment.
- Author
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Jue, Tswen-Chyuan, Wu, Horng-Wen, Hsueh, Ying-Chien, and Guo, Zhi-Wei
- Subjects
NUSSELT number ,FINITE element method ,REYNOLDS number ,ELECTRONIC equipment ,NATURAL heat convection - Abstract
The periodic nature of stream-wise flow occurs in a cooling channel so frequently due to the multiple heat sources in electronic equipment, demanding the creation of an effective technique to improve the heat-cooling convection. This work explores thermal convection enhancement in a heated-block duct for periodic boundary conditions using the element-by-element (EBE) treatment in a semi-implicit projection finite element method (FEM) through a preconditioned conjugate gradient (PCG) solver. The effects of changing the Reynolds numbers (100, 175, and 250) on rectangular cylinders installed in the channel under periodic boundary conditions were studied using time-mean Nusselt number enhancement, friction factor enhancement, and thermal performance coefficient. The results show that the rectangular cylinders installed stream-wise above an upstream block promote thermal convection in the heated-block duct due to modifying the flow of no cylinders. However, increasing the number of rectangular cylinders increases the friction factor enhancement. As a result, the case for periodic boundary conditions with a rectangular cylinder above every two blocks has the best thermal performance coefficient. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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20. Numerical Study of the Effects of Roughness Coupled with Inclination on a Turbulent Flow around an Obstacle.
- Author
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Brahimi, Amine, Rebhi, Redha, and Alliche, Mounir
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TURBULENT flow ,TURBULENCE ,NUSSELT number ,HEAT convection ,AIR flow ,CONVECTIVE flow ,PHENOMENOLOGICAL theory (Physics) - Abstract
In this study, we simulate the cooling of a microprocessor by thermal convection in three different shapes: a square, a trapezoidal, and a triangular shape. The latter is improved by a variety of types of roughness, including square roughness, triangular roughness Type 1, triangular roughness Type 2, and triangular roughness Type 3. The microprocessors are kept at a constant temperature, the air flow is constant, and the geometry is fixed. The physical phenomenon is simulated by the ANSYS software. The numerical results reported in this study cover the ranges of the obstacle's angle of inclination, 0 ° ≤ θ ≤ 45 ° , (square obstacles, θ = 0 ° , trapezoidal obstacles, 0 ° < θ < 45 ° , triangular obstacles, θ = 45 ° ) and Reynolds number, 2500 ≤ R e ≤ 10 , 000 . The findings relate to streamlines, dynamic pressure (max), mean velocity, temperature field, mean Nusselt number (Nu/Nu
0 ) profiles, local coefficient of friction (Cf/f0 ), mean coefficient of friction (f/f0 ) profiles, mean velocity field with roughness, and fluid temperature field with roughness. The aim of the study is to show the interaction between the roughness parameter and the obstacle geometry. In the case of a triangular obstacle, the contact between the cold air and the obstacle is significant downstream of the obstacle, which gives us good cooling, and the Nusselt number has an important value because the agitation of the flow increases convective heat transfer, and the coefficient of friction is low because the air flow is uniform. [ABSTRACT FROM AUTHOR]- Published
- 2023
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21. Thermo-Hydraulic Management System Employing Single-Phase Water Flow through Microchannels with Micro-Inserts Added Aiming for Performance Improvement.
- Author
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Kumar, Shailesh Ranjan and Singh, Satyendra
- Subjects
SINGLE-phase flow ,MICROCHANNEL flow ,PRESSURE drop (Fluid dynamics) ,REYNOLDS number ,HEAT transfer ,HEAT exchangers - Abstract
A microchannel heat exchanger effectively evacuates heat from a confined space. This paper attempts to gain insight into the combinatorial repercussions of simultaneously coupling two factors that affect a microchannel's performance, of which channel size and micro-insert complexity are the two main contributors. With water as the working fluid, an ANSYS-based numerical analysis was carried out for two distinct channel sizes, 1 and 2 mm, both with and without micro-inserts. The Reynolds numbers varied between 125 and 4992 and between 250 and 9985 for the 1 and 2 mm channels, respectively. For the 2 mm diameter channel, adding micro-inserts raised the overall pressure drop with increased Reynolds number. The inclusion of micro-inserts increased the pressure drop in the 1 mm channel at first, and thereafter the pressure drop decreased. Incorporating micro-inserts into the channel resulted in enhanced heat transfer. The trade-off between enhanced heat transfer performance and a larger pressure drop was calculated by evaluating the channel's overall performance using the thermal performance factor. Micro-inserts were found to be most useful for improving overall performance in the low-to-moderate Reynolds number range, and their effectiveness increased with decreasing channel size. Changing the channel diameter and structure of the design can improve heat transmission through microchannels. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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22. Large Eddy Simulation of Flow and Heat Transfer in a Ribbed Channel for the Internal Cooling Passage of a Gas Turbine Blade: A Review.
- Author
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Ahn, Joon
- Subjects
LARGE eddy simulation models ,GAS turbine blades ,FLOW simulations ,HEAT transfer ,ENERGY futures - Abstract
Herein, 50 articles published over the past 20 years on using large eddy simulation (LES) for the internal cooling passage of a gas turbine, especially the mid-chord ribbed channel, are reviewed for the first time. First, the numerical challenges of performing LES on a ribbed channel and experimental verification are summarized. Next, LES data and the major engineering findings that are difficult to obtain experimentally or using Reynolds-averaged Navier–Stokes simulation (RANS) are covered, and heat transfer on and inside the rib, and the effects of rotation and buoyancy are discussed. Next, recent LES studies related to the shape of the ribbed channel are reviewed, and finally, the contribution of using LES for research on the internal cooling of gas turbines in the future, including those with ribbed channels, is anticipated. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
23. Alternative Internal Configurations for Enhancing Heat Transfer in Telecommunication Cabinets.
- Author
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Jobby, Antony, Khatamifar, Mehdi, and Lin, Wenxian
- Subjects
HEAT transfer ,TELECOMMUNICATION ,NATURAL heat convection ,TELECOMMUNICATION management ,TELECOMMUNICATION systems ,TELECOMMUNICATION equipment - Abstract
Telecommunication systems have become a critical part of society which enables connectivity to many essential and trivial services. Consequently, telecommunication equipment is housed in cabinets to protect the electronics from a variety of hazards; one of which is temperature-related failure. Current practices use a notable amount of power for the thermal management of telecommunication cabinets which can be reduced by considering alternative methods of cooling. In this paper, experiments were carried out to investigate the effectiveness of different internal mounting configurations of electronic components on the thermal performance of a telecommunication cabinet. The investigation tested inclinations (0–90°), different staggered offsets (0–50 mm), changing stream-wise spacing (29–108 mm), and fan speed (with a Reynolds number in the range of 1604 to 5539). The experimental study revealed that heat transfer was enhanced by 9.99 % by altering component inclination to 90°, 25.90% by increasing stream-wise spacing from 29 mm to 108 mm, and 36.02% by increasing the Reynolds number from 1604 to 5539. However, the staggered arrangement of internal components decreased N u by 3.26% for the natural convection condition but increased by 5.69% for the forced convection condition over the tested range and increasing the centre offset of the staggered components with respect to the cabinet did not influence N u in any significant manner. Natural convection and forced convection also had notable influence on the heat transfer rate. Hence it was seen that alternative internal configurations positively influence heat transfer in telecommunication cabinets for the cases studied. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
24. Numerical Investigation of Pressure Loss in a Rectangular Channel with a Sharp 180-Degree Turn: Influence of Design Variables and Geometric Shapes.
- Author
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Kim, Byunghui and Kim, Seokho
- Subjects
GEOMETRIC shapes ,GAS turbine blades ,REYNOLDS number ,REGRESSION analysis ,PREDICTION models ,AERODYNAMICS of buildings - Abstract
Gas turbine blade cooling typically uses a cooling air passage with a sharp 180° turn in the midchord area of the airfoil. Its geometric shape and dimensions are strictly constrained within the airfoil to ensure both aerodynamic and cooling performance. These characteristics imply the importance of understanding the relationships between the geometric dimensions and the cooling channel performance. In this study, we validated a numerical method using the commercial software, Ansys Fluent 2021 R2, by predicting a total pressure loss coefficient with less than 6% deviation from the experimental results of Metzger et al. for four different Reynolds numbers. Through parameter studies, the divider tip-to-wall clearance was found to be the most significant parameter influencing the pressure loss. Parameter correlations and predictive models between the design variables and the pressure loss were derived by regression analysis using the R language; the regression model predicted the pressure loss to within 2.29% of the numerical method. As the geometries changed, the response surface and the adjoint solver improved the pressure loss by approximately 20.87% and 25.96%, respectively, at the representative Reynolds number of 24,230; this showed that the adjoint solver was a relatively simple and effective method with minimal geometric changes. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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25. A Review of Combustion and Flame Spread over Thermoplastic Materials: Research Advances and Prospects.
- Author
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Chen, Yanqiu, Feng, Qianhang, Nie, Yifan, Zhang, Jiwei, and Yang, Lizhong
- Subjects
FLAME spread ,FLAME ,PYROLYSIS kinetics ,IGNITION temperature ,FIRE prevention ,CURTAIN walls ,HEAT release rates ,FIRE resistant polymers - Abstract
As thermoplastic materials are widely used in buildings, the fire hazards of thermoplastic materials are increasingly becoming a central issue in fire safety research due to their unique pyrolysis and melting mechanisms. In this paper, the features and common types of thermoplastic materials are introduced first. Then, the combustion behavior of thermoplastic materials is theoretically analyzed based on the empirical formulas and heat balance equations, such as the pyrolysis kinetics, ignition time, melting and dripping, flame, burning rate and mass loss rate, temperature and heat flow, gas products, and influencing factors. The influencing factors basically include the sample properties (width, incline angle, and thickness, etc.), the façade structure (sidewalls, curtain wall, etc.), the ambient conditions (altitude, pressure, and gravity, etc.), and the flame retardant treatment. Similarly, this study also illustrates the vertical and horizontal flame spread behavior of the thermoplastic materials and the influencing factors. The utilized methods include the experimental methods, the analytical methodologies, and the approaches for numerical simulation. Finally, the problems encountered at this stage and worthy of further study in the future are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
26. RANS Modeling of Turbulent Flow and Heat Transfer in a Droplet-Laden Mist Flow through a Ribbed Duct.
- Author
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Pakhomov, Maksim A. and Terekhov, Viktor I.
- Subjects
HEAT transfer in turbulent flow ,SINGLE-phase flow ,FLOW separation ,TURBULENT flow ,TURBULENCE ,TWO-phase flow - Abstract
The local structure, turbulence, and heat transfer in a flat ribbed duct during the evaporation of water droplets in a gas flow were studied numerically using the Eulerian approach. The structure of a turbulent two-phase flow underwent significant changes in comparison with a two-phase flow in a flat duct without ribs. The maximum value of gas-phase turbulence was obtained in the region of the downstream rib, and it was almost twice as high as the value of the kinetic energy of the turbulence between the ribs. Finely dispersed droplets with small Stokes numbers penetrated well into the region of flow separation and were observed over the duct cross section; they could leave the region between the ribs due to their low inertia. Large inertial droplets with large Stokes numbers were present only in the mixing layer and the flow core, and they accumulated close to the duct ribbed wall in the flow towards the downstream rib. An addition of evaporating water droplets caused a significant enhancement in the heat transfer (up to 2.5 times) in comparison with a single-phase flow in a ribbed channel. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
27. Optimal Design of Droplet Ejection for PZT Printhead Based on Surrogate Model.
- Author
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Lei, Ting, Liu, Hong, Ma, Cong, and Han, Jiang
- Subjects
COMPUTATIONAL fluid dynamics ,MATHEMATICAL ability ,GENETIC algorithms - Abstract
Droplet ejection technology is widely used in green and intelligent manufacturing. A stable jetting can be defined as no obvious satellite droplets during the whole ejection process, which is of great importance to ensure the quality and efficiency of the printed products; However, due to the multi-parameter features and the interaction between different physics, using traditional analytical-based approaches to analyze and/or optimize is usually difficult and even unfeasible. Experimental tests using a PZT printhead design-optimization method based on surrogate modeling are proposed in this paper to overcome this challenge, which can synthesize the advantages of numerical simulation. The basic data for surrogate model construction was obtained by the Computational Fluid Dynamics (CFD) numerical-based model, which was developed to predict the flow characteristic under different parameter settings of the printhead. The accuracy of the developed numerical model was validated by performing experimental tests; thereby, the predictive ability of the numerical model in droplet ejection was verified. With the validated numerical model, the Design of Experiments (DoE) was performed to generate the necessary training and validation sample dataset required by the surrogate modeling. Thereafter, four surrogate modeling methods were adopted to construct the relationship between the design parameters and flow features, where the Kriging (KRG) was identified as the optimal modeling method. Based on the developed KRG model, global sensitivity analysis (GSA) of the parameters was carried out with Sobol's method; thereby, the influence of different parameters can be quantified. Finally, a genetic algorithm (GA) was used to optimize the structure of the droplet printhead. Through validation, the optimized design model increases the droplet ejection speed by 20.84% while keeping no satellite droplet formation, confirming the efficient and stable printhead ejection, and verifying the feasibility and effectiveness of the analysis/optimization method proposed in this paper. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
28. Advances in Aptamer-Based Biosensors and Cell-Internalizing SELEX Technology for Diagnostic and Therapeutic Application.
- Author
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Gan, Zixuen, Roslan, Muhamad Aidilfitri Mohamad, Abd Shukor, Mohd Yunus, Halim, Murni, Yasid, Nur Adeela, Abdullah, Jaafar, Md Yasin, Ina Salwany, and Wasoh, Helmi
- Subjects
APTAMERS ,BIOSENSORS ,SINGLE-stranded DNA ,NUCLEIC acids ,PATHOGENIC microorganisms - Abstract
Aptamers are a group of synthetic single-stranded nucleic acids. They are generated from a random library of single-stranded DNA or RNA by a technology named systematic evolution of ligands by exponential enrichment (SELEX). SELEX is a repetitive process to select and identify suitable aptamers that show high affinity and specificity towards target cells. Great strides have been achieved in the design, construction, and use of aptamers up to this point. However, only a small number of aptamer-based applications have achieved widespread commercial and clinical acceptance. Additionally, finding more effective ways to acquire aptamers with high affinity remains a challenge. Therefore, it is crucial to thoroughly examine the existing dearth and advancement in aptamer-related technologies. This review focuses on aptamers that are generated by SELEX to detect pathogenic microorganisms and mammalian cells, as well as in cell-internalizing SELEX for diagnostic and therapeutic purposes. The development of novel aptamer-based biosensors using optical and electrical methods for microbial detection is reported. The applications and limitations of aptamers are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
29. Experimental Study on Microchannel with Addition of Microinserts Aiming Heat Transfer Performance Improvement.
- Author
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Kumar, Shailesh Ranjan and Singh, Satyendra
- Subjects
MICROCHANNEL flow ,HEAT transfer ,FUEL cell power plants ,SINGLE-phase flow ,FLUID flow ,DRAG (Hydrodynamics) - Abstract
Microchannel technology rapidly established itself as a practicable solution to the problem of the removal of extremely concentrated heat generation in present-day cooling fields. By implementing a better design structure, altering the working fluids and flow conditions, using various materials for fabrication, etc., it is possible to increase the heat transfer performance of microchannels. Two parameters that affect how well a microchannel transfers heat were only recently coupled, and the complicated coupling of the parameter that affects how well a microchannel sink transfers heat is still not well understood. The newest industrial developments, such as micro-electro-mechanical systems, high performance computing systems, high heat density generating future devices, such as 5G/6G devices, fuel cell power plants, etc., all present thermal challenges that require the use of microchannel technology. In this paper, single-phase flow in microchannels of various sizes, with or without microinserts, is described in terms of its thermal-fluid flow properties, including fluid flow characteristics and heat transfer characteristics considering the compound effects of variations of channel size and addition of microinserts. The trials were carried out using distilled water that had thermo-physical characteristics that varied with temperature. A microchannel with microinserts was developed for managing the high heat generation density equipment. The fluid flow and heat transfer characteristics are explored and analyzed for Reynolds numbers ranges from 125 to 4992, for 1 mm channel size, and from 250 to 9985, for 2 mm channel size. The cooling performance criteria are pressure drop characteristics, heat transfer characteristics, and overall performance, whereas the testing parameters were chosen for the variations in channel size and the addition of microinserts. The influence of inserting microinserts on microchannels is discussed. Results suggest that by inserting microinserts, the performance of the heat transfer of microchannels is significantly improved and, also, fluid flow resistance is increased. The criteria of the thermal performance factor are employed to assess the overall performance of the microchannel. Significant intensification of heat transfer is observed with indication that the addition of microinserts to microchannels and reduction in channel sizes exhibited improved overall performance. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
30. Squeeze-Type Piezoelectric Inkjet Printhead Actuating Waveform Design Method Based on Numerical Simulation and Experiment.
- Author
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Liu, Ning, Sheng, Xianjun, Zhang, Mingcong, Han, Wei, and Wang, Kexin
- Subjects
COMPUTER simulation ,PRINTMAKING ,INK ,INK-jet printers ,NOZZLES - Abstract
The piezoelectric inkjet printing technique has been commonly used to produce conductive graphics. In this paper, a trapezoidal waveform design method for squeeze-type piezoelectric inkjet printhead is presented to provide a modified steady ejection and optimal droplet shape, in which a coupled multi-physics model of a piezoelectric inkjet printhead is developed. This research describes the effects of parameters, including rising time t
r , falling time tf , and dwelling time td , of the trapezoidal waveform on the pressure at the nozzle through numerical simulations. These parameters are initially optimized based on numerical simulations and further optimized based on experimental results. When the printhead is actuated by the optimized waveform with the tr = 5 µs, td = 10 µs, and tf = 2 µs, the droplets are in optimal shape, and their size is about half the diameter of the nozzle. The experimental results validate the efficacy of this waveform design method, which combines numerical simulation and experiment, as well as demonstrating that ink droplet formation can be studied from the point of pressure variation at the nozzle. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
31. Micro-Channel Oscillating Heat Pipe Energy Conversion Approach of Battery Heat Dissipation Improvement: A Review.
- Author
-
Zhao, Xiaohuan, Zhu, Yue, and Li, Hailiang
- Subjects
ENERGY conversion ,THERMAL resistance ,HEAT transfer ,WORKING fluids ,HEAT pipes ,STORAGE batteries - Abstract
The application of batteries has become more and more extensive, and the heat dissipation problem cannot be ignored. Oscillating Heat Pipe (OHP) is a good means of heat dissipation. In this paper, the methods to improve the energy conversion and flow thermal performance of micro-channel OHP are studied and summarized. The working principle, heat transfer mechanism, advantages and applications of PHP are also introduced in detail in this study. Proper adjustment of the micro-channel layout can increase the heat transfer limit of PHP by 44%. The thermal resistance of two-diameter channel PHP is 45% lower than that of conventional PHP. The thermal resistance of PHP under uneven heating can be reduced to 50% of the original. PHP pulse heating can alleviate the phenomenon of dryness. Different working fluids have different effects on PHP. The use of graphene nano-fluids as the work medium can reduce the thermal resistance of PHP by 83.6%. The work medium obtained by the mixture of different fluids has the potential to compensate for the defects while inheriting the advantages of a single fluid. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
32. Analysis of Microchannel Heat Sink of Silicon Material with Right Triangular Groove on Sidewall of Passage.
- Author
-
Saha, Surojit, Alam, Tabish, Siddiqui, Md Irfanul Haque, Kumar, Mukesh, Ali, Masood Ashraf, Gupta, Naveen Kumar, and Dobrotă, Dan
- Subjects
HEAT sinks ,SOLAR air heaters ,NUSSELT number ,COMPUTATIONAL fluid dynamics ,NAVIER-Stokes equations ,ANGLES - Abstract
Microchannel heat sink (MCHS) is a promising solution for removing the excess heat from an electronic component such as a microprocessor, electronic chip, etc. In order to increase the heat removal rate, the design of MCHS plays a vital role, and can avoid damaging heat-sensitive components. Therefore, the passage of the MCHS has been designed with a periodic right triangular groove in the flow passage. The motivation for this form of groove shape is taken from heat transfer enhancement techniques used in solar air heaters. In this paper, a numerical study of this new design of microchannel passage is presented. The microchannel design has five variable groove angles, ranging from 15° to 75°. Computational fluid dynamics (CFD) is used to simulate this unique microchannel. Based on the Navier–Stokes and energy equations, a 3D model of the microchannel heat sink was built, discretized, and laminar numerical solutions for heat transfer, pressure drop, and thermohydraulic performance were derived. It was found that Nusselt number and thermo-hydraulic performance are superior in the microchannel with a 15° groove angle. In addition, thermohydraulic performance parameters (THPP) were evaluated and discussed. THPP values were found to be more than unity for a designed microchannel that had all angles except 75°, which confirm that the proposed design of the microchannel is a viable solution for thermal management. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
33. Analysis of Potential Fluctuation in Flow.
- Author
-
Li, Wei
- Subjects
POTENTIAL flow ,COOLING towers ,REFRIGERANTS - Abstract
Understanding the physics of flow instabilities is important for processes in a wide range of engineering applications. Flow instabilities occur at the interfaces between moving fluids. Potential fluctuations are generated at the interfaces between two moving fluids based on the relationship of continuity. Theoretical analysis demonstrated that, in flow instabilities, potential fluctuation exhibits a potential oscillatory wave surface concurrently in the temporal and spatial dimensions. Potential fluctuations already internally exist in flow before flow instabilities begin to develop; these potential fluctuations greatly affect the formation of interpenetrating structures after forces act on the interfaces. Experimental studies supported the theoretical study: Experiments visualizing condensation flows using refrigerant in one smooth tube and one three-dimensional enhanced tube were conducted to show the development of potential fluctuation in spatial dimensions, and an experiment with cooling tower fouling in seven helically ridged tubes and one smooth tube were conducted to show the development of potential fluctuation in the temporal dimension. Both experimental studies confirmed that potential fluctuation was determined by the densities and velocities of the two fluids in the instability as indicated by the relationship of continuity. In addition, the results of numerical simulation in the literature qualitatively confirm the theoretical study. This paper is a first attempt to provide a comprehensive analysis of the potential fluctuation in flow. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
34. Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel: Reynolds Number Effect.
- Author
-
Ahn, Joon, Song, Jeong Chul, and Lee, Joon Sik
- Subjects
REYNOLDS number ,HEAT transfer ,TURBULENT flow ,TURBULENCE ,THERMAL conductivity ,LAMINAR flow ,LARGE eddy simulation models - Abstract
Large eddy simulations were performed for the conjugate heat transfer in a ribbed channel with a geometry, that mimics the internal cooling passage of a gas turbine, using 566, 100, 10, and 1 as the solid and fluid thermal conductivity ratios (K*) and 30,000, 7000 (turbulent flow), and 1000 (laminar flow) as the Reynolds numbers. A fully coupled simulation was conducted using the immersed boundary method (IBM) and a dynamic sub-grid-scale (SGS) model. In pure convection, a decrease in the Reynolds number from 30,000 to 7000 increased the heat transfer on the channel wall by 5% but decreased that on the rib by 20%. When K* > 10, the Reynolds number effect is stronger in the rib than in the wall. In the laminar flow, the effect of conduction appears at a low K*, and the heat transfer promotion is poor in the typical ribbed channel geometry. In the turbulent flow, if K* ≥ 100, then a heat transfer promotion is expected in the ribbed channel even at a low Reynolds number. For K* < 10, the thermal performance in the turbulent flow is worse than that in the laminar flow, and thus, no rib effect is expected. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
35. A Novel Manifold Dual-Microchannel Flow Field Structure with High-Performance Heat Dissipation.
- Author
-
Yang, Xing, Lin, Kabin, Zhang, Daxing, Liu, Shaoyi, Han, Baoqing, Wang, Zhihai, Yu, Kunpeng, Wu, Wenzhi, Ge, Dongming, and Wang, Congsi
- Subjects
HEAT flux ,HEAT transfer ,ELECTRONIC equipment ,HEAT capacity ,MICROCHANNEL flow ,ACTINIC flux - Abstract
With the development of miniaturization and integration of electronic devices, the conventional manifold microchannels (MMCs) structure has been unable to meet the heat dissipation requirements caused by the rapid growth of internal heat flux. There is an urgent need to design a new heat dissipation structure with higher heat dissipation capacity to ensure the working stability and life of electronic devices. In this paper, we designed a novel manifold dual-microchannel (MDMC) cooling system that embedded the microchannel structure into the manifold microchannel structure. The MDMC not only has good heat dissipation performance that can meet the development needs of electronic equipment to miniaturization and integration, but also has a compact structure that does not increase the overall thickness and volume compared with MMC. The high temperature uniformity and heat transfer performance of MDMC are significantly improved compared to MMC. The T
max is reduced by 13.6% and 17.5% at the heat flux density of 300 W/cm2 and 700 W/cm2 , respectively. In addition, the influence of the inlet−2 velocity and the total microchannels number on the heat transfer performance of the MDMC structure are numerically investigated. The results show that the decrease rate of Tmax and ΔT is about 6.69% and 16% with the increase of inlet−2 velocity from 1.2 m/s to 2.4 m/s and microchannels number from 10 to 48, respectively. At the same time, the best temperature uniformity is obtained when the number of microchannels is 16. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
36. Applications of Smartphone-Based Aptasensor for Diverse Targets Detection.
- Author
-
Lan, Ying, He, Baixun, Tan, Cherie S., and Ming, Dong
- Subjects
NUCLEIC acids ,CHRONOBIOLOGY ,APTAMERS ,POINT-of-care testing ,METAL ions - Abstract
Aptamers are a particular class of functional recognition ligands with high specificity and affinity to their targets. As the candidate recognition layer of biosensors, aptamers can be used to sense biomolecules. Aptasensors, aptamer-based biosensors, have been demonstrated to be specific, sensitive, and cost-effective. Furthermore, smartphone-based devices have shown their advantages in binding to aptasensors for point-of-care testing (POCT), which offers an immediate or spontaneous responding time for biological testing. This review describes smartphone-based aptasensors to detect various targets such as metal ions, nucleic acids, proteins, and cells. Additionally, the focus is also on aptasensors-related technologies and configurations. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
37. Modal Decomposition Techniques: Application in Coherent Structures for a Saccular Aneurysm Model.
- Author
-
Yu, Paulo and Durgesh, Vibhav
- Subjects
PARTICLE image velocimetry ,PROPER orthogonal decomposition ,SINUS of valsalva ,ANEURYSMS ,RECIPROCATING pumps ,DECOMPOSITION method - Abstract
Aneurysms are localized expansions of blood vessels which can be fatal upon rupture. Studies have shown that aneurysm flows exhibit complex flow phenomena which consist of single or multiple vortical structures that move within the flow cycle. Understanding the complex flow behaviors of aneurysms remain challenging. Thus, the goal of this study is to quantify the flow behavior and extract physical insights into aneurysm flows using advance data decomposition methods, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The velocity field data were obtained by performing 2D Particle Image Velocimetry (2D PIV) on the mid-plane of an idealized, rigid, saccular aneurysm model. The input flow conditions were set to R e p = 50 and 150 for a fixed α = 2 using a precisely controlled piston pump system. POD was used to quantify the spatial features of the flows, while DMD was used to obtain insight on the dynamics. The results obtained from POD and DMD showed the capability of both methods to quantify the flow field, with the modes obtained providing different insights into the flow evolution in the aneurysm. The curve-fitting step of the POD time-varying coefficients, and the appropriate selection of DMD modes based on their energy contribution, allowed the mathematical flow models from POD and DMD to reconstruct flow fields at any given time step. This can be used for validation of numerical or computational data. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
38. Comparison of Flow Behavior in Saccular Aneurysm Models Using Proper Orthogonal Decomposition.
- Author
-
Yu, Paulo and Durgesh, Vibhav
- Subjects
PROPER orthogonal decomposition ,ORTHOGONAL decompositions ,PARTICLE image velocimetry ,ANEURYSMS ,MODE shapes ,GEOMETRIC modeling - Abstract
Aneurysms are abnormal ballooning of a blood vessel. Previous studies have shown presence of complex flow structures in aneurysms. The objective of this study was to quantify the flow features observed in two selected saccular aneurysm geometries over a range of inflow conditions using Proper Orthogonal Decomposition (POD). For this purpose, two rigid-wall saccular aneurysm models geometries were used (i.e., the bottleneck factor of 1 and 1.6), and the inflow conditions were varied using a peak Reynolds number ( R e p ) from 50 and 270 and Womersley number (α) from 2 and 5. The velocity flow field data for the studied aneurysm geometries were acquired using Particle Image Velocimetry (PIV). The average flow field from the PIV measurement showed that the model geometry and R e p have more significant impact on the average flow field than the variations in α. The POD results showed that the method was able to quantify the flow field characteristics between the two model geometries. The mode shapes obtained showed different spatial structures for each inflow scenarios and models. The POD energy results showed that more than 80 % of the fluctuating kinetic energy were captured within five POD modes for B F = 1.0 flow scenarios, while they were captured within ten modes for B F = 1.6 . The time varying coefficient results showed the complex interplay of POD modes at different inflow scenarios, highlighting important modes at different phases of the flow cycle. The low-order reconstruction results showed that the vortical structure either proceeded outward or stayed within the aneurysm, and this behavior was highly dependent on α , R e p , and model geometry that were not evident in average PIV results. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
39. Analysis of thermo-hydraulic and entropy generation characteristics for flow through ribbed-wavy channel.
- Author
-
Mehta, Sumit Kumar, Pati, Sukumar, Ahmed, Shahid, Bhattacharyya, Prangan, and Bordoloi, Jishnu Jyoti
- Subjects
THERMAL hydraulics ,NUSSELT number ,ENTROPY ,LAMINAR flow ,REYNOLDS number ,TRANSPORT equation - Abstract
Purpose: The purpose of this study is to analyze the thermal, hydraulic and entropy generation characteristics for laminar flow of water through a ribbed-wavy channel with the top wall as wavy and bottom wall as flat with ribs of three different geometries, namely, triangular, rectangular and semi-circular. Design/methodology/approach: The finite element method-based numerical solver has been adopted to solve the governing transport equations. Findings: A critical value of Reynolds number (Re
cri ) is found beyond which, the average Nusselt number for the wavy or ribbed-wavy channel is more than that for a parallel plate channel and the value of Recri decreases with the increase in a number of ribs and for any given number of ribs, it is minimum for rectangular ribs. The performance factor (PF) sharply decreases with Reynolds number (Re) up to Re = 50 for all types of ribbed-wavy channels. For Re > 50, the change in PF with Re is gradual and decreases for all the ribbed cases and for the sinusoidal channel, it increases beyond Re = 100. The magnitude of PF strongly depends on the shape and number of ribs and Re. The relative magnitude of total entropy generation for different ribbed channels varies with Re and the number of ribs. Practical implications: The findings of the present study are useful to design the economic heat exchanging devices. Originality/value: The effects of shape and the number of ribs on the heat transfer performance and entropy generation have been investigated for the first time for the laminar flow regime. Also, the effects of shape and number of ribs on the flow and temperature fields and entropy generation have been investigated in detail. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
40. Effect of divider wall-to-end wall distance on the vortical structures and heat transfer characteristics of two-pass channel using topological analysis.
- Author
-
Zhao, Zhiqi, Luo, Lei, Qiu, Dandan, Wang, Songtao, Wang, Zhongqi, and Sunden, Bengt Ake
- Subjects
HEAT transfer ,FLOW separation ,SHEAR flow ,THREE-dimensional flow ,GAS turbine blades ,VORTEX generators ,JET impingement - Abstract
Purpose: This study aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis and critical points principles of three-dimensional vortex flow. Design/methodology/approach: This aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis as well as critical points principles of three-dimensional vortex flow. Findings: The endwall heat transfer in the narrow spacing passage is significantly stronger than that in a wide spacing channel. As the gap clearance is kept at 0.87 times of the hydraulic diameter, the endwall heat transfer and thermal performance can be accordingly enhanced with low pressure drops, which is because a relatively strong concentrated impingement flow for the medium gap clearance helps to restrain the downstream fluid flow and enhance the shear effect of the secondary flow. Practical implications: The numerical results can be applied in designing sharp turn of serpentine channel in heat exchangers, heat sinks, piping system, solar receiver and gas turbine blades. Originality/value: The evolution mechanism of the vortices in the turning region under different gap clearance was analyzed, and thermal enhancement characteristics were predicted innovatively using topological analysis method. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
41. Heat Transfer and Friction in a Low-Aspect-Ratio Rectangular Channel with Staggered Slit-Ribbed Walls.
- Author
-
JENN-JIANG HWANG and TONG-MIIN LIOU
- Published
- 1998
42. Numerical Design and Laboratory Testing of Encapsulated PCM Panels for PCM-Air Heat Exchangers.
- Author
-
Santos, Thiago, Wrobel, Luiz C., Hopper, Nick, and Kolokotroni, Maria
- Subjects
HEAT exchangers ,TESTING laboratories ,HEAT transfer ,TEST design ,INDUSTRIAL costs - Abstract
Heat transfer between encapsulated PCM panels and air plays an important role in PCM-Air heat exchangers. A new design for the encapsulation panel was developed considering practical aspects such as the cost of production and ease of manufacturing, in addition to heat transfer and pressure drop. A number of encapsulated panel surfaces were first investigated via 3D CFD simulations and compared with an existing panel in use by a commercial PCM-Air heat exchanger manufacturer. After validation, 2D CFD simulations were carried out for 32 different geometries to select the most effective design, which was fabricated and tested in the laboratory. Laboratory parameters tested included heat transfer, pressure drop and melting/solidifying. The laboratory results confirmed the improvements of the new panel in comparison with the existing panel and a flat panel. It was found that the proposed design doubled the heat transfer, holds 13.7% more material and the fan can overcome the increased pressure drop. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
43. Particle Image Velocimetry Measurements of the Flow-Diverting Effects of a New Generation of the eCLIPs Implant for the Treatment of Intracranial Bifurcation Aneurysms.
- Author
-
G. Yazdi, Sina, Mercier, Daniel, Bernard, Renee, Tynan, Adam, and Ricci, Donald R.
- Subjects
INTRACRANIAL aneurysms ,ENDOVASCULAR surgery ,FLUID dynamics ,PARTICLE image velocimetry - Abstract
Flow diverters (FDs) for the endovascular treatment of intracranial aneurysms are effective for sidewall aneurysms, but their use at a bifurcation is problematic because FDs only partially cover the aneurysm neck and impede flow into a daughter branch; they are thus not employed routinely in this anatomy. eCLIPs was developed as a non-tubular implant to completely cover the neck of an aneurysm and serve as a coil retention device necessary for the adequate treatment of wide-neck bifurcation aneurysms. eCLIPs has shown some flow diversion effects in bifurcation anatomy but not equal to those exhibited by clinically accepted flow diverters in sidewall anatomy. A new generation of eCLIPs implant, the eCLIPs bifurcation flow diverter (eBFD), with higher metal coverage, was developed to achieve a similar flow diversion as a Pipeline Embolization Device (PED), a prototypical FD. Particle image velocimetry was used to capture the fluid dynamics and velocity reduction within silicone aneurysm replicas. A circulatory mimicking loop was developed to circulate the flow through the silicone models. All generations of eCLIPs implants had some flow-diverting effect, with increasing metal coverage density of the implant proportionately increasing the flow diversion effect. The eBFD, with a metal density of 35%, showed greater flow diversion than PED, with 30% metal density, for bifurcation anatomy. The eBFD showed similar reduction of flow in a bifurcation anatomy to PED in a sidewall, both sufficient to permit early thrombosis of the aneurysm. Thus, the eBFD can potentially provide sufficient flow diversion for the treatment of bifurcation aneurysms to avoid adjunctive coiling. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
44. Baffle orientation and geometry effects on turbulent heat transfer of a constant property incompressible fluid flow inside a rectangular channel.
- Author
-
Menni, Younes, Chamkha, A., Zidani, Chafika, and Benyoucef, Boumédiène
- Subjects
TURBULENT heat transfer ,FLUID flow ,INCOMPRESSIBLE flow ,COMPUTATIONAL fluid dynamics ,NEWTONIAN fluids ,FORCED convection - Abstract
Purpose: A computational fluid dynamics (CFD) analysis has been carried out on the aerodynamic and thermal behavior of an incompressible Newtonian fluid having a constant property and flowing turbulently through a two-dimensional horizontal high-performance heat transfer channel with a rectangular cross section. The top surface of the channel was kept at a constant temperature, while it was made sure to maintain the adiabatic condition of the bottom surface. Two obstacles, with different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel; they were fixed to the top and bottom surfaces of the channel in a periodically staggered manner to force vortices to improve the mixing and consequently the heat transfer. The first fin-type obstacle is placed on the heated top channel surface, and the second baffle-type one is placed on the insulated bottom surface. Five different obstacle situations were considered in this study, which are referred as cases FF (flat fin and flat baffle), FVD (flat fin and V-downstream baffle), FVU (flat fin and V-upstream baffle), VVD (V-downstream fin and V-downstream baffle) and VVU (V-Upstream fin and V-upstream baffle). Design/methodology/approach: The flow model is governed by Reynolds-averaged Navier–Stokes equations with the k-epsilon turbulence model and the energy equation. These governing equations are discretized by the finite volume method, in two dimensions, using the commercial CFD software FLUENT software with the Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm for handling the pressure-velocity coupling. Air is the test fluid with the flow rate in terms of Reynolds numbers ranging from 12,000 to 32,000. Findings: Important deformations and large recirculation regions were observed in the flow field. A vortex causes a rotary motion inside the flow field, which enhances the mixing by bringing the packets of fluid from the near-wall region of the channel to the bulk and the other way around. The largest value of the axial variations of the Nusselt number and skin friction coefficient is found in the region facing the baffle, while the smallest value is in the region near the fin, for all cases. The thermal enhancement factor (TEF) was also introduced and discussed to assess the performance of the channel for various obstacle situations. It is found that the TEF values are 1.273-1.368, 1.377-1.573, 1.444-1.833, 1.398-1.565 and 1.348-1.592 for FF, FVD, FVU, VVD and VVU respectively, depending on the Re values. In all cases, the TEF was found to be much larger than unity; its maximum value was around 1.833 for FVU at the highest Reynolds number. Therefore, the FVU may be considered as the best geometrical configuration when using the obstacles to improve the heat transfer efficiency inside the channel. Originality/value: This study can be a real application in the field of shell-and-tube heat exchangers and flat plate solar air collectors. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
45. Enhanced heat transfer in a labyrinth channels with ribs of different shape.
- Author
-
Du, Wei, Luo, Lei, Wang, Songtao, Liu, Jian, and Sunden, Bengt Ake
- Subjects
HEAT transfer ,NUSSELT number ,NAVIER-Stokes equations ,REYNOLDS number ,GAS turbines ,VORTEX shedding - Abstract
Purpose: The purpose of this study is to enhance the thermal performance in the labyrinth channel by different ribs shape. The labyrinth channel is a relatively new cooling structure to decrease the temperature near the trailing region of gas turbine. Design/methodology/approach: Based on the geometric similarity, a simplified geometric model is used. The k − ω turbulence model is used to close the Navier–Stokes equations. Five rib shapes (one rectangular rib, two arched ribs and two trapezoid ribs) and five Reynolds numbers (10,000 to 50,000) are considered. The Nusselt number, flow structure and friction factor are analyzed. Findings: Nusselt number is tightly related to the rib shape in the labyrinth channel. The different shapes of the ribs result in different horseshoe vortex and wake region. In general, the arched rib brings the highest Nusselt number and friction factor. The Nusselt number is increased by 15.8 per cent compared to that of trapezoidal ribs. High Nusselt number is accompanied by the high friction factor in a labyrinth channels. The friction factor is increased by 64.6 per cent compared to rectangular ribs. However, the rib shape has a minor effect on the overall thermal performance. Practical implications: This study is useful to protect the trailing region of advanced gas turbine. Originality/value: This paper presents the flow structure and heat transfer characteristics in a labyrinth channel with different rib shapes. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
46. Experimental Study of the Influence of the Shape of the Gap between the Rib and Flat Plate on the Near-Wall Flow Structure and Heat Transfer.
- Author
-
Isaev, S. A., Afanasiev, V. N., Egorov, K. S., and Kong, Dehai
- Subjects
TURBULENT boundary layer ,THERMAL boundary layer ,HEAT transfer ,BOUNDARY layer (Aerodynamics) ,PLATING - Abstract
The article presents an analysis of the results of an experimental study of the dynamic and thermal characteristics of the turbulent boundary layer of the air near a heated plate at q
w = const with rectangular ribs having slit channels of different geometry: confusor, diffuser, and plane-parallel. The slit channel is located between the plate and the lower rib wall. The results are compared with similar data for a solid rib without the slit channel. A Pitot–Prandtl microprobe with a microthermocouple and the Dantec Dynamics hot-wire anemometer were used, thus making it possible to study the laminar sublayer, the transition domain, and the outer part of the boundary layer. The influence of the slit profile on the average and the pulsation characteristics of the turbulent dynamic and thermal boundary layers in the median section of the plate with the slit rib is revealed. It is found that the separated zone disappears in the flow behind the ribs with the confusor slit. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
47. Numerical investigation of flame splitting phenomenon in upward flame spread over solids with a two-stage pyrolysis model.
- Author
-
Li, Chengyao and Liao, Ya-Ting T.
- Subjects
FLAME ,PYROLYSIS ,SOLIDS ,NUMERICAL analysis ,PRESSURE - Abstract
Upward flame spread over thin solids is numerically studied using an in-house three-dimensional transient numerical model with a two-stage solid pyrolysis. The simulation results reveal fundamentally different flame behaviors in different pressure conditions. At low pressures, conventional continuous flame spread is observed. Upon ignition, the flame grows and spreads upward until it reaches the end of the sample. At high pressures, the flame splits into two flames shortly after ignition. The two flames spread upward separately at different spread rates. In a transitional pressure region, cyclic flame splitting was observed. The flame splits periodically during the upward spreading process. In each splitting cycle, the bottom flame extinguishes shortly after splitting while the top flame continuously spreads upward and starts a new splitting cycle. This flame splitting phenomenon was previously observed experimentally, but to the authors’ knowledge is numerically captured for the first time in this study. The splitting process is presented in detail and compared with the continuous flame spread process. The numerical results indicate that the multi-stage pyrolysis is responsible for the flame splitting. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
48. Numerical Investigation of Forced Convection Flow of Nanofluids in Rotating U-Shaped Smooth and Ribbed Channels.
- Author
-
Kanikzadeh, Mokhtar and Sohankar, Ahmad
- Subjects
CHANNELS (Hydraulic engineering) ,CONVECTIVE flow ,HEAT convection ,FORCED convection ,HEAT transfer ,NANOFLUIDS ,NANOPARTICLES - Abstract
The impact of the nanoparticles and ribs on the thermal performance of the rotating U-type cooling channel are investigated for turbulent forced convection flow of nanofluids. The nanofluids are provided by the inclusion of the nanoparticles of TiO2and Al2O3in water as the base fluid, namely, water/Al2O3and water/TiO2nanofluids mixtures. The simulations are performed for three-dimensional turbulent flow and heat transfer using an RNG k-ϵ turbulence model for Reynolds number range of 5000 to 20,000. To show the effectiveness of the ribs and nanofluids, three criteria are employed: heat transfer enhancement, pressure drop or power consumed, and the thermal performance factor. It is found that the contribution of turbulence promotion in heat transfer enhancement of the ribbed channel is more effective than that of enlarging the heat surface area. The results show that using ribs at the lowest Reynolds number and utilizing nanofluids at the highest one provide high heat transfer rate and thermal performance. At the middle Reynolds numbers, the effects of these two methods on heat transfer enhancement are relatively close to each other. In this case, if the pumping power is the main concern, using nanofluids is recommended due to providing a smaller pressure drop penalty. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
49. Thermal Behavior in Rectangular Channel Duct Fitted With V-Shaped Perforated Baffles.
- Author
-
Chamoli, Sunil and Thakur, Narender Singh
- Subjects
THERMAL properties ,AIR heater efficiency ,EXPANSION of liquids ,ENERGY conversion ,THERMAL analysis ,ELECTROMAGNETIC waves ,FRICTION - Abstract
An experimental investigation has been carried out to study the heat transfer and friction factor characteristics of a V-down-perforated baffled roughened solar air heater duct. The roughened wall was uniformly heated and the rest three walls of the duct were kept insulated. Measurements have been carried out for the duct aspect ratio of 10, Reynolds number range of 3800–19,000, relative hole position range of 0.429–0.571, relative roughness pitch range of 2–4, and open area ratio range of 12–44%. The relative roughness height of 0.4 and angle of attack of 60° are kept constant during the entire experimentation. The heat transfer and friction factor data obtained were compared with the data obtained from a smooth duct under similar operating conditions. In comparison to the smooth duct the V-shaped perforated baffle roughened duct enhanced the Nusselt number and friction factor by 2.57 and 5.96 times, respectively. The thermohydraulic performance parameter is found superior for the open area ratio of 24% and relative roughness pitch of 2.5. [ABSTRACT FROM PUBLISHER]
- Published
- 2015
- Full Text
- View/download PDF
50. Numerical Optimization of Turbulent Flow and Heat Transfer Characteristics in a Ribbed Channel.
- Author
-
Yang, Yue-Tzu and Chen, Peng-Jen
- Subjects
HEAT transfer ,TURBULENT flow ,COMPUTER simulation ,GENETIC algorithms ,STEAM ,HEAT losses ,METHODOLOGY - Abstract
By using an optimal method coupled with the numerical simulation of the response surface methodology and genetic algorithm, the geometric configuration for two-dimensional ribbed channels is optimized in this paper. The parameters studied are the height of rib, the thickness of rib, and the pitch. The objective of optimization is to maximize the performance factor of the ribbed channel. The results show that the optimal method works for an optimized design of a two-dimensional ribbed channels. The ribs are demonstrated such that they can significantly affect the heat transfer rate and the friction factor. For the in-line ribbed channel, the performance factor increased by 1.1–1.5. In a staggered ribbed channel, the performance factor reached 2.681. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
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