3,367 results on '"hydraulic diameter"'
Search Results
2. Comparison of Experimental and Analytical Results of Impact of Various Geometrical Configurations on Pressure Drop Through Micro-channel
- Author
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Kale, Sachin M., Kashid, Digambar T., Parkhe, Avinash K., Wangikar, Sandip S., Jadhav, Chetan C., Gaikwad, Sunil S., Pawar, Prashant M., editor, Ronge, Babruvahan P., editor, Gidde, Ranjitsinha R., editor, Pawar, Meenakshi M., editor, Misal, Nitin D., editor, Budhewar, Anupama S., editor, More, Vrunal V., editor, and Reddy, P. Venkata, editor
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- 2024
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3. Hydro-dynamically and thermally fully developed flow analysis of magneto-hydrodynamic fluid through annular duct.
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Ahmed, Farhan, Akbar, Noreen Sher, and Tripathi, Dharmendra
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HEAT convection , *MAGNETIC field effects , *MAGNETOHYDRODYNAMICS , *PARTIAL differential equations , *ANNULAR flow , *FORCED convection , *FREE convection - Abstract
A hydro-dynamic thermal fully developed forced convective heat transfer analysis of magneto-hydrodynamics fluid flow through an annular sector duct is presented in this paper. Two types of thermal boundary conditions i.e., axially uniform heat flux along with peripherally uniform temperature (known as H1-condition) and, axially and peripherally uniform temperature (known as T condition), have been considered to carry out the thermal analysis of fluid. The velocity components along r and θ direction are transformed into algebraic form by using power law discretized scheme, whereas cross-sectional pressure P (r , θ) is estimated with the help of well know technique S I M P L E R. The governing partial differential equations are solved by numerically with the help of M A T L A B code. Furthermore, simulated results have been compared with the existing results of literature to validate the results. From the results, it is noted that hydro-dynamically and thermally impacts relate directly by increasing the Hartman number, (M). It is further reported that the effect of magnetic field becomes insignificant for the higher number of fins, N. The findings of the present analysis will be applicable in various types of thermal systems. [ABSTRACT FROM AUTHOR]
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- 2024
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4. Fluid Mechanics and Momentum Transfer
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Nandagopal, Nuggenhalli S. and Nandagopal, Nuggenhalli S.
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- 2023
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5. Numerical Analysis of Smooth and Wavy Wall Microchannel Heat Sink for Electronic Cooling Applications
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Sathish Kumar, D., Jayavel, S., Cavas-Martínez, Francisco, Series Editor, Chaari, Fakher, Series Editor, di Mare, Francesca, Series Editor, Gherardini, Francesco, Series Editor, Haddar, Mohamed, Series Editor, Ivanov, Vitalii, Series Editor, Kwon, Young W., Series Editor, Trojanowska, Justyna, Series Editor, Maity, D., editor, Patra, P. K., editor, Afzal, M.S., editor, Ghoshal, R., editor, Mistry, C. S., editor, Jana, P., editor, and Maiti, D. K., editor
- Published
- 2022
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6. Propagation characteristics of unstable detonation waves in a round tube with annular perturbation.
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Zhao, Huanjuan, Liu, Keqing, Lin, Min, Dong, Shiming, and Lin, Wei
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DETONATION waves , *TUBES , *CELL anatomy , *CELL aggregation , *CELL size - Abstract
The detonation propagation characteristics of the mixtures, 2H 2 + O 2 +3Ar and CH 4 + 2O 2 , were investigated. Accordingly, the mixtures were tested in round tube with inner diameter of D = 80 mm and annular tubes with widths of w = 25 mm, 15 mm, and 5 mm. The two mixtures represent stable mixture with regular cell pattern and unstable mixture with irregular cell pattern, respectively. Smoked foils were utilized to record cellular structure under various initial conditions. Subsequently, the length scale L dsc was measured, which represents the length from the start of the test section to the position where the cellular structure changes drastically (the cell size obviously increases or the structure disappears). The results reveal that both mixtures can successfully propagate in round tube and annular tubes of 25 mm and 15 mm, but fail in 5 mm annular tube. The L dsc value of 2H 2 + O 2 + 3Ar is higher than that of CH 4 + 2O 2 in 80 mm and 15 mm tubes, but it is opposite in 25 mm tube. Moreover, the relationship between L dsc and hydraulic diameter D H was analysed. For a given tube, the values of L dsc and L dsc / D H increased when the initial pressure increased. And the variation trend of L dsc and L dsc / D H of CH 4 + 2O 2 is steeper. Furthermore, the mixtures 2H 2 + O 2 + 3Ar and CH 4 + 2O 2 resulted in over-driven detonation in 15 mm and 25 mm annular tubes, respectively. The ratio between the total reaction length (sum of the induction length and exothermic length) and the hydraulic diameter (D H /(Δ i + Δ e)) correspond to critical values of 18 for hydrogen-oxygen-argon and 6 for methane-oxygen, below which the detonation will fail. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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7. The thermal performance of ground-coupled heat exchanger with different geometrical shapes – a numerical study.
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Kumar, Sudhir and Gajbhiye, Narendra
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HEAT exchangers , *ATMOSPHERIC temperature , *TEMPERATURE , *VELOCITY - Abstract
The thermal performance of different cross-sectional areas of a U-shape ground-coupled heat exchanger (GCHE) is numerically investigated for summer and winter conditions in the present paper. The four different cross-sectional tubes, viz. square, circular, triangular, and rectangular, of fixed hydraulic diameter and length are considered. Numerical simulations are carried out for different velocities ranging from 2 m/s − 5 m/s using K-epsilon turbulent model. It is found that the rectangular cross-sectional area GCHE provides a more stable air temperature for both summer and winter conditioning, and a maximum temperature drop/rise is observed at a shorter length in this condition. The temperature drop of 14.2 K is observed at a length of 12.6 m in the case of GCHE with rectangular cross-section, while the same drop is reported at 19.2 m, 17.4 m, and 16.5 m for circular, square, and triangular cross-sectional areas, respectively. A maximum temperature rise of 8.3 K is reported at 14.8 m, 20.7 m, 18.2 m, and 17.5 m in rectangular, circular, square, and triangular cross-sectional GCHE for heating conditions. Therefore, the rectangular cross-section GCHE may be preferred for space constraints. The net temperature difference is found to be dependent on inlet air temperature. It increases with an increase in the inlet air temperature for summer cooling conditions and reverses in winter conditions. The inlet velocity greatly influences the thermal performance of GCHE, and optimum performance is found at a lower velocity of 2 m/s due to the more settling time. The effectiveness is found to increase initially along the length, and it attains a maximum value at a shorter length in the case of rectangular cross-section compared to other sections. The maximum effectiveness is achieved between 14 m to 15 m length of the pipe for the case of rectangular cross-sectional GCHE. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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8. Analysis on heat transfer enhancement mechanism in a cross-wavy primary surface heat exchanger based on advection thermal resistance method.
- Author
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Zhang, Bo, Chu, Wenxiao, and Wang, Qiuwang
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REYNOLDS number , *THERMAL resistance , *HEAT transfer , *BOUNDARY layer (Aerodynamics) , *HEAT exchangers - Abstract
• Flow and heat transfer characteristics in CW-type PSHE are numerically studied. • The effect of hydraulic diameter is analyzed. • The effect of airflow shuttling on heat transfer enhancement is explained. • The local thermal resistance analysis method is applied. This paper numerically investigates the flow and heat transfer characteristics in the primary surface heat exchanger (PSHE) with cross-wavy (CW) structures. The comprehensive performance affected by hydraulic diameters is evaluated. Moreover, the airflow shuttling behavior at the mixing area of CW-type PSHE is discussed, showing rapid heat transfer enhancement. The advection thermal resistance method and local thermal resistance analysis is proposed, while the impacts of longitudinal pitch and flowrates are considered. Results show that the case with a large hydraulic diameter displays much better comprehensive performance at lower flowrates. When raising the hydraulic diameter from 1.58 mm to 15.8 mm, the heat transfer rate per unit pumping power grows by 36.1 %. However, the priority of large channel is gradually disappeared after increasing the flowrates. Meanwhile, the larger longitudinal pitch of the CW channel may result in pronounced improvement on the heat transfer performance due to the presence of airflow shutting behavior at the mixing area as well as the secondary flow near the channel boundary layers. When no airflow shuttling exists, very high advection thermal resistance region can be observed due to the formation of boundary layers. It can be recognized that the case with airflow shuttling behavior can display similar heat transfer improvement compared to that with increasingly high Reynolds numbers, yet the pressure loss is rarely increased. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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9. Numerical investigation of friction laws for laminar and turbulent flow in undulated channels
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Benim, Ali Cemal and Maddala, Sai Bhagavan
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- 2021
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10. HEAT TRANSFER DURING LIQUID FILTRATION IN AN ANNULAR CHANNEL FILLED WITH POROUS MEDIUM
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Ruslan A. Dekhtyar
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filtration ,heat exchange ,porous media ,annular channel ,hydraulic diameter ,Engineering geology. Rock mechanics. Soil mechanics. Underground construction ,TA703-712 - Abstract
The relevance of the work is caused by the wide use of porous media, both in the design and optimization of compact heat exchangers and in the engineering calculations of the characteristics of heat and mass transfer in the channels with a grainy medium and when flowing around the bodies immersed in the porous medium. The main aim of the research is the experimental study of heat transfer in an annular channel filled with a granular medium at various modes of liquid filtration; to obtain semi-empirical correlations for heat transfer in the inertial mode of fluid filtration in an annular channel. Objects: annular channel with a porous insert consisting of glass beads of the same diameter with different types of both regular and chaotic pakings. Methods: experimental methods for finding the patterns of heat exchange processes. In experiments, using thermocouples, the temperature of the heated outer wall of the annular channel was measured in four sections and the temperature of the heater at two different points. The temperatures at the inlet to the working station and at the output of it were measured as well. Simultaneously with thermal investigation, the fluid flow was measured when filtering through a porous insert. Porosity was determined by the usual weighty way. In special calibration experiments, the heat losses of the working section were determined separately. The calculation of the heat transfer coefficient was carried out according to the flow of heat to the outer wall of the annular channel, taking into account heat losses and, along the difference in the measured wall temperature and the medium-mass fluid temperature in this section. The paper introduces the results of the experimental study of liquid filtration flow heat exchange with the walls of the annular channel filled with a porous medium at constant heat flux on the outer wall. The study was conducted on ring channels with different widths. The width of the channel was laid either one layer of the balls of one diameter with two types of packages: cubic and rhombohedral, or several layers of balls, but already with arbitrary packaging (from 3 to 10 ball width). When processing the experimental data, hydraulic grain diameter is selected as the determining geometric parameter. It is shown that, depending on the filtration mode, various laws of heat exchange exist through a porous insert. So for the turbulent filtering mode, the obtained data for heat exchange is well summarized by the universal «law of two-thirds». The paper introduces the comparison with the data of other authors, both for heat exchange in the annular channel and in a round tube. It is shown that in the inertial mode of filtration, the heat exchange corresponds to the regularity of Nu~Re1/2.
- Published
- 2021
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11. The hydraulic and thermal performances of rectangular and square microchannel with different hydraulic diameters cooled by graphene–platinum hybrid nanofluid.
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Kumar R, Avinash, M, Kavitha, Kumar, P Manoj, and Seshadri S, Arvindh
- Abstract
The objective of this paper is to analyze the effect of hydraulic diameter and channel shape on the thermal and hydrodynamic characteristics of a microchannel cooled by Graphene–Platinum/water hybrid nanofluid for electronic cooling applications. The study was performed numerically using mathematical software called Maple 19.0. Microchannels having square and rectangular cross-sections, and hydraulic diameters ranging from 200 µm to 1,000 µm were taken into consideration. Thermal resistance, heat transfer coefficient, pressure drop, and friction factor were evaluated for different conditions and their corresponding graphs are presented and discussed. It was evident from the results that low thermal resistance and high heat transfer coefficient was achieved upon decreasing the hydraulic diameter, which is favorable for the cooling of electronic chips and devices. Based on the Reynolds number, the heat transfer coefficient increased by 2–4 times for both rectangular and square microchannels, on decreasing the hydraulic diameter from highest value (1,000 µm) to lowest value (200 µm). However, friction factor and pressure drop increased for channels with lower hydraulic diameters. In addition, rectangular microchannels exhibited better heat transfer performance, while square microchannels had lower friction factor and pressure drop. Rectangular microchannels presented a maximum enhancement of 30% in heat transfer coefficient and a reduction of 18% in thermal resistance, when compared to square microchannels. The results also suggested that the performance of microchannels with 500 µm hydraulic diameter is balanced, considering both heat transfer performance and pressure drop constraints. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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12. Effect of Channel Confinement and Hydraulic Diameter on Heat Transfer in a Micro-channel
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Sathishkumar, D., Jayavel, S., Srinivasacharya, D., editor, and Reddy, K. Srinivas, editor
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- 2019
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13. Contrasting Carbon Allocation Strategies of Ring-Porous and Diffuse-Porous Species Converge Toward Similar Growth Responses to Drought.
- Author
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Buttó, Valentina, Millan, Mathilde, Rossi, Sergio, and Delagrange, Sylvain
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DROUGHTS ,TREE growth ,SOIL moisture ,CLIMATE extremes ,MIXED forests ,SPECIES ,RED oak - Abstract
Extreme climatic events that are expected under global warming expose forest ecosystems to drought stress, which may affect the growth and productivity. We assessed intra-annual growth responses of trees to soil water content in species belonging to different functional groups of tree-ring porosity. We pose the hypothesis that species with contrasting carbon allocation strategies, which emerge from different relationships between wood traits and canopy architecture, display divergent growth responses to drought. We selected two diffuse-porous species (Acer saccharum and Betula alleghaniensis) and two ring-porous species (Quercus rubra and Fraxinus americana) from the mixed forest of Quebec (Canada). We measured anatomical wood traits and canopy architecture in eight individuals per species and assessed tree growth sensitivity to water balance during 2008–2017 using the standardized precipitation evapotranspiration index (SPEI). Stem elongation in diffuse-porous species mainly depended upon the total number of ramifications and hydraulic diameter of the tree-ring vessels. In ring-porous species, stem elongation mainly depended upon the productivity of the current year, i.e., number of vessels and basal area increment. Diffuse-porous and ring-porous species had similar responses to soil water balance. The effect of soil water balance on tree growth changed during the growing season. In April, decreasing soil temperature linked to wet conditions could explain the negative relationship between SPEI and tree growth. In late spring, greater water availability affected carbon partitioning, by promoting the formation of larger xylem vessels in both functional groups. Results suggest that timings and duration of drought events affect meristem growth and carbon allocation in both functional groups. Drought induces the formation of fewer xylem vessels in ring-porous species, and smaller xylem vessels in diffuse-porous species, the latter being also prone to a decline in stem elongation due to a reduced number of ramifications. Indeed, stem elongation of diffuse-porous species is influenced by environmental conditions of the previous year, which determine the total number of ramifications during the current year. Drought responses in different functional groups are thus characterized by different drivers, express contrasting levels of resistance or resilience, but finally result in an overall similar loss of productivity. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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14. Effect of Hydraulic Diameter on Potential Core Decay of Supersonic Jets
- Author
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Prasanta Kumar MOHANTA and B. T. N. SRIDHAR
- Subjects
non-circular jet ,potential core ,exit-geometry ,hydraulic diameter ,decay characteristics ,jet mixing ,Motor vehicles. Aeronautics. Astronautics ,TL1-4050 - Abstract
Various studies dealing with decay characteristics of circular and noncircular supersonic jets were conducted by previous researchers. But in these studies due emphasis was not given to the hydraulic diameter (Dh), shape factor (ζ) & the nozzle lip parameters which have significant impact on the characteristics of noncircular supersonic jet. In this study, it has been shown that these parameters played a significant role on supersonic core decay characteristics [2, 3, 6] of the jet. The scope of this study included supersonic core length (Lc), decay pattern, due to noncircular shaped nozzle. In the literature, the supersonic jet characterization and the related experimental correlation are available for optimum expansion conditions whereas for other expansion (under and over) conditions the experimental correlation is barely available. While investigating experimentally, new empirical relations were obtained which were the improved forms of earlier correlations for supersonic core length [4]. For experiments, six different types of nozzles (circular, hexagon, square, triangular, elliptical and rectangular) with the same exit to throat area ratio, convergent length and divergent length were used. The results obtained from the experimentally developed correlations were coherent with numerical results, experimental data and flow visualization.
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- 2020
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15. Numerical investigation on the performance of a solar air heater using jet impingement with absorber plate.
- Author
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Yadav, Siddhita and Saini, R.P.
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JET impingement , *SOLAR air heaters , *SOLAR thermal energy , *FLUID dynamics , *REYNOLDS number , *HEAT transfer - Abstract
• A 3D-CFD study has been carried out using RNG k–ɛ turbulence model. • Jet diameter ratio and jet height ratio are varied with Reynolds number. • A significant amount of heat transfer enhancement is achieved. • Best performance is found at jet height ratio of 0.216 with jet diameter ratio of 0.0650. • Maximum thermo-hydraulic performance parameter is determined as 3.66. Solar air heater is the simplest heating device for utilizing solar thermal energy. Jet impingement technique can be used to amplify the performance of a solar air heater by increasing the heat transfer between fluid and heated surface. Under the present study, an attempt has been made to carry out a numerical investigation on heat transfer behaviour of a solar air heater having absorber plate with impinging jet. 3D-Computational fluid dynamics (CFD) simulation using ANSYS-18.1 has been carried out with RNG k–ɛ turbulence model, and the upwind scheme is applied for the discretization of governing equations. Jet diameter ratio and jet height ratio are the considered system parameters, and their considered ranges are 0.065 to 0.195 and 0 to 0.433, respectively. The performance of solar air heater with jet impingement is investigated under different flow conditions taking Reynolds number ranging from 3500 to 17,500. It has been found that a significant increase in heat transfer for jet impinging solar air heaters is achieved in comparison to smooth solar air heater under similar operating conditions. The maximum heat transfer enhancement of 7.58 with a friction factor penalty of 9.01 times is obtained at jet diameter ratio of 0.0650 and jet height ratio of 0.216 for Reynolds number of 17,500. Maximum thermal-hydraulic performance parameter value of 3.66 is obtained correspond to jet height ratio of 0.216 and jet diameter ratio of 0.065 for Reynolds number of 15,500. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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16. CFD investigation on the characteristics of annular pulse tube.
- Author
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Pang, Xiaomin, Dai, Wei, Wang, Xiaotao, and Ma, Suxia
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ANNULAR flow , *THERMAL conductivity , *TUBES , *INVESTIGATIONS , *HEAT transfer , *HEAT losses - Abstract
• Numeric analysis of the annular and circular pulse tube have been done and compared. • Heat transfer between gas and two walls has an apparent effect on the expansion efficiency of annular pulse tube. • Effects of pulse tube hydraulic diameter and wall thermal conductivity on the thermal performance are investigated. CFD models are used to study the performance of circular and annular pulse tubes working at 77–300 K. The oscillating flow and heat transfer characteristics are investigated. In terms of pulse tube impedance, simulation results indicate that the annular shape has negligible influence when the length and flow area are kept the same as circular pulse tube. However, compared with the circular pulse tube, the thermal performance of annular pulse tube apparently deteriorates which is mainly due to the increased thermal losses caused by heat transfer between the internal gas and two cylindrical tube walls (instead of one in the case of circular pulse tube). The expansion efficiency (defined as the enthalpy flow divided by acoustic power at the cold end) of annular pulse tube is lower by about 14% compared with that of circular pulse tube. Among the influencing factors, hydraulic diameter of annular pulse tube has a significant influence on the performance, and smaller hydraulic diameter leads to a reduced expansion efficiency. The effects of tube wall thermal conductivity are also discussed. This study provides a better understanding on the mechanism of annular pulse tube which sets the basis for optimizing a compact low temperature cryocooler for future applications. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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17. Effect of Hydraulic Diameter on Potential Core Decay of Supersonic Jets.
- Author
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MOHANTA, Prasanta Kumar and SRIDHAR, B. T. N.
- Subjects
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FLOW visualization , *DIAMETER , *DATA modeling , *NOZZLES , *HEXAGONS - Abstract
Various studies dealing with decay characteristics of circular and noncircular supersonic jets were conducted by previous researchers. But in these studies due emphasis was not given to the hydraulic diameter (Dh), shape factor (ζ) & the nozzle lip parameters which have significant impact on the characteristics of noncircular supersonic jet. In this study, it has been shown that these parameters played a significant role on supersonic core decay characteristics [2, 3, 6] of the jet. The scope of this study included supersonic core length (Lc), decay pattern, due to noncircular shaped nozzle. In the literature, the supersonic jet characterization and the related experimental correlation are available for optimum expansion conditions whereas for other expansion (under and over) conditions the experimental correlation is barely available. While investigating experimentally, new empirical relations were obtained which were the improved forms of earlier correlations for supersonic core length [4]. For experiments, six different types of nozzles (circular, hexagon, square, triangular, elliptical and rectangular) with the same exit to throat area ratio, convergent length and divergent length were used. The results obtained from the experimentally developed correlations were coherent with numerical results, experimental data and flow visualization. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
18. Effects of slip length and hydraulic diameter on hydraulic entrance length of microchannels with superhydrophobic surfaces.
- Author
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Gong, Wenchi, Shen, Jun, Dai, Wei, Deng, Zeng, Dong, Xueqiang, and Gong, Maoqiong
- Abstract
This paper investigated effects of slip length and hydraulic diameter on the hydraulic entrance length of laminar flow in superhydrophobic microchannels. Numerical investigations were performed for square microchannels with Re ranging between 0.1 and 1000. It is found that superhydrophobic microchannels have a longer hydraulic entrance length than that of conventional ones by nearly 26.62% at a low Re. The dimensionless hydraulic entrance length slightly increases with the increasing slip length at approximately Re<10, and does not vary with the hydraulic diameter. A new correlation to predict the entrance length in square microchannels with different slip lengths was developed, which has a satisfying predictive performance with a mean absolute relative deviation of 5.69%. The results not only ascertain the flow characteristics of superhydrophobic microchannels, but also suggest that super hydrophobic microchannels have more significant advantages for heat transfer enhancement at a low Re. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
19. Immediate and carry‐over effects of insect outbreaks on vegetation growth in West Greenland assessed from cells to satellite.
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Prendin, Angela Luisa, Carrer, Marco, Karami, Mojtaba, Hollesen, Jørgen, Bjerregaard Pedersen, Nanna, Pividori, Mario, Treier, Urs A., Westergaard‐Nielsen, Andreas, Elberling, Bo, Normand, Signe, and Zurell, Damaris
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TREE-rings , *SPATIO-temporal variation , *SATELLITE cells , *NORMALIZED difference vegetation index , *GROWING season , *PLANTS , *SEAS - Abstract
Aim: Tundra ecosystems are highly vulnerable to climate change, and climate–growth responses of Arctic shrubs are variable and altered by microsite environmental conditions and biotic factors. With warming and drought during the growing season, insect‐driven defoliation is expected to increase in frequency and severity with potential broad‐scale impacts on tundra ecosystem functioning. Here we provide the first broad‐scale reconstruction of spatio‐temporal dynamics of past insect outbreaks by assessing their effects on shrub growth along a typical Greenlandic fjord climate gradient from the inland ice to the sea. Location: Nuuk Fjord (64°30′N/51°23′W) and adjacent areas, West Greenland. Taxa: Great brocade (Eurois occulta L.) and grey willow (Salix glauca L.). Methods: We combined dendro‐anatomical and remote sensing analyses. Time series of ring width (RW) and wood‐anatomical traits were obtained from chronologies of >40 years established from 153 individuals of S. glauca collected at nine sites. We detected anomalies in satellite‐based Normalized Difference Vegetation Index (NDVI) related to defoliation and reconstructed past changes in photosynthetic activity across the region. Results: We identified outbreaks as distinctive years with reduced RW, cell‐wall thickness and vessel size, without being directly related to climate but matching with years of parallel reduction in NDVI. The two subsequent years after the defoliation showed a significant increase in RW. The reconstructed spatio‐temporal dynamics of these events indicate substantial regional variation in outbreak intensity linked to the climate variability across the fjord system. Main conclusions: Our results highlight the ability of S. glauca to cope with severe insect defoliation by changing carbon investment and xylem conductivity leading to high resilience and rapid recovery after the disturbance. Our multiproxy approach allows us to pinpoint biotic drivers of narrow ring formation and to provide new broad‐scale insight on the C‐budget and vegetation productivity of shrub communities in a widespread arctic ecosystem. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
20. Radial growth, wood anatomical traits and remote sensing indexes reflect different impacts of drought on Mediterranean forests
- Author
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Governo Italiano, National Research Centre for Agricultural Technologies (Italy), European Commission, Ministerio de Economía y Competitividad (España), Camarero, Jesús Julio [0000-0003-2436-2922], Colangelo, Michele [0000-0002-6687-3125], Pizarro Gavilán, Manuel [0000-0002-6981-0154], Italiano, Santain Settimio, Camarero, Jesús Julio, Borghetti, Marco, Colangelo, Michele, Pizarro Gavilán, Manuel, Ripullone, Francesco, Governo Italiano, National Research Centre for Agricultural Technologies (Italy), European Commission, Ministerio de Economía y Competitividad (España), Camarero, Jesús Julio [0000-0003-2436-2922], Colangelo, Michele [0000-0002-6687-3125], Pizarro Gavilán, Manuel [0000-0002-6981-0154], Italiano, Santain Settimio, Camarero, Jesús Julio, Borghetti, Marco, Colangelo, Michele, Pizarro Gavilán, Manuel, and Ripullone, Francesco
- Abstract
Drought reduces canopy cover, productivity and tree growth in forests. However, there is still little knowledge on how drought affects coupling between canopy greenness assessed by remote sensing and hydraulic conductivity detected by wood anatomy. This combination could improve the understanding of forest response to climate change. Thus, we investigated the impacts of a hot drought, which occurred in summer 2017, on radial growth, earlywood hydraulic diameter (Dh), a proxy of conductivity, and several remote-sensing indices in mixed Mediterranean hardwood forests (Quercus pubescens Willd. – Fraxinus ornus L.). In general, growth showed a higher coherence among trees and a higher responsiveness to climate. Growth decreased during the drought year, particularly for Q. pubescens, which showed high defoliation and dieback intensity. Both species showed a decline of Dh in 2018 after the drought and subsequent warm winter conditions. We found positive relationships between Dh and remote-sensing data for Q. pubescens in some of these vulnerable sites, where (i) growth was constrained by dry spring-summer conditions and (ii) Dh and growth covaried. These findings indicate a high variability among sites and tree species in their responses to drought considering earlywood anatomy, growth canopy cover and water content. However, some common patterns emerge such as links between potential hydraulic conductivity (Dh), tree cover and Dh-growth covariation in the most impacted sites. Further, F. ornus seem to perform better in terms of growth under drought conditions, showing less mortality and dieback than Q. pubescens. Future studies could explore how water transport and changes in canopy cover respond to dry and warm conditions and if that covariation indicates vulnerability to drought.
- Published
- 2023
21. Radial growth, wood anatomical traits and remote sensing indexes reflect different impacts of drought on Mediterranean forests.
- Author
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Italiano, Santain S.P., Julio Camarero, J., Borghetti, Marco, Colangelo, Michele, Pizarro, Manuel, and Ripullone, Francesco
- Subjects
DROUGHTS ,REMOTE sensing ,FOREST management ,WOOD ,HARDWOOD forests ,HYDRAULIC conductivity - Abstract
• Remote sensing indexes and tree-rings/wood anatomy data were compared. • High variability among sites and tree species in their responses to drought. • Ash seem to perform better then oak in terms of growth under drought. • Relevant effect for forest management and ecosystem services. Drought reduces canopy cover, productivity and tree growth in forests. However, there is still little knowledge on how drought affects coupling between canopy greenness assessed by remote sensing and hydraulic conductivity detected by wood anatomy. This combination could improve the understanding of forest response to climate change. Thus, we investigated the impacts of a hot drought, which occurred in summer 2017, on radial growth, earlywood hydraulic diameter (Dh), a proxy of conductivity, and several remote-sensing indices in mixed Mediterranean hardwood forests (Quercus pubescens Willd. – Fraxinus ornus L.). In general, growth showed a higher coherence among trees and a higher responsiveness to climate. Growth decreased during the drought year, particularly for Q. pubescens , which showed high defoliation and dieback intensity. Both species showed a decline of Dh in 2018 after the drought and subsequent warm winter conditions. We found positive relationships between Dh and remote-sensing data for Q. pubescens in some of these vulnerable sites, where (i) growth was constrained by dry spring-summer conditions and (ii) Dh and growth covaried. These findings indicate a high variability among sites and tree species in their responses to drought considering earlywood anatomy, growth canopy cover and water content. However, some common patterns emerge such as links between potential hydraulic conductivity (Dh), tree cover and Dh-growth covariation in the most impacted sites. Further, F. ornus seem to perform better in terms of growth under drought conditions, showing less mortality and dieback than Q. pubescens. Future studies could explore how water transport and changes in canopy cover respond to dry and warm conditions and if that covariation indicates vulnerability to drought. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
22. The Effect of Hydraulic Diameter on Flow Boiling within Single Rectangular Microchannels and Comparison of Heat Sink Configuration of a Single and Multiple Microchannels
- Author
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Konstantinos Vontas, Manolia Andredaki, Anastasios Georgoulas, Nicolas Miché, and Marco Marengo
- Subjects
flow boiling ,hydraulic diameter ,microchannels ,multiphase flow ,VOF ,conjugate heat transfer ,Technology - Abstract
Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter Dh whose effects on fluid flow and heat transfer characteristics are not clearly defined yet. The objective of the present work is to numerically investigate the first transient flow boiling characteristics from the bubble inception up to the first stages of the flow boiling regime development, in rectangular microchannels of varying hydraulic diameters, utilising an enhanced custom VOF-based solver. The solver accounts for conjugate heat transfer effects, implemented in OpenFOAM and validated in the literature through experimental results and analytical solutions. The numerical study was conducted through two different sets of simulations. In the first set, flow boiling characteristics in four single microchannels of Dh = 50, 100, 150, and 200 μm with constant channel aspect ratio of 0.5 and length of 2.4 mm were examined. Due to the different Dh, the applied heat and mass flux values varied between 20 to 200 kW/m2 and 150 to 2400 kg/m2s, respectively. The results of the two-phase simulations were compared with the corresponding initial single-phase stage of the simulations, and an increase of up to 37.4% on the global Nu number Nuglob was revealed. In the second set of simulations, the effectiveness of having microchannel evaporators of single versus multiple parallel microchannels was investigated by performing and comparing simulations of a single rectangular microchannel with Dh of 200 μm and four-parallel rectangular microchannels, each having a hydraulic diameter Dh of 50 μm. By comparing the local time-averaged thermal resistance along the channels, it is found that the parallel microchannels configuration resulted in a 23.3% decrease in the average thermal resistance R¯l compared to the corresponding single-phase simulation stage, while the flow boiling process reduced the R¯l by only 5.4% for the single microchannel case. As for the developed flow regimes, churn and slug flow dominated, whereas liquid film evaporation and, for some cases, contact line evaporation were the main contributing flow boiling mechanisms.
- Published
- 2021
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23. Diffusion
- Author
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Schomburg, Werner Karl, RWTH Aachen Univ, and Schomburg, Werner Karl
- Published
- 2015
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24. Micro Valves
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Schomburg, Werner Karl, RWTH Aachen Univ, and Schomburg, Werner Karl
- Published
- 2015
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25. Effects of baffles and vortex generators on cooling performance of a gas turbine combustion chamber: Numerical assessment
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Ali J. Chamkha, Hamed Arjmandi, Reza Amini, Hamid Rahmani, and Ali Ghaffari
- Subjects
Materials science ,Turbulence ,General Engineering ,Reynolds number ,Baffle ,Mechanics ,Vortex generator ,Computational fluid dynamics ,Performance evaluation criteria ,Engineering (General). Civil engineering (General) ,Nusselt number ,Vortex ,Physics::Fluid Dynamics ,symbols.namesake ,Gas turbine cooling methods ,symbols ,Hydraulic diameter ,Baffles and vortex generators ,Combustion chamber ,TA1-2040 - Abstract
In this work, the effect of using baffles and vortex generators on the cooling performance of a gas turbine combustion chamber is numerically investigated. The RNG k-ɛ model is utilized in order to simulate the flow turbulence. The effects of baffles and vortex generator pitch, hydraulic diameter and bypass ratio on the Nusselt number and friction coefficient at different Reynolds number are studied. The cooling performance of applying baffles and vortex generators are also evaluated and compared based on the Performance Evaluation Criterion (PEC). The numerical results are verified with available experimental data. The results show that the pitch increment results in the decrement of the Nusselt number and the wall friction coefficient due to the lower vortices generation and the turbulence kinetic energy dissipation. Also, the Nusselt number is increased by increasing both the bypass ratio and the hydraulic diameter. It is also found that vortex generators and baffles improve the cooling performance of the gas turbine combustion chamber by 18.8% and 26% respectively through decreasing the external wall temperature.
- Published
- 2022
26. Investigation of Gas Permeability of Fibrous Composite Material in a Vacuum.
- Author
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Kalinkin, D. A., Belova, O. V., and Andreev, R. O.
- Subjects
- *
PRESSURE , *POROSITY , *FIBROUS composites , *COMPOSITE materials , *PERMEABILITY , *LATTICE gas , *QUARTZ - Abstract
The investigation of gas pressure variation during its porosity trough fibrous composite material is offered. Rarefied gas pressure diffusion model is used for calculate the gas permeability of fibrous composite material. Simulation results are compared with the crystalline material regular lattice gas permeability, for example quartz. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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27. Effect of nozzle geometry on pressure drop in submerged gas injection.
- Author
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Xiao, Jun-bing, Yan, Hong-jie, Schubert, Markus, Unger, Sebastian, Liu, Liu, Schleicher, Eckhard, and Hampel, Uwe
- Abstract
Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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- 2019
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28. Effect of hydraulic diameter on flow boiling in rectangular microchannels.
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Markal, Burak, Aydin, Orhan, and Avci, Mete
- Subjects
- *
MICROCHANNEL flow , *HEAT transfer coefficient , *FLOW visualization , *HEAT flux , *DIAMETER , *DEIONIZATION of water - Abstract
An experimental study is conducted to investigate the effect of hydraulic diameter on the saturated flow boiling characteristics of deionized water in parallel rectangular microchannels. Experiments have been performed for the mass fluxes of 51, 65, 78 and 93 kg m−2 s−1, and the hydraulic diameters of 100, 150, 200 and 250 μm. The wall heat flux ranges from 35.9 to 105.6 kW m−2. To eliminate the effect of aspect ratio and to address clearly the effect of hydraulic diameter, all the channels are designed with square cross section. Flow visualization studies are performed for a better understanding of the underlying physical phenomena. Effects of heat flux, mass flux and vapor quality on the heat transfer and total pressure drop have been investigated, too. It is concluded that hydraulic diameter has significant influence on both of the local two phase heat transfer coefficient and the total pressure drop. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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29. A standardization method to disentangle environmental information from axial trends of xylem anatomical traits.
- Author
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Lechthaler, Silvia, Turnbull, Tarryn L, Gelmini, Ylenia, Pirotti, Francesco, Anfodillo, Tommaso, Adams, Mark A, and Petit, Giai
- Subjects
- *
XYLEM , *VASCULAR plants , *X-ray diffraction , *NANOPARTICLES , *CRYSTAL structure , *VASCULAR system of plants - Abstract
Anatomical traits such as xylem conduit diameter and vessel connectivity are fundamental characteristics of the hydraulic architecture of vascular plants. Stem xylem conduits are narrow at the stem apex, and this confers resistance to embolisms that might otherwise be induced by large, negative water potentials at the top of tall trees. Below the apex, conduits progressively widen and this characteristic minimizes effects of path length on total hydraulic resistance. While interconnections among xylem vessels have been noted for decades, their role(s) are not fully clarified. For example, we do not know if they allow water to bypass embolized vessels, or increase the risk of spread of embolisms, or how their arrangement varies within a tree. Here we demonstrate the benefit of removing the independent effect of stem length on assessment of effects of external (e.g. climatic) factors on such xylem traits. We measured the hydraulic diameter (Dh) and vessel conductivity index (VCI) along the stem of 21 shrubs/trees of similar height (1.19 < H < 5.45 m) belonging to seven Acacia species, across a wide aridity gradient in Australia. All trees showed similar scaling exponents of Dh (b = 0.33) and VCI (b = 0.53) vs axial distance from the apex (L), thus conforming with general patterns in woody plants. After de-trending for L, neither Dh (P = 0.21) nor VCI (P = 0.109) differed across the aridity gradient. We found that across a wide gradient of aridity, climate had no effect on xylem anatomy of Acacia spp, which was instead dictated by axial distances from stem apices. We argue that the use of standardization procedures to filter out intrinsic patterns of vascular traits is an essential step in assessing climate-driven modifications of xylem architecture. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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30. Analysing the porous structure of packed beds of spheres using a semi-analytical approach.
- Author
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du Toit, Charl G.
- Subjects
- *
PACKED beds (Chemical industry) , *POROSITY , *HYDRAULICS , *CRYSTAL structure , *SIMPSON'S rule (Numerical analysis) - Abstract
Abstract In this paper methodologies are described for the analysis of the porous structure of cylindrical and annular packed beds consisting of spheres when the coordinates and sizes of the spheres are known. Methodologies to determine the overlap between adjacent spheres and between the spheres and the walls of the container; axial variation in the porosity and hydraulic diameter; and the radial variation in the porosity are described. The determination of the overall bulk porosity, as well as the average porosity of selected regions, from the results are also discussed. The methodologies are based on analytical geometry and Simpson's rule is used to perform the numerical integration of the relevant integrals. The validity of the methodologies is demonstrated and the application of the methodologies to analyse the porous structure of selected packed beds is illustrated. Graphical abstract Unlabelled Image Highlights • Analyse porous structure of packed bed when coordinates and size of spheres known. • Use analytical and semi-analytical methods to analyse porous structure. • Areas integrated using Simpson's rule with angular or axial increments. • Perform analysis of axial variation in porosity and hydraulic diameter. • Perform analysis of radial variation in porosity using line- and area-based methods. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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31. Effects of channel diameter on flow pattern and pressure drop for air–water flow in serpentine gas channels of PEM fuel cell-An Ex situ experiment.
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Malhotra, Sneha and Ghosh, Sumana
- Subjects
- *
FUEL cells , *HYDRAULICS , *MICROCHANNEL flow , *FRICTION , *VELOCITY - Abstract
Highlights • Air–water flow in serpentine mini and microchannels visualized by high speed camera. • Influence of orientation on flow regimes disappears for micro channel. • Horizontal orientation of serpentine micro channel prone to mal-distribution. • Serpentine micro channel favors the formation of annular flow. • Vertical serpentine micro channel drains water easily, desired for PEMFC. • Modified friction factor proposed for predicting the pressure drop. Abstract Ex-situ experimental investigation of air–water two phase flow characteristics are carried out in rectangular serpentine mini and micro-channels. The test sections to be studied are made up of acrylic and are of three different hydraulic diameters of 1.65 mm, 1.00 mm and 0.65 mm with the corresponding length of 50 mm. Experiments are performed for different combinations of superficial velocities of air and water ranging between 0.0011 m/s and 0.33 m/s and 0.33 m/s to 16.66 m/s, respectively. The effect of channel orientation on various parameters is also studied. The visualisation of two phase is accomplished by high-speed camera. The flow pattern maps developed by closely scrutinizing each flow rate combinations are presented. Mal-distribution occurred in horizontal orientation of micro channel. However, vertical orientation of micro channel favoured draining of water, thereby encountered lesser pressure drop than mini channel. New correlation based on various dimensionless numbers has been proposed for modelling the pressure drop. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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32. Improvement of the subcooled boiling model for the prediction of the onset of flow instability in an upward rectangular channel
- Author
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Jae Jun Jeong, Byong-Jo Yun, Myeong Kwan Seo, and Adnan Wisudhaputra
- Subjects
Subcooling ,Mass flux ,geography ,Materials science ,geography.geographical_feature_category ,Nuclear Energy and Engineering ,Heat flux ,Boiling ,Evaporation ,Hydraulic diameter ,Mechanics ,Inlet ,Communication channel - Abstract
The MARS code has been assessed for the prediction of onset of flow instability (OFI) in a vertical channel. For assessment, we built an experiment database that consists of experiments under various geometry and thermal-hydraulic condition. It covers pressure from 0.12 to 1.73 MPa; heat flux from 0.67 to 3.48 MW/m2; inlet sub-cooling from 39 to 166 °C; hydraulic diameters between 2.37 and 6.45 mm of rectangular channels and pipes. It was shown that the MARS code can predict the OFI mass flux for pipes reasonably well. However, it could not predict the OFI in a rectangular channel well with a mean absolute percentage error of 8.77%. In the cases of rectangular channels, the error tends to depend on the hydraulic diameter. Because the OFI is directly related to the subcooled boiling in a flow channel, we suggest a modified subcooled boiling model for better prediction of OFI in a rectangular channel; the net vapor generation (NVG) model and the modified wall evaporation model were modified so that the effect of hydraulic diameter and heat flux can be accurately considered. The assessment of the modified model shows the prediction of OFI mass flux for rectangular channels is greatly improved.
- Published
- 2022
33. Phase inversion phenomena in vertical three-phase flow: Experimental study on the influence of fluids viscosity, duct geometry and gas flow rate.
- Author
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Colmanetti, Alex Roger Almeida, de Castro, Marcelo Souza, Barbosa, Marcel Cavallini, and Rodriguez, Oscar Mauricio Hernandez
- Subjects
- *
MULTIPHASE flow , *PETROLEUM industry , *FLUID dynamics , *PETROLEUM pipelines , *VISCOSITY , *GAS flow - Abstract
Improper sizing of pipelines and production tubings in the petroleum industry is often caused by lack of understanding of three-phase flow, which is characterized by gas flowing together with an immiscible water-oil mixture. There is the presence of a continuous liquid phase and a liquid dispersed phase, as observed in liquid-liquid flows, i.e., one can observe either a dispersion or emulsion of oil in water (o/w) or dispersion or emulsion of water in oil (w/o). The transition from o/w to w/o, or the other way around, is defined as phase-inversion. This phenomenon is characterized by a sharp increase in the pressure gradient, leading to significant pressure loss in the oil production system. The goal is to investigate the effects of oil viscosity, channel geometry (circular pipe or annular duct) and superficial gas velocity on the phenomenon of phase inversion in vertical liquid-liquid-gas flows, using oil with three different viscosities (ranging from 70 mPa s to 280 mPa s), tap water and compressed air as working fluids. The experiments were carried out in three different geometries: (i) glass pipe of 50 mm i.d., (ii) glass pipe of 95 mm i.d. and (iii) concentric annular duct with 95 mm of hydraulic diameter (glass outer pipe and PVC internal pipe). The experiments were performed under equivalent Reynolds number to evaluate the geometry effect. New data as total pressure gradient and volumetric fractions were obtained for all geometries. The results suggest that the extrapolation of results obtained in circular pipes with low viscosity oil and low gas flow rates to annular-duct flow with viscous oils and high gas flow rates can lead to significant errors. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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- View/download PDF
34. Prediction of the Limiting Flux and Its Correlation with the Reynolds Number during the Microfiltration of Skim Milk Using an Improved Model
- Author
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Carolina Astudillo-Castro, Andrés Cordova, Vinka Oyanedel-Craver, Carmen Soto-Maldonado, Pedro Valencia, Paola Henriquez, and Rafael Jimenez-Flores
- Subjects
hydraulic diameter ,limiting flux ,Reynolds number ,skim milk ,microfiltration ,ceramic membranes ,Chemical technology ,TP1-1185 - Abstract
Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R2 > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R2 = 84.11%) for the whole set of experiments
- Published
- 2020
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35. AN EXPERIMENTAL INVESTIGATION OF GASEOUS FLOW CHARACTERISTICS IN MICROCHANNELS
- Author
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Kenjiro Suzuki, Hiroshi Iwai, Min Soo Kim, and Takuto Araki
- Subjects
Microchannel ,Materials science ,Physics and Astronomy (miscellaneous) ,Mechanical Engineering ,Materials Science (miscellaneous) ,Flow (psychology) ,Rarefaction ,Thermodynamics ,Slip (materials science) ,Mechanics ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Physics::Fluid Dynamics ,Mechanics of Materials ,Heat transfer ,Mass flow rate ,General Materials Science ,Hydraulic diameter ,Boundary value problem - Abstract
The microchannel is one of the essential components for the construction of various micro systems. However, it has been reported that the flow and heat transfer behavior in a microchannel deviates from predictions based on the conventional assumption generally accepted in macro-scale channels. Frictional characteristics of nitrogen and helium flows in three different microchannels (hydraulic diameter range 3-10 w m) have been investigated experimentally. The frictional resistance of gaseous flow in a trapezoidalcross-section microchannel was observed to be smaller than that in the conventional-sized channel. The reduced frictional resistance in microchannels is caused by the rarefaction effect due to extremely small dimensions of flow passages. By using Maxwell's first-order slip boundary condition, we can well predict the mass flow rate through microchannels and the friction constant.
- Published
- 2023
36. Heat transfer characteristics of flat and concave surfaces by circular and elliptical jet impingement
- Author
-
Santosh Kumar Sahu and Jaykumar Joshi
- Subjects
Physics::Fluid Dynamics ,Materials science ,Aspect ratio ,Control and Systems Engineering ,Nozzle ,Thermal ,Heat transfer ,Hydraulic diameter ,Jet impingement ,Mechanics ,Electrical and Electronic Engineering ,Instrumentation - Abstract
The present paper reports the thermal behavior of flat and curved surfaces with impinging jets employing circular and elliptical nozzle for identical equivalent diameter (de). Tests are performed w...
- Published
- 2021
37. Design optimization and experimental investigation of CPU heat sink cooled by alumina-water nanofluid
- Author
-
M.J. Hoseini, Ali Akbar Ranjbar, S. Mohsenian, and Seyed Ebrahim Ghasemi
- Subjects
Pressure drop ,Mining engineering. Metallurgy ,Materials science ,Central composite design ,Nuclear engineering ,TN1-997 ,Metals and Alloys ,Response surface methodology (RSM) ,Heat sink ,Surfaces, Coatings and Films ,Volumetric flow rate ,Biomaterials ,Electronic chips ,Nanofluid ,Heat transfer ,Ceramics and Composites ,Nanoparticles ,Working fluid ,Hydraulic diameter ,Thermal management ,Desirability - Abstract
In this study, an experimental evaluation on the use of Al2O3 nanoparticles in a circular structure of minichannel heat sink is conducted for heat dissipation from electronic components such as Central Processing Unit (CPU). The experiments are prepared for various hydraulic diameter of channels and different values of coolant flow rates. After a hydro-thermal analysis on the obtained data, as a main outcome, findings indicate that decreasing the channel diameter and increasing the flow rate of Al2O3-water as working fluid are the most effective approaches to improve the cooling performance of heat sinks. An optimization study using Response Surface Methodology (RSM) based on Central Composite Design (CCD) is performed due to complex effect of channel size, nanofluid volume flow rates and channel numbers on pressure drop and heat transfer to reach the best operating design.
- Published
- 2021
38. Suction force on high-sphericity seeds in an air-suction seed-metering device
- Author
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Junhong Li, Tiantian Wang, Jinwen Zhao, Zhang Zhaoguo, Lai Qinghui, and Hui Zhang
- Subjects
Materials science ,Suction ,Flow (psychology) ,Suction force ,Soil Science ,Mechanics ,Sphericity ,Control and Systems Engineering ,Drag ,Hydraulic diameter ,Metering mode ,Agronomy and Crop Science ,Pressure gradient ,Food Science - Abstract
The suction force on high-sphericity seeds is important to the design of air-suction seed-metering devices. However, little systematic research has been conducted on the suction force. A self-designed suction force measurement device and idealised model were used to conduct CFD simulation, single factor experiments, and orthogonal experiments to improve the model of the suction force on seeds with sphericity over 90.34% and equivalent diameter 6.63–7.16 mm under the following conditions: suction hole diameter 4–6 mm, suction hole vacuum 3–5 kPa, seed-filling angle ±π/8, and horizontal distance from the seed centre to the suction hole 3.5–5.5 mm. The verification experiment conducted using the seeds of soybean, pea, and Panax notoginseng showed that the accuracy was higher for the improved suction force model. Simulation of flow behaviours under different factors revealed that the changes in the air velocity gradient and pressure gradient are the main causes of the change in the suction force. The relationship between the drag force model and the suction force model was studied by comparing the predicted value of the drag force and the measured value of the suction force under the same conditions.
- Published
- 2021
39. Constructal Design of Rectangular Conjugate Cooling Channels
- Author
-
Bello-Ochende, T., Olakoyejo, O. T., Meyer, J. P., Rocha, Luiz A.O., editor, Lorente, Sylvie, editor, and Bejan, Adrian, editor
- Published
- 2013
- Full Text
- View/download PDF
40. Static Components
- Author
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O’Kelly, Peter and O'Kelly, Peter
- Published
- 2013
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41. Set of benchmarks for verification of k − eps models in system computer codes
- Author
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Kolev, Nikolay Ivanov and Kolev, Nikolay Ivanov
- Published
- 2012
- Full Text
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42. Pipe networks
- Author
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Kolev, Nikolay Ivanov and Kolev, Nikolay Ivanov
- Published
- 2012
- Full Text
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43. Effect of the refrigerant charge, expansion restriction, and compressor speed interactions on the energy performance of household refrigerators
- Author
-
Adriano F. Ronzoni, Christian J.L. Hermes, and Fernando T. Knabben
- Subjects
Range (particle radiation) ,Work (thermodynamics) ,Materials science ,Capillary action ,020209 energy ,Mechanical Engineering ,Refrigerator car ,02 engineering and technology ,Building and Construction ,Mechanics ,Energy consumption ,021001 nanoscience & nanotechnology ,Refrigerant ,0202 electrical engineering, electronic engineering, information engineering ,Hydraulic diameter ,0210 nano-technology ,Gas compressor - Abstract
This work is aimed at investigating the effects of the refrigerant charge, expansion device restriction, compressor speed, and their interactions on the performance of a household refrigerator. To this end, a micrometric valve was installed in series with the capillary tube of a frost-free refrigerator to vary the expansion restriction within a range equivalent to capillary tubes with inner diameters spanning from 0.55 to 0.85 mm. The refrigerant charge was manually changed from 35 to 65 g whereas the compressor speed was adjusted between 2500 and 4500 rpm. In total, 294 steady-state energy consumption tests were conducted, being 147 at a surrounding temperature of 32 °C, and the rest at 16 °C. It was noticed that low energy consumptions can be achieved for several combination of refrigerant charge and expansion restriction, albeit the minimal energy consumption figures were always achieved for the highest charges and restrictions. It was also verified that the refrigerator operates in a sub-optimum region so that increasing the charge from 42 g to 52 g while decreasing the capillary tube diameter from 0.64 mm to 0.60 mm led to a 3% decrease on the energy consumption. It was also found that a single combination of refrigerant charge and equivalent diameter provided satisfactory performance levels regardless of the compressor speed. Finally, a method to reduce the number of tests was proposed, in such a way that only 9 datapoints are required to generate a full energy consumption map for a given compressor speed and surrounding temperature.
- Published
- 2021
44. Experimental study on effects of geometric and hydrodynamic parameters on performance of multi-holed orifice flowmeters
- Author
-
Atta Ullah, Asim Ibrahim, Mansoor Hameed Inayat, Aneeq Raheem, and Abdus Saboor Baseer Siddiqi
- Subjects
Pressure drop ,Physics ,Turbulence ,Fourth power ,General Chemical Engineering ,Reynolds number ,General Chemistry ,Mechanics ,Volumetric flow rate ,Physics::Fluid Dynamics ,symbols.namesake ,Cavitation ,symbols ,Hydraulic diameter ,Body orifice - Abstract
Multi-holed Orifices (MOs) are widely used in swirling, cavitating and developing flows to reduce pressure losses. This study focuses on analysis of MOs for developing turbulent flows. A large number of experiments were performed, exploring the number of holes (n), Equivalent Diameter Ratio (EDR), compactness ratio (C), plate thickness ratio (s/d) and upstream developing length (L/D) in the Reynolds number (ReD) range of 24,500–55,500. An empirical correlation of pressure loss coefficient and flow rate is formulated. It is observed that pressure loss coefficient decays with the fourth power of EDR. A comparative study of the experimental data with the literature is presented to ensure consistency and reliability.
- Published
- 2021
45. Ozark Graphene Nanopore for Efficient Water Desalination
- Author
-
Greta Markey, Zhonglin Cao, and Amir Barati Farimani
- Subjects
Ions ,Membranes ,Materials science ,Nanoporous ,Graphene ,Water ,Permeation ,Desalination ,Surfaces, Coatings and Films ,Ion ,law.invention ,Nanopores ,Nanopore ,Chemical engineering ,law ,Materials Chemistry ,Graphite ,Hydraulic diameter ,Physical and Theoretical Chemistry ,Reverse osmosis - Abstract
A nanoporous graphene membrane is crucial to energy-efficient reverse osmosis water desalination given its high permeation rate and ion selectivity. However, the ion selectivity of the common circular graphene nanopore is dependent on the pore size and scales inversely with the water permeation rate. Larger, circular graphene nanopores give rise to the high water permeation rate but compromise the ability to reject ions. Therefore, the pursuit of a higher permeation rate while maintaining high ion selectivity can be challenging. In this work, we discover that the geometry of graphene nanopore can play a significant role in its water desalination performance. We demonstrate that the ozark graphene nanopore, which has an irregular slim shape, can reject over 12% more ions compared with a circular nanopore with the same water permeation rate. To reveal the physical reason behind the outstanding performance of the ozark nanopore, we compared it with circular, triangular, and rhombic pores from perspectives including interfacial water density, energy barrier, water/ion distribution in pores, the ion-water RDF in pores, and the hydraulic diameter. The ozark graphene nanopore further explores the potential of graphene for efficient water desalination.
- Published
- 2021
46. The tribological response of nanoparticles' equivalent diameter to the oil film thickness
- Author
-
Rongqin Gao, Kai Gao, Bin Wang, and Qiuying Chang
- Subjects
Materials science ,Oil film ,Materials Chemistry ,Nanoparticle ,Hydraulic diameter ,Composite material ,Tribology ,Surfaces, Coatings and Films - Published
- 2021
47. Investigation of manufacturability and efficiency of micro channels with different geometries produced by direct metal laser sintering
- Author
-
Mert Coşkun, Cemal İrfan Çalışkan, Turgut Azer Vurkır, Gökay Yöndem, Ebubekir Koç, and Gökhan Özer
- Subjects
Conformal cooling channel ,Materials science ,business.industry ,Mechanical Engineering ,Flow (psychology) ,Mechanical engineering ,Computational fluid dynamics ,Cooling capacity ,Industrial and Manufacturing Engineering ,Computer Science Applications ,Design for manufacturability ,Direct metal laser sintering ,Control and Systems Engineering ,Hydraulic diameter ,business ,Software ,Communication channel - Abstract
Manufacturability without supports in design studies for additive manufacturing (AM) brings many advantages such as time, cost, part surface quality, and design freedom. It is thought that the geometries that can be produced without support will help the more widespread use of AM technologies. In this study, the unsupported manufacturability and efficiency research of conformal cooling channel (CCC) geometries created in cylindrical, wide oval, drop, hexagonal, narrow oval, and pentagonal cross-sections were conducted in the direct metal laser sintering (DMLS) system. The study offers innovation in terms of showing the usability of different channel geometries in CCC applications. The study shows that the pentagon form has the most efficient cooling capacity among the comparatively handled geometries. The results are obtained by a computational fluid dynamics (CFD) analysis study on computer-aided design (CAD) data of the actual state channel geometry obtained by CAD and post-production micro-CT scanning of the design and presented in tables. This research shows that the production-induced sagging problem affects the flow by narrowing the channel hydraulic diameter in channel geometries produced without CCC supports.
- Published
- 2021
48. Mathematical simulation of two-phase flow and slag entrainment during steel bloom continuous casting
- Author
-
Sha Ji, Lifeng Zhang, Wen Yang, Wei Chen, Yadong Wang, and Ying Ren
- Subjects
Entrainment (hydrodynamics) ,Materials science ,General Chemical Engineering ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Continuous casting ,020401 chemical engineering ,Casting (metalworking) ,Volume of fluid method ,Hydraulic diameter ,Two-phase flow ,0204 chemical engineering ,Slag (welding) ,0210 nano-technology ,Large eddy simulation - Abstract
A three-dimensional computational model, coupled with the Large Eddy Simulation (LES) model and Volume of Fluid (VOF) multiphase model, was established to investigate the two-phase flow and slag entrainment during steel bloom continuous casting. The influence of the in-mold electromagnetic stirring (M-EMS), casting speed, and submerged entry nozzle (SEN) immersion depth on the flow pattern and slag entrainment were evaluated. The number, size, velocity, and spatial distribution of slag droplets were counted and the location, velocity and probability of the slag entrainment on the meniscus were exported in real time through a user defined function. The result shows that the slag entrainment mainly occurred around the 1/4 width of the mold. The equivalent diameter of most slag droplets was 2–6 mm under the current casting condition. A formula for the equivalent diameter distribution of slag droplets was proposed according to the statistical result.
- Published
- 2021
49. 3D Fe-Rich Phases Evolution and Its Effects on the Fracture Behavior of Al–7.0Si–1.2Fe Alloys by Mn Neutralization
- Author
-
Daoxi Li, Yiwang Jia, Zhi Wang, Weiwen Zhang, Yanan Fu, Yuliang Zhao, Dongfu Song, and Datong Zhang
- Subjects
Materials science ,Morphology (linguistics) ,Alloy ,Metals and Alloys ,engineering.material ,Industrial and Manufacturing Engineering ,Sphericity ,Phase (matter) ,Volume fraction ,engineering ,Hydraulic diameter ,Composite material ,Ductility ,Tensile testing - Abstract
The evolution of the 3D Fe-rich phases of Al–7.0Si–1.2Fe alloys with different Mn contents was visualized and characterized using synchrotron X-ray computed tomography, and the effect of Fe-rich phases with typical morphologies on the fracture behavior during tensile testing was analyzed. The results showed that the Fe-rich phase changed from platelet-like β-Al5FeSi into α-Al15(FeMn)3Si2 with various morphologies after the addition of Mn. The Mn addition not only significantly reduced the volume fraction, equivalent diameter and interconnectivity of the Fe-rich phase but also greatly increased the sphericity, surface thickness, and distribution of the mean curvature and surface thickness. Furthermore, the equivalent diameter of α-Al15(FeMn)3Si2 had an inverse exponential function relationship with its sphericity. The 3D morphology of α-Al15(FeMn)3Si2 can be summarized as massive and regular polyhedrons, hollow and regular polyhedrons, and multibranched polyhedrons. The fraction of the different 3D morphologies in each alloy is related to the Mn content, where excess Mn increased the number and volume fraction of the large Fe-rich particles with a low sphericity. The ductility of each alloy was significantly improved by the addition of Mn but gradually decreased when the Mn/Fe ratio exceeded 1.2. The increase in large α-Al15(MnFe)3Si2 with a low sphericity was the main reason for the decreased ductility of alloys with a high Mn content.
- Published
- 2021
50. Application of the Hydraulic Diameter of Interdendritic Space for Calculating the Ultimate Tensile Strength of Gray Cast Iron
- Author
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Stanislav V. Palatkin, A. A. Baron, and Lyubov' V. Palatkina
- Subjects
Radiation ,Materials science ,Ultimate tensile strength ,engineering ,General Materials Science ,Hydraulic diameter ,Cast iron ,Composite material ,engineering.material ,Condensed Matter Physics ,Space (mathematics) - Abstract
A comparative analysis of methods for estimating the gray cast iron ultimate tensile strength σu by the hydraulic diameter of interdendritic space DHydIP and the volume fraction of primary austenite dendrites fdc is performed. Almost the same accuracy of cast iron castings σu estimation according to both these parameters DHydIP and fdc of the primary microstructure is shown.
- Published
- 2021
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