Samuel Tomlinson, Michael D. Mayer, Toby Kirk, Marc Hodes, Demetrios Papageorgiou
Abstract A pressure-driven channel flow between a longitudinally ridged superhydrophobic surface (SHS) and solid wall is studied, where a constant heat flux enters the channel from either the SHS or solid wall. First, a model is developed which neglects thermocapillary stresses (TCS) in the transverse direction. The caloric, convective, and total thermal resistance are evaluated, and their dependence on the shape of the liquid–gas interface (meniscus), gas ridge width, texture period, channel height, streamwise TCS, Péclet number, and channel length is established. The caloric resistance is minimized with menisci that protrude into the gas cavity, large slip fractions, small channel heights, and small streamwise TCSs. When heating from the SHS, the convective resistance increases, and therefore, a design compromise exists between caloric and convective resistances. However, when heating from the solid wall, the convective resistance remains the same and SHSs that minimize caloric resistance are optimal. We investigate both water and Galinstan for microchannel applications and find that both configurations can have a lower total thermal resistance than a smooth-walled channel. Heating from the solid wall is shown to always have the lowest total thermal resistance. Numerical simulations are used to analyze the effect of transverse TCSs. Our model captures much of the physics in heated superhydrophobic channels but is computationally inexpensive when compared to the numerical simulations.
{"title":"Thermal Resistance Of Heated Superhydrophobic Channels with Streamwise Thermocapillary Stress","authors":"Samuel Tomlinson, Michael D. Mayer, Toby Kirk, Marc Hodes, Demetrios Papageorgiou","doi":"10.1115/1.4063880","DOIUrl":"https://doi.org/10.1115/1.4063880","url":null,"abstract":"Abstract A pressure-driven channel flow between a longitudinally ridged superhydrophobic surface (SHS) and solid wall is studied, where a constant heat flux enters the channel from either the SHS or solid wall. First, a model is developed which neglects thermocapillary stresses (TCS) in the transverse direction. The caloric, convective, and total thermal resistance are evaluated, and their dependence on the shape of the liquid–gas interface (meniscus), gas ridge width, texture period, channel height, streamwise TCS, Péclet number, and channel length is established. The caloric resistance is minimized with menisci that protrude into the gas cavity, large slip fractions, small channel heights, and small streamwise TCSs. When heating from the SHS, the convective resistance increases, and therefore, a design compromise exists between caloric and convective resistances. However, when heating from the solid wall, the convective resistance remains the same and SHSs that minimize caloric resistance are optimal. We investigate both water and Galinstan for microchannel applications and find that both configurations can have a lower total thermal resistance than a smooth-walled channel. Heating from the solid wall is shown to always have the lowest total thermal resistance. Numerical simulations are used to analyze the effect of transverse TCSs. Our model captures much of the physics in heated superhydrophobic channels but is computationally inexpensive when compared to the numerical simulations.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":" 23","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135191701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract In this article, the confined jet impingement cooling of a semi-cylindrical concave plate is analyzed numerically. The investigation is done for different jet Reynolds numbers (Rej)ranging from 100 to 1000, as the Richardson number (Ri) corresponding to this interval ranges between 0.1 and 10. For any Richardson number, the modified Grashof number (Gr*) is fixed at 105. When analyzing the impact of inter-surface radiation between the target plate and confined surfaces on the overall cooling performance, three emissivity values (ε0.05, 0.5 and 0.9) are taken into consideration. Additionally, simulations are done for the pure convective heat transfer, ignoring inter-surface radiation (ε=0.0). The influence of surface emissivity and the Richardson number on velocity, temperature and pressure distribution in the flow region, local dimensionless temperature (θ) alterations on the target plate and confined walls, alterations in convective (Nuc), radiative (Nur), overall Nusselt numbers (Nuover), pressure coefficient (Cp) and ratio of radiative Nusselt number to overall Nusselt number (Nur/Nuover) on the target plate are highlighted. The findings demonstrate that surface emissivity has significant influence on thermal and hydrodynamic boundary layer formation, buoyancy induced flow and heat transfer, and the proportion of inter-surface radiation in overall heat transfer rises as the Richardson number and surface emissivity increase. At low Richardson numbers, the pressure in the stagnation region is greater than the atmospheric pressure. However, as the buoyancy effect increases, the pressure in the stagnation region falls below the atmospheric pressure and rises towards the exit.
{"title":"Influence of Buoyancy and Inter-Surface Radiation on Confined Jet Impingement Cooling of a Semi-Cylindrical Concave Plate","authors":"Bugra Sarper","doi":"10.1115/1.4064038","DOIUrl":"https://doi.org/10.1115/1.4064038","url":null,"abstract":"Abstract In this article, the confined jet impingement cooling of a semi-cylindrical concave plate is analyzed numerically. The investigation is done for different jet Reynolds numbers (Rej)ranging from 100 to 1000, as the Richardson number (Ri) corresponding to this interval ranges between 0.1 and 10. For any Richardson number, the modified Grashof number (Gr*) is fixed at 105. When analyzing the impact of inter-surface radiation between the target plate and confined surfaces on the overall cooling performance, three emissivity values (ε0.05, 0.5 and 0.9) are taken into consideration. Additionally, simulations are done for the pure convective heat transfer, ignoring inter-surface radiation (ε=0.0). The influence of surface emissivity and the Richardson number on velocity, temperature and pressure distribution in the flow region, local dimensionless temperature (θ) alterations on the target plate and confined walls, alterations in convective (Nuc), radiative (Nur), overall Nusselt numbers (Nuover), pressure coefficient (Cp) and ratio of radiative Nusselt number to overall Nusselt number (Nur/Nuover) on the target plate are highlighted. The findings demonstrate that surface emissivity has significant influence on thermal and hydrodynamic boundary layer formation, buoyancy induced flow and heat transfer, and the proportion of inter-surface radiation in overall heat transfer rises as the Richardson number and surface emissivity increase. At low Richardson numbers, the pressure in the stagnation region is greater than the atmospheric pressure. However, as the buoyancy effect increases, the pressure in the stagnation region falls below the atmospheric pressure and rises towards the exit.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":" 9","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135286147","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Drying front propagation and coupled heat and mass transfer analysis from porous media is critical for soil–water dynamics, electronics cooling, and evaporative drying. In this study, de-ionized water was evaporated from three 3D printed porous structures (with 0.41 mm, 0.41 mm, and 0.16 mm effective radii, respectively) created out of acrylonitrile butadiene styrene (ABS) plastic using stereolithography technology. The structures were immersed in water until all the pores were invaded and then placed on the top of a sensitive scale to record evaporative mass loss. A 1000 W/m2 heat flux was applied with a solar simulator to the top of each structure to accelerate evaporation. The evaporative mass losses were recorded at 15 min time intervals and plotted against time to compare evaporation rates from the three structures. The evaporation phenomena were captured with a high-speed camera from the side of the structures to observe the drying front propagation during evaporation, and a high-resolution thermal camera was used to capture images to visualize the thermal gradients during evaporation. The 3D-structure with the smallest effective pore radius (i.e., 0.16 mm) experienced the sharpest decrease in the mass loss as the water evaporated from 0.8 g to 0.1 g within 180 min. The designed pore structures influenced hydraulic linkages, and therefore, evaporation processes. A coupled heat-and-mass-transfer model modeled constant rate evaporation, and the falling rate period was modeled through the normalized evaporation rate.
{"title":"Analysis of Drying Front Propagation and Coupled Heat and Mass Transfer During Evaporation From Additively-Manufactured Porous Structures Under a Solar Flux","authors":"Partha P. Chakraborty, Melanie Derby","doi":"10.1115/1.4063766","DOIUrl":"https://doi.org/10.1115/1.4063766","url":null,"abstract":"Abstract Drying front propagation and coupled heat and mass transfer analysis from porous media is critical for soil–water dynamics, electronics cooling, and evaporative drying. In this study, de-ionized water was evaporated from three 3D printed porous structures (with 0.41 mm, 0.41 mm, and 0.16 mm effective radii, respectively) created out of acrylonitrile butadiene styrene (ABS) plastic using stereolithography technology. The structures were immersed in water until all the pores were invaded and then placed on the top of a sensitive scale to record evaporative mass loss. A 1000 W/m2 heat flux was applied with a solar simulator to the top of each structure to accelerate evaporation. The evaporative mass losses were recorded at 15 min time intervals and plotted against time to compare evaporation rates from the three structures. The evaporation phenomena were captured with a high-speed camera from the side of the structures to observe the drying front propagation during evaporation, and a high-resolution thermal camera was used to capture images to visualize the thermal gradients during evaporation. The 3D-structure with the smallest effective pore radius (i.e., 0.16 mm) experienced the sharpest decrease in the mass loss as the water evaporated from 0.8 g to 0.1 g within 180 min. The designed pore structures influenced hydraulic linkages, and therefore, evaporation processes. A coupled heat-and-mass-transfer model modeled constant rate evaporation, and the falling rate period was modeled through the normalized evaporation rate.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":" 90","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135191835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
GuiCheng Cui, ChengLong Zhou, Yong Zhang, Hongliang Yi
Abstract The near-field radiative heat transfer of heterostructure consisting of SiC gratings and graphene is investigated in this work. The rigorous coupled-wave analysis is employed to calculate the spectral heat flux. Nevertheless, monolayer heterostructure and nonmisaligned bilayer heterostructure consistently suffer from a lack of spectral heat flux. In this work, we investigate the prominent effect of misaligned bilayer heterostructure in enhancing near-field radiative heat transfer by plotting energy transmission coefficients and electromagnetic fields. The results show that when the misalignment reaches half a period, the bilayer heterostructure exhibits optimal performance with a total heat flux of 3.5 × 104 W/m2. Besides the well-known coupled surface phonon polaritons supported by SiC gratings, the surface plasmon polaritons supported by graphene dominate the enhancement of heat flux from 0.01 × 1014 rad/s to 1.5 × 1014 rad/s. Due to the spatial misalignment of the upper and lower gratings, the lower layer graphene surface plasmon polaritons are intensified, compensating for the lack of spectral heat flux. Meanwhile, the graphene surface plasmon polaritons and SiC surface phonon polaritons can be hybridized to form surface plasmon-phonon polaritons. In addition, the dynamic modulation of near-field radiative heat transfer in the misalignment state is achieved by manipulating the Fermi level of graphene. We finally show that the superiority of misaligned heterostructure is robust with respect to the frequency shift in the phonon band, providing an effective way to improve the near-field radiative heat transfer in different configuration.
{"title":"Significant Enhancement of Near-Field Radiative Heat Transfer by Misaligned Bilayer Heterostructure of Graphene-Covered Gratings","authors":"GuiCheng Cui, ChengLong Zhou, Yong Zhang, Hongliang Yi","doi":"10.1115/1.4063644","DOIUrl":"https://doi.org/10.1115/1.4063644","url":null,"abstract":"Abstract The near-field radiative heat transfer of heterostructure consisting of SiC gratings and graphene is investigated in this work. The rigorous coupled-wave analysis is employed to calculate the spectral heat flux. Nevertheless, monolayer heterostructure and nonmisaligned bilayer heterostructure consistently suffer from a lack of spectral heat flux. In this work, we investigate the prominent effect of misaligned bilayer heterostructure in enhancing near-field radiative heat transfer by plotting energy transmission coefficients and electromagnetic fields. The results show that when the misalignment reaches half a period, the bilayer heterostructure exhibits optimal performance with a total heat flux of 3.5 × 104 W/m2. Besides the well-known coupled surface phonon polaritons supported by SiC gratings, the surface plasmon polaritons supported by graphene dominate the enhancement of heat flux from 0.01 × 1014 rad/s to 1.5 × 1014 rad/s. Due to the spatial misalignment of the upper and lower gratings, the lower layer graphene surface plasmon polaritons are intensified, compensating for the lack of spectral heat flux. Meanwhile, the graphene surface plasmon polaritons and SiC surface phonon polaritons can be hybridized to form surface plasmon-phonon polaritons. In addition, the dynamic modulation of near-field radiative heat transfer in the misalignment state is achieved by manipulating the Fermi level of graphene. We finally show that the superiority of misaligned heterostructure is robust with respect to the frequency shift in the phonon band, providing an effective way to improve the near-field radiative heat transfer in different configuration.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":" 33","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135191967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Slip flows in small-scale flow networks involve simultaneous presence of multiple factors governing the flow field. In addition, conditions of upstream wall need to be clearly defined. The present work addresses these aspects by analyzing the heat transfer aspects of slip flows. The complete form of the governing equations are solved. The fully developed Nusselt number (Nufd) is found to rise first, before dropping continuously with rise in Knudsen number (Kn). The pair of Kn and maximum Nufd is found to be dependent on Peclet number (Pe) of the system. Local Nu is found to drop to a minimum, lower than Nufd for Kn ~ O(10-3) due to a significant radial advection. The presence of an adiabatic upstream wall reveals that heat may propagate up to the inlet for Kn ≳ 0.015. An analytical solution is developed to approximate this limiting value of Kn and it agrees well with the numerical results. The observed flow behavior leads to the categorization of flow regime into three types: (i) Kn < 0.001, possessing dependence on change in Pe only, (ii) 0.001 ≤ Kn < 0.01, possessing concurrence of effects due to change in Pe and Kn, and (iii) 0.01 ≤ Kn < 0.1, possessing dependence on change in Kn only. Further, Pe is shown to represent Nubulk for the flow, where in the range 0.01 ≤ Kn < 0.1, Nutot ≈ Nubulk as Kn approaches 0.01 and Nutot ≈ Nuin as Kn approaches 0.1.
{"title":"Significance of Upstream Wall Conditions in Characterizing the Heat Transfer Phenomena of Rarefied Flows","authors":"Ambuj A Jha, Amit Agrawal","doi":"10.1115/1.4063991","DOIUrl":"https://doi.org/10.1115/1.4063991","url":null,"abstract":"Abstract Slip flows in small-scale flow networks involve simultaneous presence of multiple factors governing the flow field. In addition, conditions of upstream wall need to be clearly defined. The present work addresses these aspects by analyzing the heat transfer aspects of slip flows. The complete form of the governing equations are solved. The fully developed Nusselt number (Nufd) is found to rise first, before dropping continuously with rise in Knudsen number (Kn). The pair of Kn and maximum Nufd is found to be dependent on Peclet number (Pe) of the system. Local Nu is found to drop to a minimum, lower than Nufd for Kn ~ O(10-3) due to a significant radial advection. The presence of an adiabatic upstream wall reveals that heat may propagate up to the inlet for Kn ≳ 0.015. An analytical solution is developed to approximate this limiting value of Kn and it agrees well with the numerical results. The observed flow behavior leads to the categorization of flow regime into three types: (i) Kn &lt; 0.001, possessing dependence on change in Pe only, (ii) 0.001 ≤ Kn &lt; 0.01, possessing concurrence of effects due to change in Pe and Kn, and (iii) 0.01 ≤ Kn &lt; 0.1, possessing dependence on change in Kn only. Further, Pe is shown to represent Nubulk for the flow, where in the range 0.01 ≤ Kn &lt; 0.1, Nutot ≈ Nubulk as Kn approaches 0.01 and Nutot ≈ Nuin as Kn approaches 0.1.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":"237 8","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135476227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The function of a heat exchanger is to transfer heat. In this paper, a 2nd law-based hypothesis is advanced that the entropy generated as a result of heat transfer alone, termed productive entropy, is the desired irreversibility and should be maximized while the entropy generated (irreversibilities) by other factors like friction and mixing that do not contribute to this function should be minimized or eliminated to reduce the needed heat transfer area. The hypothesis is proven mathematically for heat transfer between two fluids in a heat exchanger and between one hot and two cold fluids in a network of up to four heat exchangers. There currently are two approaches for minimizing the total area (minimum initial cost) of a heat exchanger network (HEN). One uses some empirically based best practices that are generally rooted in the second law, and the other uses optimization algorithms. This paper provides a third approach for HEN optimization, outlining a systematic approach to minimize the area, based on the maximization of productive entropy. The approach identifies the global minimum area for networks with any number of hot and cold streams. It constitutes another method for HEN optimization and an improvement over the existing methods that provide approximate solutions. The methodology is applied to two test cases, and it is shown that this approach improves on the results obtained using the traditional approaches. The approach can be applied to networks using any type of heat exchanger or a combination of different types of heat exchangers.
{"title":"Maximization of the Heat Transfer Irreversibility","authors":"Ahmad Fakheri","doi":"10.1115/1.4063990","DOIUrl":"https://doi.org/10.1115/1.4063990","url":null,"abstract":"Abstract The function of a heat exchanger is to transfer heat. In this paper, a 2nd law-based hypothesis is advanced that the entropy generated as a result of heat transfer alone, termed productive entropy, is the desired irreversibility and should be maximized while the entropy generated (irreversibilities) by other factors like friction and mixing that do not contribute to this function should be minimized or eliminated to reduce the needed heat transfer area. The hypothesis is proven mathematically for heat transfer between two fluids in a heat exchanger and between one hot and two cold fluids in a network of up to four heat exchangers. There currently are two approaches for minimizing the total area (minimum initial cost) of a heat exchanger network (HEN). One uses some empirically based best practices that are generally rooted in the second law, and the other uses optimization algorithms. This paper provides a third approach for HEN optimization, outlining a systematic approach to minimize the area, based on the maximization of productive entropy. The approach identifies the global minimum area for networks with any number of hot and cold streams. It constitutes another method for HEN optimization and an improvement over the existing methods that provide approximate solutions. The methodology is applied to two test cases, and it is shown that this approach improves on the results obtained using the traditional approaches. The approach can be applied to networks using any type of heat exchanger or a combination of different types of heat exchangers.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":"58 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135479624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Computational modeling using the high-viscosity laminar flow approach was applied to study the effect of slab crossing time on slab heating and scale growth. Simulation of an existing industrial walking beam reheating furnace with four zones, outer refractory body, skid, slab, and fluid zone is considered. The fuel used was a mixture of coke oven and blast furnace gas. Preheated air is supplied co-axially with the fuel mixture. The combustion simulation is performed using the constrained equilibrium mixture fraction model. From the results, it has been observed that with an increase in slab residence time, the slab temperature and scale growth increase across the slab. For the system considered, with a fuel mass flowrate of 70,000 kg/h, 150–180 min of slab crossing time is appropriate to obtain desired slab temperature at the discharge end. The overall equivalence ratio is taken as Φ = 1 (fuel/air ratio is the same as stoichiometric ratio). The maximum slab scale thickness is evaluated as 2.4 mm at the discharged end for 180 min of slab crossing time.
{"title":"Computational Modeling of Walking Beam Type Reheat Furnace for the Prediction of Slab Heating and Scale Formation","authors":"Saurabh Singh, Vineet Kumar, Prakash Ghose","doi":"10.1115/1.4063643","DOIUrl":"https://doi.org/10.1115/1.4063643","url":null,"abstract":"Abstract Computational modeling using the high-viscosity laminar flow approach was applied to study the effect of slab crossing time on slab heating and scale growth. Simulation of an existing industrial walking beam reheating furnace with four zones, outer refractory body, skid, slab, and fluid zone is considered. The fuel used was a mixture of coke oven and blast furnace gas. Preheated air is supplied co-axially with the fuel mixture. The combustion simulation is performed using the constrained equilibrium mixture fraction model. From the results, it has been observed that with an increase in slab residence time, the slab temperature and scale growth increase across the slab. For the system considered, with a fuel mass flowrate of 70,000 kg/h, 150–180 min of slab crossing time is appropriate to obtain desired slab temperature at the discharge end. The overall equivalence ratio is taken as Φ = 1 (fuel/air ratio is the same as stoichiometric ratio). The maximum slab scale thickness is evaluated as 2.4 mm at the discharged end for 180 min of slab crossing time.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":"12 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135544651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bin Hu, Di Qi, Yongsheng Xu, Mei Lin, Qiuwang Wang
Abstract With the continuous development of power electronic devices toward miniaturization and compactness, it is necessary to develop more efficient flow boiling heat transfer technologies. In this work, the flow boiling heat transfer and pressure drop characteristics of Novec649 in a pin finned channel under two kinds of flow orientations (horizontal and vertical upward) are experimentally investigated. Heat flux, inlet flow velocity, and inlet subcooling are considered as the variable parameters. The results show that among all boiling operating conditions, the heat transfer performances between two orientations are basically consistent, while the pressure drop of vertical upward pin finned channel is relatively lower, indicating that the comprehensive flow boiling heat transfer performance of vertical oriented channel is better. Subsequently, a series of flow visualization experiments are performed in vertical upward pin finned channel. With the increase of heat flux, four kinds of flow pattern are discovered in the order of dispersed bubble flow, bubble flow, homogeneous flow, and annular flow. In the region of annular flow, although a vapor flow has already formed in the channel, there is still a large amount of liquid phase surrounding the wall and pin fins. Therefore, no obvious heat transfer deterioration was observed in the pin finned channel. Along the flow direction, the diameter of bubbles will increase first, and then present obvious oscillation. As the heat flux increases, both the average bubble detachment diameter and the frequency increase correspondingly. As the fluid velocity increases, the average bubble detachment diameter presents a downward trend, while the average bubble detachment frequency presents an upward trend.
{"title":"A Comparative Study of Flow Boiling Heat Transfer and Pressure Drop Characteristics in a Pin-Finned Heat Sink At Horizontal/Vertical Upward Flow Orientations","authors":"Bin Hu, Di Qi, Yongsheng Xu, Mei Lin, Qiuwang Wang","doi":"10.1115/1.4063765","DOIUrl":"https://doi.org/10.1115/1.4063765","url":null,"abstract":"Abstract With the continuous development of power electronic devices toward miniaturization and compactness, it is necessary to develop more efficient flow boiling heat transfer technologies. In this work, the flow boiling heat transfer and pressure drop characteristics of Novec649 in a pin finned channel under two kinds of flow orientations (horizontal and vertical upward) are experimentally investigated. Heat flux, inlet flow velocity, and inlet subcooling are considered as the variable parameters. The results show that among all boiling operating conditions, the heat transfer performances between two orientations are basically consistent, while the pressure drop of vertical upward pin finned channel is relatively lower, indicating that the comprehensive flow boiling heat transfer performance of vertical oriented channel is better. Subsequently, a series of flow visualization experiments are performed in vertical upward pin finned channel. With the increase of heat flux, four kinds of flow pattern are discovered in the order of dispersed bubble flow, bubble flow, homogeneous flow, and annular flow. In the region of annular flow, although a vapor flow has already formed in the channel, there is still a large amount of liquid phase surrounding the wall and pin fins. Therefore, no obvious heat transfer deterioration was observed in the pin finned channel. Along the flow direction, the diameter of bubbles will increase first, and then present obvious oscillation. As the heat flux increases, both the average bubble detachment diameter and the frequency increase correspondingly. As the fluid velocity increases, the average bubble detachment diameter presents a downward trend, while the average bubble detachment frequency presents an upward trend.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":"16 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135585234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract This article proposes a new formulation for a phase change model based on the enthalpy-porosity idea. A general one-energy equation model (1EEM) is extended to deal with the melting and solidification of pure substances and alloys. Before melting and after solidification, solid material is seen as a porous media with low porosity and very small permeability. During phase change, thermal equilibrium in the mushy zone is assumed. Viscous and form drag in the volume-averaged momentum equation are reduced as the temperature rises above the melting point. In the energy equation, latent heat is treated implicitly in the accumulation term instead of explicitly as in most works in the literature. Liquid fraction for the entire field is updated after a new temperature field is calculated. Thermophysical properties are updated with the new liquid fraction field. Governing equations are discretized according to the control-volume method. Algebraic equation sets are relaxed with the Simple Method. Inner iterations make use of the Strong Implicit Procedure. Preliminary results indicate good agreement with the literature for pure substances.
{"title":"A Fully-Implict Enthalpy-Porosity Model for Phase-Change","authors":"Marcelo J.S. de Lemos, Anatole Hodierne","doi":"10.1115/1.4063732","DOIUrl":"https://doi.org/10.1115/1.4063732","url":null,"abstract":"Abstract This article proposes a new formulation for a phase change model based on the enthalpy-porosity idea. A general one-energy equation model (1EEM) is extended to deal with the melting and solidification of pure substances and alloys. Before melting and after solidification, solid material is seen as a porous media with low porosity and very small permeability. During phase change, thermal equilibrium in the mushy zone is assumed. Viscous and form drag in the volume-averaged momentum equation are reduced as the temperature rises above the melting point. In the energy equation, latent heat is treated implicitly in the accumulation term instead of explicitly as in most works in the literature. Liquid fraction for the entire field is updated after a new temperature field is calculated. Thermophysical properties are updated with the new liquid fraction field. Governing equations are discretized according to the control-volume method. Algebraic equation sets are relaxed with the Simple Method. Inner iterations make use of the Strong Implicit Procedure. Preliminary results indicate good agreement with the literature for pure substances.","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":"12 9","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135544652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract In this paper, a systematic numerical study of pool boiling heat transfer on a mixed wettability heated surface is done using the lattice Boltzmann method (LBM) with a multiple relaxation time (MRT)-based collision operator. The effect of the design parameters, viz, size of the hydrophobic patch (D), spacing between hydrophobic patches (L), number of hydrophobic patches (N), and uneven-sized patches, on pool boiling was studied and results are explained through detailed analysis of bubble nucleation, growth, coalescence, and departure from the heated surface. The results show that mixed wettability surfaces with strategically sized and positioned hydrophobic patches on a hydrophilic surface can result in high heat flux for pool boiling across the entire range of surface superheat or Jacob number (Ja) by combining the advantages of hydrophobic surface in nucleate boiling and hydrophilic surface in transition and film boiling. Further, the mixed wettability surface can delay the onset of film boiling compared to a pure or superhydrophilic surface thereby resulting in higher critical heat flux (CHF). A hydrophobic to total surface area ratio of 30–40% was found to be optimal for all ranges of surface superheat or Jacob number (Ja), which agrees well with the experimental result of 38.46% reported by Motezakker et al. (2019, “Optimum Ratio of Hydrophobic to Hydrophilic Areas of Biphilic Surfaces in Thermal Fluid Systems Involving Boiling,” Int. J. Heat Mass Transfer, 135, pp. 164–174).
{"title":"Numerical Investigations On Enhancement of Pool Boiling Heat Transfer On a Mixed Wettability Surface Employing Lattice Boltzmann Method (LBM)","authors":"Sonali Priyadarshini Das, Anandaroop Bhattacharya","doi":"10.1115/1.4063647","DOIUrl":"https://doi.org/10.1115/1.4063647","url":null,"abstract":"Abstract In this paper, a systematic numerical study of pool boiling heat transfer on a mixed wettability heated surface is done using the lattice Boltzmann method (LBM) with a multiple relaxation time (MRT)-based collision operator. The effect of the design parameters, viz, size of the hydrophobic patch (D), spacing between hydrophobic patches (L), number of hydrophobic patches (N), and uneven-sized patches, on pool boiling was studied and results are explained through detailed analysis of bubble nucleation, growth, coalescence, and departure from the heated surface. The results show that mixed wettability surfaces with strategically sized and positioned hydrophobic patches on a hydrophilic surface can result in high heat flux for pool boiling across the entire range of surface superheat or Jacob number (Ja) by combining the advantages of hydrophobic surface in nucleate boiling and hydrophilic surface in transition and film boiling. Further, the mixed wettability surface can delay the onset of film boiling compared to a pure or superhydrophilic surface thereby resulting in higher critical heat flux (CHF). A hydrophobic to total surface area ratio of 30–40% was found to be optimal for all ranges of surface superheat or Jacob number (Ja), which agrees well with the experimental result of 38.46% reported by Motezakker et al. (2019, “Optimum Ratio of Hydrophobic to Hydrophilic Areas of Biphilic Surfaces in Thermal Fluid Systems Involving Boiling,” Int. J. Heat Mass Transfer, 135, pp. 164–174).","PeriodicalId":15937,"journal":{"name":"Journal of Heat Transfer-transactions of The Asme","volume":"20 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135585442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：