Coldplates are a crucial component in various cooling applications, such as cooling data center servers and power electronics. The unprecedented growth in electronics power density, along with the resulting ultra-high heat fluxes, demands a transition from single-phase forced convection to two-phase flow boiling heat transfer. The majority of studies in the literature have focused on flow boiling in fin-enhanced silicon microgaps and microchannels, with only a few addressing flow boiling in millimeter-scale heat sinks. In the present study, flow boiling of HFE-7200 dielectric fluid in a millimeter-scale pin-fin coldplate is experimentally investigated under non-uniform heating conditions. Four background heaters represent the low-dissipating-power devices. On the other hand, five hotspot heaters mimic the high-heat-flux devices and generate heat fluxes ranging from 50 W/cm2 to 1,000 W/cm2, corresponding to hotspot heat inputs ranging from 62.5 W to 1.25 kW, respectively. The coldplate's thermohydraulic performance is investigated for various flow rates and inlet temperature ranging from 0.5 L/min to 1.5 L/min and from 25°C to 60°C, respectively. A high-speed camera is utilized for a narrow field of view (FOV) flow visualization at a frame rate of 2229 fps, while a digital camera is used for a wider FOV at 60 fps. Flow visualization demonstrated the transition between bubbly, slug/churn, and stratified two-phase flow regimes.
{"title":"Thermal Characterization of Subcooled Flow Boiling in a Pin-Fin Coldplate with Non-Uniform Heating","authors":"A. Osman, Yogendra Joshi","doi":"10.1115/1.4064709","DOIUrl":"https://doi.org/10.1115/1.4064709","url":null,"abstract":"\u0000 Coldplates are a crucial component in various cooling applications, such as cooling data center servers and power electronics. The unprecedented growth in electronics power density, along with the resulting ultra-high heat fluxes, demands a transition from single-phase forced convection to two-phase flow boiling heat transfer. The majority of studies in the literature have focused on flow boiling in fin-enhanced silicon microgaps and microchannels, with only a few addressing flow boiling in millimeter-scale heat sinks. In the present study, flow boiling of HFE-7200 dielectric fluid in a millimeter-scale pin-fin coldplate is experimentally investigated under non-uniform heating conditions. Four background heaters represent the low-dissipating-power devices. On the other hand, five hotspot heaters mimic the high-heat-flux devices and generate heat fluxes ranging from 50 W/cm2 to 1,000 W/cm2, corresponding to hotspot heat inputs ranging from 62.5 W to 1.25 kW, respectively. The coldplate's thermohydraulic performance is investigated for various flow rates and inlet temperature ranging from 0.5 L/min to 1.5 L/min and from 25°C to 60°C, respectively. A high-speed camera is utilized for a narrow field of view (FOV) flow visualization at a frame rate of 2229 fps, while a digital camera is used for a wider FOV at 60 fps. Flow visualization demonstrated the transition between bubbly, slug/churn, and stratified two-phase flow regimes.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"97 9-10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139849090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As a main part of multi-channel wall jet cooling structure, channel impingement cooling is a cooling strategy of great concern at the leading edge inside of the turbine blade. In this paper, heat transfer and flow behavior in the channel impingement cooling structure are investigated by Large Eddy Simulation (LES). The results imply that impingement created by curvature-induced centrifugal instabilities in the turning region of the cooling channel is dominated by a streamwise vortex system containing a counter-rotating Dean vortex, which presents high heat transfer streaks along the streamwise direction on the target wall. The intensely unsteady nature of the cooling jet induced by a lack of equilibrium between the pressure gradient and the centrifugal force are precisely captured herein by LES. An attaching-wall jet formed on the outer wall downstream of the cooling channel has highly three-dimensional characteristics not observed by Reynolds-averaged Navier-Stokes equations (RANS). Heat transfer augmentation on the target wall of the cooling channel is mainly due to the intensifying streamwise vortex system developing in the turning region as driven by the centrifugal force. This research work will provide a reference for the optimization and application of multi-channel wall jet cooling for gas turbine blades.
{"title":"Heat Transfer and Flow Characteristics of Channel Impingement Cooling Structure at Leading Edge Inside Turbine Blades Using Large Eddy Simulation","authors":"Huihui Wang, Qinghua Deng, Zhenping Feng","doi":"10.1115/1.4064706","DOIUrl":"https://doi.org/10.1115/1.4064706","url":null,"abstract":"\u0000 As a main part of multi-channel wall jet cooling structure, channel impingement cooling is a cooling strategy of great concern at the leading edge inside of the turbine blade. In this paper, heat transfer and flow behavior in the channel impingement cooling structure are investigated by Large Eddy Simulation (LES). The results imply that impingement created by curvature-induced centrifugal instabilities in the turning region of the cooling channel is dominated by a streamwise vortex system containing a counter-rotating Dean vortex, which presents high heat transfer streaks along the streamwise direction on the target wall. The intensely unsteady nature of the cooling jet induced by a lack of equilibrium between the pressure gradient and the centrifugal force are precisely captured herein by LES. An attaching-wall jet formed on the outer wall downstream of the cooling channel has highly three-dimensional characteristics not observed by Reynolds-averaged Navier-Stokes equations (RANS). Heat transfer augmentation on the target wall of the cooling channel is mainly due to the intensifying streamwise vortex system developing in the turning region as driven by the centrifugal force. This research work will provide a reference for the optimization and application of multi-channel wall jet cooling for gas turbine blades.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"46 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139850181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Coldplates are a crucial component in various cooling applications, such as cooling data center servers and power electronics. The unprecedented growth in electronics power density, along with the resulting ultra-high heat fluxes, demands a transition from single-phase forced convection to two-phase flow boiling heat transfer. The majority of studies in the literature have focused on flow boiling in fin-enhanced silicon microgaps and microchannels, with only a few addressing flow boiling in millimeter-scale heat sinks. In the present study, flow boiling of HFE-7200 dielectric fluid in a millimeter-scale pin-fin coldplate is experimentally investigated under non-uniform heating conditions. Four background heaters represent the low-dissipating-power devices. On the other hand, five hotspot heaters mimic the high-heat-flux devices and generate heat fluxes ranging from 50 W/cm2 to 1,000 W/cm2, corresponding to hotspot heat inputs ranging from 62.5 W to 1.25 kW, respectively. The coldplate's thermohydraulic performance is investigated for various flow rates and inlet temperature ranging from 0.5 L/min to 1.5 L/min and from 25°C to 60°C, respectively. A high-speed camera is utilized for a narrow field of view (FOV) flow visualization at a frame rate of 2229 fps, while a digital camera is used for a wider FOV at 60 fps. Flow visualization demonstrated the transition between bubbly, slug/churn, and stratified two-phase flow regimes.
{"title":"Thermal Characterization of Subcooled Flow Boiling in a Pin-Fin Coldplate with Non-Uniform Heating","authors":"A. Osman, Yogendra Joshi","doi":"10.1115/1.4064709","DOIUrl":"https://doi.org/10.1115/1.4064709","url":null,"abstract":"\u0000 Coldplates are a crucial component in various cooling applications, such as cooling data center servers and power electronics. The unprecedented growth in electronics power density, along with the resulting ultra-high heat fluxes, demands a transition from single-phase forced convection to two-phase flow boiling heat transfer. The majority of studies in the literature have focused on flow boiling in fin-enhanced silicon microgaps and microchannels, with only a few addressing flow boiling in millimeter-scale heat sinks. In the present study, flow boiling of HFE-7200 dielectric fluid in a millimeter-scale pin-fin coldplate is experimentally investigated under non-uniform heating conditions. Four background heaters represent the low-dissipating-power devices. On the other hand, five hotspot heaters mimic the high-heat-flux devices and generate heat fluxes ranging from 50 W/cm2 to 1,000 W/cm2, corresponding to hotspot heat inputs ranging from 62.5 W to 1.25 kW, respectively. The coldplate's thermohydraulic performance is investigated for various flow rates and inlet temperature ranging from 0.5 L/min to 1.5 L/min and from 25°C to 60°C, respectively. A high-speed camera is utilized for a narrow field of view (FOV) flow visualization at a frame rate of 2229 fps, while a digital camera is used for a wider FOV at 60 fps. Flow visualization demonstrated the transition between bubbly, slug/churn, and stratified two-phase flow regimes.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":" 34","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139789469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marco Bizzarri, Paolo Conti, L. Glicksman, E. Schito, D. Testi
The purpose of our study is to evaluate the surface temperature distribution on a radiant floor, particularly focusing on space cooling operations, to assess the presence of non-uniformities. In fact, knowing the temperature difference between the average superficial temperature and the coldest spot can be a useful indication for condensation prevention. Primarily, we performed an experimental campaign in test rooms using temperature sensors and liquid crystal thermography. This allowed us to evaluate the floor temperature distribution both on a local scale, influenced by the discontinuous presence of buried water pipes, and on a macro scale, influenced by internal use, objects, and boundary conditions of the surrounding space. Then, the experimental temperature field on the radiant floor surface has been compared with analytical and numerical models in steady-state and transient phases, respectively. The results indicate limited superficial temperature variations that become more significant at larger tube spacings and under transient conditions. In particular, the numerical transient analysis showed that shortly after a step change in the pipe's temperature boundary condition, a larger variation is locally observable on the floor, which then decays to the new steady-state conditions, presenting more uniformity. However, local effects are generally overshadowed by macro effects, especially for practical scenarios where many objects, furnishings, and different boundary conditions are present. Finally, as a conservative guideline for the cooling system control, we recommend maintaining the average superficial floor temperature at least 1°C above the dew point, to account for the described non-uniformities.
{"title":"Evaluation by Liquid Crystal Thermography of Transient Surface Temperature Distribution in Radiant Floor Cooling Applications and Assessment of Analytical and Numerical Models","authors":"Marco Bizzarri, Paolo Conti, L. Glicksman, E. Schito, D. Testi","doi":"10.1115/1.4064707","DOIUrl":"https://doi.org/10.1115/1.4064707","url":null,"abstract":"\u0000 The purpose of our study is to evaluate the surface temperature distribution on a radiant floor, particularly focusing on space cooling operations, to assess the presence of non-uniformities. In fact, knowing the temperature difference between the average superficial temperature and the coldest spot can be a useful indication for condensation prevention. Primarily, we performed an experimental campaign in test rooms using temperature sensors and liquid crystal thermography. This allowed us to evaluate the floor temperature distribution both on a local scale, influenced by the discontinuous presence of buried water pipes, and on a macro scale, influenced by internal use, objects, and boundary conditions of the surrounding space. Then, the experimental temperature field on the radiant floor surface has been compared with analytical and numerical models in steady-state and transient phases, respectively. The results indicate limited superficial temperature variations that become more significant at larger tube spacings and under transient conditions. In particular, the numerical transient analysis showed that shortly after a step change in the pipe's temperature boundary condition, a larger variation is locally observable on the floor, which then decays to the new steady-state conditions, presenting more uniformity. However, local effects are generally overshadowed by macro effects, especially for practical scenarios where many objects, furnishings, and different boundary conditions are present. Finally, as a conservative guideline for the cooling system control, we recommend maintaining the average superficial floor temperature at least 1°C above the dew point, to account for the described non-uniformities.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":" 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139790044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.
{"title":"Effect of Finite Thermal Conductivity Bounding Walls On Darcy-bénard Convection","authors":"Parvez Alam, Umesh Madanan","doi":"10.1115/1.4064687","DOIUrl":"https://doi.org/10.1115/1.4064687","url":null,"abstract":"\u0000 Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139852073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.
{"title":"Spray Cooling Heat Transfer of a Two-Fluid Spray Atomizer","authors":"S. Hsieh, Ching-Feng Huang, Jhen Lin, Yu-Ru Chen","doi":"10.1115/1.4064686","DOIUrl":"https://doi.org/10.1115/1.4064686","url":null,"abstract":"\u0000 The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"67 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139853808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.
{"title":"Effect of Finite Thermal Conductivity Bounding Walls On Darcy-bénard Convection","authors":"Parvez Alam, Umesh Madanan","doi":"10.1115/1.4064687","DOIUrl":"https://doi.org/10.1115/1.4064687","url":null,"abstract":"\u0000 Natural convection in fluid-saturated, horizontal porous-media is quintessential to many applications like geothermal reservoirs and solar thermal storage systems. Researchers have dedicated substantial effort over the years in pursuit of altering natural convection within a horizontal porous-media (Darcy-Bénard) system. Although significant research efforts have been directed towards understanding the effects of bounding walls in horizontal (Rayleigh-Bénard) convection systems, similar investigations for Darcy-Bénard convection systems are still lacking. Therefore, the present study examines the effect of thermal properties of horizontal bounding plates on porous-media Nusselt number at high Rayleigh-Darcy numbers (105-107). Numerical simulations are performed by employing Darcy-Forchheimer model within a three-dimensional cylindrical computational domain to emulate Darcy-Bénard systems for two aspect ratios (1 and 2)and six different plate materials having non-dimensional plate thicknesses of 0.02, 0.08, and 0.16. Polypropylene and compressed CO2 gas are chosen as solid and fluid phases for the porous media, respectively, that encompass a range of Darcy numbers (10-6-10-3). Findings reveal that when the ratio of thermal resistances of porous layer and plates falls below 4.61, the corrected Nusselt number deviates by more than 10% from the corresponding ideal Nusselt number with infinitely conducting bounding plates. The study also proposes a correction factor to estimate this deviation, which shows a good agreement with numerical results.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":" 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139792262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.
{"title":"Green's Function for Laminar Flow in Channels with Porous Walls in the Presence of a Transverse Magnetic Field","authors":"C. Tisdell","doi":"10.1115/1.4064689","DOIUrl":"https://doi.org/10.1115/1.4064689","url":null,"abstract":"\u0000 Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":" 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139791439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.
{"title":"Spray Cooling Heat Transfer of a Two-Fluid Spray Atomizer","authors":"S. Hsieh, Ching-Feng Huang, Jhen Lin, Yu-Ru Chen","doi":"10.1115/1.4064686","DOIUrl":"https://doi.org/10.1115/1.4064686","url":null,"abstract":"\u0000 The paper presents an experimental study on the droplet size and velocity, as well as temperature distribution, of a two-fluid atomizer (dj=1.6mm; spray nozzle exit diameter) through optical non-intrusive interferometric particle image (IPI) and particle image velocimetry (PIV) measurements with five different air liquid ratios (Rs) at three spray heights with three target-plate initial temperatures. Cold flow visualization was made for the spray height of 50 mm at 25oC. The Saunter-mean diameter (d32) was measured at the target temperature of 25°C without heating and found to be in the range of 34.22µm to 42.62µm in terms of a correlation with We(dj) Re(dj). The measured impact velocity at the spray height of 50 mm was of 10m/s to 30m/s with three different initial target temperatures. It was found that the impact velocity displayed a strong function of the initial temperature. Furthermore, both the cooling curve and transient boiling curve were obtained with the identified cooling/boiling parameters of the cooling rate, critical heat flux (CHF), Leidenfrost temperature (LFT), as well as the onset of nucleate boiling (ONB). The best cooling performance was found at R=0.242 for a spray height of 50 mm with the corresponding cooling rate of -19.1°/s, CHF of 486 W/cm2, and heat transfer coefficient (HTC) of 2.85 W/cm2K.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"76 s322","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139793926","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.
{"title":"Green's Function for Laminar Flow in Channels with Porous Walls in the Presence of a Transverse Magnetic Field","authors":"C. Tisdell","doi":"10.1115/1.4064689","DOIUrl":"https://doi.org/10.1115/1.4064689","url":null,"abstract":"\u0000 Despite the significant and ongoing interest in Green's functions from scientists, engineers and mathematicians, the area remains underdeveloped with respect to understanding problems from laminar fluid flow and magnetohydrodynamics in porous media. The purpose of this paper is to partially address this gap by constructing a new and explicit representation of the Green's function for a boundary value problem that is derived from laminar flow in channels with porous walls in the presence of a transverse magnetic field. We discuss some interesting consequences of our constructed Green's function, including: the establishment of an equivalent integral equation; and the generation of new information regarding solutions to our boundary value problem. We discover that, for any given transverse magnetic field, our laminar flow problem has a unique solution in a particular location provided the Reynolds number is sufficiently small, and that the solution may be approximated by Picard iterations.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"61 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139851312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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