Large eddy simulation was performed to investigate heat transfer performance of a pulsating flow over teardrop-shaped dimples. A total of six geometries of dimpled surfaces were examined for dimple arrangements of in-line/staggered/original and dimple inclination angle of 0-60 deg. Pulsating flows were generated by sinusoidally varying the volume-averaged velocity. The pulsation frequency and amplitude were changed for the Strouhal number of 0-0.60 and the root-mean-square velocity amplitude normalized by the bulk flow velocity of 0-0.14. The results showed that the surface-averaged Nusselt number and friction factor were larger for the pulsating flow case than those for the steady flow case. The surface-averaged Nusselt number ratio and the friction factor increased with the Strouhal number up to the Strouhal number of 0.30. For the Strouhal number larger than 0.30, they decreased with the Strouhal number or stayed almost constant. Consequently, the heat transfer efficiency index increased with the Strouhal number. The increase in the local Nusselt number ratio due to the flow pulsation was observed at the leading-edge region of the dimples. The results of the streamlines near the dimple showed that the swirling separation bubble was located closer to the leading-edge region due to the pulsation, which resulted in the increase of the absolute values of the turbulent heat flux and the local Nusselt number ratio.
{"title":"Effects of Flow Pulsation and Surface Geometry On Heat Transfer Performance in a Channel with Teardrop-shaped Dimples Investigated by Large Eddy Simulation","authors":"K. Inokuma, Yuki Yawata, A. Murata, K. Iwamoto","doi":"10.1115/1.4064735","DOIUrl":"https://doi.org/10.1115/1.4064735","url":null,"abstract":"\u0000 Large eddy simulation was performed to investigate heat transfer performance of a pulsating flow over teardrop-shaped dimples. A total of six geometries of dimpled surfaces were examined for dimple arrangements of in-line/staggered/original and dimple inclination angle of 0-60 deg. Pulsating flows were generated by sinusoidally varying the volume-averaged velocity. The pulsation frequency and amplitude were changed for the Strouhal number of 0-0.60 and the root-mean-square velocity amplitude normalized by the bulk flow velocity of 0-0.14. The results showed that the surface-averaged Nusselt number and friction factor were larger for the pulsating flow case than those for the steady flow case. The surface-averaged Nusselt number ratio and the friction factor increased with the Strouhal number up to the Strouhal number of 0.30. For the Strouhal number larger than 0.30, they decreased with the Strouhal number or stayed almost constant. Consequently, the heat transfer efficiency index increased with the Strouhal number. The increase in the local Nusselt number ratio due to the flow pulsation was observed at the leading-edge region of the dimples. The results of the streamlines near the dimple showed that the swirling separation bubble was located closer to the leading-edge region due to the pulsation, which resulted in the increase of the absolute values of the turbulent heat flux and the local Nusselt number ratio.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139781574","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}
Performance of a novel ultracompact thermal energy storage (TES) heat exchanger, designed as a micro-channel finned-tube exchanger is presented. With water as the heating-cooling fluid in the micro-channels, a salt hydrate phase change material (PCM), lithium nitrate trihydrate (LiNO3∙3H2O), was encased on the fin side. To establish the hypothesis that small-length-scale encasement (< 3 mm) of PCM substantially enhances heat transfer to yield very high power-density energy storage, heat exchanger designs with 10 and 24 fins/inch were considered. They were subjected to thermal cycling, or repeated heating (melting) and cooling (freezing), with inlet fluid flow mimicking diurnal variation between 42? - 25? (representing typical arid-region conditions) over an accelerated time period. By employing salt self-seeding to obviate subcooling during cooling or recrystallization, the TES was found to exhibit stable long-term (100 heating-cooling cycles) operation with very high PCM-side heat transfer coefficients (~ 100-500 W/m2∙K) and storage power density (~ 160-175 kW/m3). In fact, with optimization of heating-cooling fluid flow rate for given charging-discharging time period and exchanger size, power density > 300 kW/m3 can be achieved. The results clearly establish that highly compact heat exchangers used as TES units can provide very high-performance alternatives to conventional ones.
{"title":"High Power Density Thermal Energy Storage with Phase Change Material in Enhanced Compact Heat Exchangers","authors":"Sarath Kannan, M. Jog, R. M. Manglik","doi":"10.1115/1.4064710","DOIUrl":"https://doi.org/10.1115/1.4064710","url":null,"abstract":"\u0000 Performance of a novel ultracompact thermal energy storage (TES) heat exchanger, designed as a micro-channel finned-tube exchanger is presented. With water as the heating-cooling fluid in the micro-channels, a salt hydrate phase change material (PCM), lithium nitrate trihydrate (LiNO3∙3H2O), was encased on the fin side. To establish the hypothesis that small-length-scale encasement (< 3 mm) of PCM substantially enhances heat transfer to yield very high power-density energy storage, heat exchanger designs with 10 and 24 fins/inch were considered. They were subjected to thermal cycling, or repeated heating (melting) and cooling (freezing), with inlet fluid flow mimicking diurnal variation between 42? - 25? (representing typical arid-region conditions) over an accelerated time period. By employing salt self-seeding to obviate subcooling during cooling or recrystallization, the TES was found to exhibit stable long-term (100 heating-cooling cycles) operation with very high PCM-side heat transfer coefficients (~ 100-500 W/m2∙K) and storage power density (~ 160-175 kW/m3). In fact, with optimization of heating-cooling fluid flow rate for given charging-discharging time period and exchanger size, power density > 300 kW/m3 can be achieved. The results clearly establish that highly compact heat exchangers used as TES units can provide very high-performance alternatives to conventional ones.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139790743","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":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139849795","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}
Performance of a novel ultracompact thermal energy storage (TES) heat exchanger, designed as a micro-channel finned-tube exchanger is presented. With water as the heating-cooling fluid in the micro-channels, a salt hydrate phase change material (PCM), lithium nitrate trihydrate (LiNO3∙3H2O), was encased on the fin side. To establish the hypothesis that small-length-scale encasement (< 3 mm) of PCM substantially enhances heat transfer to yield very high power-density energy storage, heat exchanger designs with 10 and 24 fins/inch were considered. They were subjected to thermal cycling, or repeated heating (melting) and cooling (freezing), with inlet fluid flow mimicking diurnal variation between 42? - 25? (representing typical arid-region conditions) over an accelerated time period. By employing salt self-seeding to obviate subcooling during cooling or recrystallization, the TES was found to exhibit stable long-term (100 heating-cooling cycles) operation with very high PCM-side heat transfer coefficients (~ 100-500 W/m2∙K) and storage power density (~ 160-175 kW/m3). In fact, with optimization of heating-cooling fluid flow rate for given charging-discharging time period and exchanger size, power density > 300 kW/m3 can be achieved. The results clearly establish that highly compact heat exchangers used as TES units can provide very high-performance alternatives to conventional ones.
{"title":"High Power Density Thermal Energy Storage with Phase Change Material in Enhanced Compact Heat Exchangers","authors":"Sarath Kannan, M. Jog, R. M. Manglik","doi":"10.1115/1.4064710","DOIUrl":"https://doi.org/10.1115/1.4064710","url":null,"abstract":"\u0000 Performance of a novel ultracompact thermal energy storage (TES) heat exchanger, designed as a micro-channel finned-tube exchanger is presented. With water as the heating-cooling fluid in the micro-channels, a salt hydrate phase change material (PCM), lithium nitrate trihydrate (LiNO3∙3H2O), was encased on the fin side. To establish the hypothesis that small-length-scale encasement (< 3 mm) of PCM substantially enhances heat transfer to yield very high power-density energy storage, heat exchanger designs with 10 and 24 fins/inch were considered. They were subjected to thermal cycling, or repeated heating (melting) and cooling (freezing), with inlet fluid flow mimicking diurnal variation between 42? - 25? (representing typical arid-region conditions) over an accelerated time period. By employing salt self-seeding to obviate subcooling during cooling or recrystallization, the TES was found to exhibit stable long-term (100 heating-cooling cycles) operation with very high PCM-side heat transfer coefficients (~ 100-500 W/m2∙K) and storage power density (~ 160-175 kW/m3). In fact, with optimization of heating-cooling fluid flow rate for given charging-discharging time period and exchanger size, power density > 300 kW/m3 can be achieved. The results clearly establish that highly compact heat exchangers used as TES units can provide very high-performance alternatives to conventional ones.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139850635","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":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139790280","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}
Aleksandra Nastic, Larry Pershin, Prof. Javad Mostaghimi
During plasma spraying, interaction between splats and surface micro-sized features can be critical to the splat dynamic progress and consequently to the coating microstructural development and interfacial bonding. The transient spreading of molten alumina impacting a flat substrate exhibiting micro-obstructions, commonly produced during surface machining, grinding and/or even polishing, is numerically investigated using a three-dimensional model comprising of splat solidification and shrinkage developments. Single isolated splats are also experimentally characterized using top surface scanning electron microscope (SEM) analysis. Droplets impacting directly onto a micro-sized surface protuberance show no signs of pre-mature splashing behavior. The microscopic features (˂5µm) are not able to generate flow instabilities to initially affect the splat inherent overall spreading. However, subsequent splat peripheral contact with target surface micro-obstructions, characterized by peak and valley features, induces peripheral lift, waviness, and instability. It follows that the ejected destabilized material shears/fractures during stretching triggering the formation of splash fingers. Solidification plays a major role in detracting the role of surface micro-obstructions, i.e. surface roughness, in splashing phenomena.
{"title":"Microscale Surface Defects Influence on Thermally Sprayed Alumina Droplets Deformation Dynamics","authors":"Aleksandra Nastic, Larry Pershin, Prof. Javad Mostaghimi","doi":"10.1115/1.4064708","DOIUrl":"https://doi.org/10.1115/1.4064708","url":null,"abstract":"\u0000 During plasma spraying, interaction between splats and surface micro-sized features can be critical to the splat dynamic progress and consequently to the coating microstructural development and interfacial bonding. The transient spreading of molten alumina impacting a flat substrate exhibiting micro-obstructions, commonly produced during surface machining, grinding and/or even polishing, is numerically investigated using a three-dimensional model comprising of splat solidification and shrinkage developments. Single isolated splats are also experimentally characterized using top surface scanning electron microscope (SEM) analysis.\u0000 Droplets impacting directly onto a micro-sized surface protuberance show no signs of pre-mature splashing behavior. The microscopic features (˂5µm) are not able to generate flow instabilities to initially affect the splat inherent overall spreading. However, subsequent splat peripheral contact with target surface micro-obstructions, characterized by peak and valley features, induces peripheral lift, waviness, and instability. It follows that the ejected destabilized material shears/fractures during stretching triggering the formation of splash fingers. Solidification plays a major role in detracting the role of surface micro-obstructions, i.e. surface roughness, in splashing phenomena.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139848958","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}
Aleksandra Nastic, Larry Pershin, Prof. Javad Mostaghimi
During plasma spraying, interaction between splats and surface micro-sized features can be critical to the splat dynamic progress and consequently to the coating microstructural development and interfacial bonding. The transient spreading of molten alumina impacting a flat substrate exhibiting micro-obstructions, commonly produced during surface machining, grinding and/or even polishing, is numerically investigated using a three-dimensional model comprising of splat solidification and shrinkage developments. Single isolated splats are also experimentally characterized using top surface scanning electron microscope (SEM) analysis. Droplets impacting directly onto a micro-sized surface protuberance show no signs of pre-mature splashing behavior. The microscopic features (˂5µm) are not able to generate flow instabilities to initially affect the splat inherent overall spreading. However, subsequent splat peripheral contact with target surface micro-obstructions, characterized by peak and valley features, induces peripheral lift, waviness, and instability. It follows that the ejected destabilized material shears/fractures during stretching triggering the formation of splash fingers. Solidification plays a major role in detracting the role of surface micro-obstructions, i.e. surface roughness, in splashing phenomena.
{"title":"Microscale Surface Defects Influence on Thermally Sprayed Alumina Droplets Deformation Dynamics","authors":"Aleksandra Nastic, Larry Pershin, Prof. Javad Mostaghimi","doi":"10.1115/1.4064708","DOIUrl":"https://doi.org/10.1115/1.4064708","url":null,"abstract":"\u0000 During plasma spraying, interaction between splats and surface micro-sized features can be critical to the splat dynamic progress and consequently to the coating microstructural development and interfacial bonding. The transient spreading of molten alumina impacting a flat substrate exhibiting micro-obstructions, commonly produced during surface machining, grinding and/or even polishing, is numerically investigated using a three-dimensional model comprising of splat solidification and shrinkage developments. Single isolated splats are also experimentally characterized using top surface scanning electron microscope (SEM) analysis.\u0000 Droplets impacting directly onto a micro-sized surface protuberance show no signs of pre-mature splashing behavior. The microscopic features (˂5µm) are not able to generate flow instabilities to initially affect the splat inherent overall spreading. However, subsequent splat peripheral contact with target surface micro-obstructions, characterized by peak and valley features, induces peripheral lift, waviness, and instability. It follows that the ejected destabilized material shears/fractures during stretching triggering the formation of splash fingers. Solidification plays a major role in detracting the role of surface micro-obstructions, i.e. surface roughness, in splashing phenomena.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139789382","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":null,"pages":null},"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}
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":null,"pages":null},"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":null,"pages":null},"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}
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：