In this article, the linear stability of non-isothermal plane Couette flow (NPCF) in an anisotropic and inhomogeneous porous layer underlying a fluid layer is investigated. The Darcy model is utilized to describe the flow in the porous layer. The stability analysis indicates that the introduction of media-anisotropy (K∧ *) and media-inhomogeneity (in terms of inhomogeneity parameter, A) still renders the isothermal plane Couette flow (IPCF) in such superposed fluid-porous systems unconditionally stable. For NPCF, three different modes: unimodal (porous or fluid mode), bimodal (porous and fluid mode) and trimodal (porous, fluid and porous mode), are observed along the neutral stability curves, and characterized by the secondary flow patterns. It has been found that the instability of the fluid-porous system increases on increasing the media permeability and inhomogeneity along the vertical direction. Contrary to natural convection, at d ∧ = 0.2 (d ∧ = depth of fluid layer/depth of porous layer) and K∧ * = 1, in which the critical wavelength shows both increasing and decreasing characteristic with increasing values of A (0 = A = 5), here in the present study, the same continuously decreases with increasing values of A. Finally, scale analysis indicates that the onset of natural convection requires a relatively higher temperature difference (ΔT) between lower and upper plates in the presence of Couette flow. However, by including media anisotropy and inhomogeneity in the porous media, the system becomes unstable even for a small critical temperature difference of about 2°C.
本文研究了流体层下各向异性非均质多孔层中的非等温平面库尔特流（NPCF）的线性稳定性。采用达西模型来描述多孔层中的流动。稳定性分析表明，引入介质各向异性（K∧*）和介质非均质性（非均质参数 A）仍能使等温平面库尔特流（IPCF）在这种叠加的流体-多孔系统中无条件稳定。对于 NPCF，沿着中性稳定曲线可以观察到三种不同的模式：单模态（多孔或流体模式）、双模态（多孔和流体模式）和三模态（多孔、流体和多孔模式），并以次级流动模式为特征。研究发现，流体-多孔系统的不稳定性随着介质渗透率和垂直方向不均匀性的增加而增加。与自然对流相反，在 d ∧ = 0.2（d ∧ = 流体层深度/多孔层深度）和 K∧ * = 1 时，临界波长随着 A 值（0 = A = 5）的增大而显示出增大和减小的特征，而在本研究中，临界波长同样随着 A 值的增大而持续减小。最后，尺度分析表明，在存在库尔特气流的情况下，自然对流的发生需要下板和上板之间相对较高的温度差（ΔT）。然而，由于多孔介质中存在介质各向异性和不均匀性，即使临界温差很小（约 2°C），系统也会变得不稳定。
{"title":"Non-Isothermal Plane Couette Flow and Its Stability in an Anisotropic and Inhomogeneous Porous Layer Underlying a Fluid Layer Saturated by Water","authors":"Nandita Barman, Anjali Aleria, Premananda Bera","doi":"10.1115/1.4064736","DOIUrl":"https://doi.org/10.1115/1.4064736","url":null,"abstract":"\u0000 In this article, the linear stability of non-isothermal plane Couette flow (NPCF) in an anisotropic and inhomogeneous porous layer underlying a fluid layer is investigated. The Darcy model is utilized to describe the flow in the porous layer. The stability analysis indicates that the introduction of media-anisotropy (K∧ *) and media-inhomogeneity (in terms of inhomogeneity parameter, A) still renders the isothermal plane Couette flow (IPCF) in such superposed fluid-porous systems unconditionally stable. For NPCF, three different modes: unimodal (porous or fluid mode), bimodal (porous and fluid mode) and trimodal (porous, fluid and porous mode), are observed along the neutral stability curves, and characterized by the secondary flow patterns. It has been found that the instability of the fluid-porous system increases on increasing the media permeability and inhomogeneity along the vertical direction. Contrary to natural convection, at d ∧ = 0.2 (d ∧ = depth of fluid layer/depth of porous layer) and K∧ * = 1, in which the critical wavelength shows both increasing and decreasing characteristic with increasing values of A (0 = A = 5), here in the present study, the same continuously decreases with increasing values of A. Finally, scale analysis indicates that the onset of natural convection requires a relatively higher temperature difference (ΔT) between lower and upper plates in the presence of Couette flow. However, by including media anisotropy and inhomogeneity in the porous media, the system becomes unstable even for a small critical temperature difference of about 2°C.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"128 35","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139780869","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 optimization of heat source layout (HSLO) is able to facilitate superior heat dissipation, thereby addressing the complexities associated with thermal management. However, HSLO is characterized by numerous degrees of freedom and complex interrelations between components. Conventional optimization methodologies often exhibit limitations such as high computational demands and diminished efficiency, particularly with large-scale predicaments. This study introduces the application of deep learning surrogate models grounded in backpropagation neural (BP) networks to optimize heat source layouts. These models afford rapid and precise evaluations, diminishing computational loads and enhancing the efficiency of HSLO. The suggested framework integrates coarse and fine search modules to traverse the layout space and pinpoint optimal configurations competently. Parametric examinations are taken to explore the impact of refinement grades and conductive ratios, which dominates the optimization problem. The pattern changes of the conductive channel have been presented. Moreover, the critical conductive ratio has been found, below which the conductive material can not contribute to heat dissipation. The outcomes elucidate the fundamental processes of HSLO, providing valuable insights for pioneering thermal management strategies.
{"title":"Investigation of Heat Source Layout Optimization by Using Deep Learning Surrogate Models","authors":"Ji Lang, Qianqian Wang, Shan Tong","doi":"10.1115/1.4064733","DOIUrl":"https://doi.org/10.1115/1.4064733","url":null,"abstract":"\u0000 The optimization of heat source layout (HSLO) is able to facilitate superior heat dissipation, thereby addressing the complexities associated with thermal management. However, HSLO is characterized by numerous degrees of freedom and complex interrelations between components. Conventional optimization methodologies often exhibit limitations such as high computational demands and diminished efficiency, particularly with large-scale predicaments. This study introduces the application of deep learning surrogate models grounded in backpropagation neural (BP) networks to optimize heat source layouts. These models afford rapid and precise evaluations, diminishing computational loads and enhancing the efficiency of HSLO. The suggested framework integrates coarse and fine search modules to traverse the layout space and pinpoint optimal configurations competently. Parametric examinations are taken to explore the impact of refinement grades and conductive ratios, which dominates the optimization problem. The pattern changes of the conductive channel have been presented. Moreover, the critical conductive ratio has been found, below which the conductive material can not contribute to heat dissipation. The outcomes elucidate the fundamental processes of HSLO, providing valuable insights for pioneering thermal management strategies.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139780588","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}
Ramon Peruchi Pacheco da Silva, K. Woodbury, F. Samadi, Joseph Carpenter
An experimental apparatus was constructed to correlate water flow rate and temperature rise under an external band heater. Due to the physical characteristics of the band heater, its transient heating behavior is unknown. This paper investigates the application of Inverse Heat Conduction Problem (IHCP) methods to characterize the heat flux from the band heater. Three experiments with different heating times (5, 10, and 20 seconds) and no flow rate were conducted to measure the transient temperature under the 400 W band heater. Type-T thermocouples measure surface temperature at the centerline of the band heater. The experimental results are computed with five different heat conduction models. The models are chosen to identify how the heat flux response varies from a simplified to a realistic model. Additionally, the results of the experimental heat flux are compared to the manufacturer band heater data (58.9 kW/m2) for each model. The minimum time needed for the heater to fully energize the system is from 10 to 12 seconds. The residuals for each model are analyzed and used to evaluate the appropriateness of the five different models. The results show that the use of simpler models can achieve results similar to those of complex models, with less time and computational cost.
{"title":"Heat Flux Characterization From a Band Heater to Pipe Using Inverse Heat Conduction Problem Method","authors":"Ramon Peruchi Pacheco da Silva, K. Woodbury, F. Samadi, Joseph Carpenter","doi":"10.1115/1.4064731","DOIUrl":"https://doi.org/10.1115/1.4064731","url":null,"abstract":"\u0000 An experimental apparatus was constructed to correlate water flow rate and temperature rise under an external band heater. Due to the physical characteristics of the band heater, its transient heating behavior is unknown. This paper investigates the application of Inverse Heat Conduction Problem (IHCP) methods to characterize the heat flux from the band heater. Three experiments with different heating times (5, 10, and 20 seconds) and no flow rate were conducted to measure the transient temperature under the 400 W band heater. Type-T thermocouples measure surface temperature at the centerline of the band heater. The experimental results are computed with five different heat conduction models. The models are chosen to identify how the heat flux response varies from a simplified to a realistic model. Additionally, the results of the experimental heat flux are compared to the manufacturer band heater data (58.9 kW/m2) for each model. The minimum time needed for the heater to fully energize the system is from 10 to 12 seconds. The residuals for each model are analyzed and used to evaluate the appropriateness of the five different models. The results show that the use of simpler models can achieve results similar to those of complex models, with less time and computational cost.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":"100 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139781246","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}
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":"63 8","pages":""},"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":" 41","pages":""},"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":"163 6","pages":""},"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":"116 2","pages":""},"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":" 7","pages":""},"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":" 39","pages":""},"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}
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":"117 1-2","pages":""},"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}
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