Pool boiling as a mechanism for effective heat dissipation in battery thermal management systems can considerably mitigate this risk. In this study, we electrochemically deposited one smooth nickel specimen and three specimens with a porous nickel-stacked structure. The four samples underwent microstructural characterization via scanning electron microscopy. Through visual experiments, we evaluated their wettability, and through pool boiling experiments, we tested their boiling heat transfer properties. Our findings suggest that samples incorporating a porous nickel structure consistently outperform unmodified samples regarding heat transfer efficiency. Specifically, samples with a current density of 0.5 A·cm-2 demonstrated the most optimal boiling heat transfer performance, evidenced by a 65.6% reduction in temperature at the onset of boiling, a 16.1% increase in critical heat flux density, and a 160.7% larger maximum heat transfer coefficient compared to the smooth nickel sample. The superior performance of samples with porous nickel structures can be attributed to the availability of a more significant number of nucleation sites. Additionally, specimens with a current density of 0.5 A·cm-2 displayed smaller micro-crystalline dendritic structures, an attribute that further favorably influenced their boiling heat transfer performance.
{"title":"Pool boiling heat transfer characteristics of porous nickel microstructure surfaces","authors":"Kun-Man Yao, Mou Xu, Shuo Yang, Xi-Zhe Huang, Dong-chuan MO, Shu-Shen Lv","doi":"10.1615/jenhheattransf.2024051598","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2024051598","url":null,"abstract":"Pool boiling as a mechanism for effective heat dissipation in battery thermal management systems can considerably mitigate this risk. In this study, we electrochemically deposited one smooth nickel specimen and three specimens with a porous nickel-stacked structure. The four samples underwent microstructural characterization via scanning electron microscopy. Through visual experiments, we evaluated their wettability, and through pool boiling experiments, we tested their boiling heat transfer properties. Our findings suggest that samples incorporating a porous nickel structure consistently outperform unmodified samples regarding heat transfer efficiency. Specifically, samples with a current density of 0.5 A·cm-2 demonstrated the most optimal boiling heat transfer performance, evidenced by a 65.6% reduction in temperature at the onset of boiling, a 16.1% increase in critical heat flux density, and a 160.7% larger maximum heat transfer coefficient compared to the smooth nickel sample. The superior performance of samples with porous nickel structures can be attributed to the availability of a more significant number of nucleation sites. Additionally, specimens with a current density of 0.5 A·cm-2 displayed smaller micro-crystalline dendritic structures, an attribute that further favorably influenced their boiling heat transfer performance.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"21 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139769523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-01DOI: 10.1615/jenhheattransf.2024050403
Yanchen Fu, Han Qi, Guoqiang Xu, Weitong Liu, Lina Zhang
An experimental research on flow and heat transfer characteristics of staggered tube bundles with different tube diameters (2mm, 3mm and 5mm) is conducted. In the experiment, the number of rows (4-12), the mass rate of the air (0.06kg/s-0.18kg/s), and the transverse tube pitch (S1/d=2, S1/d=3) are variables to study the characteristics of the airside flow resistance and heat transfer. The three main conclusions of the experimental results are as follows: (1) Under the same conditions, the smaller tube diameter leads to the larger airside convective heat transfer coefficient. Besides, the deviation between the Nusselt number of the experiment and the empirical correlation of Žukauskas is in the range between -14% and -10%; (2) The effect of transverse distance on heat transfer is not obvious, but the convective heat transfer coefficient increases significantly with the increase of row number; (3) The external pressure drop of the tube exhibits an exponential increase with the air flow rate. Particularly in the experimental samples with smaller diameters, the outflow resistance of the tube is noticeably higher compared to other tubes. Finally, new empirical correlations of the airside convection heat transfer for the small-diameter staggered tube bundles are fitted according to the experimental data, and it is hoped to provide a reference for the more accurate design of tube bundle heat exchangers.
{"title":"Flow and Heat Transfer Characteristics in Small Diameter Tube Bundles with a Staggered Layout: an experimental study","authors":"Yanchen Fu, Han Qi, Guoqiang Xu, Weitong Liu, Lina Zhang","doi":"10.1615/jenhheattransf.2024050403","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2024050403","url":null,"abstract":"An experimental research on flow and heat transfer characteristics of staggered tube bundles with different tube diameters (2mm, 3mm and 5mm) is conducted. In the experiment, the number of rows (4-12), the mass rate of the air (0.06kg/s-0.18kg/s), and the transverse tube pitch (S1/d=2, S1/d=3) are variables to study the characteristics of the airside flow resistance and heat transfer. The three main conclusions of the experimental results are as follows: (1) Under the same conditions, the smaller tube diameter leads to the larger airside convective heat transfer coefficient. Besides, the deviation between the Nusselt number of the experiment and the empirical correlation of Žukauskas is in the range between -14% and -10%; (2) The effect of transverse distance on heat transfer is not obvious, but the convective heat transfer coefficient increases significantly with the increase of row number; (3) The external pressure drop of the tube exhibits an exponential increase with the air flow rate. Particularly in the experimental samples with smaller diameters, the outflow resistance of the tube is noticeably higher compared to other tubes. Finally, new empirical correlations of the airside convection heat transfer for the small-diameter staggered tube bundles are fitted according to the experimental data, and it is hoped to provide a reference for the more accurate design of tube bundle heat exchangers.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"85 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139579186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-01DOI: 10.1615/jenhheattransf.2024050060
Ngoctan Tran, Jane-Sunn Liaw, Chi-Chuan Wang
The present study numerically examines the effects of tube diameter (12 to 35 mm), arrangement, pitch-to-diameter ratio (1.25 to 2.5), length (300 to 1500 mm), and passage number (1-4 passes) on the thermofluidic characteristics of cross-flow tube bundles. Especially, five new cam-shaped tubes are proposed in comparison with the conventional round tube. The air temperatures at the cold and hot side inlets are kept constant at 25 °C and 600 °C, respectively. The numerical method is verified by the existing experimental results. The findings show that a cam-shaped tube with an equal diameter (Cam_1818) is a promising tube for tube bundles, which apply in waste heat recovery. Indeed, it can offer the same minimum gap as that of the round tube; however, it improves the total thermal resistance up to about 28% and enhances the heat transfer rate up to an average of 42.3% compared to that of the round tubes at the same pumping power.
{"title":"A parametric and comparative study on bare-tube banks and new-cam-shaped tube banks for waste heat recovery applications","authors":"Ngoctan Tran, Jane-Sunn Liaw, Chi-Chuan Wang","doi":"10.1615/jenhheattransf.2024050060","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2024050060","url":null,"abstract":"The present study numerically examines the effects of tube diameter (12 to 35 mm), arrangement, pitch-to-diameter ratio (1.25 to 2.5), length (300 to 1500 mm), and passage number (1-4 passes) on the thermofluidic characteristics of cross-flow tube bundles. Especially, five new cam-shaped tubes are proposed in comparison with the conventional round tube. The air temperatures at the cold and hot side inlets are kept constant at 25 °C and 600 °C, respectively. The numerical method is verified by the existing experimental results. The findings show that a cam-shaped tube with an equal diameter (Cam_1818) is a promising tube for tube bundles, which apply in waste heat recovery. Indeed, it can offer the same minimum gap as that of the round tube; however, it improves the total thermal resistance up to about 28% and enhances the heat transfer rate up to an average of 42.3% compared to that of the round tubes at the same pumping power.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"201 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139579196","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The thermal insulation performance of pipeline is significant for the safety and economical operation of vapor steam network. In order to investigate the long-time insulation performance of pipeline, a field test was carried out in 12 different heating networks with the operating time ranging from 1 to 11 years. Two different type of insulation coating layer were included. The total heat flux and surface heat flux in pipeline were measured to obtained the equivalent thermal conductivity of the insulation coating layer, respectively. And a deterioration coefficient was applied to analyze the insulation deterioration characteristics. The results show that the one-dimensional thermal conduction method is feasible to calculate the heat flux of the pre-manufactured pipeline with hard insulation materials. And an error less than 2% for pipeline 1 was obtained. Further, a proper size of slip in the insulation coating layer has improved the insulation performance by 13.6% in this work. For the soft type insulation coating, the structure has been changed under the long-term effect of gravity. Accordingly, a single thermal conductivity cannot accurately characterize the heat transfer process within the insulation layer. The surface heat flux only account for less than 30% of the total heat loss. The insulation deterioration trend with operating time cannot exactly obtained by the surface heat flux. In addition to the thickness reduction at top and hollow at bottom, the convection heat leakage from the gaps should also be concerned for long time operation.
{"title":"Field experimental investigation of the insulation deterioration characteristics of overhead pipeline for steam heating network","authors":"Junguang Lin, Jianfa Zhao, Xiaotian Wang, Kailun Chen, Liang Zhang","doi":"10.1615/jenhheattransf.2024051807","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2024051807","url":null,"abstract":"The thermal insulation performance of pipeline is significant for the safety and economical operation of vapor steam network. In order to investigate the long-time insulation performance of pipeline, a field test was carried out in 12 different heating networks with the operating time ranging from 1 to 11 years. Two different type of insulation coating layer were included. The total heat flux and surface heat flux in pipeline were measured to obtained the equivalent thermal conductivity of the insulation coating layer, respectively. And a deterioration coefficient was applied to analyze the insulation deterioration characteristics. The results show that the one-dimensional thermal conduction method is feasible to calculate the heat flux of the pre-manufactured pipeline with hard insulation materials. And an error less than 2% for pipeline 1 was obtained. Further, a proper size of slip in the insulation coating layer has improved the insulation performance by 13.6% in this work. For the soft type insulation coating, the structure has been changed under the long-term effect of gravity. Accordingly, a single thermal conductivity cannot accurately characterize the heat transfer process within the insulation layer. The surface heat flux only account for less than 30% of the total heat loss. The insulation deterioration trend with operating time cannot exactly obtained by the surface heat flux. In addition to the thickness reduction at top and hollow at bottom, the convection heat leakage from the gaps should also be concerned for long time operation.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"10 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139647306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-01DOI: 10.1615/jenhheattransf.2024051524
Cheol-Hwan Kim, Niccolo Giannetti, Nae-Hyun Kim, Kiyoshi Saito
This study investigates two-phase flow distribution of R-1234yf into two-branched channels. Especially, the effect of unbalanced pressure drop and tube diameter on the flow distribution was characterized and modeled. The experiments were conducted for a mass flux ranging from 393 to 1179 kg/m2s and the inlet quality was fixed at 0.2. The flow distribution was mainly governed by the pressure drop ratio between two branched channels. The mal-distribution under the unbalanced pressure drop condition was mitigated by increasing mass flux, whereas sustained mal-distribution was observed under unbalanced tube diameter conditions. Correspondingly, a theoretical representation of the phenomenon, based on the principle of minimum entropy production, was developed and adopted to predict two-phase flow distribution in an unbalanced flow network. The characteristics of the experimental data were clearly and quantitatively reflected in the prediction results. Under the unbalanced pressure drop condition, the predictions agreed well with the experimental data maintaining the maximum deviation within ±30%, whereas it exceeded ± 30% under the unbalanced tube diameter condition. The analysis of such theoretical formulation suggested the necessity of appropriate pressure drop models of flow impact, contraction, and merging at the outlet channel, that are compatible with the extremization of entropy production for further improving the prediction accuracy without compromising its generality.
{"title":"EXPERIMENTAL AND THEORETICAL CHARACTERIZATION OF TWO-PHASE FLOW DISTRIBUTION IN UNBALANCED FLOW NETWORKS","authors":"Cheol-Hwan Kim, Niccolo Giannetti, Nae-Hyun Kim, Kiyoshi Saito","doi":"10.1615/jenhheattransf.2024051524","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2024051524","url":null,"abstract":"This study investigates two-phase flow distribution of R-1234yf into two-branched channels. Especially, the effect of unbalanced pressure drop and tube diameter on the flow distribution was characterized and modeled. The experiments were conducted for a mass flux ranging from 393 to 1179 kg/m2s and the inlet quality was fixed at 0.2. The flow distribution was mainly governed by the pressure drop ratio between two branched channels. The mal-distribution under the unbalanced pressure drop condition was mitigated by increasing mass flux, whereas sustained mal-distribution was observed under unbalanced tube diameter conditions. Correspondingly, a theoretical representation of the phenomenon, based on the principle of minimum entropy production, was developed and adopted to predict two-phase flow distribution in an unbalanced flow network. The characteristics of the experimental data were clearly and quantitatively reflected in the prediction results. Under the unbalanced pressure drop condition, the predictions agreed well with the experimental data maintaining the maximum deviation within ±30%, whereas it exceeded ± 30% under the unbalanced tube diameter condition. The analysis of such theoretical formulation suggested the necessity of appropriate pressure drop models of flow impact, contraction, and merging at the outlet channel, that are compatible with the extremization of entropy production for further improving the prediction accuracy without compromising its generality.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"306 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139647304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-01DOI: 10.1615/jenhheattransf.2023050891
Hamid-Reza Bahrami, Mahziyar Ghaedi
With the integration of electronic devices advancing, effectively dissipating heat generated has become a challenging task. One promising solution is utilizing heat convection as a powerful tool. However, a notable issue arises when encountering an obstacle, such as a resistor requiring cooling. In these cases, the flow slows down, weakening heat transfer. In order to model this obstacle, it can be perceived as a sudden compression. The critical area of interest lies where the horizontal wall approaches the vertical side of the obstacle. This study examines the use of non-uniform magnetic fields to explore various arrangements aimed at enhancing thermal energy transfer in this critical region. These arrangements include placing a single dipole beneath either the lower or upper walls and utilizing two or three single dipoles simultaneously beneath the heated wall. The ferrofluid used in this study is EMG-308. The findings of this study demonstrate that heat transfer improves when single or multiple dipoles are positioned downstream of the step wall on the heated wall. For instance, by having three dipoles of equal strength in that area, the minimum Nusselt number is enhanced by 300%, resulting in a Nusselt number before the step that surpasses the Nusselt number immediately after the step.
{"title":"Using a non-uniform magnetic field to enhance heat transfer before a sudden compression in a 2D milli-channel","authors":"Hamid-Reza Bahrami, Mahziyar Ghaedi","doi":"10.1615/jenhheattransf.2023050891","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2023050891","url":null,"abstract":"With the integration of electronic devices advancing, effectively dissipating heat generated has become a challenging task. One promising solution is utilizing heat convection as a powerful tool. However, a notable issue arises when encountering an obstacle, such as a resistor requiring cooling. In these cases, the flow slows down, weakening heat transfer. In order to model this obstacle, it can be perceived as a sudden compression. The critical area of interest lies where the horizontal wall approaches the vertical side of the obstacle. This study examines the use of non-uniform magnetic fields to explore various arrangements aimed at enhancing thermal energy transfer in this critical region. These arrangements include placing a single dipole beneath either the lower or upper walls and utilizing two or three single dipoles simultaneously beneath the heated wall. The ferrofluid used in this study is EMG-308. The findings of this study demonstrate that heat transfer improves when single or multiple dipoles are positioned downstream of the step wall on the heated wall. For instance, by having three dipoles of equal strength in that area, the minimum Nusselt number is enhanced by 300%, resulting in a Nusselt number before the step that surpasses the Nusselt number immediately after the step.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"35 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138561432","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-01DOI: 10.1615/jenhheattransf.2023050383
Yicun Tang, Yuan Zhang, Jingchun Min
In the convective drying of a wet porous medium by hot air, the medium surface exposed to the air fluid may experience three stages namely the fully wet, partly wet, and fully dry stages. At the fully wet stage, the medium surface is fully covered by a water film, with the convective moisture transfer taking place all over the medium surface; at the partly wet stage, the medium surface is partly covered by water film, with the convective moisture transfer occurring only at the wet surface where free water is present. In this research, a theoretical model is presented to simulate the convective drying of a wet porous medium, and experiments on hot air convective drying of a wet porous sand layer are carried out to investigate the sand layer temperature and water content variations during the drying, in which the sand layer thickness is 4 mm, the initial water film thickness is 0.4 mm, and the hot air temperatures are 45, 60 and 75℃, respectively. Inverse calculations are conducted to get some insight into the water film coverage function based on the experimental data, which is necessary for quantitatively evaluating the effective moisture transfer surface area when calculating the convective moisture transfer at the partly wet stage. By combining the coverage function with the wet porous medium drying model, a comprehensive model is obtained. Calculations are implemented to simulate the convective drying of the wet porous sand layer, and the effects of the two constants included in that function on the wet sand layer drying characteristics are discussed. The calculation results are compared with the experimental data, they agree very well, supporting the effectiveness o
{"title":"Modelling and simulations of wet porous medium convective drying","authors":"Yicun Tang, Yuan Zhang, Jingchun Min","doi":"10.1615/jenhheattransf.2023050383","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2023050383","url":null,"abstract":"In the convective drying of a wet porous medium by hot air, the medium surface exposed to the air fluid may experience three stages namely the fully wet, partly wet, and fully dry stages. At the fully wet stage, the medium surface is fully covered by a water film, with the convective moisture transfer taking place all over the medium surface; at the partly wet stage, the medium surface is partly covered by water film, with the convective moisture transfer occurring only at the wet surface where free water is present. In this research, a theoretical model is presented to simulate the convective drying of a wet porous medium, and experiments on hot air convective drying of a wet porous sand layer are carried out to investigate the sand layer temperature and water content variations during the drying, in which the sand layer thickness is 4 mm, the initial water film thickness is 0.4 mm, and the hot air temperatures are 45, 60 and 75℃, respectively. Inverse calculations are conducted to get some insight into the water film coverage function based on the experimental data, which is necessary for quantitatively evaluating the effective moisture transfer surface area when calculating the convective moisture transfer at the partly wet stage. By combining the coverage function with the wet porous medium drying model, a comprehensive model is obtained. Calculations are implemented to simulate the convective drying of the wet porous sand layer, and the effects of the two constants included in that function on the wet sand layer drying characteristics are discussed. The calculation results are compared with the experimental data, they agree very well, supporting the effectiveness o","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"11 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138545952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper investigates the heat transfer characteristics of a channel system consisting of a finned heat sink and two piezoelectric devices, the piezoelectric fan (PF) and the piezoelectric translational agitator (PTA), both experimentally and computationally. In the proposed system, the mean flow is generated by a cantilevered PF, and the flow between the fins is agitated using a PTA. A single channel system consisting of a PTA, the PF, and two fins is analyzed numerically using ANSYS Fluent software after validating numerical predictions against experimental measurements. The effect of design variables such as frequency ratio, phase difference, PF's tip distance from PTA, and squeezing fraction is explored. A PTA increases the heat transfer from the heated surfaces without incrementally aiding in the mass flow rate. Velocity and temperature fields are plotted to understand the physics of the system for one complete cycle of a PTA blade. The concept of total Reynolds number that incorporates the effect of both axial and transverse fluid flow is used in this study. The Nusselt number increases with an increment in the total Reynolds number. It is noted that the integration of the PF and the PTA with the finned heat sink system has enhanced the heat transfer coefficient by 76.88% compared to the system with PTA and by 30.92% as compared to the system with the PF only.
{"title":"Heat Transfer Analysis of a Combined Piezoelectric Fan -Translational Agitator Cooling System","authors":"Rutuja Ramachandra Bilaskar, Abhishek Singh, Sripriya Ramamoorthy, Shankar Krishnan","doi":"10.1615/jenhheattransf.2023049372","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2023049372","url":null,"abstract":"This paper investigates the heat transfer characteristics of a channel system consisting of a finned heat sink and two piezoelectric devices, the piezoelectric fan (PF) and the piezoelectric translational agitator (PTA), both experimentally and computationally. In the proposed system, the mean flow is generated by a cantilevered PF, and the flow between the fins is agitated using a PTA. A single channel system consisting of a PTA, the PF, and two fins is analyzed numerically using ANSYS Fluent software after validating numerical predictions against experimental measurements. The effect of design variables such as frequency ratio, phase difference, PF's tip distance from PTA, and squeezing fraction is explored. A PTA increases the heat transfer from the heated surfaces without incrementally aiding in the mass flow rate. Velocity and temperature fields are plotted to understand the physics of the system for one complete cycle of a PTA blade. The concept of total Reynolds number that incorporates the effect of both axial and transverse fluid flow is used in this study. The Nusselt number increases with an increment in the total Reynolds number. It is noted that the integration of the PF and the PTA with the finned heat sink system has enhanced the heat transfer coefficient by 76.88% compared to the system with PTA and by 30.92% as compared to the system with the PF only.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"197 3","pages":""},"PeriodicalIF":2.3,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138508425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-01DOI: 10.1615/jenhheattransf.2023049163
E. Martínez-Sandoval, Dulce Graciano, Fernando Zenaido SIERRA Espinosa, J García Castrejón
The film cooling is investigated numerically for gas turbine blade cooling. Film cooling performance is vital for blade safe operation. By calculating the film cooling effectiveness, the wall roughness inside the cooling hole effect is evaluated. Wall roughness by a turbulence promoter of aspect ratio K = L/h from 6 to 14, varying the pitch L and keeping constant the height h. Blowing ratio range from M = 0.5 to 2 and fixed mainstream Reynolds number, Re = 2.0 x 105 are tested. The cooling hole and flat plate surface with angle of 35o is used to compare the results and validate the CFD approach assessing the turbulence models k-ε RNG and RSM. A swirl flow develops inside the cooling hole due to installing the turbulence promoter. The coolant discharge turbulence parameters modify the normal case. The momentum and heat transfer rates have an impact on the film cooling performance. The results indicate film cooling effectiveness and surface protection enhancement of 9.84%, and 19.4%, respectively, for the best aspect ratio and blowing ratio. The coolant roughness may be used to improve the design of coolant hole and to reduce the number of orifices needed for safe gas turbine blades.
对用于燃气轮机叶片冷却的薄膜冷却进行了数值研究。薄膜冷却性能对叶片的安全运行至关重要。通过计算薄膜冷却效果，评估了冷却孔内壁粗糙度的影响。测试了长宽比 K = L/h 从 6 到 14 的湍流促进器的壁面粗糙度，改变了间距 L 并保持高度 h 不变。使用冷却孔和夹角为 35o 的平板表面对结果进行比较，并对评估湍流模型 k-ε RNG 和 RSM 的 CFD 方法进行验证。由于安装了湍流促进器，冷却孔内出现了漩涡流。冷却剂排放湍流参数改变了正常情况。动量和传热速率对薄膜冷却性能有影响。结果表明，在最佳长径比和吹气比下，薄膜冷却效果和表面保护效果分别提高了 9.84% 和 19.4%。冷却液粗糙度可用于改进冷却液孔的设计，减少安全燃气轮机叶片所需的孔口数量。
{"title":"Enhanced film cooling effectiveness by wall-roughness in cooling hole of turbine blade","authors":"E. Martínez-Sandoval, Dulce Graciano, Fernando Zenaido SIERRA Espinosa, J García Castrejón","doi":"10.1615/jenhheattransf.2023049163","DOIUrl":"https://doi.org/10.1615/jenhheattransf.2023049163","url":null,"abstract":"The film cooling is investigated numerically for gas turbine blade cooling. Film cooling performance is vital for blade safe operation. By calculating the film cooling effectiveness, the wall roughness inside the cooling hole effect is evaluated. Wall roughness by a turbulence promoter of aspect ratio K = L/h from 6 to 14, varying the pitch L and keeping constant the height h. Blowing ratio range from M = 0.5 to 2 and fixed mainstream Reynolds number, Re = 2.0 x 105 are tested. The cooling hole and flat plate surface with angle of 35o is used to compare the results and validate the CFD approach assessing the turbulence models k-ε RNG and RSM. A swirl flow develops inside the cooling hole due to installing the turbulence promoter. The coolant discharge turbulence parameters modify the normal case. The momentum and heat transfer rates have an impact on the film cooling performance. The results indicate film cooling effectiveness and surface protection enhancement of 9.84%, and 19.4%, respectively, for the best aspect ratio and blowing ratio. The coolant roughness may be used to improve the design of coolant hole and to reduce the number of orifices needed for safe gas turbine blades.","PeriodicalId":50208,"journal":{"name":"Journal of Enhanced Heat Transfer","volume":"38 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138745879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-01DOI: 10.1615/jenhheattransf.2023049890
Max Noelker, Mark Owoola, Laith Ismael, Shahab Keshavarz Mohammadian, Hongbin Ma
This paper presents a comprehensive experimental study on the influence of Microencapsulated Phase Change Materials (MPCMs) on the heat transfer performance in an oscillating heat pipe (OHP) to improve its heat transfer efficiency. The concept is based on the sensible heat enhancement of MPCMs within the OHP: as the thermally excited oscillations propel MPCMs from the condenser to the evaporator, they undergo a phase change from solid to liquid, effectively absorbing and storing more thermal energy. Subsequently, when these MPCMs reach the condenser section, they change back to a solid state, releasing the stored thermal energy. In the investigation, MPCMs of various diameters (ranging from 10 μm to 27 μm) were prepared and added to water, the working fluid. The study explored the effects of encapsulation ratio, encapsulation efficiency, geometric dimensions, density, and latent heat of MPCMs on the overall thermal performance of the OHP. The experimental findings demonstrated that the incorporation of MPCMs into the working fluid enhanced the OHP's heat transport capability. The optimal performance was observed at an MPCM weight concentration of 3% in the base fluid (water), which resulted in an impressive 15.5% increase in thermal conductance for the OHP. These results highlight the promising potential of MPCMs as effective enhancers for OHPs, paving the way for more efficient and advanced heat transfer systems in various engineering applications.
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