Liquid lithium is widely regarded as an optimal cooling medium for space nuclear reactors due to its exceptional heat transfer properties and low density. However, the helium bubbles generated by liquid lithium under space irradiation pose significant hazards to the safe and stable operation of nuclear reactions. In this study, the localized accumulation of helium bubbles in liquid lithium is investigated using a two-phase flow turbulence model. The effects of helium bubble distribution and inlet velocities on various parameters in the pipeline are focused on. A non-isothermal model for bubble flow is developed to examine the influence of gas-liquid mixture concentrations on overall heat transfer performance under low concentration conditions. Agglomerated bubbles with radii between 5 μm and 150 μm are classified into three categories based on local concentrations: circular (≤20.37%), irregular elongated (up to 30.44%), and banded (up to 36.31%). Interconnected banded bubbles can be up to 8 times larger than irregularly elongated ones, impacting physical properties and wall temperature disturbance in the pipeline. Elevated inlet velocity initiates the occurrence of bubble impact and fragmentation. However, high flow rates near the wall do not diminish wall temperature disturbance. Mixed flows with bubbles scales <15 μm show no significant impact on overall heat transfer up to 1% concentration. This study reveals the effects of bubble number and distribution, providing insights for manipulating bubble structure and guiding localized and comprehensive thermal analyses.
{"title":"Numerical study on the local aggregation of helium bubbles in liquid lithium and its thermal analysis","authors":"Yongfu Liu, Yi He, Peng Tan","doi":"10.1115/1.4065467","DOIUrl":"https://doi.org/10.1115/1.4065467","url":null,"abstract":"\u0000 Liquid lithium is widely regarded as an optimal cooling medium for space nuclear reactors due to its exceptional heat transfer properties and low density. However, the helium bubbles generated by liquid lithium under space irradiation pose significant hazards to the safe and stable operation of nuclear reactions. In this study, the localized accumulation of helium bubbles in liquid lithium is investigated using a two-phase flow turbulence model. The effects of helium bubble distribution and inlet velocities on various parameters in the pipeline are focused on. A non-isothermal model for bubble flow is developed to examine the influence of gas-liquid mixture concentrations on overall heat transfer performance under low concentration conditions. Agglomerated bubbles with radii between 5 μm and 150 μm are classified into three categories based on local concentrations: circular (≤20.37%), irregular elongated (up to 30.44%), and banded (up to 36.31%). Interconnected banded bubbles can be up to 8 times larger than irregularly elongated ones, impacting physical properties and wall temperature disturbance in the pipeline. Elevated inlet velocity initiates the occurrence of bubble impact and fragmentation. However, high flow rates near the wall do not diminish wall temperature disturbance. Mixed flows with bubbles scales <15 μm show no significant impact on overall heat transfer up to 1% concentration. This study reveals the effects of bubble number and distribution, providing insights for manipulating bubble structure and guiding localized and comprehensive thermal analyses.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141015801","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}
To address the issue of excessive temperature rises within the field of electronic device cooling, this study adopts a multi-parameter optimization method. The primary objective is to explore and realize the design optimization of the shell structure of the high voltage control box, aiming to effectively mitigate the temperature rise in internal components and enhance their thermal management efficacy without altering the fan performance, environmental conditions, or spatial layout. Initially, the study employs computational fluid dynamics methods to investigate the heat dissipation characteristics of the high voltage control box, subsequently verifying the simulation parameters' accuracy through temperature rise tests. Building upon this foundation, the article conducts a thorough analysis of how the position and shape of the box's openings impact the device's temperature rise. The findings suggest that configuring circular openings on the front and rear sides can optimize the heat dissipation effect. Moreover, the SHERPA algorithm was employed to refine the size and distribution of the openings on the outer shell of the high voltage control box through multi-parameter optimization, yielding locally optimal structural parameters. Post-optimization, the temperature measurement points within the high voltage control box exhibited a maximum reduction in temperature rise of 27.16%. The pivotal contribution of this methodology is the application of a data-driven decision-making process for the enhancement of conventional heat dissipation designs. This research offers invaluable practical insights and novel perspectives on the optimization of thermal management designs for box-type electronic devices.
{"title":"Design and optimization of heat dissipation for a high-voltage control box in energy storage systems","authors":"Jiajing Zhang, Hongqing Li, Yun Chen, Bingyun Jiang","doi":"10.1115/1.4065472","DOIUrl":"https://doi.org/10.1115/1.4065472","url":null,"abstract":"\u0000 To address the issue of excessive temperature rises within the field of electronic device cooling, this study adopts a multi-parameter optimization method. The primary objective is to explore and realize the design optimization of the shell structure of the high voltage control box, aiming to effectively mitigate the temperature rise in internal components and enhance their thermal management efficacy without altering the fan performance, environmental conditions, or spatial layout. Initially, the study employs computational fluid dynamics methods to investigate the heat dissipation characteristics of the high voltage control box, subsequently verifying the simulation parameters' accuracy through temperature rise tests. Building upon this foundation, the article conducts a thorough analysis of how the position and shape of the box's openings impact the device's temperature rise. The findings suggest that configuring circular openings on the front and rear sides can optimize the heat dissipation effect. Moreover, the SHERPA algorithm was employed to refine the size and distribution of the openings on the outer shell of the high voltage control box through multi-parameter optimization, yielding locally optimal structural parameters. Post-optimization, the temperature measurement points within the high voltage control box exhibited a maximum reduction in temperature rise of 27.16%. The pivotal contribution of this methodology is the application of a data-driven decision-making process for the enhancement of conventional heat dissipation designs. This research offers invaluable practical insights and novel perspectives on the optimization of thermal management designs for box-type electronic devices.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141129834","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}
In the present work, we have studied the performance of vertical plate finned heat sinks that protrude from a vertical base. The difference between the heat sinks base temperature and the ambient, i.e., ΔT, has been varied in the range of 10° C to 60° C, and the flow undergoes a natural convection regime. To enhance the thermal performance, we have explored different configurations of the heat sink by providing rectangular slots, varying the neck thickness, changing the neck location from the fin base, and providing interruptions along the fin height. The pertinent quantities, i.e., heat dissipation rate, Nusselt number, effectiveness, mass of heat sink, and heat dissipation per unit mass, have been obtained by performing 3D computational simulations. The results obtained are compared to assess the thermal performance of Heat sinks. We found that among various designs of heat sinks proposed, the heat sink with two slots, with the location of neck closer to the fin base (xm = 9 mm), and with interrupted fins dissipates maximum heat (12.86% more compared to the commonly used rectangular plate finned heat sink). In addition to the heat transfer improvement, 19.82% mass reduction has also been achieved. Based on the simulation data, we have proposed a correlation for the mean Nusselt number as a function of relevant non-dimensional parameters.
在本研究中，我们对从垂直基座伸出的垂直板式翅片散热器的性能进行了研究。散热器底座温度与环境温度之差（即 ΔT）在 10° C 至 60° C 范围内变化，气流处于自然对流状态。为了提高散热性能，我们探索了散热器的不同配置，包括提供矩形槽、改变颈部厚度、改变颈部与鳍片基座的位置以及沿鳍片高度提供间断。通过进行三维计算模拟，获得了相关数量，即散热率、努塞尔特数、散热效果、散热器质量和单位质量散热量。通过对所得结果进行比较，评估了散热器的散热性能。我们发现，在所提出的各种散热器设计中，带有两个槽、颈部位置更靠近鳍片基座（xm = 9 毫米）、鳍片间断的散热器散热量最大（与常用的矩形板式鳍片散热器相比，散热量增加了 12.86%）。除了传热性能的提高，质量也减少了 19.82%。根据模拟数据，我们提出了平均努塞尔特数与相关非尺寸参数的函数关系。
{"title":"A novel plate fin heat sink design with rectangular slots and interruptions: A computational approach","authors":"Rahul Ray, Santosh Senapati, Aurovinda Mohanty","doi":"10.1115/1.4065359","DOIUrl":"https://doi.org/10.1115/1.4065359","url":null,"abstract":"\u0000 In the present work, we have studied the performance of vertical plate finned heat sinks that protrude from a vertical base. The difference between the heat sinks base temperature and the ambient, i.e., ΔT, has been varied in the range of 10° C to 60° C, and the flow undergoes a natural convection regime. To enhance the thermal performance, we have explored different configurations of the heat sink by providing rectangular slots, varying the neck thickness, changing the neck location from the fin base, and providing interruptions along the fin height. The pertinent quantities, i.e., heat dissipation rate, Nusselt number, effectiveness, mass of heat sink, and heat dissipation per unit mass, have been obtained by performing 3D computational simulations. The results obtained are compared to assess the thermal performance of Heat sinks. We found that among various designs of heat sinks proposed, the heat sink with two slots, with the location of neck closer to the fin base (xm = 9 mm), and with interrupted fins dissipates maximum heat (12.86% more compared to the commonly used rectangular plate finned heat sink). In addition to the heat transfer improvement, 19.82% mass reduction has also been achieved. Based on the simulation data, we have proposed a correlation for the mean Nusselt number as a function of relevant non-dimensional parameters.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140693504","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}
S. Kalita, Pulak Sen, D. Sen, Sudev Das, Bidyut Baran Saha
Owing to their exceptionally high thermal conductivity, there is a growing demand for graphene nanoparticles in phase transition heat transfer applications. This research delves into the exploration of various critical phenomena within the realm of surface science, specifically focusing on interactions at solid-liquid and liquid-liquid interfaces. In this work, graphene nanoparticles at varying concentrations are subject to electrochemical deposition on a microporous copper substrate to form Graphene Coated Over Microporous Copper (GCOMC). The study encompasses a comprehensive analysis of surface characteristics, such as porosity, roughness, and wettability. Furthermore, the study involves the calculation of two key heat transfer metrics, the Critical Heat Flux (CHF) and the Boiling Heat Transfer Coefficient (BHTC), through the execution of pool boiling experiments. The findings of this research underscore the remarkable superiority of GCOMC surfaces over their uncoated copper counterparts in terms of boiling performance. Particularly, GCOMC surface showcases an impressive 87.5% enhancement in CHF and 233% increase in BHTC compared to the bare copper surface. Furthermore, this investigation delves into a detailed quantitative analysis of bubble behavior, encompassing parameters such as bubble departure diameter, bubble departure frequency, and nucleation site density, employing high-speed camera techniques to comprehensively understand the underlying processes.
{"title":"Phase transition heat transfer enhancement of agraphene-coated microporous copper surface using two-step electrodeposition method","authors":"S. Kalita, Pulak Sen, D. Sen, Sudev Das, Bidyut Baran Saha","doi":"10.1115/1.4065358","DOIUrl":"https://doi.org/10.1115/1.4065358","url":null,"abstract":"\u0000 Owing to their exceptionally high thermal conductivity, there is a growing demand for graphene nanoparticles in phase transition heat transfer applications. This research delves into the exploration of various critical phenomena within the realm of surface science, specifically focusing on interactions at solid-liquid and liquid-liquid interfaces. In this work, graphene nanoparticles at varying concentrations are subject to electrochemical deposition on a microporous copper substrate to form Graphene Coated Over Microporous Copper (GCOMC). The study encompasses a comprehensive analysis of surface characteristics, such as porosity, roughness, and wettability. Furthermore, the study involves the calculation of two key heat transfer metrics, the Critical Heat Flux (CHF) and the Boiling Heat Transfer Coefficient (BHTC), through the execution of pool boiling experiments. The findings of this research underscore the remarkable superiority of GCOMC surfaces over their uncoated copper counterparts in terms of boiling performance. Particularly, GCOMC surface showcases an impressive 87.5% enhancement in CHF and 233% increase in BHTC compared to the bare copper surface. Furthermore, this investigation delves into a detailed quantitative analysis of bubble behavior, encompassing parameters such as bubble departure diameter, bubble departure frequency, and nucleation site density, employing high-speed camera techniques to comprehensively understand the underlying processes.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140690298","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}
Lei Lang, Zhijie Liu, Yishu Liu, Dr. Jiang Qin, Xiaobin Zhang, Hongyan Huang
As a typical fuel-oil heat exchanger, the offset strip fin heat exchanger (OSFHX) can ensure the efficient and stable operation of the aero engine lubrication system. The paper establishes 20 kinds of numerical models of OSFHX that are verified by experiments. The heat transfer characteristics of oil inside the OSFHX are systematically studied. Based on dimensional analysis, the prediction model which can describe the whole performance of the OSFHX is obtained. The results show that with the decrease of s, l, h, t, and α, the heat transfer performance of the OSFHX is enhanced and the resistance is increased. With the decrease of s and h, and the increase of t and α, the comprehensive performance of the OSFHX is enhanced. When l = 4 mm, the comprehensive performance of the OSFHX is the best. For the heat transfer performance and comprehensive performance of the OSFHX, the α has the most significant effect, followed by h, and s, l, and t are the weakest. The average error of j factor and f factor prediction models is 4.09% and 5.31% respectively which can realize the theoretical calculation of the performance of the OSFHX for aviation.
偏置带翅式热交换器（OSFHX）作为一种典型的燃油-油热交换器，可确保航空发动机润滑系统的高效稳定运行。本文建立了 20 种 OSFHX 数值模型，并通过实验进行了验证。系统研究了 OSFHX 内部油的传热特性。在尺寸分析的基础上，得到了能够描述 OSFHX 整体性能的预测模型。结果表明，随着 s、l、h、t 和 α 的减小，OSFHX 的传热性能增强，阻力增大。随着 s 和 h 的减小，t 和 α 的增大，OSFHX 的综合性能增强。当 l = 4 mm 时，OSFHX 的综合性能最好。对于 OSFHX 的传热性能和综合性能，α 的影响最大，其次是 h，s、l 和 t 的影响最小。j 因子和 f 因子预测模型的平均误差分别为 4.09% 和 5.31%，可以实现航空 OSFHX 性能的理论计算。
{"title":"Performance Analysis of a Compact Offset Strip Fin Heat Exchanger for Lubrication System in Aero Engine","authors":"Lei Lang, Zhijie Liu, Yishu Liu, Dr. Jiang Qin, Xiaobin Zhang, Hongyan Huang","doi":"10.1115/1.4065357","DOIUrl":"https://doi.org/10.1115/1.4065357","url":null,"abstract":"\u0000 As a typical fuel-oil heat exchanger, the offset strip fin heat exchanger (OSFHX) can ensure the efficient and stable operation of the aero engine lubrication system. The paper establishes 20 kinds of numerical models of OSFHX that are verified by experiments. The heat transfer characteristics of oil inside the OSFHX are systematically studied. Based on dimensional analysis, the prediction model which can describe the whole performance of the OSFHX is obtained. The results show that with the decrease of s, l, h, t, and α, the heat transfer performance of the OSFHX is enhanced and the resistance is increased. With the decrease of s and h, and the increase of t and α, the comprehensive performance of the OSFHX is enhanced. When l = 4 mm, the comprehensive performance of the OSFHX is the best. For the heat transfer performance and comprehensive performance of the OSFHX, the α has the most significant effect, followed by h, and s, l, and t are the weakest. The average error of j factor and f factor prediction models is 4.09% and 5.31% respectively which can realize the theoretical calculation of the performance of the OSFHX for aviation.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140691192","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}
Thermal processes constitute a significant portion of energy consumption in the industrial sector. In this context, Pinch Analysis has emerged as a powerful method for achieving substantial energy savings. By systematically analyzing process streams and their heat transfer characteristics, Pinch Analysis enables the identification of heat re-covery opportunities, leading to the design of an optimized heat exchangers network (HEN) that minimizes energy requirements. In this study, a formulated stream split-ting method is proposed to design feasible Minimum Energy Requirement (MER) heat exchangers network. This method aims to achieve two main goals. Firstly, it gives a practical formulated method to help the designer when splitting streams and focuses on splitting the streams in such a way that creates sub-streams with the exact enthalpy required to satisfy heat exchanges with a specific number of streams, in order to minimize the need for process-utility heat exchangers whenever possible. Additionally, the method aims to eliminate exergy destruction caused by temperature differences in the mixer used to recombine the split streams, by ensuring an isothermal mixture of streams, preventing unnecessary energy losses. The design of the heat exchanger net-work is conducted using the HINT software, allowing for a comprehensive and detailed analysis of each step. The results obtained shows that the heat exchangers network attained not only achieves the minimum energy consumption but also mitigates exergy destruction and avoid unnecessary process-utility heat exchangers, resulting in enhanced overall system performance
热工过程在工业领域的能源消耗中占很大比重。在这种情况下，"夹点分析 "已成为实现大量节能的有力方法。通过系统分析工艺流程及其传热特性，掐头分析法能够识别热量回收机会，从而设计出优化的热交换器网络（HEN），最大限度地降低能源需求。在这项研究中，提出了一种制定流分割方法来设计可行的最低能源需求（MER）热交换器网络。该方法旨在实现两个主要目标。首先，它提供了一种实用的分流方法，帮助设计人员进行分流，并重点关注分流方式，以创建具有满足特定数量热交换所需的确切焓值的子流，从而尽可能减少对工艺-实用热交换器的需求。此外，该方法旨在通过确保流体的等温混合，防止不必要的能量损失，从而消除用于重新混合分流的混合器中的温差造成的放能破坏。热交换器网络结构的设计使用 HINT 软件进行，可以对每个步骤进行全面详细的分析。结果表明，所设计的热交换器网络不仅实现了最低能耗，还减少了热能破坏，避免了不必要的工艺-公用热交换器，从而提高了系统的整体性能。
{"title":"A formulated method for streams splitting in heat exchanger network design using pinch analysis","authors":"Anass Lebnaiti, Najwa Jbira, Sanaa Hayani","doi":"10.1115/1.4065284","DOIUrl":"https://doi.org/10.1115/1.4065284","url":null,"abstract":"\u0000 Thermal processes constitute a significant portion of energy consumption in the industrial sector. In this context, Pinch Analysis has emerged as a powerful method for achieving substantial energy savings. By systematically analyzing process streams and their heat transfer characteristics, Pinch Analysis enables the identification of heat re-covery opportunities, leading to the design of an optimized heat exchangers network (HEN) that minimizes energy requirements. In this study, a formulated stream split-ting method is proposed to design feasible Minimum Energy Requirement (MER) heat exchangers network. This method aims to achieve two main goals. Firstly, it gives a practical formulated method to help the designer when splitting streams and focuses on splitting the streams in such a way that creates sub-streams with the exact enthalpy required to satisfy heat exchanges with a specific number of streams, in order to minimize the need for process-utility heat exchangers whenever possible. Additionally, the method aims to eliminate exergy destruction caused by temperature differences in the mixer used to recombine the split streams, by ensuring an isothermal mixture of streams, preventing unnecessary energy losses. The design of the heat exchanger net-work is conducted using the HINT software, allowing for a comprehensive and detailed analysis of each step. The results obtained shows that the heat exchangers network attained not only achieves the minimum energy consumption but also mitigates exergy destruction and avoid unnecessary process-utility heat exchangers, resulting in enhanced overall system performance","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140731784","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}
Yajiao Liu, Yu Zhao, Tao Li, Ye Xiong, Li Liu, Zhiyong Li, Yuan Wang, Zizi Chen
A novel three-dimensional numerical simulation model for the helix ground heat exchanger was proposed in this paper, which takes into account unsaturated soil properties. This model is more suitable for real working conditions. To validate its accuracy, a miniature model heat transfer experimental platform was constructed. Additionally, the study conducted simulation research using three types of soil with significantly different thermal and moisture characteristics. Moreover the comprehensive thermal conductivity and water diffusion coefficient of these three soil types were determined by relevant literature and experimental tests. The aim was to comprehensively explore the impact of different soil types on the heat and mass transfer of the helix ground heat exchanger. The results indicate that the numerical model developed in this paper accurately captures the heat and mass transfer characteristics of the helix ground heat exchanger to a certain extent. Increasing the comprehensive thermal conductivity and water diffusion coefficient of the soil can significantly enhance the heat exchange capacity of the exchanger. For instance, under sandy loam condition, the heat exchange capacity is approximately 20.73% higher compared to clay loam conditions. The study also identifies two distinct areas around the helix ground heat exchanger: the severe change region and the soft change region. In the severe change region, there is a notable decrease in soil water content near the exchanger, which inevitably weakens the thermal conductivity of the soil. It is advised to minimize this effect through measures like active water spraying.
{"title":"A novel numerical model considering unsaturated soil properties and computational study on heat and moisture transfer characteristics of helix ground heat exchanger","authors":"Yajiao Liu, Yu Zhao, Tao Li, Ye Xiong, Li Liu, Zhiyong Li, Yuan Wang, Zizi Chen","doi":"10.1115/1.4065283","DOIUrl":"https://doi.org/10.1115/1.4065283","url":null,"abstract":"\u0000 A novel three-dimensional numerical simulation model for the helix ground heat exchanger was proposed in this paper, which takes into account unsaturated soil properties. This model is more suitable for real working conditions. To validate its accuracy, a miniature model heat transfer experimental platform was constructed. Additionally, the study conducted simulation research using three types of soil with significantly different thermal and moisture characteristics. Moreover the comprehensive thermal conductivity and water diffusion coefficient of these three soil types were determined by relevant literature and experimental tests. The aim was to comprehensively explore the impact of different soil types on the heat and mass transfer of the helix ground heat exchanger. The results indicate that the numerical model developed in this paper accurately captures the heat and mass transfer characteristics of the helix ground heat exchanger to a certain extent. Increasing the comprehensive thermal conductivity and water diffusion coefficient of the soil can significantly enhance the heat exchange capacity of the exchanger. For instance, under sandy loam condition, the heat exchange capacity is approximately 20.73% higher compared to clay loam conditions. The study also identifies two distinct areas around the helix ground heat exchanger: the severe change region and the soft change region. In the severe change region, there is a notable decrease in soil water content near the exchanger, which inevitably weakens the thermal conductivity of the soil. It is advised to minimize this effect through measures like active water spraying.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140729685","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}
Cooling of heavy-duty electrical machines such as generators and motors is crucial for smooth operations without thermal runaway. A commonly employed technique for cooling of rotors in these machines is to place channels at different radial locations for the continuous passage of coolant. These channels are therefore rotating about a parallel axis, and the rotation-induced forces alter the flow and thermal behaviour of the coolant compared to stationary channels. The present study reports a detailed numerical investigation on a long circular channel rotating about a parallel axis. The objective is to analyze the flow, heat transfer, and rotation-induced forces (Coriolis and centrifugal forces) in the entry region as well as in the region where flow is stable (the term ‘stable’ is used rather than ‘developed’ due to the presence of secondary flows in this region). The rotating channel was subjected to constant wall heat flux and constant wall temperature conditions at different Rotation numbers of 0, 0.15, 0.4, and 0.6. The Coriolis force is strong enough in the entry region to influence the flow. In the “stable flow” region, the centrifugal force becomes more dominant and forms counter-rotating secondary vortex pair, which causes circumferential variation in the Nusselt number. The flow and heat transfer characteristics for constant wall heat flux and wall temperature boundaries are the same for conditions with similar values of rotational Grashof number. A correlation is presented for the circumferential variation of the Nusselt number in the stable flow region.
{"title":"Flow and heat transfer characteristics in the entry and stabilized flow regions of a circular channel rotating about a parallel axis","authors":"S. A. Narayan, Satyanand Abraham","doi":"10.1115/1.4065282","DOIUrl":"https://doi.org/10.1115/1.4065282","url":null,"abstract":"\u0000 Cooling of heavy-duty electrical machines such as generators and motors is crucial for smooth operations without thermal runaway. A commonly employed technique for cooling of rotors in these machines is to place channels at different radial locations for the continuous passage of coolant. These channels are therefore rotating about a parallel axis, and the rotation-induced forces alter the flow and thermal behaviour of the coolant compared to stationary channels. The present study reports a detailed numerical investigation on a long circular channel rotating about a parallel axis. The objective is to analyze the flow, heat transfer, and rotation-induced forces (Coriolis and centrifugal forces) in the entry region as well as in the region where flow is stable (the term ‘stable’ is used rather than ‘developed’ due to the presence of secondary flows in this region). The rotating channel was subjected to constant wall heat flux and constant wall temperature conditions at different Rotation numbers of 0, 0.15, 0.4, and 0.6. The Coriolis force is strong enough in the entry region to influence the flow. In the “stable flow” region, the centrifugal force becomes more dominant and forms counter-rotating secondary vortex pair, which causes circumferential variation in the Nusselt number. The flow and heat transfer characteristics for constant wall heat flux and wall temperature boundaries are the same for conditions with similar values of rotational Grashof number. A correlation is presented for the circumferential variation of the Nusselt number in the stable flow region.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140731651","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}
It is well known that the pressure drop of heat exchanger tube increases when heat transfer is enhanced, entropy generation analysis is an effective way to comprehensively analyze the heat transfer and pressure drop. In this paper, the refrigerants R513A and R134a are used in a horizontal single tube to carry out an experimental study of in-tube condensation heat transfer in six test tubes, the test tubes are divided into smooth and microfin tubes with outer diameters of 9.52 mm and 12.7 mm, where microfin tubes are available in two tube types with 60 and 65 fin, respectively. Helix angles of 18 degrees. The experimental conditions: mass flow rate of 50-300kg/m2·s, condensation temperatures of 35°C, 38°C and 40°C. The results show that it is feasible to replace R134a by R513A. It is analyzed that the comprehensive heat transfer performance of 9.52mm microfin tube is better than that of 12.7mm microfin tube, and the comprehensive heat transfer performance of 65-fin microfin tube is significantly lower than that of 60-fin microfin tube, i.e., microfin tubes with small pipe diameters and reasonable number of fin are conducive to the enhancement of condensation heat transfer performance.
{"title":"Entropy generation of R513A condensation flow inside the horizontal microfin tubes","authors":"Suhan Zhang, Leren Tao, Lihao Huang, Cheng Jin","doi":"10.1115/1.4065281","DOIUrl":"https://doi.org/10.1115/1.4065281","url":null,"abstract":"\u0000 It is well known that the pressure drop of heat exchanger tube increases when heat transfer is enhanced, entropy generation analysis is an effective way to comprehensively analyze the heat transfer and pressure drop. In this paper, the refrigerants R513A and R134a are used in a horizontal single tube to carry out an experimental study of in-tube condensation heat transfer in six test tubes, the test tubes are divided into smooth and microfin tubes with outer diameters of 9.52 mm and 12.7 mm, where microfin tubes are available in two tube types with 60 and 65 fin, respectively. Helix angles of 18 degrees. The experimental conditions: mass flow rate of 50-300kg/m2·s, condensation temperatures of 35°C, 38°C and 40°C. The results show that it is feasible to replace R134a by R513A. It is analyzed that the comprehensive heat transfer performance of 9.52mm microfin tube is better than that of 12.7mm microfin tube, and the comprehensive heat transfer performance of 65-fin microfin tube is significantly lower than that of 60-fin microfin tube, i.e., microfin tubes with small pipe diameters and reasonable number of fin are conducive to the enhancement of condensation heat transfer performance.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140737706","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}
Jeremy Spitzenberger, James Hoelle, Ahmed Abuheiba, Ramy Abdelhady, Laith Ismael, D. Agonafer, Pengtao Wang, Stephen Kowalski, Kashif Nawaz, Hongbin Ma
Wicking structures have been widely used within passive heat transfer devices with high heat fluxes, such as heat pipes, to enhance their thermal performance. While wicking structures promote capillary pumping of the working fluid enhances and thin film evaporation, they can result in capillary evaporation and further enhance the evaporation heat transfer. In this study, a 0.5 mm thick layer of 105 μm sintered copper particles was added to the inner wall of a copper tube, aiming to form an “annular flow” and enhance the heat transfer characteristics by taking advantage of thin film and capillary evaporation. Acetone was chosen as the working fluid, and the performance of an evaporation tube was tested for power inputs of 10, 30, 50, and 70 W. For each power input, trials were run at inclination angles varying from −90° to 90° to investigate the capillary effects. The temperature measurements showed the temperature distribution along the evaporation tube is always downward sloping, meaning the temperature at the fluid inlet is larger than the outlet. Results show that an “annular flow” formed by a thin layer of sintered particles can promote thin-film and capillary evaporation and, therefore, boost the evaporation heat transfer coefficient.
{"title":"An Experimental Investigation of Sintered Particle Effect on Heat Transfer Performance in an “Annular Flow” Evaporation Tube","authors":"Jeremy Spitzenberger, James Hoelle, Ahmed Abuheiba, Ramy Abdelhady, Laith Ismael, D. Agonafer, Pengtao Wang, Stephen Kowalski, Kashif Nawaz, Hongbin Ma","doi":"10.1115/1.4065259","DOIUrl":"https://doi.org/10.1115/1.4065259","url":null,"abstract":"\u0000 Wicking structures have been widely used within passive heat transfer devices with high heat fluxes, such as heat pipes, to enhance their thermal performance. While wicking structures promote capillary pumping of the working fluid enhances and thin film evaporation, they can result in capillary evaporation and further enhance the evaporation heat transfer. In this study, a 0.5 mm thick layer of 105 μm sintered copper particles was added to the inner wall of a copper tube, aiming to form an “annular flow” and enhance the heat transfer characteristics by taking advantage of thin film and capillary evaporation. Acetone was chosen as the working fluid, and the performance of an evaporation tube was tested for power inputs of 10, 30, 50, and 70 W. For each power input, trials were run at inclination angles varying from −90° to 90° to investigate the capillary effects. The temperature measurements showed the temperature distribution along the evaporation tube is always downward sloping, meaning the temperature at the fluid inlet is larger than the outlet. Results show that an “annular flow” formed by a thin layer of sintered particles can promote thin-film and capillary evaporation and, therefore, boost the evaporation heat transfer coefficient.","PeriodicalId":17404,"journal":{"name":"Journal of Thermal Science and Engineering Applications","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140750185","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}
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