Pub Date : 2024-09-01DOI: 10.1615/heattransres.2024053033
Dongwei Zhang, Jian Guan, Zhuantao He, Chao Shen, Hongxin Li, Songzhen Tang, Lin Wang, Yonggang Lei
In this work, based on the compressible SIMPLE algorithm, a calculation model of the combined thermoacoustic engine was established. The results presented the changes in thermoacoustic engine evolution process before and after adding the refrigerator part. Subsequently, the flow field in the oscillation period of the thermoacoustic engine-driven refrigerators was analyzed, and it was found that during the flow velocity transformation, the velocity interface was formed near the middle position of the resonant tube. Additionally, the performance optimization of the thermoacoustic engine-driven refrigerator was studied. It can be found that the added refrigerator part will increase the start-up temperature difference by more than 25 K, as well as decreasing the vibration amplitude at stable stage. The temperature difference between the two ends of the refrigerator part increases with the addition of the temperature difference of the engine. This work provides a useful reference for the application of thermoacoustic engine to drive the same type of refrigerator.
在这项工作中，基于可压缩 SIMPLE 算法，建立了组合式热声发动机的计算模型。结果表明了热声发动机在加入冰箱部分前后的演变过程。随后，分析了热声发动机驱动冰箱振荡期的流场，发现在流速转换过程中，在谐振管中间位置附近形成了速度界面。此外，还对热声发动机驱动冰箱的性能优化进行了研究。研究发现，增加制冷机部分会使启动温差增加 25 K 以上，并降低稳定阶段的振幅。制冷部分两端的温差随着发动机温差的增加而增大。这项工作为应用热声发动机驱动同类型冰箱提供了有益的参考。
{"title":"Numerical analysis of thermoacoustic heat pump driving by prime mover","authors":"Dongwei Zhang, Jian Guan, Zhuantao He, Chao Shen, Hongxin Li, Songzhen Tang, Lin Wang, Yonggang Lei","doi":"10.1615/heattransres.2024053033","DOIUrl":"https://doi.org/10.1615/heattransres.2024053033","url":null,"abstract":"In this work, based on the compressible SIMPLE algorithm, a calculation model of the combined thermoacoustic engine was established. The results presented the changes in thermoacoustic engine evolution process before and after adding the refrigerator part. Subsequently, the flow field in the oscillation period of the thermoacoustic engine-driven refrigerators was analyzed, and it was found that during the flow velocity transformation, the velocity interface was formed near the middle position of the resonant tube. Additionally, the performance optimization of the thermoacoustic engine-driven refrigerator was studied. It can be found that the added refrigerator part will increase the start-up temperature difference by more than 25 K, as well as decreasing the vibration amplitude at stable stage. The temperature difference between the two ends of the refrigerator part increases with the addition of the temperature difference of the engine. This work provides a useful reference for the application of thermoacoustic engine to drive the same type of refrigerator.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193065","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 : 2024-09-01DOI: 10.1615/heattransres.2024054447
Ragıp Yıldırım, Kazım Kumaş, Ali Akyüz, Azim Doğuş Tuncer
A thorough evaluation of the new generation of refrigerants before their application in vapor compression cooling cycles enables prudent action to be taken. This study presents a comparative analysis between R463A and R410A in vapor compression refrigeration cycles. R463A exhibits notable advantages: it demonstrates higher mass flow rates owing to its elevated density at -25°C evaporator temperature, resulting in superior cooling capacities at 40°C and 45°C. However, this superiority comes at the cost of higher energy demand than R410A, which is evident in its increased energy consumption at these temperatures. Despite its enhanced cooling capacity, R463A displays slightly lower COP attributed to its higher compressor energy utilization. Moreover, both refrigerants exhibit increased exergy destruction with rising temperatures, consequently impacting exergy efficiency, which is slightly lower for R463A due to its elevated exergy destruction rates. Environmental impact analyses also highlight R463A's consistently higher environmental index than R410A across varied temperatures. This comprehensive evaluation contributes insights into R463A's performance as an alternative refrigerant to R410A in vapor compression systems.
{"title":"Evaluation of the performance of using R410A and R463A in a vapor compression refrigeration system: Energetic-exergetic analysis and Environmental Impact Index (EII) assessmen","authors":"Ragıp Yıldırım, Kazım Kumaş, Ali Akyüz, Azim Doğuş Tuncer","doi":"10.1615/heattransres.2024054447","DOIUrl":"https://doi.org/10.1615/heattransres.2024054447","url":null,"abstract":"A thorough evaluation of the new generation of refrigerants before their application in vapor compression cooling cycles enables prudent action to be taken. This study presents a comparative analysis between R463A and R410A in vapor compression refrigeration cycles. R463A exhibits notable advantages: it demonstrates higher mass flow rates owing to its elevated density at -25°C evaporator temperature, resulting in superior cooling capacities at 40°C and 45°C. However, this superiority comes at the cost of higher energy demand than R410A, which is evident in its increased energy consumption at these temperatures. Despite its enhanced cooling capacity, R463A displays slightly lower COP attributed to its higher compressor energy utilization. Moreover, both refrigerants exhibit increased exergy destruction with rising temperatures, consequently impacting exergy efficiency, which is slightly lower for R463A due to its elevated exergy destruction rates. Environmental impact analyses also highlight R463A's consistently higher environmental index than R410A across varied temperatures. This comprehensive evaluation contributes insights into R463A's performance as an alternative refrigerant to R410A in vapor compression systems.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193066","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 : 2024-08-01DOI: 10.1615/heattransres.2024053614
Yu-qing Ji, Jing Wang, Shi-chun Xiao, Wen-jie Shen, An Li
The suboptimal photoelectric conversion efficiency of light-emitting diodes (LEDs) leads to increased temperature. There is a growing interest in using micro-structure ionic wind pumps to regulate the chip temperature. But the ionic wind flow and thermal transfer characteristics of thin-plate electrode pumps used for cooling LED chips is unclear. This study proposes ionic wind pumps equipped with wedged and zigzag-emitters to effectively manage the heat generated by high-power LED chips. Experimental investigations were conducted to analyze the electrohydrodynamic characteristics of pumps with different emitter types. A two-dimensional model with a wedged-electrode and a three-dimensional model with a zigzag-electrode were developed for flow distribution analysis and energy efficiency comparison. The cooling capacity of pumps with different configurations was examined. The results show that the pump equipped with a zigzag-electrode exhibits improved stability in corona discharge and approximately 1.53 times higher energy efficiency compared to the pump with a wedged-electrode. Moreover, the pump with the zigzag-electrode covers a larger area, generating a higher intensity of ionic wind. The angle between the emitter and the ground electrode significantly affects the characteristics of the characteristics of the ionic wind flow. The optimal angle is 70° for pumps with wedged-emitters and 30° for those with zigzag emitters. Both pumps can produce a steady wall jet at their optimal angle, causing significant disruption in the surrounding area. The pump with zigzag-electrode exhibits superior cooling performance and is more effective with low power consumption.
发光二极管（LED）的光电转换效率不理想会导致温度升高。人们对使用微结构离子风泵调节芯片温度的兴趣与日俱增。但用于冷却 LED 芯片的薄板电极泵的离子风流和热传导特性尚不清楚。本研究提出了配备楔形和人字形发射器的离子风泵，以有效管理大功率 LED 芯片产生的热量。实验研究分析了具有不同发射器类型的泵的电动流体力学特性。开发了楔形电极的二维模型和人字形电极的三维模型，用于流量分布分析和能效比较。研究了不同配置水泵的冷却能力。结果表明，与采用楔形电极的泵相比，采用人字形电极的泵在电晕放电时表现出更高的稳定性，能效大约高出 1.53 倍。此外，装有人字形电极的泵覆盖面积更大，产生的离子风强度更高。发射器和接地电极之间的角度对离子风流的特性有很大影响。楔形发射器泵的最佳角度为 70°，人字形发射器泵的最佳角度为 30°。这两种泵都能在最佳角度产生稳定的壁面射流，对周围区域造成严重破坏。人字形电极泵的冷却性能更优越，功耗更低。
{"title":"Employing thin planar electrodes to expand the ionic wind flow coverage area and achieve enhanced heat dissipation","authors":"Yu-qing Ji, Jing Wang, Shi-chun Xiao, Wen-jie Shen, An Li","doi":"10.1615/heattransres.2024053614","DOIUrl":"https://doi.org/10.1615/heattransres.2024053614","url":null,"abstract":"The suboptimal photoelectric conversion efficiency of light-emitting diodes (LEDs) leads to increased temperature. There is a growing interest in using micro-structure ionic wind pumps to regulate the chip temperature. But the ionic wind flow and thermal transfer characteristics of thin-plate electrode pumps used for cooling LED chips is unclear. This study proposes ionic wind pumps equipped with wedged and zigzag-emitters to effectively manage the heat generated by high-power LED chips. Experimental investigations were conducted to analyze the electrohydrodynamic characteristics of pumps with different emitter types. A two-dimensional model with a wedged-electrode and a three-dimensional model with a zigzag-electrode were developed for flow distribution analysis and energy efficiency comparison. The cooling capacity of pumps with different configurations was examined. The results show that the pump equipped with a zigzag-electrode exhibits improved stability in corona discharge and approximately 1.53 times higher energy efficiency compared to the pump with a wedged-electrode. Moreover, the pump with the zigzag-electrode covers a larger area, generating a higher intensity of ionic wind. The angle between the emitter and the ground electrode significantly affects the characteristics of the characteristics of the ionic wind flow. The optimal angle is 70° for pumps with wedged-emitters and 30° for those with zigzag emitters. Both pumps can produce a steady wall jet at their optimal angle, causing significant disruption in the surrounding area. The pump with zigzag-electrode exhibits superior cooling performance and is more effective with low power consumption.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193104","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 : 2024-08-01DOI: 10.1615/heattransres.2024052874
Ozgen Acikgoz
For living spaces, radiant thermal mats are seen to be a good substitute for traditional heating systems. These devices, which are often powered by electricity, are installed on the floors, walls, and ceilings of rooms. The heat generated by the mat's absolute temperature causes direct and focused heating. The natural convection heat transfer properties of radiant heating and cooling systems have been well studied, while the properties of radiant mats placed on surfaces have received relatively less attention. Mats of square and rectangular dimensions (axb=0.5 m x 0.5 m, 1 m x 1 m, 1.2 m x 1.2 m, 1.4 m x 1.4 m, 1 m x 1.2 m, 1 m x 1.4 m, and 1 m x 1.6 m) are installed on the walls of an enclosure with floor dimensions (LxL= 4 m x 4 m) and a height of H= 3 m in order to address this gap in the literature. Average convective, radiative, and overall heat transfer characteristics—which are important for building energy simulation programs—are found and correlated for different mat dimensions using the surface-to-surface (S2S) radiation model and the k-ε RNG turbulence model in the numerical program, with error ranges of ±5%, ±5%, and ±15%, respectively.
在居住空间，辐射热垫被认为是传统供暖系统的良好替代品。这些设备通常由电力驱动，安装在房间的地板、墙壁和天花板上。热垫的绝对温度产生的热量可直接集中加热。人们对辐射供暖和制冷系统的自然对流传热特性进行了深入研究，而对表面辐射垫的特性关注相对较少。为了解决文献中的这一空白，我们在一个地面尺寸（LxL= 4 m x 4 m）和高度 H= 3 m 的围墙墙壁上安装了正方形和长方形（axb=0.5 m x 0.5 m、1 m x 1 m、1.2 m x 1.2 m、1.4 m x 1.4 m、1 m x 1.2 m、1 m x 1.4 m 和 1 m x 1.6 m）的辐射垫。利用数值程序中的面到面（S2S）辐射模型和 k-ε RNG 湍流模型，找到了不同垫层尺寸下的平均对流、辐射和整体传热特性（这些特性对建筑能耗模拟程序非常重要），并将其相关联，误差范围分别为 ±5%、±5% 和 ±15%。
{"title":"An investigation over the influence of a radiant thermal mat’s dimensions on its local and average convective and radiative heat transfer characteristics","authors":"Ozgen Acikgoz","doi":"10.1615/heattransres.2024052874","DOIUrl":"https://doi.org/10.1615/heattransres.2024052874","url":null,"abstract":"For living spaces, radiant thermal mats are seen to be a good substitute for traditional heating systems. These devices, which are often powered by electricity, are installed on the floors, walls, and ceilings of rooms. The heat generated by the mat's absolute temperature causes direct and focused heating. The natural convection heat transfer properties of radiant heating and cooling systems have been well studied, while the properties of radiant mats placed on surfaces have received relatively less attention. Mats of square and rectangular dimensions (axb=0.5 m x 0.5 m, 1 m x 1 m, 1.2 m x 1.2 m, 1.4 m x 1.4 m, 1 m x 1.2 m, 1 m x 1.4 m, and 1 m x 1.6 m) are installed on the walls of an enclosure with floor dimensions (LxL= 4 m x 4 m) and a height of H= 3 m in order to address this gap in the literature. Average convective, radiative, and overall heat transfer characteristics—which are important for building energy simulation programs—are found and correlated for different mat dimensions using the surface-to-surface (S2S) radiation model and the k-ε RNG turbulence model in the numerical program, with error ranges of ±5%, ±5%, and ±15%, respectively.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193099","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 : 2024-08-01DOI: 10.1615/heattransres.2024053465
Rasim BEHÇET, Melih ATEŞ, Yahya ÖZ
Equipment used in the aviation industry heats up over time depending on working conditions. It is possible to preserve the properties of equipment affected by heat by either cooling the system and returning it to initial conditions or by producing the system from materials that are not affected by heat much. One of the areas where nanocomposite materials will be used is avionic systems in the aviation and space industry. These systems are structures in which elements such as sensors, cabling and processors, which form the basis of the electronic structure of flight, are brought together in very small volumes. It is important that the material used in these structures is light and has high strength and has electromagnetic properties selected accordingly. In this study, the thermal analysis of Vapor Grown Carbon Fiber (VGCF) nanocomposite materials produced by adding them to the epoxy matrix in terms of the thermal performance of avionic boxes was carried out by comparing them with the thermal properties of the aluminum material. As a result of the findings obtained from thermal analysis studies carried out in four stages for this purpose; It was observed that by using VGCF composite instead of aluminum material, approximately 23% improvement in temperature output and 17% improvement in thermal load was achieved. Thus, it is anticipated that energy efficiency will be increased with the use of lightweight and high-strength nanocomposite materials, which is considered one of the most important goals of the aviation industry.
{"title":"COOLING EFFECT OF DIFFERENT TYPES OF MATERIALS IN AN AVIONICS SYSTEM","authors":"Rasim BEHÇET, Melih ATEŞ, Yahya ÖZ","doi":"10.1615/heattransres.2024053465","DOIUrl":"https://doi.org/10.1615/heattransres.2024053465","url":null,"abstract":"Equipment used in the aviation industry heats up over time depending on working conditions. It is possible to preserve the properties of equipment affected by heat by either cooling the system and returning it to initial conditions or by producing the system from materials that are not affected by heat much. One of the areas where nanocomposite materials will be used is avionic systems in the aviation and space industry. These systems are structures in which elements such as sensors, cabling and processors, which form the basis of the electronic structure of flight, are brought together in very small volumes. It is important that the material used in these structures is light and has high strength and has electromagnetic properties selected accordingly. In this study, the thermal analysis of Vapor Grown Carbon Fiber (VGCF) nanocomposite materials produced by adding them to the epoxy matrix in terms of the thermal performance of avionic boxes was carried out by comparing them with the thermal properties of the aluminum material. As a result of the findings obtained from thermal analysis studies carried out in four stages for this purpose; It was observed that by using VGCF composite instead of aluminum material, approximately 23% improvement in temperature output and 17% improvement in thermal load was achieved. Thus, it is anticipated that energy efficiency will be increased with the use of lightweight and high-strength nanocomposite materials, which is considered one of the most important goals of the aviation industry.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141934584","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 study investigates the stability and rheological properties of water-ethylene glycol (W/EG) based non-Newtonian hybrid nanofluids incorporating SiC, Al2O3 and MWCNT nanoparticles. A two-step method was employed to prepare the hybrid nanofluids, using X-ray diffraction (XRD) and scanning electron microscopy (SEM) for the characterization of the nanoparticles. Stability assessment showed that Al2O3-MWCNT hybrid nanofluids are more optically stable than SiC-MWCNT as W/EG based Al2O3-MWCNT hybrid nanofluids took longer to sediment. Al2O3-MWCNT hybrid nanofluids exhibited superior stability in visual tests over a period of 19–21 days while SiC-MWCNT nanofluid took 12-14 days to sediment. Rheological analysis showed that increasing particle concentration increased the viscosity by 3.56 and 3.98 times for SiC-MWCNT and Al2O3-MWCNT hybrid nanofluids, respectively, compared to the base fluid. In contrast, increasing the temperature from 25 °C to 55 °C decreased the shear stress by 72.8% and 64.8% for SiC-MWCNT and Al2O3-MWCNT hybrid nanofluids respectively. Furthermore, the viscosity versus shear rate trends indicated a pseudoplastic or shear-thinning nature for both hybrid nanofluids with particle volume fraction above or equal to 0.1%.
{"title":"Comparative experimental investigation on viscosity and stability of W/EG based non-Newtonian hybrid nanofluids for the heat transfer applications","authors":"Ayush Painuly, Niraj Mishra, Prabhakar Zainith, Gaurav Joshi","doi":"10.1615/heattransres.2024053694","DOIUrl":"https://doi.org/10.1615/heattransres.2024053694","url":null,"abstract":"This study investigates the stability and rheological properties of water-ethylene glycol (W/EG) based non-Newtonian hybrid nanofluids incorporating SiC, Al2O3 and MWCNT nanoparticles. A two-step method was employed to prepare the hybrid nanofluids, using X-ray diffraction (XRD) and scanning electron microscopy (SEM) for the characterization of the nanoparticles. Stability assessment showed that Al2O3-MWCNT hybrid nanofluids are more optically stable than SiC-MWCNT as W/EG based Al2O3-MWCNT hybrid nanofluids took longer to sediment. Al2O3-MWCNT hybrid nanofluids exhibited superior stability in visual tests over a period of 19–21 days while SiC-MWCNT nanofluid took 12-14 days to sediment. Rheological analysis showed that increasing particle concentration increased the viscosity by 3.56 and 3.98 times for SiC-MWCNT and Al2O3-MWCNT hybrid nanofluids, respectively, compared to the base fluid. In contrast, increasing the temperature from 25 °C to 55 °C decreased the shear stress by 72.8% and 64.8% for SiC-MWCNT and Al2O3-MWCNT hybrid nanofluids respectively. Furthermore, the viscosity versus shear rate trends indicated a pseudoplastic or shear-thinning nature for both hybrid nanofluids with particle volume fraction above or equal to 0.1%.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193100","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 : 2024-07-01DOI: 10.1615/heattransres.2024053249
Vitor Costa
It is proposed an approach of the network method for radiation in enclosures that expresses radiosities and irradiations as functions of the blackbody emissive powers and of the radiation fluxes entering the enclosure through its partially transparent walls. These results are used to express the radiation heat flow exchanged between two surfaces and the net radiation heat flux leaving each of the enclosure’s surfaces as depending on these true driving forces for radiation heat transfer. This reduces the problem to its essential, as these are the true driving forces for the radiation heat transfer. Net radiation heat fluxes leaving each of the enclosure’s surfaces form an equations’ system from which are evaluated the relevant radiation heat transfer parameters for each surface. Proposed approach is based on elementary matrices operations, the main attention being dedicated to the problem setting and leaving the (just essential) calculations to the calculator or to the computer. It is introduced for enclosures with all opaque walls and illustrated for one example, and then extended to enclosures with partially transparent walls. Proposed simplifying and unifying approach is relevant not only for radiation heat transfer analysis and calculations, but also for pedagogical purposes, retaining attention on the essential of the radiation heat transfer problem formulation, setting aside intermediate/auxiliary variables calculations that are usually aversive, fastidious, distractive and prone to errors.
{"title":"A step forward on the network method for radiation heat transfer analysis in enclosures","authors":"Vitor Costa","doi":"10.1615/heattransres.2024053249","DOIUrl":"https://doi.org/10.1615/heattransres.2024053249","url":null,"abstract":"It is proposed an approach of the network method for radiation in enclosures that expresses radiosities and irradiations as functions of the blackbody emissive powers and of the radiation fluxes entering the enclosure through its partially transparent walls. These results are used to express the radiation heat flow exchanged between two surfaces and the net radiation heat flux leaving each of the enclosure’s surfaces as depending on these true driving forces for radiation heat transfer. This reduces the problem to its essential, as these are the true driving forces for the radiation heat transfer. Net radiation heat fluxes leaving each of the enclosure’s surfaces form an equations’ system from which are evaluated the relevant radiation heat transfer parameters for each surface. Proposed approach is based on elementary matrices operations, the main attention being dedicated to the problem setting and leaving the (just essential) calculations to the calculator or to the computer. It is introduced for enclosures with all opaque walls and illustrated for one example, and then extended to enclosures with partially transparent walls. Proposed simplifying and unifying approach is relevant not only for radiation heat transfer analysis and calculations, but also for pedagogical purposes, retaining attention on the essential of the radiation heat transfer problem formulation, setting aside intermediate/auxiliary variables calculations that are usually aversive, fastidious, distractive and prone to errors.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141608463","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 : 2024-07-01DOI: 10.1615/heattransres.2024053911
Mahdi Tabatabaei Malazi, Faraz Afshari, Kenan Kaya
Phase Change Materials (PCMs) play a pivotal role in various sectors, particularly in automotive engineering, electric vehicles (EVs), and building construction. In the automotive sector, PCMs are crucial for thermal management systems, aiding in temperature regulation of components such as batteries and engines. In EVs, PCMs are instrumental in enhancing battery performance and lifespan by effectively managing thermal loads during charging and discharging cycles, thus ensuring optimal operating conditions. Moreover, in buildings, PCMs contribute significantly to energy efficiency by storing and releasing heat as required, reducing reliance on conventional heating and cooling systems. Their ability to store and release large amounts of energy at specific temperatures makes PCMs indispensable for sustainable solutions in automotive and building applications, contributing to improved performance, efficiency, and environmental sustainability.
{"title":"PHASE CHANGE MATERIALS (PCMS) FOR BUILDINGS AND AUTOMOTIVE APPLICATIONS: A REVIEW STUDY","authors":"Mahdi Tabatabaei Malazi, Faraz Afshari, Kenan Kaya","doi":"10.1615/heattransres.2024053911","DOIUrl":"https://doi.org/10.1615/heattransres.2024053911","url":null,"abstract":"Phase Change Materials (PCMs) play a pivotal role in various sectors, particularly in automotive engineering, electric vehicles (EVs), and building construction. In the automotive sector, PCMs are crucial for thermal management systems, aiding in temperature regulation of components such as batteries and engines. In EVs, PCMs are instrumental in enhancing battery performance and lifespan by effectively managing thermal loads during charging and discharging cycles, thus ensuring optimal operating conditions. Moreover, in buildings, PCMs contribute significantly to energy efficiency by storing and releasing heat as required, reducing reliance on conventional heating and cooling systems. Their ability to store and release large amounts of energy at specific temperatures makes PCMs indispensable for sustainable solutions in automotive and building applications, contributing to improved performance, efficiency, and environmental sustainability.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141743455","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 : 2024-07-01DOI: 10.1615/heattransres.2024054108
Ragıp Yıldırım, Abdullah Yıldız, Azim Doğuş Tuncer
In this study, two different hydrochlorofluorocarbon (HFC) / Hydrofluoroolefin (HFO) binary blends (R134a/R1234yf (75/25) and R134a/R1234yf (25/75)) are studied experimentally. Energetic, exergetic and LCCP (life cycle climate performance) evaluations of the heat pump for HFC/HFO binary blends were carried out. In the literature, no studies are available on the use of HFC/HFO in heat pumps or cooling systems at these blend ratios. This study differs from previous studies on HFC/HFO binary mixtures. Therefore, it will contribute to the literature on binary HFC/HFO blends with lower global warming potential (GWP). HFC/HFO binary blends for different temperature of evaporator (-10 °C, -5 °C, 0 °C) and fixed temperature of condenser (35 °C) were studied. The performance of R134a/R1234yf (75/25) refrigerant blend is superior to R134a/R1234yf (25/75) refrigerant blend based on the 1st and 2nd laws of thermodynamics. Although the GWP of R134a/R1234yf (75/25) is higher than that of R134a/R1234yf (25/75), R134a/R1234yf (75/25) has a relatively smaller total LCCP than R134a/R1234yf (25/75). Low GWP is not the only criterion for selecting a refrigerant. Energy and exergy are also important. Because an important part of the overall system emissions of the heat pump is seen to be caused by the consumption of energy.
{"title":"Experimental evaluation of HFC/HFO binary mixtures in a small-scale water-to-water heat pump system","authors":"Ragıp Yıldırım, Abdullah Yıldız, Azim Doğuş Tuncer","doi":"10.1615/heattransres.2024054108","DOIUrl":"https://doi.org/10.1615/heattransres.2024054108","url":null,"abstract":"In this study, two different hydrochlorofluorocarbon (HFC) / Hydrofluoroolefin (HFO) binary blends (R134a/R1234yf (75/25) and R134a/R1234yf (25/75)) are studied experimentally. Energetic, exergetic and LCCP (life cycle climate performance) evaluations of the heat pump for HFC/HFO binary blends were carried out. In the literature, no studies are available on the use of HFC/HFO in heat pumps or cooling systems at these blend ratios. This study differs from previous studies on HFC/HFO binary mixtures. Therefore, it will contribute to the literature on binary HFC/HFO blends with lower global warming potential (GWP). HFC/HFO binary blends for different temperature of evaporator (-10 °C, -5 °C, 0 °C) and fixed temperature of condenser (35 °C) were studied. The performance of R134a/R1234yf (75/25) refrigerant blend is superior to R134a/R1234yf (25/75) refrigerant blend based on the 1st and 2nd laws of thermodynamics. Although the GWP of R134a/R1234yf (75/25) is higher than that of R134a/R1234yf (25/75), R134a/R1234yf (75/25) has a relatively smaller total LCCP than R134a/R1234yf (25/75). Low GWP is not the only criterion for selecting a refrigerant. Energy and exergy are also important. Because an important part of the overall system emissions of the heat pump is seen to be caused by the consumption of energy.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141532233","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 : 2024-07-01DOI: 10.1615/heattransres.2024054158
Alexander Mazo, Evgeniy Kalinin, Valery Molochnikov, Dmitry Okhotnikov, Anton Paereliy, Olga Dushina
Direct numerical simulation of heat transfer behind a spanwise obstacle was carried out in a steady channel flow. Reynolds numbers corresponded to transition to turbulence in the separation region behind the obstacle. The obstacle was mounted either on the channel wall or with a gap from the wall. Thorough verification of numerical results (visual flow pattern and flow statistics) against experimental data was carried out. Distributions of local coefficients of heat transfer and skin friction behind the obstacle were found to correlate with vortical structure of the flow. For both positions of the obstacle relative to the channel wall, the study discovered principal regularities in the behavior of local and averaged across the channel values of heat transfer behind the obstacle with the varying Reynolds number of the oncoming flow. The effect of obstacle position on the total increase in heat transfer coefficient on the wall behind the obstacle was estimated in comparison with the smooth wall.
{"title":"Heat transfer enhancement behind an obstacle in a channel flow undergoing transition to turbulence","authors":"Alexander Mazo, Evgeniy Kalinin, Valery Molochnikov, Dmitry Okhotnikov, Anton Paereliy, Olga Dushina","doi":"10.1615/heattransres.2024054158","DOIUrl":"https://doi.org/10.1615/heattransres.2024054158","url":null,"abstract":"Direct numerical simulation of heat transfer behind a spanwise obstacle was carried out in a steady channel flow. Reynolds numbers corresponded to transition to turbulence in the separation region behind the obstacle. The obstacle was mounted either on the channel wall or with a gap from the wall. Thorough verification of numerical results (visual flow pattern and flow statistics) against experimental data was carried out. Distributions of local coefficients of heat transfer and skin friction behind the obstacle were found to correlate with vortical structure of the flow. For both positions of the obstacle relative to the channel wall, the study discovered principal regularities in the behavior of local and averaged across the channel values of heat transfer behind the obstacle with the varying Reynolds number of the oncoming flow. The effect of obstacle position on the total increase in heat transfer coefficient on the wall behind the obstacle was estimated in comparison with the smooth wall.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141568169","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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