Numerical and experimental investigation of a thermosiphon solar water heater system thermal performance used in domestic applications

The thermosiphon is a passive heat exchange method, which circulates a fluid within a system without the need for any electrical or mechanical pumps. The thermosiphon is based on natural convection where the thermal expansion occurs when the temperature difference has a corresponding difference in density across the loop. Thermosiphons are used in different applications such as solar energy collection, automotive systems, and electronics. The current study aims to investigate thermosiphon thermal performance used in domestic applications. The thermal performance of a thermosiphon has been studied by many researchers; however, according to the knowledge of the authors, the influence of the amount of the working fluid on the thermal output has not yet been investigated. Therefore, the influence of the amount of working fluid within the riser pipe has been investigated on the thermal performance of the thermosiphon. In the current study, a computational fluid dynamics model is involved. This model has been validated by comparison with experimental findings. The maximum variation between numerical and experimental results is 14.2% and 11.2% for the working fluid at the inlet and outlet of the absorber pipe, respectively. Furthermore, the results show that the amount of working fluid inside the closed thermosiphon has a great influence on the thermal performance of the system. Additionally, it is found that Case-B, when the amount of working fluid is less than by 10% compared to the traditional model, is the best case among all cases under study. Furthermore, a correlation equation to predict water temperature at the exit of the absorber pipe has been established with an accuracy of 95.05%.     

新型太阳能无泵溴化锂制冷系统的实验研究

建立了太阳能热水型无泵溴化锂吸收式制冷系统(包括降膜吸收器、降温蒸发器、弦月形热虹吸提升管、冷凝器等)。为提高制冷系统的整体运行效果,设计了一套二次发生装置,并改良了吸收器和蒸发器的结构,使系统能在较低的初始溶液浓度范围(46%~54%)下运行,在80~93℃热源温度下,随热源温度的升高,溶液提升量和浓度增大,使吸收器保持较高的放气范围(6%)和吸收率,从而强化吸收器性能,并使冷剂水产量提高为未开二次发生装置时的1.68倍,明显改善蒸发效果。二次发生装置有效地使热源温度降低到最低启动温度68℃,有效地提高了太阳能利用率。     

热虹吸油冷却系统：数学模型与理论计算篇

近年来，热虹吸油冷却系统在国内逐步推广应用，但目前仍缺乏理论分析与计算模型，所以在实际应用中仍存在一些分歧与争论。本文尝试从建立数学模型开始，进行理论计算，从而得出能够指导实践的理论依据。     

小直径热虹吸管传热性能实验研究

进行了小直径热虹吸管性能试验，试验结果表明：热管运行时，管内流型及流型变化对热管壁面温度有影响．表面温度波动大；热源温度对热管内流型有影响，热源温度越高，冷凝段温差越小；热源温度低时．热管长度对表面温度影响大：加热段长度越长，热管表面温度越高；热管传输功率并不随热源温度升高而线型增加．     

热虹吸窄矩形流道内多元非理想物系流动沸腾传热

以乙醇－水、正丙醇－水、乙醇－正丙醇－水以及乙醇－苯－水作为工质，在热虹吸矩形流道内研究了多元物系流动沸腾传热。使用校正的渐进模型关联式，结合Thome核沸腾传质阻力效应校正，构造出多元物系流动沸腾传热计算方法。     

小型太阳能吸收式空调多管弦月形通道溶液提升泵的性能研究

设计了一种多管弦月形通道溶液提升泵,对其提升性能进行了实验研究和分析。在给定运行条件下,研究了运行温度和压力、加热水和冷却水流量以及稀溶液浸没高度等对溶液提升量和冷剂水产量的影响,给出了实验曲线。实验结果表明,多管弦月形通道溶液提升泵具有起动温度低、运行温度范围大、运行连续稳定等显著特点,能够满足一般小型吸收式空调系统溶液循环流量的要求。     

热虹吸管能量回收设备夏季工作特性的实验研究

在研究热虹吸管工作机理的基础上,开发设计出热虹吸管能量回收装置。通过实验分析了空调新风温度、工质充注率、倾角、管排数以及迎面风速等参数对热虹吸管换热器温度效率的影响,探讨了迎面风速与热虹吸管换热器回收热量的关系,得到了充注率、倾角、迎面风速、管排数等参数之间的最佳匹配方案,为工程实际应用提供了参考依据。     

Experimental study on the double-evaporator thermosiphon for cooling HTS (high temperature superconductor) system

A cryogenic thermosiphons is an efficient heat transfer device between a cryocooler and a thermal load that is to be cooled. This paper presents an idea of thermosiphon which contains two vertically-separated evaporators. This unique configuration of the thermosiphon is suitable for the purpose of cooling simultaneously two superconducting bearings of the HTS (high temperature superconducting) flywheel system at the same temperature. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure condition. The interior thermal condition of the double-evaporator thermosiphon was examined in detail during its cool-down process according to the internal thermal states. The double-evaporator thermosiphon has operated successfully at steady-state operation under sub-atmospheric pressure. At the heat flow of 10.6 W, the total temperature difference of the thermosiphon was only 1.59 K and the temperature difference between the evaporators was 0.64 K. The temperature difference of two evaporators is attributed to the conductive thermal resistance of the adiabatic section between the evaporators. The method to reduce this temperature difference has been investigated and presented in this paper. The proper area selection of condenser, evaporator 1, and evaporator 2 was studied by using thermal resistance model to optimize the performance of a thermosiphon. The superior heat transfer characteristic of the double-evaporator thermosiphon without involving any cryogenic pump can be a great potential advantage for cooling HTS bulk modules that are separated vertically.     

两相闭式热虹吸管传热极限的实验研究

本文对大型热虹吸管进行了各种不同工况的传热极限实验,取得了238组不同条件下的极限实验数据。根据液阻限制极限功率的机理,考虑到热虹吸管的特点,给出了适用范围较宽的热虹吸管两相流液阻判据式和计算极限功率关联式,误差不超过20％。同时还给出了分别适用于几种工质的简便计算式。     

盐酸汽提塔再沸器改造

针对盐酸汽提塔管壳式石墨立式热虹吸再沸器在运行中出现的问题,结合圆块孔换热器的特点,应用新型分体式圆块孔石墨再沸器替代原管壳式石墨再沸器。