【作者】 李伟；

【导师】 赵军；

【作者基本信息】 天津大学 ， 热能工程， 2010， 博士

【摘要】 管壳式相变蓄热器与封装球体内的相变蓄热问题是相变蓄热技术研究的热点。但近年来,对考虑对流的水平管外相变传热问题的研究少见于文献报道,相变蓄热系统性能和效率方面的研究也比较少,球体内相变传热过程的规律掌握地还不够透彻。本文针对以上几点,对管外和球体内的相变蓄热问题进行了数值模拟与实验研究。对方形槽内水平圆管外伴有对流的相变传热问题建立数学模型及其定解条件,并与实验结果进行对比,验证了模型的可靠性。给出温度场和固液相界面随时间的变化情况,分析了不同管壁温度对温度场和相变的影响。为得到具有普遍意义的结果,进行了管壁温度和相变材料初温对融化、凝固过程影响的无量纲分析。结果表明:圆管壁温对熔化过程的影响随其增大是逐渐减小的,对凝固过程则随其降低而逐渐减小。以石蜡为相变材料,空气和水作换热流体,对管壳式相变蓄热装置的蓄热特性进行了数值模拟分析;以水作换热流体为例,研究了运行参数、结构尺寸、材料物性等对相变蓄热系统运行和效率的影响。结果表明:空气和水作换热流体的管壳式相变蓄热装置的蓄热特性明显不同;提高相变材料的导热能力是改善相变蓄热系统整体性能的最有效措施。实验研究了球体内石蜡相变过程的特点,以及水浴温度和石蜡初温对熔化和凝固的影响,并在球体中加入不同量的铝粉,进行对比分析;数值模拟了各因素对球体内石蜡熔化率的影响。结果表明:水浴温度从55℃升高到60℃,熔化时间缩短50%;石蜡初温从15℃升高到30℃,熔化时间缩短23%;石蜡初温对凝固过程的影响很小;加入1%和2%的铝粉,石蜡的熔化时间分别缩短22%和34%,凝固时间缩短36%,添加铝粉是改善球体相变蓄热性能的有效措施。最后,本文设计了一种翅片管簇式相变蓄热器,针对不同换热流体流量对其蓄、放热特性的影响进行了实验研究,并应用到天津某示范工程中,发现其缓解了水箱温度波动较大的问题,具有重要的工程价值。更多还原

【Abstract】 The latent heat storage problems of shell-and-tube latent heat storage device and packaging phase change material inside a sphere are the research focus of the latent heat storage technology. But in recent years, the phase change heat transfer problem around a horizontal tube considering the convection is rarely reported, and the performance and efficiency study of latent heat storage system is less in other papers, and the law of phase change heat transfer process inside a sphere is not enough to thoroughly grasp. Therefore, the issues of latent heat storage around tube and inside sphere have been studied numerically and experimentally in this dissertation.The mathematical model for phase change heat transfer around a horizontal tube in a rectangular groove, which is validated by experimental data, and its boundary conditions have been developed. The changes of temperature field around the tube and solid-liquid interface with time, as well as the effect of wall temperature are presented. In order to obtain universal results, dimensionless analyses on the effects of wall temperature and initial temperature of phase change material on the melting and solidification processes are carried out. The results show the effect of wall temperature is gradually decreased with its increasing on the melting process, and is decreased with its decreasing on the solidification process.The thermal behaviors of the latent thermal energy storage unit with paraffin as the phase change material and air or water as the heat transfer fluid are studied. The effects of working conditions, geometric parameters, material properties on the operation and efficiency of the latent heat storage system with water as heat transfer fluid are studied. The results show obviously different behaviors of the shell-and-tube latent heat storage unit when air and water are as the heat transfer fluid. Increasing the thermal capacity of phase change material is the most effective method to improve the overall performance of the shell-and-tube latent heat storage system.An experimental study is performed. The phase change process of paraffin inside a sphere capsule and the effect of bath temperature and paraffin initial temperature on the melting and solidification processes are analyzed. The influence of aluminum is compared with the pure paraffin by adding different amounts of aluminum powder to the sphere capsule. The effects of various factors on the paraffin melting rate inside the sphere capsule are studied using numerical method. The results indicate that the melting time of the sphere capsule decrease 50% and 23%, respectively, when the bath temperature increases from 55℃to 60℃and the initial temperature of paraffin increases from 15℃to 30℃. A weak influence of the initial temperature of paraffin on the solidification process can be expected. By adding 1% and 2% quality amounts of aluminum powder, the melting time is shortened 22% and 34%, and the solidification time is shortened 36%. Adding aluminum is an effective measure to improve the performance of phase change material inside a sphere capsule.Finally, this dissertation designs a cluster-type fin-tube latent heat storage unit. The effect of different flow rates of heat transfer fluid on the behaviors of heat storage and releasing is studied experimentally. The cluster-type fin-tube latent heat storage unit is applied to a demonstration project in Tianjin, and the problem of volatile temperature in water tank is found to be relieved.更多还原