相变储能型太阳能真空集热管内相变传热研究

发布时间：2018-05-18 11:03

  本文选题：太阳能 + 真空管　； 参考：《东南大学》2015年硕士论文

【摘要】：太阳能是取之不尽,用之不竭的清洁能源,在当今能源供给紧张,环境问题日益突出的形势下太阳能的利用备受重视。太阳能与建筑一体化是现在太阳能集热器发展的主流方向之一。本文提出一种新型的相变储能型太阳能真空集热管,该真空集热管组成的热水系统与传统太阳能热水系统相比不需要储热水箱,利用相变蓄热原理将太阳辐射能储存在相变材料内并在需要时释放出来。结合数值模拟计算与试验研究,对集热管内的相变传热过程进行了分析与探讨,并对翅片的结构参数进行优化。在太阳辐射基本原理的基础上,以南京地区为例,计算各时间段内太阳辐射强度,为下文真空管内的传热研究提供基础数据。选择管长为1800mm,内径105mm的玻璃管作为新型相变储能型集热管的真空管,选择石蜡为蓄热材料,径向分布有金属翅片的U型铜管作为流体换热通道。对太阳能真空集热管进行传热分析,计算单位时间内集热管吸收的太阳能辐射以及对周围环境的热损失,得出集热管获得的有用能。对比相变储能传热过程的求解方法,确定焓——孔隙率法作为相变过程的计算模型并给出控制方程。运用CFD软件对带金属翅片的相变储能型真空集热管建立三维模型,采用用户自定义函数UDF对真空管8：00-17：00获得的有效辐射热流编程,并导入模拟软件作为边界条件。模拟结果表明,上午10：00左右,集热管顶部石蜡开始熔化,石蜡整体温度较为平均,10：00-14：20为石蜡相变蓄热时间段,此过程石蜡体平均温度上升缓慢,但内部石蜡温差不断变大,13：00时顶部石蜡与底部石蜡的温差达到了90K。石蜡完全熔化后,温度上升加快,自然对流加速了石蜡的换热过程,进一步缩小内部温差。优化金属翅片的结构参数,对翅片厚度lmm,2mm,4mm,8mm,翅片间距为10mm,20mm, 40mm,80mm的蓄热单元进行模拟,分析不同翅片结构对石蜡熔化过程及熔化时间的影响。结果表明,石蜡的熔化时间随着翅片厚度的增加与间距的减小而减小,翅片间距对相变传热的影响要大于翅片的厚度,当翅片间距达到80mm时翅片厚度对传热过程的影响甚微。当翅片间距小于10mm时,翅片间距对熔化时间的影响也逐渐减小。研制并搭建新型相变储能型真空集热管的试验平台,测试所设计新型相变真空集热管的集热传热性能。分析对比试验数据与模拟结果,验证数值模拟的准确性。对集热管夜间实际运行工况进行研究,当石蜡处于凝固释热状态,入口水温17℃,流速为0.071m/s,0.144m/s,0.248m/s时,出水温度分别为41.5℃-55.96℃,32.89℃-42.4℃,29.5℃-33.7℃。
[Abstract]:Solar energy is an inexhaustible clean energy, the utilization of solar energy is paid more and more attention under the situation that energy supply is tight and environmental problems become more and more serious. The integration of solar energy and architecture is one of the main trend of solar collector development. In this paper, a new type of phase change solar energy storage vacuum collector is proposed. Compared with the traditional solar water heating system, the hot water system composed of the vacuum collector does not need a hot water tank. Solar radiation energy is stored in phase change materials and released when needed. Based on the numerical simulation and experimental study, the phase change heat transfer process in the collector tube is analyzed and discussed, and the structural parameters of the fin are optimized. Based on the basic principle of solar radiation, the solar radiation intensity in Nanjing area is calculated in different time periods, which provides the basic data for the study of heat transfer in vacuum tubes below. The glass tube with a length of 1800mm and an inner diameter of 105mm is selected as the vacuum tube of a new type of phase change energy storage collector, and a U-shaped copper tube with metal fins distributed in the radial direction is chosen as the fluid heat transfer channel, and the paraffin is used as the heat storage material. The heat transfer analysis of solar vacuum collector tube is carried out, the solar radiation absorbed by the collector tube and the heat loss to the surrounding environment are calculated in unit time, and the useful energy obtained by the collector tube is obtained. The enthalpy-porosity method is used as the calculation model of the phase change process and the governing equation is given by comparing the solution method of the phase change energy storage heat transfer process. The three-dimensional model of the phase change energy storage vacuum collector with metal fin was established by using CFD software. The effective radiation heat flux obtained from the vacuum tube 8: 00-17: 00 was programmed by the user defined function UDF, and the simulation software was introduced as the boundary condition. The simulation results show that at about 10:00 in the morning, the paraffin at the top of the collector pipe begins to melt, and the overall temperature of paraffin wax is 10: 00-14: 20, which is the average temperature of paraffin phase change, and the average temperature of paraffin increases slowly. However, the temperature difference between the top paraffin and the bottom paraffin reached 90 K. when the temperature difference between the internal paraffin wax and the bottom paraffin increased to 13: 00. After the paraffin is completely melted, the temperature rises faster, the natural convection accelerates the heat transfer process of the paraffin, and further reduces the internal temperature difference. The structural parameters of the metal fin were optimized, and the heat storage units with a thickness of lmm2 mm ~ 4 mm ~ 8 mm, a fin spacing of 10 mm ~ 20 mm, and a fin distance of 40 mm ~ 80 mm were simulated. The effects of different fin structures on the melting process and melting time of the paraffin were analyzed. The results show that the melting time of paraffin decreases with the increase of fin thickness and the decrease of fin spacing. The effect of fin spacing on phase change heat transfer is greater than that of fin thickness. When the fin spacing reaches 80mm, the fin thickness has little effect on the heat transfer process. When the fin spacing is smaller than 10mm, the influence of fin spacing on melting time decreases gradually. The experimental platform of a new type of phase change energy storage vacuum collector tube was developed and built to test the heat transfer performance of the designed new type of phase change vacuum collector tube. The accuracy of numerical simulation is verified by analyzing and comparing experimental data and simulation results. The actual operation condition of the collector pipe at night was studied. When the temperature of inlet water was 17 鈩，

本文编号：1905587