【作者】 郭震；

【导师】 梁若冰；

【作者基本信息】 大连理工大学 ， 供热、供燃气、通风及空调工程， 2020， 硕士

【摘要】 国家能源局《太阳能发展“十三五”规划》指出,在未来相当长时期内,我国对于可再生能源的需求将大幅增长。同时,建筑能耗量在全国能耗总量中的占比也在近年来迅速增长。作为可再生能源的重要组成部分,太阳能资源对于降低建筑领域的能源消耗量和社会能源消耗总量具有重要意义,太阳能利用技术也是当下的研究热点和产业焦点。其中,能够实现热电联产的太阳能光电光热一体化(Photovoltaic/Thermal,PV/T)技术具有广泛的研究意义与应用前景。针对以水作为循环工质的自然循环集热器所存在的启动时间长、重力热管式集热器需依靠循环泵等问题,本文采用实验研究与数值模拟相结合的研究方法,以一种新型的环路热管式太阳能PV/T系统为研究对象,对其热电性能及影响因素展开研究,主要包括以下研究内容。首先,结合太阳能PV/T技术的研究现状,以及热管在太阳能制热领域的应用,本文对现有研究存在的问题进行了分析,探究了影响系统性能的主要因素,明确了环路热管式PV/T系统的实验原理,并明确实验分析与数值模拟的具体研究思路与研究内容。根据系统实验原理,本文首先确定了具体实验方案、所需测量的物理量、主要部件的规格、测量系统的仪器仪表以及实验工况,为实验分析提供平台基础。其次,完成了不同稳定辐照度下环路热管式PV/T系统热电性能,实验结果表明,PV/T组件进出口温差及平均温升速率随辐照度增大而提高;高辐照度(850W/m~2~1000W/m~2)下的光热功率波动性较小,换热效果更加稳定,但最大光热效率在不同工况下无明显变化;蓄热水箱水温最高可达40.64℃,高辐照度下的光电部分有效能量利用率也会有所降低;此外,系统在不同工况下的启动特性相似,850W/m~2工况性能为实验范围内的最优表现;此类系统形式下的PV/T组件进出口压力范围无明显差别,组件出口过热度集中于3℃~7.5℃。第三,本文对适用于研究内容的相关源项及多相流模型进行了理论分析,并利用标准模型验证法对模型准确性进行了验证,从而为数值模拟提供基础。模拟过程中首先对环路热管流道及吹胀式蒸发板建立三维ICEM模型,以相关实验数据作为边界条件,对模拟参数进行合理设置,并根据理论分析编写能够描述工质相变过程的UDF,同时对制冷剂热工参数进行变物性处理。第四,通过对不同边界条件下的模拟结果分析可知,相比于不同热流边界,入口质量流量对于管内截面气相体积分数的沿程分布影响更大;工质在流动前中期的相变速率明显快于中后期,截面含气率曲线的斜率在后期明显减小;在换热状态达到稳定后,850W/m~2~1000W/m~2加热边界的入口速度增速要高于其余工况,而出口流速与入口段相比未显著提高,流速在管内并非沿程逐渐增大;此外,流量变化对于流速分布的影响要远高于热流变化所造成的影响,且加热条件对入口段速度影响要大于出口段;增大截面宽高比将主要影响高循环流量情况下的工质相变速率,同时质量流量对蒸发过程的影响将进一步增大。最后,研究发现增大入口流量、热流边界条件或截面宽高比均能够提高流道的换热系数。在15/7.5的截面宽高比下,模拟工况流量范围内的传热系数最大相差21.36%,且加热边界的影响要小于流量的影响;改变截面比例后的换热系数最高达1338.25W/m~2·K,平均值最大相差31.67%;此外,高加热条件下的换热系数增幅更加明显,并且流量对于换热的影响将进一步增强。综上所示,本文通过实验研究与数值模拟相结合的研究方法,对环路热管式太阳能PV/T系统进行了研究。在验证了此类系统形式可行性的同时,针对其运行特性进行了分析,确定了不同边界条件下各影响因素对其性能的影响,对于环路热管与太阳能PV/T技术相结合的系统设计形式,具有一定的参考价值与借鉴意义。更多还原

【Abstract】 According to the Thirteenth Five-Year Plan for Solar Energy Development of the National Energy Administration,the demand for renewable energy of our country will grow rapidly in the future for a long period of time.At the same time,the proportion of building energy consumption in the country’s total energy consumption has also increased rapidly in recent years.As an important part of renewable energy,solar energy resources play an important role in reducing energy consumption in the construction field and total energy consumption in society.Solar energy utilization technology is also the current research hotspot and industry focus.Among all the solar energy utilization technologies,the photovoltaic/thermal integration(PV/T),which can achieve combined heat and power generation,has extensive research significance and application prospects.For the problem of long start-up period of natural circulation collectors with water as working medium,and gravity heat pipe collectors relying on circulation pumps,etc.,this paper studies a new type of loop heat pipe solar PV/T system through a combination of experimental research and numerical simulation,which mainly includes the following content.First of all,on the basis of related research status of PV/T technology and the application of heat pipe in the field of solar energy,this paper analyzes the existing research problems,explores the main factors that affect the performance of the system,clarifies the schematic diagram of the loop heat pipe PV/T system,and determines the specific research contents and ideas of experimental analysis and numerical simulation.According to the schematic diagram,this paper first determines the specific experiment plan,the physical quantity required to be measured,the specifications of the main equipments,the instrumentation of the measurement system and the experimental working conditions,to provide a platform basis for experimental analysis.Secondly,through experiments on system performance under different stable irradiances,it can be known that the temperature differences between inlet and outlet of PV/T unit and the average temperature rise rate increases with the increase of irradiance.The fluctuation of thermal power at 850W/m~2~1000W/m~2 can be significantly reduced,and the heat exchange effect is more stable,but the maximum thermal efficiencies has no obvious change under different working conditions.The water temperature is up to 40.64℃.The energy effective utilization efficiency of photovoltaic part under high irradiance will be reduced.In addition,there is no obvious change of start-up characteristics under different irradiances.The performance at 850W/m~2 irradiance condition is the best one in the experiments.Thirdly,this paper theoretically analyzes the source term model and multiphase flow model which are suitable for this research.And the standard model verification method is used to verify the accuracy of the model and provide a basis for numerical simulation.This paper firstly establishes a three-dimensional ICEM model for the loop heat pipe flow channel and the evaporation plate.Then it uses the relevant experimental data as the boundary conditions,sets the simulation parameters reasonably,and compiles the required UDF code according to the theoretical analysis.At the same time,the thermal properties of the refrigerant are treated with variable physical properties.Fourthly,through the analysis of the simulation results under different boundary conditions,this paper finds that compared with different heat flux boundary conditions,changing the inlet mass flow rate has a greater influence on the distribution of the cross-sectional vapor volume fraction.The phase change rate in the early stage is faster than that in the late period,and the slope of dryness reduces significantly.After the heat exchange state is stable,the inlet velocities at 850W/m~2~1000W/m~2 heating boundary increase faster than other conditions,while the outlet velocity does not increase evidently.In addition,the impact of mass flow rate changes on the velocity distribution is much higher than that of heat flux changes.Increasing the cross-sectional aspect ratio will mainly affect the phase change rate in the case of high circulation flow rate,and the influence of mass flow rate on the evaporation process is further increased.Finally,the study found that increasing the inlet flow rate,heat flux boundary conditions,or cross-sectional aspect ratio will all increase the heat transfer coefficient of the flow channel.At a cross-sectional aspect ratio of 15/7.5,the maximum heat transfer coefficient differs by21.36%,and the influence of the heating boundary is lower than that of the flow rate.The maximum heat transfer coefficient after changing the aspect ratio is 1338.25W/m~2·K,and the average difference is 31.67%.The increase of heat transfer coefficient under high heating conditions is more obvious,and the influence of flow rate on heat transfer is further enhanced.In summary,this paper studies the loop heat pipe solar PV/T system through a combination of experimental research and numerical simulation.While verifying the feasibility of this type of system,the performance and operating characteristics are analyzed,and the influence of various factors under different boundary conditions is determined.This paper has a certain reference value for the system design form of the combination of loop heat pipe and solar PV/T technology.更多还原