Characteristics Analysis And Optimization Of Solar Air Collector With Composite Phase Change Materials

In order to optimize the energy consumption structure,alleviate the ecological environment pollution,and improve the heating status of rural residents in northern and Western China,this research takes the solar air collector using clean energy as the object.Through theoretical analysis,experimental research and evaluation index analysis,the thermal characteristics and optimization of the air collector combined with phase change material(PCM)are analyzed,and the high-quality solar air collector model that meets the actual use requirements is explored,which provides reference for the transformation practice of solar air collector It also provides guidance for the popularization and application of solar air collector.Firstly,in order to solve the time mismatch between the air collector and the heating demand due to the intermittency of solar energy,a new type of solar air collector with composite phase change material(Type 2)was designed by optimizing the ordinary solar air collector model(Type 1),and the comparative experiments were conducted.Secondly,in order to further explore the composite of PCM and air collector and analyze the influence of PCM filling position on the thermal performance of air collector,four kinds of solar air collector models with different PCM filling positions are established(Type ⅰ: air collector with 50% PCM in the upper part;Type ⅱ: air collector with 50% PCM in the middle part;Type ⅲ: air collector with 50% PCM in the lower part;Type ⅳ: air collector with 50% PCM on both sides),and the experimental platform was built for comparative experiments.Finally,in order to solve the problem that the low thermal conductivity of PCM material affects the heat collection efficiency of air collector,on the basis of PCM-air collector(Type Ⅰ),the PCM-air collector model(Type Ⅱ)of composite copper foam was established based on the characteristics of high porosity and high thermal conductivity of copper foam,and a comparative test was carried out.Through the evaluation index of heat collection performance,the data of the three comparative experiments were evaluated and analyzed,and the following conclusions were drawn:(1)Compared with Type 1 collector,Type 2 collector has the ability of heat transfer,which can store part of the heat energy in the daytime and release it at night to achieve the purpose of continuous heating day and night.(2)The average daily heat collection efficiency of the solar air collector filled with PCM on the upper part was 38.11%,which was the lowest among the four different PCM filled positions.However,the outlet temperature and useful energy at night were the highest,and the heat release time lasted until 3 o ’clock in the morning of the next day.Therefore,among the four different PCM filling positions,the upper filling of PCM is most conducive to heat storage in day and night,heat release in night and day,and continuous heat supply in day and night is balanced.(3)For the collector filled with PCM in the lower part,the PCM in the collector does not reach the phase transition point,and the PCM is still in solid state,so the PCM is not stored in the solar day.Therefore,Type III has the highest heat collection efficiency in the daytime and the worst heat supply effect at night.(4)The thermal conductivity of the copper foam and phase change material composite test block is about 0.084 W/(m·k),which is 2.2～2.3 times that of the phase change material test block,indicating that the copper foam and phase change material composite has better thermal conductivity.(5)The average daily heat collection efficiency of type II collector is 34%,which is16.77% lower than that of type I collector,indicating that type II collector transfers more heat stored in daytime to release at night.Therefore,type II collector has stronger heat transfer ability,and type II is a high-quality solar air collector model.