Study On Characteristics Of The Direct Contact Refrigeration System For Photovoltaic-Driven Phase-Change Material Energy Storage

With the improvement of people's living standards,energy consumption has increased year by year.The use of solar cooling systems can effectively alleviate the energy consumption of air conditioners in summer and achieve the goal of carbon neutrality.By storing energy,the problem of solar intermittency and fluctuation in solar cooling systems is solved.Due to the problems of high investment and environmental protection in the early stage of battery recovery,the development of ice storage instead of battery energy storage mode can effectively solve the problems of solar refrigeration energy storage and cost.At the same time,in order to solve the problems of low heat transfer efficiency and undercooling degree of evaporator in the later ice storage mode of ice storage system,a direct contact heat exchange refrigeration energy storage system was proposed.Firstly,in this paper,a direct contact heat exchange refrigeration system was built,and the problem of nozzle ice blockage in the process of refrigeration and heat exchange was solved by using different refrigerants and phase change materials.Secondly,the experimental research and performance analysis of the direct contact heat transfer refrigeration and energy storage system were carried out under different concentrations of phase change materials.Finally,the direct contact heat transfer refrigeration and energy storage system with photovoltaic drive phase change materials was used to obtain the characteristics of solar photovoltaic refrigeration system with high energy storage,which provided certain theoretical framework and technical support for the actual solar refrigeration.The main research work of this paper is as follows:(1).In this paper,a 0.15 k W direct contact heat exchange refrigeration energy storage system was constructed to solve the ice blockage problem in the traditional system.It was found that the direct contact between refrigerant and water at the nozzle during the experiment was the main reason for the deterioration of system stability,low efficiency and unstable operation.(2).In view of the above problems,four refrigerants R22,R134a,R410A and HR223 were studied by using the characteristics of heat transfer difference between refrigerant and water.The experimental results showed that the system using R134a refrigerant experiment,the lowest efficiency,COP(Coefficient of performance)only0.93;HR223 refrigerant has the highest efficiency,but the COP is only1.68.Because the difference between refrigerant inlet temperature and water temperature decreases,the volumetric heat transfer coefficient suddenly changes greatly.The refrigerant could not completely solve the ice blockage.Therefore,by looking for phase change energy storage materials instead of water to solve the problem of nozzle ice blockage in the system.(3).By studying the properties of phase change energy storage materials,tetrabutylammonium bromide hydrate was selected as the phase change material in this experiment.The heat exchange of the direct contact heat exchange refrigeration energy storage system is analyzed,and the temperature during the phase change is increased,so that the water temperature can always be kept above 0°C when the phase change material is stored in the phase change,so as to solve the ice blockage of the system nozzle.(4).Through the experimental study of 30wt%,35wt%,40wt%and 45wt%phase change materials,the heat transfer uniformity of the system was calculated by the volume heat transfer coefficient,and the volume heat transfer coefficient of the system under different concentrations of phase change materials was in the range of 4-10 k W/(m~3 K).When the concentration of phase change material is 35%,the COP of the system reaches 6.23,and 2.4 kg of energy storage material could be phase changed within 10 min.The COP of the performance parameters of the direct contact refrigeration and energy storage system was higher than that of the existing traditional ice storage system.The study provides a reference for further improving the performance of solar driven refrigeration system(5).Match the photovoltaic energy system with the direct contact heat exchange refrigeration and energy storage system to explore the energy transfer method between the two systems.In this paper,by constructing a photovoltaic drive direct contact refrigeration system,the electrical characteristics and cold storage performance of the system are experimentally studied.When the instantaneous irradiance is 802W/m~2-907W/m~2,the output power of photovoltaic power generation meets the stable operation of the compressor.At this time,the real-time operating frequency of the compressor is 50 Hz,and the average photoelectric conversion efficiency?of the photovoltaic system is 14.86%;The volumetric heat transfer coefficients of the materials are similar,and the system is stable in operation.The volumetric heat transfer coefficients(U_v)of different concentrations of phase change materials are in the range of 4-10k W/(m~3·K);when the system is running,direct contact with the refrigeration system has a positive impact on COP_ref.The COP_ref of the 35%phase change material refrigeration system is the highest,which is 5.82,and the photovoltaic system efficiency(COP_pv)is 0.846;the 45%phase change material refrigeration system has the lowest COP_ref,which is 3.19,and the photovoltaic efficiency(COP_pv)is 0.501.The system efficiency is higher than the traditional photovoltaic direct drive ice storage system.