Research On The Heat Transfer Characteristics Of Solid-Liquid Phase Change Thermal Storage Devices On The Energy Supply Side Of Photovoltaic Buildings

In recent years,the excessive consumption of fossil fuels has created opportunities for the development of renewable energy.China has abundant solar energy resources,but photovoltaic power generation is susceptible to weather,thus making the supply and demand of photovoltaic power generation mismatched in time,and electricity cannot be utilized through heating and other means.At the same time,the cost of electricity storage is very high,resulting in serious abandonment of light phenomenon.In contrast,thermal storage technology can convert the rich electric energy into thermal energy stored by electric heating device to realize thermal electrolytic coupling.Solid-Liquid phase change thermal storage technology has the advantages of high thermal storage density and small output temperature variation range,and has received wide attention,so it is urgent and necessary to optimize and test the performance of thermal storage devices.In this paper,we propose an air source heat pump-phase change thermal storage combined heating system based on photovoltaic power supply,which is powered by photovoltaic for air source heat pump and can solve the problems of renewable energy consumption and building energy consumption at the same time.By adding phase change heat storage equipment on the heat supply side,it can play the role of peak-shaving and valley-filling,compensate for the defects of volatility and intermittency of PV,and improve the system reliability.In this paper,we use a combination of numerical simulation and experiment to analyze the heat storage process of phase change heat storage devices in heating systems,mainly carrying out the following work:(1)In order to improve the thermal conductivity of the solid-liquid phase change material,the thermal storage process of four groups of models with different fin spacing is numerically simulated and the law of thermal storage characteristics with the change of fin spacing is obtained.By analyzing the simulation results,it is found that the complete melting time is reduced in order to shorten the fin spacing,however,because the fins will occupy the volume of the phase change material,the heat storage capacity will also be reduced in order.(2)According to the experimental results of(1),a set of models is selected to numerically simulate the effects of different inlet water temperature and flow rate on its heat storage characteristics,and the numerical calculation results show that the complete melting time is shortened with the increase of the inlet water temperature.As the final temperature of the phase change material is elevated,the heat storage in the form of liquid sensible heat increases,and the total heat increases accordingly;the flow rate size is elevated,which promotes the melting rate of the phase change material,but has little effect on the heat storage.(3)Considering the numerical calculation results and the model fabrication cost,a visualized experimental test system was built from two of the four groups of models,and the heat storage and release processes of the two groups of fin spacing models were investigated separately.It was found that the storage/release process of the model with smaller fin spacing was faster and more obvious in the heat release process.Although the heat storage/release of this model was significantly reduced,its heat transfer efficiency reached 83.47%.Considering the advantages of heat storage time and heat transfer efficiency,this model was selected as the research object for subsequent experiments;(4)For changing the inlet water temperature and flow rate of the heat storage experiment conclusions are consistent with the numerical simulation,and the results of the heat release experiment show that: in the heat release experiments of different inlet water temperature experimental groups,the available heat in the heat storage unit is similar from about 3h,so the heat storage temperature can be selected according to the demand;upgrading the inlet water flow rate promotes heat exchange,and there is a threshold flow rate.In conclusion,the inlet water flow rate has limited effect on heat exchange,and the flow rate can be reduced appropriately to avoid pump work consumption.The exothermic efficiencies of the models are all around 83%,with good thermal performance,which proves the feasibility of the heat storage equipment for heating.In this paper,based on the above experimental results,the working characteristics of the heat storage unit are quantitatively analyzed to provide theoretical and experimental basis for the project.By optimizing the design of fin spacing and working conditions to improve the heat transfer efficiency,the development of phase change heat storage equipment in new heating systems can be promoted and the problem of renewable energy consumption can be solved.