| The heat storage device is an important part of the solar heating system,which can effectively alleviate the problem of the contradiction and mismatch between the solar heat collecting end and the heat using end.Therefore,the development of heat storage devices with efficient heat storage and rational utilization is the key to the rational operation of solar heating system.At present,scholars have done a lot of research on heat storage tanks,but more researches are on the determination of heat storage tank volume,heat loss calculation,thermal stratification effect and other related content.In fact,it is more practical to consider the efficient heat storage and directional water intake of the heat storage tank together,which can effectively avoid the low heat storage efficiency of the heat storage tank and the existence of a large number of "thermal dead zone" and other problems,so as to better meet the thermal needs of users and improve the overall efficiency of the solar thermal utilization system.In this paper,the structure and working principle of the solar heat storage tank with high efficiency heat storage and extraction are introduced,the flow process of dynamic heat storage and extraction in the heat storage tank is analyzed,and the mathematical model for the dynamic heat transfer of the solar heat storage tank is established.Through a combination of experimental research and numerical simulation,the thermal performance of the hot water storage tank is analyzed using evaluation indexes such as thermal storage efficiency,stratification efficiency,exergy efficiency,mixing reaction coefficient,and heat release efficiency.It can effectively improve the adaptability of the heat storage tank,and has the functions of efficient heat storage,directional heat extraction and rapid mixing,which can meet the diverse thermal needs of different users.The research process and main conclusions are as follows:(1)A set of thermodynamic characteristics test system of the heat storage tank was built,and the thermal performance of the heat storage tank with stratification device was studied experimentally,and the correctness of the numerical simulation model and method was verified,and the stratification and mixing double-function optimization experiment was carried out for the heat storage tank.The research shows that: the root-mean-square deviation(RMSD)between the experimental results and the simulation results is about 5%,and the deviations between the two are small.It is considered that the numerical model and the method are effective and feasible.When the heat storage tank is in stratified mode,hot water enters the heat storage tank through the stratified water inlet structure,and a better thermal stratification state is formed in the water tank.When switching to the mixing mode,hot water enters the heat storage tank through the mixing nozzle,and the mixing speed increases by more than 50%,which can quickly destroy the thermal stratification in the water tank,make the temperature of each layer in the water tank tend to be the same,make it completely mixed,and the overall thermal performance of the heat storage tank is better.(2)The effect of different influencing factors(temperature,flow,structure size)on the thermal performance of the heat storage tank is studied through numerical simulation.Compared with the conventional heat storage tank with a stratified intake structure,the heat storage tank with a stratified device has a maximum useful energy of20%.Through the analysis,it can be known that under the action of the stratified intake structure,the stratifying effect of the heat storage tank is better,and the thermal performance of the heat storage tank is significantly improved.Influences of various factors on the thermal performance of the efficient heat storage tank,temperature >flow > structure size.The higher water inlet temperature is more conducive to the formation of thermal stratification in the heat storage tank,and the thermal performance of the heat storage tank is better.In the high-efficiency stratification area of the heat storage process,the stratification phenomenon in the heat storage tank is obviously enhanced,and the optimal flow rate is 4l/min ～ 6l/min.With the increase of the size of the stratified intake structure,the heat storage efficiency increases,and the stratified intake structure of different sizes can form a good temperature stratification in the heat storage tank.(3)The CFD high-efficiency heat storage directional heat extraction heat storage tank model is established,and the heat release characteristics of the heat storage tank at different heights of the water intake process are studied through numerical simulation.The research shows that: for the heat storage tank with mixed temperature and complete heat storage process,the heat release duration is longer,which is 1-2 times longer than that of other water intakes,and the high temperature area in the heat storage tank is less.For the heat storage tank in the state of temperature stratification,water can be drawn from different temperature layers of the heat storage tank to provide water at different temperatures according to the thermal needs of users.The heat release efficiency can reach more than 90%,and the stratified heat storage tank can reflect the good thermal performance of the heat storage tank during the heat storage and heat extraction process.In this study,a heat storage tank with the integration of high efficiency heat storage and extraction is proposed.Through the study of the heat storage and release characteristics of the heat storage tank under different temperature,different flow rate and different structure size,the characteristics of the influence of different factors on the thermal performance of the heat storage tank are analyzed.It can be concluded that the solar heat storage tank with high efficiency has good thermal performance in the process of heat storage and withdrawal,which provides a basis for the structural design of this kind of heat storage tank and provides a reference for the practical application of high efficiency heat storage and recovery type of heat storage tank. |
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