Study On Thermal Storage Characteristics And Optimization Design Of Casing Pipe Phase Change Material Floor

Low temperature floor radiant heating is an effective way to meet the heating demand of buildings by using low-grade solar energy.However,the solar energy resource has the characteristics of discontinuous fluctuation and low energy flow.The sensible heat storage capacity of the concrete layer in traditional radiant heating end is difficult to guarantee the indoor thermal environment under the adverse conditions such as night,rainy days,etc.,which becomes a severe challenge for the development and application of solar floor radiant heating system.Therefore,it is urgent to scientifically combine the low-temperature floor radiant heating end with the heat storage material to effectively suppress the fluctuation of solar radiant heat energy and transfer the energy peak,so as to ensure the efficient and stable operation of the solar low-temperature floor radiant heating end.In this paper,the heat transfer control equations of hot water in coil pipe,phase change material in casing pipe structure and concrete material are established by theoretical analysis of casing pipe PCM floor which are filled casing structure with phase change material;the simplified physical model of the floor is established,the boundary conditions of each surface are defined,and the correctness of simulation calculation is verified by experiments;the strategy of setting latent heat of PCM and sensible heat of concrete is put forward,which lays a theoretical foundation for the structural design and optimization of casing pipe PCM floor.The main research conclusions are as follows:The main factors that affect the thermal characteristics of casing pipe PCM floorinclude the thermophysical parameters of phase change materials and the structural parameters of casing structure.It is found that increasing the thermal conductivity and melting temperature of phase change materials will increase and decrease the temperature amplitude on the floor surface,but the effect is not significant when the thermal conductivity is greater than 0.3 W/(m?K)or melting temperature is greater than303 K.It is found that the melting temperature of phase change material should match the fluctuation of solar hot water.Compared with other melting temperatures,when the melting temperature is 293 K,the floor surface has lower temperature amplitude and higher average temperature.The results show that under the same outer tube diameter,the increase of the diameter of the water supply and return coil pipe will weaken the latent heat storage capacity of the whole heating end,and to an extent enhance the heat transfer capacity of the heat source to the floor.When the diameter of the coil pipe is larger than 35 mm,the heat storage capacity of the casing structure is obviously degraded;properly increasing the diameter of the outer tube will improve the heat storage capacity of the floor.When the diameter of the outer tube is 40 mm,there is296 K local high point of the average temperature of the floor surface.Based on the comprehensive analysis of the thermal physical parameters of phase change materials and the casing structural parameters,the influence on the thermal characteristics of the phase change casing floor is analyzed.With the purpose of balancing the average temperature and temperature amplitude of the concrete layer surface,the optimal setting strategy of the latent heat of phase change materials and the sensible heat of concrete is obtained.When filling the same volume of phase change material,the filling strategy of the coil tube with a larger tube diameter ratio can achieve a difference of 12.3K in surface temperature amplitude of the concrete layer compared to the small tube diameter ratio;the proper ratio of the volume of the latent heat material to the volume of the sensible heat material can coordinate the heat storage and release laws of the sensible heat storage material.Compared with other volume ratios,when the volume of concrete is about 1.6 times the volume of the phase change material,it can balance the surface temperature of the concrete layer and the temperature amplitude;the increase of concrete latent heat will reduce the thermal characteristics of casing pipe PCM floor approximately linearly,which is convenient for the adjustmentof the end in engineering practice.Through the above theoretical analysis,numerical simulation and experimental research,it is clear that the change of the thermal physical parameters of phase change materials has an impact on the thermal characteristics of casing pipe PCM floor,and the different combination ratio of the casing structural parameters has an impact on the thermal characteristics of the end.After the comprehensive study of the parameters of the main influencing factors,the setting strategy of the same or different volume of phase change materials and the sensible heat of the concrete layer is obtained.Reference is made to the ratio of the phase change material in the selection of the casing structure and the filling control strategy in the practical application of casing pipe PCM floor.