Design Of Packaged Phase Change Heat Storage Unit In Tube And Simulation Study Of Electric Heat Storage Device

As a clean energy source,electrical energy shows unique advantages in solving environmental pollution and energy cascade utilization.For the problem of high energy and low usage in traditional electric heating,phase change heat storage technology makes up for this defect.Under the strong guidance of national policies,in-depth study of phase change energy storage technology,organic combination of electric heating and phase change energy storage technology,development and application of phase change thermal storage electric heating technology and products,not only can meet heating demand,but also can The load plays the role of "peak-cutting and valley-filling" to ease the pressure on the power grid.The unique advantages of phase change regenerative electric heating in power peak shaving and heating make it gradually become one of the research hotspots.In this topic,Ba(OH)2·8H2O is used as a material which is defined by phase change heat storage,and a heat storage unit based on a phase change material encapsulated in a tube is constructed,Can be combined with building envelopes,laying and walls,not only suitable for heating renovation of existing buildings,but also adapt to the development of new buildings,especially prefabricated buildings;It can also be used inside the regenerator to integrate the production of phase change regenerative electric heating devices.First,an experimental test platform for the phase change heat storage unit was built,and the heat storage and discharge performance of the heat storage unit was tested.The experimental results show that the entire heat storage process takes 900 s,and 150 s after the start of the heat storage process,the temperature of the phase change material in the heat storage unit reaches the phase change temperature(351K),and the heat storage unit continues to absorb heat within 450 s,but the temperature is basically maintained The same is the phase change latent heat storage phase of the heat storage unit,accounting for 50% of the entire heat storage process;contrasted with the heat storage process,the temperature at which the material starts to solidify is slightly lower than 351 K during the exothermic process,and the entire process lasts about 2000 s.Secondly,based on the theory of phase change heat transfer,the physical model of the heat storage unit is established by enthalpy method.The numerical calculation of the heat storage and release process is carried out by CFD software,and the simulation results are compared with the experimental data to verify the accuracy of the model.On this basis,the temperature changes of phase change materials at different positions in the thermal storage unit are simulated and analyzed,and the influencing factors of the thermal storage and release characteristics of the thermal storage unit are further analyzed.The simulation results show that the temperature change trend of the regenerator is basically the same in axial and radial direction;When the filling rate and pipe diameter are fixed,the two working conditions of natural convection and neglecting natural convection are considered.In the first 200 s,the material is in the solid-state area,and the two curves basically coincide,so the effect of natural convection is very small.When natural convection is considered,the heat storage time is obviously shortened,which is 1500 s,while the working condition of neglecting natural convection is still in the latent heat storage stage,which is contrary to the experimental results The influence of natural convection can‘t be ignored;The filling rate of phase change materials and the diameter of the thermal storage unit are closely related to the thermal storage capacity of a single thermal storage unit.When the diameter of the thermal storage unit is fixed and the filling rate is 70%,80% and 90%,the average temperature of the material area reaches the phase change temperature for 180 s,205s and 220 s respectively,and the duration of the latent heat storage process is 450 s,650s and 770 s respectively.It can be seen that with the increase of the filling rate,the average temperature of the material area reaches the phase change temperature for 180 s,205s and 220 s respectively The heat storage time of the heat storage unit is obviously prolonged;When the filling rate of the material is fixed and the diameter of the heat storage unit is 20 mm,30mm and 40 mm respectively,it takes 180 s,270s and 440 s for the average temperature of the material area to reach the phase change temperature,and the duration of the heat storage process is 900 s,1450 s and 2300 s respectively.It can be seen that with the increase of the diameter of the pipe,the heat storage time of the heat storage unit is significantly longer.Therefore,after the length of the heat storage unit is determined,the larger the filling rate,the larger the pipe diameter,the greater the heat storage capacity of the heat storage unit,but the heat storage time will be significantly prolonged,which needs to be considered comprehensively.Finally,combined with the electric heating method,the phase change heat storage unit in the tube is applied to the heat storage device to form a Electric phase change heat storage device,and the design calculation and preliminary design of the heat storage capacity of the device are carried out.A three-dimensional physical model was established for the Electric phase change heat storage device,and its overall heat storage and discharge characteristics were simulated and analyzed.The simulation results show that from the temperature field distribution,the temperature of the heat storage unit near the electric heating element first rises,and the inner phase change material melts and absorbs heat.Due to the temperature difference,the air forms a strong natural Convection,so that the peripheral heat storage unit also gradually absorbs heat and heats up,as the phase change material liquid phase ratio becomes larger and larger,the temperature field in the heat storage device will gradually become uniform.After the entire heat storage process is completed,the heat storage The temperature of the wall of the heat source in the device is close to achieve dynamic equilibrium;The heat storage process of the device lasts about 30000 s,of which the latent heat storage process is about 12000 s,accounting for 40% of the entire heat storage process.In the heat release process,compared with the heat storage unit in the middle,the cooling rate of the heat storage unit near the outer wall of the device is faster.This is because the temperature difference between the peripheral heat storage unit and the environment is large.The phase change material gradually releases heat and solidifies,the temperature in the heat storage device tends to be uniform,and finally reaches thermal equilibrium with the environment.The heat release process lasts about 20,000 s,of which the latent heat release phase accounts for 60%.The research of this paper reveals the thermal storage and release characteristics of the phase change thermal storage unit and its influencing factors.On this basis,the thermal storage unit is applied to the electric thermal storage device,and the overall thermal storage and release characteristics of the electric phase change thermal storage device are simulated and analyzed.The research results can provide theoretical basis and reference for the application of phase change heat storage electric heating.