Thermodynamic Characteristics Of Cascade Phase-change Thermal Storage Unit Applied To Distributed Energy System

In the development of distributed system,there are some outstanding problems.There are differences in quantity,form and space between the supply and demand of energy,but it is difficult for China's distributed system to access the power grid at present.In addition,when the system runs at low load rate,the phenomenon that the prime mover only produces heat and does not generate electricity greatly reduces the energy utilization rate.In view of the above problems,this paper proposes to add a heat storage device to the distributed energy supply system.By comparing single-stage heat storage with cascade heat storage,it is found that the latter can not only increase the temperature difference of heat transfer,but also stabilize the temperature difference of heat transfer,so as to achieve the purpose of strengthening heat transfer.Compared with other heat storage methods(sensible heat storage,chemical reaction heat storage,concentration difference heat storage),phase change heat storage has the advantages of high latent heat value and stable exothermic temperature.Therefore,the cascade phase change heat storage method is used to improve the energy supply system.In order to take into account the quality and quantity of waste heat,this paper presents a design method of cascade phase change heat storage device.Under the premise of satisfying the design temperature field,this method can ensure that all levels of regenerator can complete the phase transformation process at the same time.In addition,the effects of inlet velocity on phase transition time and outlet temperature are analyzed and compared.It is found that when the flow state is turbulent and near the critical state,the heat storage effect is the best.The numerical simulation of the coupled cascade phase change heat storage device shows that the device can store heat in accordance with the design requirements under the design conditions.Taking model-1 as an example,it takes 12470 seconds for the whole regenerator to complete the regeneration process,which is only 4.08%different from the theoretical design.With regard to the dynamic characteristics of the cascade phase change heat storage device under variable operating conditions,this paper simulates and analyses the two aspects of variable inlet flow rate and variable inlet temperature,and finds that compared with the inlet flow rate,the influence of inlet temperature on the stability of the system is more obvious.Finally,the thermodynamic characteristics of cascade heat storage and single-stage heat storage are compared and analyzed.The results show that cascade heat storage can shorten the phase transition time while taking into account the quality and quantity of waste heat.