Analysis Of The Influence Of Unsteady Inlet Temperature On The Performance Of Cascade Packed Of Phase Change Capsules

The heat storage technology for low temperature heat source can be effectively combined with new energy or traditional energy technology to alleviate the mismatch between current energy production,supply and demand,and has high economic and social value.Phase change heat storage,which uses phase change materials to absorb and release latent heat of phase change in the process of phase change,is an important part of heat storage technology.Compared with sensible heat storage and chemical heat storage,it has great development potential and prospect.Among them,the stepwise arrangement of phase change capsules can improve the heat transfer performance of heat storage system.Assuming the inlet temperature of the heat storage system as a constant value that does not change with time can effectively reduce the amount of calculation and the difficulty of analysis,and it is widely used in numerical research on heat transfer problems.However,in actual working conditions,the inlet temperature of the heat storage system will change according to time in many cases.Therefore,it is of practical significance to compare and study the phase change capsule cascade heat storage device under the conditions of constant inlet temperature and actual unsteady inlet temperature.In this paper,a cascading heat storage bed model with disordered packing phase change capsules was established,and the reliability of the model and the accuracy of the simulation results were confirmed by comparing the model with the relevant data of the existing experimental platform.Then,based on the established model,the numerical simulation analysis was carried out by changing the order of the heat storage bed and the physical parameters of the phase change material.The thermal performance of the packed bed under different working conditions was evaluated by using phase transition,temperature field and temperature uniformity in the packed bed,heat storage,heat storage rate density,exergy and exergy rate as indexes.The results show that the phase transformation and heat storage process can be accelerated by the packed beds.The time required for the three stage and two stage packed beds to reach full melting is 4.3% and 8.7%higher than that of the single stage packed beds,and the time required to reach maximum heat storage is also 9.5% and 6% earlier than that of the single stage packed beds.A more uniform axial temperature field is obtained.However,the exergy accumulation of packed beds will decrease by about 4.8% and 10.5%.In addition,the results show that the effect of changing the order on the total amount of heat storage is far less than that of changing the physical properties of PCMs.Finally,the operating conditions of different inlet temperature-time functions are set based on the actual conditions,and the average inlet temperature is taken as the corresponding constant inlet temperature operating conditions for comparative analysis.The results show that the unsteady condition has a large difference in each index compared with its corresponding steady condition.Under unsteady condition,the final liquid phase rate of each group increased by 12.5% on average,and the time needed to reach the highest liquid phase rate was also less.The temperature field in the packed bed is better than that in the steady condition.Overall,there was a significant difference between the exergy of the unsteady inlet temperature working condition and that of the corresponding steady condition in the whole heat storage process.After the reaction,the average difference was 30.15%,but the lowest was only 3.4%.The heat storage largely depends on the physical properties of PCMs in each arrangement.When simplifying the actual changed inlet temperature,the relationship between the simplified constant value and the melting point of PCM should be carefully considered.After careful verification,the simplification should be carried out to ensure that the simulation results will not be affected.In this paper,the heat storage and release of the phase change capsule terraced regenerative bed in the process of heat transfer were simulated and analyzed,which provided a reference for the design of the experimental bed in the future,the simplification of the simulation calculation of the regenerative bed and the optimization of the thermal performance of the regenerative bed.