| A packed bed cryogenic energy regenerator is investigated in a supercritical compressed air energy storage system.The regenerator uses NaCl as solid particle and liquid air as heat transfer fluid.This paper uses a porous heat balance model to simulate the flow and heat transfer mechanisms in a packed bed regenerator.After verifying the correctness of the model,this paper uses this model to simulate the complete cold charging and discharging process of the regenerator.During the charging process,a quite large thermocline region exist,where supercritical air is cooled down to be liquid air.At this time,the specific heat capacity accompanying the change in air state makes the temperature of the temperature of the slanting layer decrease in the middle region and rises in the front end region.When the temperature ramp in the charging process reaches the outlet,the temperature of the air at the outlet decreases rapidly,but the rate of decrease gradually decreases.During the discharging process,the temperature in the region of the inclined temperature layer first slowly rises and then rises sharply,and the outlet temperature of the cold accumulator has a sharp decrease moment after the temperature of the inclined layer reaches the outlet.Besides,the thermocline region is much smaller than that of the charging process,and thus the change of density and thermal capacity of air are much steeper than that of the charging process.The results also show that with the increase of charging/discharging mass flow rate,the fully charging/discharging time inversely decreases.The results also show that the full charging/discharging time is inversely proportional to the charging/discharging mass flow rate.In addition,the increase in working pressure will have a slight impact on the charging/discharging process.The research in this paper can provide theoretical guidance for the design and operation of supercritical compressed air regenerators. |
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