Experiment And Numerical Simulation Study On Enhancement Of The Heat And Mass Transfer Of Vacuum Tube Adsorbed Bed With Fins

The solar adsorption refrigeration technology is an environment-friendly technology and it is a technology that can replace Freon and can effectively mitigate the greenhouse effect.However,due to the poor heat and mass transfer and the long cycle time of the refrigeration system,the solar adsorption refrigeration technology has not been widely used.This paper studies the improvement of the heat and mass transfer performance and the shorten of the cycle time of the system.Firstly,in order to improve the poor heat and mass transfer performance of the adsorbent bed,an experiment was performed on a built-in finned adsorption bed of solar adsorption refrigeration unit using SAPO-34 zeolite-water as the working pair.The experiment was conducted in a sunny,cloudless,and windless weather when the number of the fin is m=2,4,6,and 8;the height of the fin is h=15 mm;and the thickness of the fin is d=1 mm.The system uses an auto-focus parabolic trough device for high solar energy utilization.The experimental results show that as the number of fins increases,the temperature in the bed increases slowly,the adsorption capacity increases,the average temperature in the bed decreases after the adsorption process ends.During preheating process,the average temperature in the bed reaches about 100?,and the pressure is about 11500 Pa.As the number of fins increases,the time of the preheating process becomes longer.During the desorption process,the temperature in the bed continues to rise,and once the condenser is connected to the condenser,the pressure will slowly rise after a sudden drop.During the cooling process,the temperature and pressure in the bed continued to decrease.The more fins is,the shorter the cooling time is.At the stage of refrigeration,the temperature in the evaporator continues to decrease,and the decrease is closely related to the number of fins.In short,as the number of fins increases,although the solar energy required by the system in the preheating,but desorption process is increased,the cooling capacity,COP,and SCP of the system both increase,and the cycle time of the system is shortened.Secondly,the software FLUENT is used to simulate the cooling process of the finned bed with silica gel-water as the working pair,and the influence of the size parameters of the fins on the cooling time is studied.The simulation results show that the addition of fins can improve the performance of the adsorbent bed,make the decrease rate of temperature in the adsorption bed becomes faster,and shorten the cooling time.It is also shown that the thickness of the fins has little effect on the cooling time,and as the height of the fins increases,the time required to reach the equilibrium temperature in the adsorption bed becomes shorter,the decrease rate of temperature becomes faster,and the radial temperature distribution of the adsorbent bed is more uniform.As the number of fins increases,the cooling time of the system also decreases.On the other hand,although the addition of fins shortens the cooling time,but the addition of fins to the cooling copper tube will reduce the amount of adsorbent material.In order to ensure the cooling capacity of the system,it is necessary to select the size parameters of the fin,and the optimum parameters of the fins are as follows: m=4,h=20mm,d=1mm,and the cooling time of the system is 2100 s.