Study On Performance Optimization Of Solar Adsorption Refrigeration System

This article mainly involves two aspects.Firstly the basic research of a solar adsorption refrigeration system is carried out experimentally.The variation of the temperature and the pressure of the adsorption bed is analyzed,and the optimization of system cycle about the adsorption time is discussed.Secondly,a numerical study is conducted to delve into the adsorption process in the annular bed by using the CFD software FLUENT.The effect of the size of the mass transfer channel and of the filling height of the adsorbent material in the bed has been optimized.To meet the heat demand in the process of solar adsorption refrigeration,a parabolic solar trough was designed and manufactured,which was able to track automatically the solar movement under the control of the preset program.The experimental system was located in the campus of Beijing University of Technology in southeast Beijing city?latitude 39°56?,longitude 116°20??.As the most important component of the system,the tubular adsorption bed captured the solar energy via the parabolic trough and then transferred the heat to the adsorbent material in the annular cavity of the bed tube.The experimental system adopted the SAPO-34 zeolite and water as the working pair for the purpose of refrigeration.The experimental results have revealed that there is no linear relationship between the adsorption uptake of the bed and the adsorption time.This relationship is mainly reflected in the variation of the uptake and the bed temperature.In the first 10minutes the adsorption was very fast and the bed temperature increased rapidly.Beyond a summit,the adsorption rate decreased gradually,and the bed temperature dropped down.Closely related to this relationship is the variation of the specific refrigeration power SCP₁ that was defined by the mere adsorption time.With the increasing of the adsorption time SCP₁ showed the tendency of simply decrement.However,the specific refrigeration power SCP₂ defined by the total cycle time was quite different.It showed a maximum value at some adsorption time.The variation of the coefficient of the performance of the system COP was of the same tendency as that of the SCP₂.These tell us that the solar adsorption refrigeration system needs to be optimized in practice.Though the adsorption time to the maximum of the COP and the SCP₂ was not the same exactly,the difference between them was no more than 40-70 min.So there is some compatibility for the SCP₂ and the COP in application.In the second part,the influence of the internal structure of the adsorbent bed on the performance was numerically investigated for the annular bed type.The numerical results presented the characteristic of the heat and mass transfer in the bed and the optimum range of the parameter of the bed structure.With the deployment of the mass transfer channel along the bed axis,the distribution of the temperature and the adsorption concentration in the bed is greatly improved in the axial direction.On the other hand,the gradient of the temperature and the concentration in the radial direction is still drastically,which was interpreted by the function of the forced cooling convection on the sidewall of the bed.The heat transfer process always dominates the mass transfer process.Wherever the temperature is lower,the adsorption concentration is higher.In the view of the enhancement of the heat and mass transfer,the shorter filling height of the material and the bigger size of the mass transfer channel are always profitable.Nevertheless,reducing the filling height or enlarging the mass channel size is to diminish the mass content of the adsorbent material.Taking into account the total cooling power output of the bed,the mass channel of r₁=6.7mm or r₁=9.5mm,which is determined concretely by the adsorption time,gives the best effect.As to the filling height of the material,the satisfactory value is in the range of H=70-100mm.