Research On Preparation Of Composite Adsorbent By Microwave Irradiation And Heat And Mass Transfer Performance

As an energy saving and environmental benign refrigeration technology,adsorption refrigeration is more and more used in the low grade heat source such as solar energy,geothermal energy,industrial waste heat and so on.But the adsorption refrigeration technology there are still some problems that need urgent resolution,the most important problem is the heat and mass transfer of the adsorbent.As the core of the adsorption refrigeration system,the adsorbent have the problems of poor heat transfer and gas permeability,while in the process of chemical adsorption will occur the phenomenon of expansion and agglomeration.To solve the problem of poor heat and mass transfer performance of adsorbent in the application process,this paper added sucrose in the original graphite/calcium chloride composite adsorbent and activated by microwave heating technology,prepare of expanded graphite/sucrose/calcium chloride composite adsorbent.Through the thermal conductivity and permeability test.analysis of the influence factors of the composite adsorbent of the heat and mass transfer such as the pressing direction,density,and the firing time.The specific contents are as follows:(1)Optimize the preparation of expanded graphite/sucrose/calcium chloride composite adsorbent,establish the adsorption performance test system and screen the optimum formula.First the microwave oven is designed to the microwave heating device with protective gas.Next calcium chloride,sucrose and expanded graphite were mixed in different ratio with water dissolving method,and different series of composite adsorbent can be acquired by microwave heating.The burning loss of calcium chloride crystallization water and sucrose pyrolysis can be cleared by calculating the burning loss rate.Finally on the basis of the constant volume method build adsorption performance test system,test and analysis the adsorption performance of the composite adsorbent.The results show that when the composite adsorbent ratio of sucrose:calcium chloride:graphite is1:4:1,the microwave power is 700W,the firing time is 15min,the composite adsorbent get the better adsorption performance.(2)On the basis of the transient plane source technique,analyzed the Hot disk thermal analyzer probe and test principle.Design and processing of the samples in different directions to mold pressing different density,pressing and curing of graphite composite adsorbent.The pressing direction select horizontal and vertical direction,the composite adsorbent select L2.By measuring the thermal conductivity of curing graphite and composite adsorbent,analyzed the effect of pressing direction,density and microwave firing time on thermal conductivity.The results show that compared with the pure calcium chloride,by adding graphite can improve the heat transfer performance of the adsorbent.As the sintering time increases,the thermal conductivity of composite adsorbent is increasing,but the difference is not great.The effect of sucrose content on the adsorbent thermal conductivity is not great.(3)According to the Ergun model to build a permeability test system,including the constant pressure nitrogen supply system and test system.By measuring the flow capacity and pressure difference can get the permeability.Test the permeability of the graphite and composite adsorbent,and analyze the influence of pressing direction,pressing density and firing time on permeability.The results show that under the same density,vertical pressing graphite and composite adsorbent permeability were greater than the parallel direction of repression,and under the same direction of pressing,curing graphite and composite adsorbent permeability decreases with increasing density and suppress.In practical application,the pressing density of the composite adsorbent does not exceed 500 kg.m-3.(4)The test of the adsorption properties,permeability and element distribution indicated that with the increase of microwave sintering time,the sucrose continuous pyrolysis of the pore structure,increasing the specific area of adsorbent,enhances the mass transfer performance.When microwave irradiation time increases further,part of the pore structure will be sintered.The adsorbent surface area decreased,the mass transfer performance gets worse.