Development And Simulation Of Absorption Refrigeration System With Membrane Energy Accumulator

Solar single-effect absorption refrigeration system can be driven by a lower temperature heat source,but the COP is lower.The solar energy double effect absorption refrigeration system has a high requirement on heat source temperature,and can not operate when the heat source temperature is low,and the effective refrigeration time is short.Therefore,in order to improve the efficiency of solar energy and prolong the effective cooling time,a solar absorption refrigeration cycle with single and double effect switching is proposed based on integrated membrane energy accumulator.Membrane energy accumulator is based on solution concentration difference energy storage.Due to the existence of semi-permeable membrane,it can effectively solve the influence of solution crystallization inside the accumulator on the system operation,and improve the operation stability of solar absorption refrigeration system.In order to study the performance of the refrigeration cycle proposed by the experimental research,the solar energy single-effect and double-effect switching absorption refrigeration system with integrated membrane energy accumulator was designed and built.The main research work completed and the main conclusions obtained include:1)The heat and mass transfer characteristics of membrane energy accumulator were analyzed,and a 3D mathematical model of heat and mass transfer in the energy release process of full-scale flat membrane energy accumulator was established,which is solved by CFD calculation software.The maximum relative deviations of mass transfer flux and solution temperature are 14.9%and 14.6%,respectively.The change rate of Li Br mass fraction in flat membrane energy accumulator is 1.38 times that of hollow fiber membrane.With the increase of vapor temperature from 1.88~oC to 13.02~oC,the mass transfer flux increased twice,and the average temperature of solution increased more than 3.75~oC within 10 minutes.When the membrane filling density increases from 1.4%to 2.1%,the mass transfer flux of the flat film accumulator increases to 2.04 times.The heat and mass transfer characteristics for membrane energy accumulattor can guide the design of the membrane accumulator,membrane technology and solution concentration difference to energy storage technology was applied to the combination of solar energy in single and double effect absorption refrigeration experimental system,increase the energy storage density of accumulator,extending the experiment system of working time,improve the efficiency of solar energy.2)Based on the study of mass transfer characteristics of membrane accumulator,a single-effect and double-effect switching absorption refrigeration system with single effect cooling of 5 k W and double-effect cooling of 10 k W with integrated membrane energy accumulator was designed and developed.The heat exchanger was designed and manufactured,and the experimental platform of solar absorption refrigeration system was set up.Through the electric valve to complete the system internal single,double effect switch rather than single,double effect unit switch.A new type of vertical tube falling film absorber and evaporator were designed and applied in the evaporator and absorber of solar energy single-double-effect switching absorption refrigeration system to reduce the difficulty of production.The generator uses the heat and mass exchange separator generator,the heat exchange is concentrated in the plate generator,strengthen the heat exchange to reduce the heat exchanger volume.The membrane energy accumulator applied to the experimental system was designed,and the hollow fiber membrane accumulator with higher strength was selected,with energy storage of 5 k W?h.3)Based on the meteorological parameters in Qingdao,a numerical simulation model of this experimental system was established.Using TRNSYS simulation software,the performance of solar single-double-effect absorption refrigeration system was analyzed.Under the same collector area and water tank volume,the cooling capacity of the single-effect and doublel-effect switching system on a typical sunny day in summer can reach 113 k W?h,which can meet the design refrigeration requirements.Compared with the single-effect and dual-effect switching system,the cooling capacity of the single-effect and double-effect switching system is 417.4%and 12.2%,respectively.The investment payback period of the single-effect and double-effect small solar absorption refrigeration system is about 8.0 years,which is shorter than that of solar single and double effect system.The annual carbon dioxide emission reduction ratio of single-effect and double-effect solar absorption refrigeration system is 86.1%.