Performance Study On A Low Concentrating Photovoltaic/Thermal-Flash Tank-Mem Brane Distillation System

Life is in endless succession due to water.Water is essential and vital resource for every aspects of human society.Nowadays,with the expansion of the world's population and the rapid development of industry and economy,the shortage of fresh water resource is becoming more and more obvious.Thus,people have strong desire to obtain freshwater from seawater,and more and more scholars have carried out studies in desalination field.However,conventional desalination requires a lot of energy.If the energy is all provided by fossil energy,it must be worse for the current situation of fossil energy.As a clean and inexhaustible alternative energy,solar energy can be used to generate electrical and thermal power.The combination of solar technology and desalination technology can save considerable fossil energy used in conventional desalination process and alleviate energy crisis.In the paper,to comprehensively utilize solar energy and desalination technology,a low concentrating photovoltaic/thermal-flash tank-membrane distillation(LCPV/T-FT-MD)system is proposed.The system mainly consists of low concentrating photovoltaic/thermal-solar thermal collector(LCPV/T-STC)module,flash tank and vacuum membrane distillation subsystem.The principle of the system is introduced,including low concentrating photovoltaic/thermal technology,flash technology and membrane distillation technology.According to heat transfer theory,first law of thermodynamics,law of mass conservation and mass transfer process of membrane,theoretical model of the system has been established.Moreover,the performance of the system has been analyzed.The results showed that when the solar radiation intensity was relatively steady(from 11:00 to 15:00 in the paper),the operation of the LCPV/T-STC module could be considered as at steady state and the theoretical and experimental results were in good agreement.Therefore,the theoretical model of the LCPV/T-STC module is valid and can be used to predict the performance of the system under different seasons.Besides,the freshwater yield of the flash tank was increased with the decreasing flash pressure and increasing water temperature.When the flow rate was relatively stable,the solar radiation intensity had positive effect on the freshwater yield of the flash tank.The gained output ratio of the flash tank(GORFT)was mainly decided by solar radiation intensity and freshwater yield.When the flow rate was relatively stable,the freshwater yield had greater effect on GORFT.What's more,as the salinity of saline water and the pressure of the membrane permeate side were increased,the freshwater yield of the vacuum membrane distillation subsystem was reduced.While,as the temperature of the saline water rise,the freshwater yield of the vacuum membrane distillation subsystem was improved.And the theoretical results meet the experimental results well.Furthermore,when considering the consumption of additional thermal power,the system performance in autumn,such as thermal efficiency of the LCPV/T-STC module,GORFT and gained output ratio of the entire system(GORtotal),was lower than that in summer.