Separation Of Saline Water And Fresh Water Based On Sunlight-thermal Localization And Its Two-phase Flow Analysis

Water-salt separation process by using the sunlight-thermal distillation is a prospective research topic in the world.Regarding the serious problems of water scarcity,soil salinization and land desertification in Southern Xinjiang,the flooding irrigation for planting on saline-alkali land causes not only the waste of water resources but also secondary pollution.It is of great strategic significance to utilize saltwater by sunlight-thermal distillation for improving the drought desert ecological environment in Southern Xinjiang.This dissertation presents a new style of active solar still with three lenses and one reflector.Changing the optical path of the sun's rays by the lenses and reflector,the saline water absorbs more heat and then evaporates quickly.The solar radiation entering the solar still heats up the blackened liner which in turn heats up the water causing evaporation.Because of partial pressure difference and temperature difference,the water vapor gets condensed along the inclined glass cover and is collected by suitable provision at the bottom.The mirror and the number of lens play significant roles in the distillate output of the proposed new design.It is experimentally found that the sunlight flux into evaporator is increased due to the added lenses and mirror,and higher yield has been observed as compared to conventional single slope still.The new style of solar still's production is higher than the traditional design,reducing the heating time(from about 38? to 50?)by 83.33%.Based on thermodynamics theory and experimental measurements,we have proposed an empirical relation for natural convection heat transfer of these stills,and the theoretical yields have been found to be in good agreement with their experimental values.The highest calculated values of radiative,convective and evaporative heat transfer coefficients from water to glass cover in the daytime for newstyle solar still according to this study are 7.419 W/(m2·?),1.214W/(m2·?)and 19.602 W/(m2·?)respectively.Radiative and evaporative heat transfer coefficients reach their peak values at 15:00 in Hangzhou.Another salt-water separation device with solar concentrated technology is constituted by a plurality of vacuum glass tubes in series to form a solar-heating unit,increasing the heat source of the evaporator and promoting the separation of gas-liquid in the evaporator,thereby improving the efficiency of desalination and water extraction.The different heat transfer mechanisms and flow conditions of the single-phase flow have been analyzed.It is found that the calculation under the vacuum condition of 10"5 mb has a significant deviation from the experimental result.This paper has established a two-phase flow model of saturated water in solar-heating vacuum tubes for the numerical simulation of the occurrence and propagation of flow boiling in tubes.The two-phase flow model has taken into account the convection heat transfer between inner and outer tubes,and its calculated and measured values of the heat-collecting efficiency are in good agreement with each other(the relative error is less than 2%).As such,the efficiency deviation problem of single-phase flow is solved.The results show the heat-collecting efficiency of the two-phase flow model nearly does not change when the mass flow rate is below 4.42 kg/h,and 4.42 kg/h is the demarcation point of single-phase flow and gas-liquid flow.The experiment on gas-liquid separation of evaporative process is conducted to test the temperature change and evaporation rate in the evaporation can.Differential equations for heat and mass transfer are developed.The heat-transfer coefficient h and mass-transfer coefficient j are calculated after the heat-transfer and mass-transfer processes are analyzed.The variables that can be used to describe heat-transfer and mass-transfer are analyzed based on ? theorem to determine three applicable dimensionless variables to the evaporator.The relationship between heat-transfer and mass-transfer in the evaporator is established by using partial experimental data to perform multiple regression on logarithmic dimensionless variables.This formula is verified using another part of the experimental data,and the calculation error is less than 10%.