Design And Performance Of Solar Powered Water Evaporator Based On Expired Yogurt

Water is the source of life,an essential substance for the survival of humans and all living things.But with the development of industrialization and the growth of the world population,drinking water resources have been seriously polluted.The shortage of drinking water and the uneven distribution of freshwater resources have become urgent crises.Therefore,the shortage of freshwater has gradually become a growing concern of mankind.Faced with the serious challenge of freshwater scarcity in the 21st century,many freshwater regeneration strategies have been developed and applied.Since seawater accounts for 96.5 percent of the world’s water reserves,desalination is considered an effective way to alleviate the water crisis.Solar energy is the most widely used renewable energy and is inexhaustible for mankind.The use of solar energy to generate steam can be used in sewage treatment,seawater desalination,steam power generation and many other fields.In recent years,the emerging technology of solar-powered interface water evaporation（SVG）has been recognized as having great potential for desalination,especially in remote and poor countries,because of its clean,abundant and free water.SVG uses photothermal materials to convert solar energy into heat and directly produce drinking water.It is mainly used for photothermal conversion at the vapor-liquid interface,which can effectively reduce heat loss and improve photothermal conversion efficiency（η）.However,the evaporator currently used for seawater desalination has some problems,such as poor mechanical strength,low photothermal conversion efficiency,excessive salt precipitation,surface bacterial growth,and inability to purify oil-contaminated seawater.It is urgent to seek a new and effective solution.In view of the above problems,this paper uses expired yogurt as the main raw material and adopts freeze-drying and calcination methods to prepare three-dimensional water evaporator.Because of its microporous structure,the prepared three-dimensional water evaporator has great potential for the purification of oil-contaminated seawater.Based on its excellent photothermal conversion performance,two kinds of three-dimensional water evaporators have been constructed to achieve seawater desalination and oil-polluted seawater purification.The main research contents are as follows:（1）A kind of three-dimensional water evaporator derived from expired yogurt was obtained by using yogurt as the main raw material,then mixing it with superabsorbent polymer（SAP）and polyvinyl alcohol（PVA）,and further freeze-drying and high-temperature calcination.The water evaporator has strong mechanical properties and can withstand a maximum pressure of 2.5 MPa.By changing the SAP and PVA content,the content of pyrrorole in the water evaporator can be effectively adjusted,and the photothermal conversion efficiency of the water evaporator can be improved by reducing the enthalpy of water evaporation.The water evaporation performance of different experimental groups was systematically investigated.The experimental results show that the water evaporation rate of the optimized water evaporator under one sunlight irradiation is 3.25 kg m^-2 h^-1,and the photothermal conversion efficiency is96.47%.The concentrations of Na⁺,K⁺,Mg²⁺and Ca²⁺in the purified water meet the standards for drinking water.The optimized water evaporator can purify oil-polluted seawater due to its unique wetting characteristics and microporous structure.The three-dimensional water evaporator derived from expired yogurt developed in this study has great application potential in the purification of oil-contaminated seawater.（2）C₃N₄ was prepared by high temperature calcination using melamine as the raw material.Then,C₃N₄ was doped with expired yogurt and PVA as described in the previous chapter.After freeze-drying,it was calcined in an argon atmosphere at high temperature,and a novel three-dimensional water evaporator was obtained.The evaporator has full spectrum absorption characteristics in the range of 200～2500 nm,which matches the solar spectrum well,and has good photothermal conversion ability.In addition,its surface also has a stable microporous water transport structure,so it has excellent water transport performance.In addition,by optimizing the content of C₃N₄,the evaporation rate of the water evaporator can be effectively increased,and theηvalue can be improved.Since C₃N₄ has good thermal stability and chemical stability,and has good antibacterial effect on Escherichia coli,the evaporator can not only be used for seawater desalination,oily seawater purification,heavy metal ion and dye wastewater purification,but also for bacterial-containing seawater purification.Therefore,this study provides a new scheme for the fabrication of low-cost solar powered water evaporator in the future.