Experimental Study On The Influence Factors Of Solar Thermal Local Evaporation System

The shortage of fresh water resources is one of the most serious global problems in the 21st century.Solar thermal local evaporation technology has great potential to solve the problem of freshwater shortage due to its high efficiency of light-thermal conversion and excellent evaporation performance.In this paper,from the perspective of thermodynamics,different solar thermal local evaporation systems are designed by reasonable experimental methods,various factors affecting the evaporation performance are optimized and the heat loss of the system is analyzed.The influences of the concentration of particles in the photothermal layer,the thickness and the porosity of the thermal insulation layer on evaporation performance are discussed.The problems of low evaporation efficiency caused by the mismatch of water supply rate and incident energy and the continuous change of outdoor solar radiation density are solved.The difficulties of poor mechanical properties and weak stability of the samples in practical application are overcomed.The details are as follows:?1?A typical double-layer structure system was prepared by coating carbon particles obtained from carbonization of biomass on air-laid paper.The microstructure,thermal conductivity,light absorption efficiency and surface temperature of the system were characterized.The effect of the thickness of the air-laid paper on evaporation performance was explored by experiment,and the best thickness for improving evaporation efficiency was obtained.The same method was utilized to study the effect of carbon particle concentration and obtained the best concentration to improve evaporation efficiency.The evaporation rate and efficiency can reach about 0.964 kg?m^-2?h^-1 and70%respectively under the irradiation of one sun intensity.The system is an ideal choice for the application of solar thermal local evaporation technology.?2?A double-layer soalr thermal local evaporation system was prepared by coating carbon particles on the sintered sawdust film.Firstly,a series of characterizations are carried out,and then the influence of porosity of thermal insulation layer on evaporation performance is discussed.The positive effect of increased water diffusion coefficient and the negative effect of increased thermal conductivity of sawdust film determine the best porosity to improve evaporation efficiency together.The evaporation rate and efficiency are 1.2 kg?m^-2?h^-1 and 77.64%respectively under 1kW?m^-2 irradiation.This work has a certain inspiration for the design of thermal insulation layer of other solar thermal local evaporation systems.?3?A unique carbon black cellulose sponge system was designed.The water in this system was not absorbed from the block water,but injected through the adjustable water injection equipment.The evaporation efficiency of the system?91.5%?can be greatly increased by nearly10%by reasonably matching the injection rate with the incident energy to reduce the energy loss.Under low irradiation density,the evaporation efficiency can exceed 100%of the theoretical value because the surface temperature is lower than the ambient temperature.Considering the characteristics of low cost,simple preparation,good thermal management performance and high evaporation efficiency,we believe that the carbon black/cellulose sponge water injection system can provide a reliable and effective way of steam generation.?4?The carbon black/polyethylenimine bacterial cellulose?CPB?photothermal membrane was prepared by vacuum filtration.Firstly,the microstructure and mechanical properties of CPB membrane were characterized,and it was confirmed that CPB membrane has good structural strength.The effects of carbon black particle concentration and polyethyleneimine concentration on light absorption and water absorption were discussed.The evaporation efficiency of CPB film can reach about 85.05%under one sun irradiation.CPB membrane has the advantages of low cost,simple fabrication,good mechanical properties,good scalability and strong desalination ability,which provides a feasible way for practical application of solar thermal local evaporation system.There are 47 picutres,2 table and 115 references in this paper.