Study Of Dehumidification Performance And Heat&Mass Transfer Characteristics In An Evaporative Cooling Assisted Externally-Cooled Mixed LiCl-CaCl₂ Solution Falling Film Dehumidifier

Liquid desiccant dehumidification has attracted the attention of scholars at home and abroad due to its high dehumidification performance and the ability to use renewable energy to regenerate solutions.In this paper,an externally-cooled dehumidifier using liquid water evaporative cooling technology to strengthen the dehumidification of solution falling film within tube is introduced.Furthermore,The study sheds light on the dehumidification performance and heat and mass transfer characteristics of lithium chloride and calcium chloride single(mixed)component solution in the externally-cooled dehumidifier with experiment and theoretical simulation.Firstly,the paper provides the calculation method of the density,surface water vapor pressure and specific heat capacity of lithium chloride and calcium chloride single(mixed)component solutions are given,and then the density and surface water vapor pressure are measured.Based on the experimental data,a modified model for calculating the surface water vapor pressure of the mixed LiCl-CaC12 solution with the ratio of 2:1,1:1 and 1:2 is presented,and the calculated value agrees well with the experimental value.Secondly,the dehumidification performance difference of LiCl and CaC12 solutions under externally evaporative cooling conditions are analyzed and compared through a series of experiments.The results show that the dehumidification performance of LiCl solution with 0.35 mass concentration is similar to that of CaC12 solution with 0.45 mass concentration,whose dehumidification rate and corresponding air outlet temperature are both higher than CaCl2 solution with 0.35 mass concentration.Moreover,the dehumidification rate of LiCl solution with 0.35 mass concentration is about 73%higher than that of CaC12 solution with 0.35 mass concentration,and the larger air flow rate leads to a greater dehumidification rate difference.In addition,the increase of evaporative cooling air flow rate can not only increase the dehumidification rate,but also reduce the corresponding air outlet temperature by about 1.4?,and the effect of the spray water temperature on the dehumidification performance of CaC12 solution is more obvious than that of LiCl solution.By analyzing the heat and mass transfer characteristics,four correlations on heat and mass transfer characteristics are given.Thirdly,this paper makes an analysis and comparisons of the dehumidification performance and the heat&mass transfer characteristics of the mixed LiCl-CaCl2 solution.The findings suggest that the dehumidification rate of the mixed solution with the ratio of 2:1,1:1 and 1:2 under standard experimental condition are 2.26kg/h,2.05kg/h and 1.99kg/h respectively.Moreover,the higher the proportion of LiCl in the mixed solution is,the higher the dehumidification rate and the corresponding air outlet temperature of the mixed solution will be.The dehumidification rate is more affected by solution temperature,concentration,and evaporation cooling parameters.By analyzing the influence of different air,solution and evaporative cooling air parameters on the heat and mass transfer coefficient of mixed solution,it is found that the heat&mass transfer coefficient has the greatest dependence on air flow.Finally,comparing with simulation analysis of different conditions,The study finds that the dehumidification rate of LiCl solution is the largest,followed by the mixed solution,and calcium chloride was the lowest.In the mixed solution,the larger the proportion of CaCl2 is,the greater the difference of dehumidification rate under the externally-cold and adiabatic conditions will be.,and the difference reaches its maximum)when the pure CaCl2 solution is used.When the air temperature falls below 32? and the relative humidity is less than 70%,the dehumidification rate of mixed LiCl-CaCl2 solution at a rate of 2:1,under the externally-cooled condition,is higher than that of the pure LiCl solution under the adiabatic condition.The research results provide a reference for the practical application of this kind of externally cooled dehumidifier.