Heat and mass transfer characteristics and dehumidification performance improvement of an evaporatively-cooled liquid dehumidifier

In this paper, an evaporatively-cooled dehumidifier and its experimental test rig is introduced. By using the LiCl and CaCl2 solutions with mass concentration of 0.35 and 0.45 as liquid desiccants, the dehumidification performance improvement compared to adiabatic falling-film dehumidification and the heat and mass transfer characteristics of LiCl and CaCl2 solutions under evaporatively-cooled conditions are analyzed. The results indicate: the dehumidification rate under evaporatively-cooled condition is about 20% higher than that under adiabatic condition and the improving extent of dehumidification performance of the evaporatively-cooled dehumidifier appears more obviously under higher environmental temperature and humidity and lower solution concentration and higher solution temperature. Meanwhile, the dehumidification rate of LiCl is about 73% higher than that of CaCl2 under the same solution concentration, and the CaCl2 with mass concentration of 0.45 shows the parallel dehumidification performance with LiCl. As for the enthalpy effectiveness, CaCl2 with mass concentration of 0.35 is the highest. By changing the air, solution, and evaporative cooling air parameters, it is found that the heat and mass transfer coefficient is most significantly affected by air flow rate, and the heat transfer coefficient increases with the increase of solution flow rate but the mass transfer coefficient decreases. Moreover, four correlations on heat and mass transfer characteristics are given. In summary, the evaporatively-cooled devices can do effectively improve the solution dehumidification performance and the study results of this paper are beneficial to the industrial application of that device.