Experimental Investigation And Thermodynamic Analysis Of Hollow Fiber Membrane-based Liquid Desiccant Module For Air Dehumidification And Cooling

Outdoor fresh air is not supplied in the traditional air-conditioning system, which willdegrade the indoor air quality. Outdoor air is to improve indoor environment, but extrarefrigeration dehumidification load is added to air-conditioning system. The dedicatedoutdoor air technology which handles air temperature and humidity separately, is a wonderfulchoice for solving this problem. Thus it is widely used in air conditioning system. However,the inherent disadvantages of conventional air dehumidification technology, such asrefrigeration dehumidification, adsorption dehumidification and membrane-baseddehumidification, become inferior when greater energy efficiency and higher indoor airquality are required. Therefore, new dehumidification method has to be found out.Hollow fiber membrane-based liquid desiccant air dehumidification is a noveltechnology for air dehumidification and cooling. The hollow fiber composite membrane isused as contact medium between air and liquid desiccant. On one hand, the corrosive liquiddroplet will be prevented frome carry over to room by fresh air. On the other hand, heat andmass transfer processes are enhanced. In this paper, experimental and numerical investigationmethods are applied to study heat and mass transfer characters and thermodynamicperformance of hollow fiber membrane-based liquid desiccant dehumidification module.Two hollow fiber membrane modules used for dehumidification/regeneration aredesigned, according to the fresh air supply requirement of Southern China in summer. Theheat and mass transfer performances of air dehumidification and cooling processes areinvestigated under different liquid desiccant and air inlet conditions. Two typical processes ofhollow fiber membrane-based liquid desiccant air dehumidification, called “dry condition”and “wet condition”, are studied.The dehumidification efficiency decrease in wet condition for dehumidificationprocesses. To improve the performance of membrane modules, polyvinyl alcohol (PVA)solution of2%mass fraction is used to modify the hollow fiber membrane through outersurface casting method. The scanning electron microscopy (SEM) analysis result shows thathollow fiber membrane outer surface is coated by activity skin layer. The pores of membrane surface layer become compact after modification. However, the membrane resistanceincreases either. Various inlet air flow rates are tested to study the effect of extra membraneresistance on heat and mass transfer performance. The results indicate that, after modification,the dehumidification performances of membrane module decrease a little in dry condition.While in wet condition, the modified membrane module shows some advantage for airdehumidification.The numerical model of conjugate heat and mass transfer in transverse flow module isdeveloped. The mathematical model-based Fortran program is designed to analyze thethermodynamic performance of dehumidification processes. According to the researches, thesimulation data is in agreement with experiment results in dry condition dehumidificationprocess. However, the numerical model is not accurate enough to describe the wet conditiondehumidification process because the mass and heat transfer characters become morecomplicated. The thermodynamic experiments are done under outdoor conditions in summer.It can be found that, the air dehumidification coefficient of performance (COP) arrives at0.364and the total heat exchange efficiency reaches0.357in design condition. In designoutdoor condition, the dehumidification COP is0.357and the total heat exchange efficiencyis0.341.