EXPERIMENTAL-DETERMINATION OF ISOTHERMAL VAPOR TRANSFER RATES BETWEENMOIST AIR AND A HYGROSCOPIC SOLUTION THROUGH A HYDROPHOBIC SYNTHETIC MEMBRANE

This paper reports on an investigation into the rates of isothermal va pour transfer taking place between moist air and a hygroscopic solutio n through a hydrophobic synthetic membrane. The membrane acts as a por ous barrier between the phases, being permeable to the vapour but not to the contacting liquid. Experimental results, obtained for a polyeth ylene membrane with a thickness of 170 mu m, show that the total mass transfer coefficient between moist air and a saturated LiCl solution i s of the order of 0.078 g/m(2)hPa at 21 degrees C, at least when the a ir phase moves at a velocity ranging from 1.5 to 3 m/s. The vapour tra nsfer rate through the membrane is essentially controlled by the conve ctive resistance to vapour transport on the air side and by the resist ance to mass transport offered by the membrane. The vapour flux exchan ged between the moist air and the hygroscopic solution, although limit ed by the membrane, appears to be sufficiently high to make the use of vapour membrane exchangers technically feasible in air dehumidificati on and conditioning.