Experimental assessment of a hydrophobic membrane-based desorber/condenser with H2O/LiBr mixture for absorption systems

Conventional desorbers in absorption systems are in general bulky and heavy; hence they are not usually used in compact systems. In addition, depending on the working mixture, they operate in a vacuum or at high pressures, which is in both cases a great disadvantage. In this study, a desorber/condenser was tested and modelled, using the Air Gap Membrane Distillation (AGMD) process, operating at atmospheric pressure conditions, with water/lithium bromide mixture for absorption system applications. The desorber/condenser used a membrane with a 0.45 μm pore size. Thirty-six experimental test runs were carried out at different operating conditions. A one-dimensional heat and mass transfer model was developed in order to describe the vapour water desorption from an aqueous LiBr mixture at atmospheric pressure conditions. The refrigerant desorption rate for the experimental conditions varied from 0.30 to 9.69 kg/m2 h. The theoretical refrigerant desorption rate calculated by the heat and mass transfer model agreed with the experimental data within ±10%. The results showed that the highest mass transfer resistance was at the boundary layer (1/Kbl) which increases with the increment of XLiBr and decreases with the increment of TLiBr.