Performance of an air-cooled membrane based microchannel desorber-condenser working with LiBr-water

Abstract

Absorption Refrigeration Systems can help to mitigate the environmental effect of the increasing energy demand in buildings. However, the size and the need of a cooling tower slow down their development. In the present study, a compact air-cooled desorber-condenser working with the LiBr-H2O solution is experimentally tested. The desorber is a stainless-steel plate provided with mini-channels. On one side water flows to heat the solution circulating in counter current flow through the other side of the plate. The vapour generated from the solution permeates through a flat membrane and directly enters the cavity of an air-cooled finned condenser. The membrane is a polytetrafluoroethylene (PTFE) membrane with a pore diameter of 45 μm. The assembly is tested for three different solution flow rates (40, 50 and 60 ml/min), three heating source temperatures (70 °C, 80 °C and 90 °C) and three inlet solution concentrations (43%, 46% and 50%wt). Measured desorption rates range from 3.10−3 to 14.10−3 kg/m2s. Heat and mass transfer in the desorber is characterized and pressure drop along the channels is also provided. Pressure drop along the solution channels varies from 70 to 105 Pa/m. The experimental results compare well with theoretical values calculated using correlations from the literature. The air-cooled condenser is able to condense the generated vapour at a rate ranging from 30 W to 100 W.