Adiabatic vs non-adiabatic membrane-based rectangular micro-absorbers for H2O-LiBr absorption chillers

In this paper a microporous membrane is used in combination with rectangular microchannels in the absorber of an absorption chiller, working in two different configurations: cooled by a water flow and adiabatically. In the non-adiabatic case, the configuration of the channels allows the heat released during absorption to be extracted using a cooling water flow. The results for solution concentration, pressure potential, absorption coefficient, absorption rate, temperatures and power exchanged/stored by the working fluids along the absorption channels are presented. The ratio between the cooling power of the chiller equipped with the simulated absorber and the absorber volume, rqV, is used to characterise the absorber compactness. A parametric analysis is also performed to evaluate the influence on the ratio rqV of the inlet solution mass flow rate, the solution inlet temperature, and the height and width of the solution channels, for both absorbers. For the base case considered in this study, both absorber configurations offer rqV higher than 1 MW m−3. This ratio is higher than usual values found in falling film absorbers using conventional circular tubes. Moreover, the new adiabatic configuration presented has significant advantages respect to the non-adiabatic one in terms of higher rqV and fabrication simplicity.