Viability on the desorption and air condensation of water in a compact membrane-based microchannel desorber-condenser for cooling applications

Abstract

A new membrane-based desorber, directly coupled with an air-cooled condenser is experimentally tested. The working fluid is a LiBr-H2O solution that flows through the desorber in micro channels 2 mm width and 100 μm thick. To desorb the vapour from the solution, hot water circulates in a counter flow arrangement in channels, with the same geometry. A hydrophobic membrane with a pore diameter of 45 μm separates the confined solution from the cavity where the generated vapour is immediately condensed. Forced air convection is used to cool the finned condenser. The experimental performance of the new compact design is evaluated. Tests have been carried out varying the solution mass flow rates (40 ml/min, 50 ml/min and 60 ml/min) and the heating water temperatures (70 °C, 80 °C and 90 °C). The experiments show the viability of operation of the new design (combination of desorber and air-cooled condenser in a unique compact device) with the production of 0.1 to 0.17 kg/h of water vapour when the power input to the desorber ranges from 150 to 275 W. The heat simultaneously dissipated in the condenser ranges from 60 W to 120 W at condensing temperatures in the range from 37 °C to 47 °C. Desorption rates obtained vary from 0.002 to 0.004 kg/m2s. Measured pressure drops through the micro channels are in the order of 70 Pa/m. The results demonstrated the feasibility of increasing compactness in absorption systems with a performance of cooling power to total volume ratio of a chiller, equal to 10.75 kW/m3, higher than conventional systems.