Design and experimental demonstration of enabling components for simultaneous water purification and space conditioning using thermally driven absorption heat pumps

Abstract A horizontal-tube, falling-film heat exchanger capable of acting as an absorber or desorber in a small-scale (300-W cooling, 10.5 kg day−1 water purification) water-purifying absorption heat pump cycle was designed with LiBr as the absorbent. A design model for the heat exchanger that accounted for both heat transfer and mass transfer effects in the falling liquid film during desorption and absorption was formulated. Parametric studies were conducted for tube lengths ranging from 0.12 to 0.30 m and for absorber equilibrium solution outlet temperatures ranging from 35 to 45 °C. Based on the results of these simulations, a tube length of 0.24 m and an absorber equilibrium solution outlet temperature of 37.5 °C were selected. Batchwise experiments were conducted to validate the component model and determine the water purification potential of the cycle. Three feed solutions were tested: DI water, synthetic graywater, and 3.5 wt% NaCl. Measurements showed 90% removal of contaminants from synthetic graywater and 99% removal of NaCl from the 3.5 wt% NaCl solution. The measured heat transfer, after correcting for the presence of air in the chamber, demonstrated an average absolute deviation (AAD) of 18.6% for operation as an absorber and an AAD of 8.6% for the desorber.