Investigations on a solar humidification dehumidification desalination system equipped with various packing materials and multi-stage bubble column dehumidifier

This work presents the theoretical and experimental investigation of a solar-powered humidification dehumidification desalination (HDD) system with different humidifier packing materials and a two-stage bubble column dehumidifier (BCD). Naturally available coconut shells (CS) and coconut shells with drilled holes (CSH) on the surface to improve water permeability were used as packing materials in the humidifier, and their performance was compared with that of commercial-type pall ring (PR) and raschig ring (RR) packings. An in-house developed numerical model of the HDD system in conjunction with a flat plate solar water collector was used in this study. Steady-state experimental results showed that CSH packing exhibited the highest volumetric mass transfer coefficient (0.00852 kg/s), resulting in maximum humidifier efficiency (96%) and freshwater yield (2.16 kg/hr), followed by PR (0.00841 kg/s, 94%, and 2.137 kg/hr), CS (0.00831 kg/s, 90%, and 2.127 kg/hr), and RR (0.0081 kg/s, 81%, and 2.087 kg/hr) at feedwater mass flow rate of 1.5 kg/min and humidifier inlet temperature of 75 degrees C. Furthermore, transient outdoor test results showed that using a two-stage configuration in a BCD increased the daily average effectiveness to 0.93, as against 0.79 for a single-stage BCD. Employing CSH instead of PR and RR packings in the humidifier reduced freshwater costs by 6.2% and 7.6%, respectively.