Theoretical and experimental investigation of a pilot-scale solar air-heated humidification dehumidification desalination system

Abstract

Among the various humidification dehumidification desalination (HDD) system configurations, the air-heated cycle has demonstrated promising results in small lab-scale setup investigations, whereas pilot-scale studies are lacking. This study theoretically and experimentally investigates the performance of a pilot-scale flat-plate solar air collector-powered HDD unit. An optical-thermal model for a solar air collector and a transport model based on heat and mass transfer for the dehumidifier have been developed and validated using experimental data. The triangular-shaped turbulators on the absorber plate of a solar collector with relative roughness pitches of 2.3, 4.61, and 6.92 are built and optimized for maximum distillate yield. Perforated turbulators with open area ratios of 5.5 %, 12.25 %, and 21.8 % are evaluated. To reduce distillate production costs in the HDD system, naturally available wood apple shell with drilled holes is tested in the humidifier. Outdoor test results revealed that at an average solar intensity of 712 W/m², the proposed system achieved a maximum distillate yield and gain output ratio of 17.34 kg/day and 0.65, respectively. Wood apple shell packing demonstrated better distillate yield, gain output ratio, and humidifier performance potential factor compared to the commercially available raschig ring and cascade mini-ring packings. Moreover, the optimal performance of the solar air collector with solid turbulators was obtained at a relative roughness pitch of 4.61 due to sufficient longitudinal space to effectively prevent flow separation and reattachment of the free shear layer. Turbulators with a 12.25 % open area ratio exhibited the highest Nusselt number and low friction factor.