Performance evaluation and optimization of humidification-dehumidification desalination system for low-grade waste heat energy applications

Abstract

A humidification-dehumidification desalination system powered by low-grade waste heat energy (45 degrees C-70 degrees C) was experimentally investigated. The seawater directly utilized as coolant (25 degrees C) for the dehumidifier was preheated by latent heat recovery from the water vapor produced by the humidifier. The effect of key performance-contributing factors such as the mass flow rate and temperature of the air and feed at the inlets of the humidifier and dehumidifier were evaluated and optimized. For a constant volume, the effect of the humidifier's surface area was evaluated comparatively considering different novel packing materials such as tripack rings, pall rings (diameter = 16 mm and 25 mm), saddle rings, and snowflake rings. It was determined that compared to other factors, air-related and water-related parameters influenced the humidifier and dehumidifier performance respectively. Maximum freshwater productivity of 1398 mL/h was achieved with 16 mm pall ring humidifier, owing to its improved wet area (188,000 m(2)/m(3)) under optimal conditions of air flow rate, feed flow rate, humidifier air inlet temperature, humidifier, and dehumidifier water inlet temperatures of 3.5 kg/min, 0.9 L/min, 70 degrees C, 55 degrees C, and 25 degrees C, respectively, with a dual-fluid preheating mechanism. Detailed chemical analysis revealed that the generated freshwater is potable.