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

Abstract

A humidification–dehumidification desalination system powered by low-grade waste heat energy (45 ◦C–70 ◦C) was experimentally investigated. The seawater directly utilized as coolant (25 ◦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 hu- midifier's surface area was evaluated comparatively considering different novel packing materials such as tri- pack 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 dehu- midifier 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 m2/m3) 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 ◦C, 55 ◦C, and 25 ◦C, respectively, with a dual-fluid preheating mechanism. Detailed chemical analysis revealed that the generated freshwater is potable.