Wettability and performance enhancement with durable super-hydrophilic surfaces for plastic liquid desiccant dehumidification systems

Abstract

Liquid desiccant air-conditioning systems are promising as they can achieve independent dehumidification. Non-metallic materials, such as plastics, are good internal working plate materials due to their natural anti-corrosion and easy-processing characteristics. However, poor wettability severely limits the application. In this study, the enhancement of surface wettability and mass transfer performance for liquid desiccant dehumidification with plastic internal plates was achieved, with a newly developed, durable, super-hydrophilic modified surface. The plastic plates were first etched into micro-rod structures to improve durability, and then the surfaces were prepared by adhering the super-hydrophilic SiO2 particles to the microstructures. Results showed that the liquid desiccant could completely spread on the coated plastic surfaces within 2 s, and the contact angle could be as low as 0°. Durability tests showed that after immersing in 40 wt% LiCl solution for 15 days, the liquid desiccant could still completely spread in 3 s. Furthermore, after 48 h of high-speed scouring (more than 1000 times of common conditions), the contact angle of desiccant maintained 0° on the coated surface, and fully spread within 22 s. By comparing coated to uncoated surfaces through experiments with dehumidification rigs, the wetted area of desiccant could be effectively increased by 1.5–5 times when the novel plates were used. The average film thickness decreased by 1.4–2.4 times and the moisture removal rate increased by 1.3–1.8 times for super-hydrophilic surfaces relative to original surfaces. For a case study with a typical building in Hong Kong, the annual energy consumption of air-conditioning systems could be predicated to decrease about 1/3 by using coated plastic plates. Therefore, this durable super-hydrophilic surface could significantly enhance the wettability, and thus enhance the performance of plastic LDACS. The manufacturing process of the surfaces is cheap and facile for industrialization. This study helps the optimization of liquid desiccant dehumidifiers, and other plastic applications with liquid-gas flows.