A new approach to enhance the heat and mass transfer of liquid desiccant dehumidification with a titanium dioxide superhydrophilic self-cleaning coating

Abstract

The cooling system with liquid desiccant dehumidification is an energy-efficient and eco-friendly solution for the ever-increasing energy consumption and environmental impact of modern buildings. By significantly influencing the wetted area, the contact angle of the liquid–air interface is critical to the performance of desiccant dehumidification. In this study, to enhance heat and mass transfer performance, a new approach was developed with a titanium dioxide superhydrophilic self-cleaning coating on the dehumidifier surfaces that was made of a highly dispersed paste with nanoscale titanium dioxide particles and activated with ultraviolet light. We first tested the effect of the coatings on samples made of three commonly used materials, SUS304, SUS316, and SUS410, with a 30% LiBr solution and deionized water. Results show that the contact angle on the coated samples dramatically decreased to only 1/7 for water and 1/6 for the LiBr solution compared to uncoated samples. The durability of the coatings was studied experimentally by repeatedly immersing the samples in 30% LiBr, exposing them for 2 months, and reactivating them. It was found that the angle changed slightly for SUS304/316 samples with good anticorrosion performance, whereas the angle increased by 10°–20° for SUS410 samples due to the accelerated catalytic oxidization of the Titanium dioxide coating, which could possibly be solved by precoating an SiO2 compact layer. Furthermore, we found numerically that the wetted area during desiccant dehumidification could be effectively increased by 5–7 times with the coating. Accordingly, the heat exchange rate and moisture removal rate between the air and the desiccant could be increased by 1.2 and 2 times, respectively. Therefore, by dramatically reducing the desiccant contact angle on dehumidifier surfaces and enlarging the wetted area accordingly, the titanium dioxide self-cleaning coating could significantly improve the heat and mass transfer performance of liquid desiccant dehumidification, especially the mass transfer performance. The coatings' manufacture is cheap and facile for industrialization. This measure can be considered an effective and economic way to improve the performance of a dehumidifier and also has other applications in heat exchangers, evaporators, and absorption towers.