Study of a nano-coated hydrophilic polymer for indirect evaporative cooler from wetting, thermal and corrosion resistance performance

Abstract

Hydrophilicity and evaporation rate of the wet channels play crucial effects on the cooling performance of an indirect evaporative cooler (IEC). Thus, great efforts are made to develop high-performance wet surface materials for IECs. However, current studies of hydrophilic coatings focus on the moisture diffusion ability of the material itself or the overall thermal performance of an IEC, with less in-depth research on the internal local thermal and quantitative wetting performance under various operating conditions. In this study, a TiO2/SiO2 nano-coating is applied to polypropylene (PP) by three treatment methods to develop a hydrophilic durable and corrosion-resistant PP for IEC application. Firstly, the hydrophilic durability of various samples was tested for 30 days. Secondly, test rigs were built for wetting and thermal performance investigation. The wetting performance was studied by both the drop-impact interaction test and the falling film experiment. The flow pattern, water film thickness, and wettability ratio were investigated under varying water flow rates, air velocity, and water distribution strategies (continuous spray, intermittent spray). The thermal performance including the internal wall temperature and supply air temperature of non-coated and coated IEC were comparatively tested. Finally, the corrosion resistance ability of samples was tested by acid salt spray. The results show that primer-aided TiO2/SiO2 coating on PP can provide durable hydrophilicity and corrosion resistance. Gaining better water retention ability, the thermal performance of nano-coated IEC can be enhanced under intermittent spray with 1.1 °C lower plate temperature and wet-bulb efficiency improved from 74.4 % to 81.4 % compared to the non-coated one.