Enhancing the cooling and dehumidification performance of indirect evaporative cooler by hydrophobic-coated primary air channels

Abstract

An indirect Evaporative Cooler (IEC) for air-conditioning (AC) energy recovery is a rapidly developing technology and has great potential applications in hot and humid regions. As the cooling potential of exhaust air is captured to evaporate the spraying water, the humid fresh air in adjacent channels can be cooled with moisture extracted. The condensation of fresh air can pose significant influences on the cooling and dehumidification performance of the cooler. However, the effect of surface modification on both sensible and latent heat transfer in dry channels of IEC was hardly discussed in the literature. In this paper, a novel IEC heat exchanger was proposed by depositing the hydrophobic nanoparticles on the surfaces of primary air channels. Visualized experiments were carried out to compare the condensation heat transfer mechanisms as well as the effects of influence factors on the performance of the hydrophobic-coated IEC and the traditional un-coated one. Results show that, larger irregular droplets drained off as water film was observed on the bare-aluminum plate, while the hydrophobic surface promoted dropwise condensation with a smaller droplet diameter. The minimized size of falling-off droplets and frequent droplet removal can enhance the convective heat transfer of the processed air flowing over the coated plate surface. The hydrophobic coating treatment on the primary air channel surfaces increased the energy-saving rate of IEC by 8.5–17.2%, which can potentially be utilized in AC applications under dehumidifying conditions.