Water Condensation and Droplet Shedding Behavior on Silica-Nanospring-Coated Tubes

In this work, the water condensation performance of methylated silica-nanospring (SN)-coated horizontal aluminum tubes is assessed. Coated samples with varying nanospring mat thicknesses, from 784 to 2902 nm, were studied, which exhibited static contact angles and CA hysteresis values of 155 degrees and 16 degrees, respectively. Dropwise condensation and increased droplet shedding were observed on these coated tubes. Video analysis determined that tubes with 15 and 20 min SN growth times experienced an 84% increase in the condensate removal rate over the baseline. Moreover, with a hybrid wettability consisting of alternating regions of SN and bare aluminum, a 96% increase in condensate removal was experienced. Additionally, the average droplet departure size was reduced on these SN-coated tubes. SEM imaging and XEDS analysis were also performed on the tubes and revealed that the coating was reasonably durable having withstood the condensation environment. Moreover, the coated tubes were shown to exhibit the same XEDS spectra both before and after testing.