Advances in defrosting: exploring the use of surface treatment to promote frost layer delamination

This work explores defrosting effectiveness of aluminium surfaces of differing wettability, achieved through the application of surface micropatterning, two different silane coatings and/or a novel silica nanospring (SN) coating. Testing was performed on each sample within a controlled environmental chamber at a prescribed relative humidity and surface temperature and consisted of three cycles each of 1-h frost growth and 10 min of defrosting. Overall, surface defrosting effectiveness ranged from 42% to 96% across all tests. The data shows only small differences (typically 5-7%) in defrosting effectiveness between samples possessing either a self-assembled monolayer silane coating or microchannels alone. Furthermore, the microchannel surface with the superhydrophobic silane coating removed only slightly more water (typically 4-5%) during defrosting as compared with the uncoated microchannel surface although higher defrosting percentages (i.e. 9-10% higher) were occasionally recorded. By contrast, surfaces with the novel SN coating consistently exhibited more complete defrosting and drainage performance over other surfaces. Moreover, surfaces combining the microchannels and a SN coating exhibited a unique defrosting characteristic, 'frost layer delamination', in which large sheets of frost detached from the surface during defrosting. As a result, this surface exhibited superior defrosting performance, reaching 94-96% effectiveness in some cycles.This article is part of the theme issue 'Heat and mass transfer in frost and ice'.