Effects of microgroove geometry on the early stages of frost formation and frost properties

Abstract

The variation of frost structure and properties with groove geometry on microgrooved brass surfaces (45 mm × 45 mm) is examined through an experimental study. Frost is grown on a number of microgrooved brass samples having a wide range of groove dimensions (groove depth ≈ 27–122 μm, pillar width ≈ 26–187 μm and fixed groove width of 130 μm), and on one flat baseline surface under a range of substrate temperature and relative humidity conditions. Frost structure on the microgrooved surfaces, especially at the early stages of frost formation, is found to be significantly affected by a variation of the groove geometry. Depending on the rate of cooling of the substrate and variation of the groove geometry, the condensed droplets, which predominantly form on top of the pillar surfaces, either merge with the droplets on the grooves and fill the grooves completely, or bridge with droplets on the adjacent pillars and grooves, or freeze on the top of the pillars. These differences in the initial frost formation pattern are also found to considerably affect the thickness and density of the frost layer in frosting cycles up to 4 h long. Microgrooved samples with the deepest groove (122 μm) and widest pillar (187 μm) within the sample space, which exhibit similar frost structure at the early stages of frost formation, are found to have lower frost thickness and higher frost density among all the microgrooved samples. The relationship between the frost structure and frost properties with groove dimensions is discussed, emphasizing the importance of the morphological features.