Condensation, Frost Formation, and Frost Melt-Water Retention Characteristics on Microgrooved Brass Surfaces Under Natural Convection

摘要

In this study, frost is grown on microgrooved and flat brass samples under specific operating conditions and a comparison of the condensation, frosting, and defrosting pattern on microgrooved and flat brass surfaces is carried out experimentally. The surfaces are fabricated by a mechanical micromachining process and no chemical alteration of the surface is conducted. It is found that the shape, size, and distribution of condensed water droplets and the subsequent frost structure are significantly affected by the presence of microgrooves on the surface. The condensed water droplets take an elongated shape and then coalesce along the pillars and grooves on the microgrooved surfaces, giving a parallel "brick-wall-like" frosting pattern. The frost crystals on these microgrooved surfaces exhibit more directional growth parallel to the surface, with numerous ice flakes growing in the perpendicular and angular directions to the grooves. This nonuniform growth of the frost layer also gives the appearance of a spongy and loose frost structure and suggests the formation of less dense frost on the microgrooved surfaces. Both qualitative and quantitative studies of the spatial and temporal distribution of retained frost melt-water on the microgrooved and flat brass surfaces after defrosting are carried out by analyzing the thermal images of the sample surface, recorded during the defrosting period. Findings of this study can give insight into the frost properties and the defrosting and melt-water retention behavior of heat transfer equipments with embedded microgrooves.