Experimental study on condensation, frost formation and condensate retention on microgrooved and plain brass surfaces under natural convection condition

Abstract

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.

In this study, frost was grown on microgrooved and baseline brass samples under specific operating conditions and a comparison of condensation, frosting and defrosting pattern on microgrooved and flat brass surfaces were carried out experimentally. The surfaces were fabricated by mechanical micro-machining process and no chemical alteration of the surface was conducted. It was found that the shape, size and distribution of condensed water droplets and subsequent frost structure are significantly affected by the micro-scale roughness on the surface. The condensed water droplets took an elongated shape and then coalesced along the pillars and grooves on grooved surfaces giving a parallel brick-like frosting pattern. The frost structure on the grooved surface was different than that on the flat surface and frost crystal exhibited more directional growth in the parallel to the surface direction, with numerous ice-flakes growing in the perpendicular and angular directions to the grooves. This non-uniform growth of the frost layer also gave the appearance of a spongy and loose frost structure and suggested the formation of less dense frost. Qualitative study of the spatial and temporal distribution of retained condensate on the grooved and plain brass surfaces after defrosting were carried out by analyzing thermal images of the sample surface during the defrosting period. Findings of this of this study can give significant insight about the frost properties and defrosting and condensate retention behaviour of heat transfer equipments with embedded microgrooves.