Comparison of frosting, defrosting and condensate retention characteristics of vertical parallel microgrooved and plain brass surfaces in forced convection condition

Abstract

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.In the present study, condensation, frosting and condensate (frost melt water) retention characteristics of brass surfaces with parallel microgrooves have been investigated experimentally and compared with the plain baseline surface. Parallel micro-scale surface features were obtained by a mechanical micromachining process (micro end-milling) without applying any chemical means to modify the surface energy. The surfaces exhibited anisotropic wettability with high static contact angles (SCA) of 1320 to about 1460 in the direction parallel to grooves. Frost was grown on sample surfaces (45 mm x 45 mm) inside a thermally controlled chamber, in the presence of very cold surrounding air (≈ -60C) under forced convection condition (air velocity of 0.25~1.0 m/s). Condensation and frosting pattern as well as condensate retention characteristics of the microgrooved surfaces were found to be significantly different than on the flat brass surfaces. Highly improved condensate drainage behavior was obtained for the microgrooved surfaces which drained up to 70% more condensate than the flat baseline. It was found that variation in the wettability (static contact angle) of the microgrooved surfaces significantly affects the condensate drainage characteristics. Improved condensate drainage was achieved for surfaces with higher static contact angle and lower wetting anisotropy. Variation of operating parameters (plate temperature, frost surface temperature etc.) during defrosting at different heating rate was also investigated. The findings of the present work provide valuable information on the frosting/defrosting characteristics of microgrooved surfaces signifying its possibility for better condensate management in a broad range of air conditioning, refrigeration and cryogenic applications.pm201