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.
