Experimental study of wetting anisotropy and condensate drainage enhancement on microgrooved aluminum surface

Minimization of condensate (frost melt water) retention on a surface operating under frosting/defrosting condition is of tremendous importance in a wide range of air conditioning and refrigeration applications. In the present study, the wetting characteristics, condensation and frosting pattern and the drainage of frost melt water from aluminum surfaces with parallel microgrooves have been examined and compared to the flat baseline surfaces. These surfaces are fabricated by topographical modification only, via standard photolithographic process. The microgrooved samples exhibit wetting anisotropy and static contact angles are as high as 149 and 112° when viewed from parallel and perpendicular directions to the grooves, respectively. Frost is grown on the samples inside a thermally controlled chamber at 3 different plate temperatures of -8°C, -13°C and -18°C, air temperature of 20±2°C and for 3 relative humidity conditions (50%, 70% and 90%). The duration of the frosting cycle is 45 minutes and tests are continued up to 5 frosting cycles, each time defrosting for a certain length of time at the end of frosting period. Significantly different size, shape and distribution of condensed and frozen water droplets on the grooved surfaces are observed from that on the flat baselines. The microgrooved samples are found to manifest better water drainage behavior and drained up to 50% more melt water compared to the flat baseline surfaces. While the amount of water retention on the baseline surfaces increases in the subsequent refrost cycles and is highest in the 5^th frost cycle, the microgrooved surfaces show consistently improved water drainage in all cycles.