An experimental study of condensation on an aluminum radiant ceiling panel surface with superhydrophobic treatment

Abstract

One of the factors that limit the cooling capacities and application potentials of radiant cooling panels is the condensation risk. The self-condensate-repellency tendency of superhydrophobic surface materials provides a possibility to mitigate the condensation risk. This paper studied the size ranges of condensate drops formed on a superhydrophobic aluminum sheet of the size 25 mm × 25 mm attached to a cooled ceiling panel in a climate chamber in the humidity range between 50% and 80% and at the temperature of 25 °C and air change rates from 0 ACH to 9 ACH. Using an optical magnifier, large drops up to the size 802.5 µm were observed in certain fixed positions in the large view area of 4.08 mm × 3.06 mm under different experimental conditions; whereas in a smaller focused view area of 0.96 mm × 0.72 mm the diameters of the largest drops were found to first increase over time and then reached around 80 µm with occasional size of 152 µm. All these were in contrast with the continuously growing drops simultaneously observed on the ordinary aluminum sheet, which reached 4 mm. The largest size of the droplets in the small focused area increased from 54.1 µm to 151.7 µm as humidity increases from 50% to 80%, but did not change much as the air change rate changed from 0 ACH to 9 ACH. This series of experiments confirm our hypothesis that condensate drop sizes can be limited within the un-perceivable range, namely below the sensory and visual thresholds, in typical indoor conditions because of the droplet jumping mechanism that occurs on the nano-engineered superhydrophobic surface, but it remains to be ascertained whether the large condensate drops formed at certain fixed points in the other parts of the tested nanostructured surface were associated with some defects in the nano-scale, and whether this can be eliminated on a larger area of practical application scale.