Effects of wide-range copper surface wettability on spray cooling heat transfer

Abstract

This study conducted a spray cooling experiment to investigate the effects of varying surface wettability on the heat transfer performance of modified copper surfaces in both single- and two-phase regimes. The contact angles of the test surfaces ranged from 0° to 150°. The spray cooling experiment was performed using deionized water. The results indicated that surface wettability influenced heat transfer performance during spray cooling. In the nonboiling regime, the surface with higher hydrophilicity exhibited higher heat transfer performance owing to the larger wetting area available for heat transfer. The surface temperature of the superhydrophobic surface reached saturation at a relatively low heat flux; therefore, nucleation occurred rapidly, and the increase in the heat transfer coefficient intensified as the heat flux increased. Consequently, the heat transfer performance of the hydrophobic surface exceeded that of the plain surface in the two-phase regime. Evaporation fraction values were derived for the various test surfaces. Finally, a dimensionless surface wettability number, defined as the ratio of the droplet contact diameter to the droplet height, was used to establish heat transfer prediction models considering surface wettability in the single-phase and two-phase regimes. The heat transfer performance in the single-phase and two-phase regimes could be predicted within error bands of 18 % and 33.3 %, respectively.