Condensation heat transfer on phase change slippery liquid-infused porous surfaces

Abstract

Phase change slippery liquid-infused porous surfaces (PC-SLIPSs) are presented with emphasis on surface wetting characteristics and droplet dynamics influencing the water vapor condensation and the corresponding heat transfer. The functionalized nano-porous copper plate is infused with paraffin wax-xylene solution via dip coating method to prepare PC-SLIPSs., where the droplet dynamics are found to be affected by low adhesion (sliding angle α of 45±5°), high adhesion (α of 60±5°) and slippery (α of 3 ± 1°) states enabled by solid (at 48 °C), mush (at 58 °C) and liquid (at 66 °C) phases, respectively. Besides the wettability and droplet adhesion characterization, the condensation heat transfer is particularly explored on PC-SLIPSs in custom-built vacuum-assisted condensation rig. Two major dropwise condensation mechanisms are unveiled depending on the phase of the infused phase change material, such as coalescence-induced droplet shedding coupled with droplet sweeping in the solid and mush phases, while discrete-droplet shedding and sweeping in the absence of additional coalescence are reported in the liquid phase. Approximately, 136.8% higher heat transfer coefficients for PC-SLIPS in the liquid phase are reported when compared with the pristine copper surface at low sub-cooling temperatures. In the liquid phase of PC-SLIPSs, theoretical heat transfer modeling on dropwise condensation has been further carried out to elucidate the heat transfer mechanism via a single droplet coupled with the droplet number density. The operational durability of PC-SLIPSs has been found to last for 8 ± 1 h as confirmed during rigorous condensation experiments. In summary, different wetting features, various droplet shedding mechanisms, promising dropwise condensation modes, high heat transfer coefficient in the liquid phase, and effective time-dependent durability are the salient findings associated with PC-SLIPSs, rendering them competitive alternatives. The most important implication is that the dropwise condensation mode can also underperform if the droplet dynamics is inefficient.