CONDENSATION OF LOW-SURFACE-TENSION FLUIDS ON MICROSTRUCTURED SURFACES AT LOW TEMPERATURE

Filmwise condensation of a low surface tension fluid (i.e. refrigerant) on microstructured aluminum surfaces is studied to investigate the effect of the structures on condensation heat transfer at low temperature. The hypothesis is that the structures may cause thinning of the condensate film at micro-scales, thus resulting in an enhancement of condensation heat transfer. However, the structures may also decrease the mobility of the condensate near the surface due to increased friction, thus potentially leading to performance deterioration. The aim of this work is to investigate which of the two counteracting mechanisms dominate during filmwise condensation. Condensation experiments are carried out in a low-temperature vacuum chamber. Compared with the Nusselt model of condensation, the microstructured surfaces, either coated or uncoated, show similar performance, with potentially slight enhancement at low subcooling degree and slight deterioration at high subcooling degree. When the microstructured and silane-coated surface is infused with a non-volatile and very low surface -tension lubricant oil, the lubricant is displaced by the condensate and there is almost no change in the condensation performance. Our results show that, unlike the case of dropwise condensation of high-surface tension fluids, microstructured and coated surfaces with/without infusing oil is not exciting to enhanced filmwise condensation of low-surface-tension fluids.