Pool boiling heat transfer of N-pentane on micro/nanostructured surfaces

In the present study, one type of uniformly nanostructured surface (NPDS) was modified by electrophoretic deposition. Two kinds of micro/nanostructured surfaces (FLS1 and FLS2) were fabricated on copper surfaces by femtosecond laser processing. The micro/nanostructured surfaces were further modified by electrophoretic deposition. Afterwards, composite micro/nanostructured surfaces (CS1 and CS2) were developed. Saturated pool boiling heat transfer of the modified surfaces was investigated experimentally. An organic fluid, n-pentane was chosen as the working liquid. Heat transfer coefficient and critical heat flux (CHF) of smooth and micro/nanostructured surfaces were studied. The results showed that the heat transfer coefficient (HTC) of all structured surfaces increased obviously with a notable decrease of wall superheat at CHF compared to the smooth surface, which was attributed to increments in nucleation site density and heat transfer area. The CHF of femtosecond laser processed surfaces was also increased compared with the smooth surface due to a much higher liquid spreading ability, while a uniformly nanostructured surface has no augmentation in CHF. Composite micro/nanostructured surfaces show the best heat transfer performance among all tested surfaces, and the critical heat flux and heat transfer coefficient were increased by more than 60% and 300% over the smooth surface, respectively. The liquid spreading ability of n-pentane on the tested surfaces was measured. For the well wetting liquid, the liquid spreading ability of the heated surface, instead of the wettability, is the main factor for CHF enhancement. It is suggested that a surface with multiscale structures can be an efficient way for boiling heat transfer enhancement.