Experimental study of pool boiling characteristics for non-azeotropic mixtures n-pentane / n-hexane on microstructure surfaces

Mixed alkanes are widely used as refrigerants in applications such as natural gas liquefaction, especially in the Floating Liquefied Natural Gas (FLNG) process. To elucidate the mechanisms underlying the weakening of phase transition in mixed refrigerants and to develop enhanced heat transfer methods, a pool boiling experimental setup is established in this study to investigate the boiling heat transfer characteristics of n-pentane/n-hexane mixtures on three different microstructure surfaces. By combining visual observation of bubble dynamics with analysis of the effects of composition conditions, micro-surface geometry, and wall heat flux conditions on the boiling heat transfer characteristics, it is revealed that the heat transfer coefficient (HTC) on the pyramid surface and the cylindrical surface, compared to the smooth surface, maximum increase by up to 345 % and 203 %, respectively. Compared with pure components, the mixture with a mass fraction of 0.5 n-pentane shows the greatest heat transfer deterioration. Microstructure surfaces significantly enhanced the HTC of the mixed refrigerants. Additionally, the microstructures activate more nucleation sites and higher bubble departure frequency. The guiding effect of the pyramid surface effectively decreases the possibility of bubble aggregation under high Eo and Ga numbers, thereby delaying the formation of mushroom bubbles. Therefore, the pyramid surface shows its advantages at different component ratios. The HTC correlations for pure and mixed refrigerants are developed. The predictions for pure and mixed refrigerants HTCs agree with most of the experimental data with a deviation of ±10 % and ±25 %, respectively.