Influence of spray pressure and alcohol additive on spray cooling heat transfer mechanisms

The primary purpose of this paper is to ascertain the effect of spray pressure and alcohol additive on different heat transfer modes and mechanisms during spray cooling. Pure water with 0–8 vol% low-carbon alcohol additives is used to conduct spray cooling experiments at three spray pressures, and the liquid film characteristics are also measured. The results indicated that a higher spray pressure decreases and increases the temperature and mass flow rate of the liquid film, respectively. The total, convective and boiling heat transfer rates are all effectively improved at higher spray pressures, while the enhancement is more pronounced in heat convection compared to boiling heat transfer. By comparison, the alcohol additives exert much more significant heat transfer augmentation than spray pressure, especially the boiling heat flux in the later period of the nucleate boiling regime. The measurements also show that the enhancement intensifies and then weakens with increased alcohol content, reaching optimum heat transfer performance with 2 vol% methanol, 4 vol% ethanol, 4 vol% 1-propanol and 2 vol% 1-butanol. A nondimensional correlation of the boiling number is further developed to predict the heat flux in the nucleate boiling regime with a satisfactory mean relative error of 12.42%, which takes the alcohol-induced changes in the average spray characteristics and thermophysical properties into account.