Experimental study of non-boiling heat transfer from a horizontal surface by water sprays

The results of an experimental study on non-boiling heat transfer from a horizontal surface by a pressure atomized water spray are presented here. A vertical circular copper cylinder was electrically heated from below; its top surface was spray cooled and sides were insulated. The target surface diameter was 20 mm. The spray was produced from a nozzle supplied with distilled water from a pump. The heat flux to the surface was 35–85 W/cm2 and the surface temperature was maintained below 95 °C. The water mass flux varied from 2.6 to 9.9 kg/m2 s, which gives spray Reynolds number of 65–285 based on the target surface diameter. Under steady state conditions, the heat transfer coefficient was between 9000 and 24,000 W/m2 K; increasing with the increase in the mass flux. The results of the study have been utilized to develop an empirical correlation, which relates the average Nusselt number to the spray Reynolds number. The experiments show that even for non-boiling conditions with a spray, heat transfer coefficients are significantly larger than for forced convection.