Spray Cooling Enhancement by Addition of a Surfactant

Abstract

An experimental study was done on the effect of dissolving a surfactant in water sprays used to cool a hot surface. A copper surface was heated to an initial temperature of 240°C and then rapidly cooled using a spray of either pure water or an aqueous solution containing 100 ppm by weight of sodium dodecyl sulfate. The variation of surface temperature was measured during cooling, and spray impact was photographed. Addition of the surfactant was found to enhance nucleate boiling heat flux by up to 300 percent. The surface temperature required to initiate vapor bubble nucleation was reduced from 118°C to 103°C. These effects were attributed to the surfactant promoting bubble nucleation and foaming in spray droplets. Nucleate boiling heat transfer enhancement was observed at all liquid mass fluxes and droplet velocities in the range of our experiments. The surfactant slightly reduced transition boiling heat transfer, and also reduced the temperature at which spray droplets started to wet the surface. Changing the orientation of the surface with respect to gravity had no effect on heat transfer.