SPRAY COOLING ENHANCEMENT BY ADDITION OF A SURFACTANT

An experimental study was done on the effect of dissolving a surfactan t in water sprays used to cool a hot surface. A copper surface was hea ted to an initial temperature of 240 degrees 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 photogra phed. Addition of the surfactant was found to enhance nucleate boiling heat flux by up to 300 percent. The surface temperature required to i nitiate vapor bubble nucleation was reduced from 118 degrees C to 103 degrees C. These effects were attributed to the surfactant promoting b ubble nucleation and foaming ill spray droplets. Nucleate boiling heat transfer enhancement was observed at all liquid mass fluxes and dropl et velocities in the range of our experiments. The surfactant slightly reduced transition boiling heat transfer and also reduced the tempera ture at which spray droplets started to wet the surface. Changing the orientation of the surface with respect to gravity had no effect on he at transfer.