Techniques of infrared thermography were used to conduct an experimental study of the evaporative cooling of a hot, low thermal conductivity, non-metallic surface heated by radiation and subject to a random array of impinging water droplets. A droplet generating and distributing apparatus and a data acquisition system employing digital image analysis devices were also developed and implemented. Real time infrared images of the heated surface were recorded and digitized using computer resident frame grabbing hardware and analyzed on a pixel by pixel basis, giving a high degree of thermal and spatial resolution. From these analyses, the instantaneous surface temperature distribution and transient surface temperature profile were obtained for a range of initial temperatures and impinging mass fluxes. The surface temperature was found to decay exponentially with time to a steady state value for the fluxes used. Three dimensional plots of the temperature distribution on the surface also showed the significant lowering of the average surface temperature, and provided a qualitative description of the cooling phenomena at various stages during the transient. Results obtained will be used in the future validation of a computer model of the phenomena.

We have performed a series of experiments to characterize the different regimes observed in drop impacts during evaporative cooling of heated surfaces. We found four regimes which were named splashing, fizzing, flat film, and marbling based on the dynamic properties of the drop impact. We found that the emergence of these regimes is primarily controlled by the Jacob number, a dimensionless group describing the ratio of sensible to latent energy absorbed during liquid-vapor phase change. Using our classification scheme, we can predict a range of useful Jacob numbers to use in the cooling of electronic components. From these Jacob numbers, we can extract the material properties of a fluid required to cool a given system.