Heat and Mass Transfer in Parallel Flow Mist Cooling

The lasing gain media (LGM) of the solid-state heat capacity laser (SSHCL) need to be cooled in a short time in between laser operations to increase the duty cycle. Parallel flow mist cooling is an attractive option to accomplish this. However, no general correlations exist to predict parallel flow mist cooling heat transfer for various fluids. In order to obtain such a correlation this study was undertaken. Drop size distribution from different nozzles was characterized by laser Doppler anemometer. A parallel flow mist cooling experimental set-up was designed and fabricated. Data from over 300 experiments with air, air-water mist, air-denatured ethanol mist and air-pure ethanol mist was obtained. The parameter ranges were: flow velocity between 5 and 50 m/s, drop diameters between 18 and 75 μm, mist concentrations as high as 0.2 kg/m³, heat fluxes up to 170000 W/m² and hydraulic diameters between 0.003 and 0.008 m. An enhancement of up to a factor of six relative to the heat flux removed by air was obtained. The experiments indicated that there are four regimes in parallel flow mist cooling. These are: 1) Mass transfer, 2) Forced convection 3), Critical Heat Flux and 4) Film boiling. Two general correlations for parallel flow mist cooling are proposed for the first two of these regimes.