Experimental and analytical investigations into enhanced peak boiling heat transfer from capillary fed porous media

Experimental and analytical techniques for enhancing the peak boiling heat transfer limit from capillary fed porous media have been investigated. The possibility of increasing peak heat transfer limits through the use of binary coolants was investigated experimentally. Ethanol, water and ethanol-water mixtures were tested with a hollow cylindrical porous structure heated from within. The porous structure was fabricated from four layers of 325 mesh stainless steel screen wrapped around a vertical tube. This wick/tube assembly was used to measure steady state and peak heat fluxes as a function of mixture composition and capillary rise height. For short capillary rise heights the addition of small amounts of ethanol to water is shown to increase peak heat transfer limits by 135% over that of pure water. As capillary rise height is increased the performance of ethanol-water coolants becomes comparable to that of pure water.; A one-dimensional, two-phase analytical model for single component fluids is also presented. The model is used to investigate the influence of design parameters on the performance of porous wick structures for use in cylindrical and flat plate heat pipes. Measured peak heat flux values for the screen wick are in reasonable agreement with predictions from the model for pure water and ethanol. Predicted peak heat transfer rates for two cylindrical sintered-copper wicks are in agreement with experimental results to within 10% for pure water. Optimized flat plate and cylindrical sintered wick structures are shown to be theoretically capable of dissipating heat fluxes up to 50 and 100 W/cm{dollar}sp2{dollar}, respectively, with water as the coolant.