APPLICATION OF DIELECTRIC BINARY MIXTURES IN ELECTRONIC COOLING — NUCLEATE POOL BOILING REGIME

Abstract

This paper presents experimental results on nucleate pool boiling in dielectric mixtures. A silicon thermal test chip was immersed in a pool filled with perfluoropolyether binary mixtures. Two pure liquids, D80 and HT110, were mixed by volume as 0%, 20%, 50%, 80%, and 100%. All experiments were performed under 50°C subcooling at one atmospheric pressure. The results indicated that nucleate boiling curves were close to each other among pure liquids and mixtures. As more less-volatile liquid (HT110) was added, the mixture boiling curve shifted to the left and merged with that of the pure liquids. The boiling heat transfer coefficient increased linearly with rising heat flux. At all heat flux levels, the boiling heat transfer coefficient decreased as more less-volatile liquid was added and reached a minimum value at the 20/80% mixture of D80/HT110. The perfluoropolyether binary mixtures showed deterioration in heat transfer coefficient similar to the hydrocarbon mixtures. The measured values were always less than the ideal heat transfer coefficients obtained from a linear interpolation of values corresponding to the single components. The degree of degradation in heat transfer coefficient decreased as the heat flux increased for a given composition. The maximum heat transfer degradation did not occur at the same liquid composition for different heat flux levels: it occurred at the 50/50% mixture for two lower heat fluxes, and at the 20/80% mixture of D80/HT110 for two higher heat fluxes. Prediction of vapor mole fraction was also pursued. The results indicated that the maximum mole fraction difference between vapor and liquid phases existed at the 50/50% mixture. This particular composition did not always reflect the occurrence of the maximum heat transfer degradation, as it was reported in the hydrocarbon mixtures. Experimental data were tested with two empirical correlations with good agreement.