Flow boiling heat transfer and pressure drop for zeotropic mixtures in a horizontal tube
Conference contribution, 1994
Flow boiling heat transfer and pressure drop have been measured in a horizontal tube. The mediums used have been three mixtures of HCFC22 and HCFCI42b, two mixtures of propane and n-butane, and the pure substances HCFC22, HCFCI42b, propane and n-butane. The experimental facility was constructed to resemble a direct expansion evaporator typical for larger heat pumps. The evaporator is 5 metres long and divided into 10 half-metre sections. The results of the measurements show a large decrease in heat transfer during vaporization of mixtures, as compared to the predicted heat transfer using the thermodynamic properties of the mixtures in correlations working well for the pure constituents. The decrease for 50/50% mixtures was about 27- 32% and for 20/80% mixtures 19-24%. The measured heat transfer and pressure drop have been compared with existing correlations from literature (20 for heat transfer and 12 for pressure drop). The correlation most accurately predicting the measured data for pure substances in this paper was the correlation of Klimenko. Including the Thome-Shakir mixture boiling correction factor, the Klimenko correlation also predicted the mixture data with good agreement. For pressure drop, a number of correlations predicted the data well both for pure substances and for mixtures.