Heat transfer to sub-cooled binary solution in horizontal tube

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

Predicted heat transfer coefficients (HTC) are widely used for calculations of various heat transfer processes. Various empirical and semi-empirical models of non-dimensional groups are used for calculating the heat transfer coefficients. The common accuracy of the predicted heat transfer coefficient is usually about ±25%; however, the accuracy is failing by the inaccurate predictions of the fluid properties. In the present study the heat transfer coefficient of subcooled organic mixture chlorodifluoromethane (R22) - dimethylacetamide (DMAC) were predicted. While the solution’s pressure-temperature-concentration, densitytemperature- concentration and viscosity-temperatureconcentration relations were previously measured in our laboratory and the heat capacity were calculated from the enthalpy of the solution, the only unknown property that was required for predicting the HTC was the mixture thermal conductivity. Various correlations and mixing rules for the mixture thermal conductivity were adopted for predicting the heat transfer coefficient. In order to validate the predicted heat transfer coefficients, an experimental system was designed, built and successfully operated. The heat transfer coefficient was measured experimentally and compared with the predicted one. Based on this comparison the best fitted thermal conductivity for the working fluid (R22-DMAC) is recommended. As a result, the deviations of the predicted heat transfer coefficients, obtained by the well-known Dittus-Boelter equation, from the experimental values were less than 15%.