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%.