Heat Transfer Coefficients and Transport Properties for Alternative Refrigerants

Practical and empirical equations of transport properties have been developed for refrigerant compounds. These equations have been used to develop correlations for experimental heat transfer coefficient (IITC) for both evaporation and condensation in smooth tubes. Model calculations have been compared with recent experimental data, and reasonable agreement has been obtained. INTRODUCTION We have previously presented IITC models for alternative refrigerants(!>. The transport properties in the models were largely based on published correlations recommended by Jung and Radermacher(2>. Since then, we have initiated laboratory experiments on the important transport properties such as viscosity and thermal conductivity for several alternative refrigerants(3>. At the same time, additional experimental data on condensation/evaporation IITC of several alternative refrigerants have been collected(4-7>. The new experimental data were used to improve our earlier correlations. In this report, we describe our correlations for both transport properties and IITC based on the new experimental data. Our intention is to make practicaVuseful correlations as general as possible. Instead of using individual experimental data (correlations) for each compound, rather generalized equations, which are based on characteristic properties of compounds such as critical point, molecular weight, etc., will be considered. In this way, necessary properties for any unknown/known alternative refrigerants may be universally calculated with little information, although the accuracy in such equations may be lower than that in experimental data correlations. Often in practice, the generality is more useful if the accuracy is reasonable. We regard uncertainties within 10-20% in both transport propertiesiHTC to be reasonable. With keeping these goals in mind, our correlations will be presented, and several examples compared with experimental data will be shown. · MODELING A) Transport Properties In this section, modeled correlations of viscosity, thermal conductivity, heat capacity, and surface tension are given with minimum explanation, since the equations are essentially empirical. A-1) Viscosity For pure compounds, when exllerimental data are not available, the following corresponding-state correlation has been developed to use for the liquid phase viscosity: