Abstract
This paper reviews currently available experimental evidence and predictive techniques for heat transfer and pressure drop during film condensation in horizontal micro-fin tubes, as used in heat pump systems. The enhanced heat transfer mechanism of condensation using micro-fin tubes is explained, and special attention is paid to the dependence of heat transfer and pressure drop on the geometric parameters of the micro-fin tube. It is shown that most of the existing predictive heat transfer and pressure drop models employ strictly empirical techniques. The difficulty of accurate (analytic) modeling of micro-fin tubes lies in the numerous dimensional variables involved in the tube surface, and these are also reported. Heat transfer and pressure drop correlations for micro-fin tubes are presented for pure single fluids and pure mixtures (i.e. R-12, R-125, R-22, R-134a, R-113, R-407C, R-410A, R-32/R-134a, and R-22/R-502/R-134a). The saturation temperatures vary between 22 to 53°C, the mass fluxes between 84 to 910 kg/(m2s), tube diameters between 5.95 to 14.18mm, the number of fins from 24 to 65, fin heights between 0.1 to 0.25mm, apex angles from 25 to 90°, and helix (spiral) angles from 7 to 30°. Correction techniques are suggested when using refrigerant mixtures. It is shown that the currently available correlations satisfy only limited experimental data for a limited number of refrigerants, and that there is little unanimity over a single correlation. The appraisal of the existing correlations by numerous researchers is presented, and recommendations for design calculations are made.
