MEASUREMENT AND PREDICTION OF VAPOR-SPACE CONDENSATION OF REFRIGERANTS ON TRAPEZOIDAL-FINNED AND TURBO-C GEOMETRIES

Abstract

This paper reports vapor-space condensation heat transfer measurements for R123, R134a, and R245fa for the integral trapezoidal fin, and the Turbo-CII geometries on vertical plates. The data consisted of heat flux and wall temperature difference measurements. Condensation heat transfer measurements on a smooth plate agreed well with both measurements and predictions from the literature. Overall, the heat transfer performance of the three refrigerants on the trapezoidal fin was within approximately 8 kW/m of one another. Similarly, the condensation heat flux for R134a and R245fa on the Turbo-CII was within approximately 18 kW/m of each other, while the heat flux of R123 on the Turbo-CII was between 10 and 80 kW/m less than that of R245fa. An existing finned tube condensation model was modified to be expressed in terms of the gradient of the condensate curvature with respect to the length of the liquid–vapor interface. Curvature gradients for the two surfaces were developed that, when substituted into the modified model, predicted the present measured driving temperature differences for the trapezoidal fin and the Turbo-CII to within 0.4 and 1.2 K, respectively, for all measurements except for R123 on the Turbo-CII surface. With the aid of the curvature gradients, simple models were developed to predict the performance of the trapezoidal, low-finned tube, and the Turbo-C tube. The heat flux to the low-finned tube and the Turbo-C tube were predicted to within 10% and 15%, respectively, of the measured values from the literature for four different fluids.