This paper reports vapor-space condensation heat transfer measurements for R123, R134a, and R245fa on two passively enhanced vertical surfaces and on a vertical smooth plate. The two enhanced surfaces were the integral trapezoidal-fin and the Turbo-CII. The data consisted of heat flux and wall temperature difference measurements. The temperature of the saturated vapor was held constant at 313.15 K for all tests. Condensation heat transfer measurements for the 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 10 % of one another. Similarly, the condensation heat flux for R134a and R245fa on the Turbo-CII was within approximately 18 kW/m2 of each other, while the heat flux of R123 on the Turbo-CII was between 10 kW/m2 and 80 kW/m2 less than that of R245fa. The poor performance of R123 on the Turbo-CII surface was possibly due to partial flooding of the heat transfer surface. 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 0.6 K 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.
Citation: Journal of Enhanced Heat Transfer
Pub Type: Journals
Vapor-space, condensation, enhanced heat transfer, integral-trapezoidal-fin, R123, R134a, R245fa, refrigerants, low-finned tube, Turbo-C