Effect of Fin Structure on the Condensation of R-134a, R-1234ze(E), and R-1233zd(E) Outside the Titanium Tubes

In order to test the effect of fin structure on the condensing heat transfer of refrigerants outside the low thermal conductivity tubes, condensation of R-134a, R-1234ze(E), and R-1233zd(E) on two enhanced titanium tubes were experimentally investigated. The two tubes have basically the same fin density while the fin structures are different. One tube is a typical low-fin (two-dimensional, 2D), and the other is a three-dimensional (3D) finned tube. In experiment heat flux was in the range of 10–80 kW·m−2. It was found that at higher heat flux, the condensing heat transfer coefficient (HTC) of 3D-finned tubes was apparently lower than that of 2D-enhanced tubes. The condensing HTC of R-134a for the two tubes was the highest. R-1233zd(E) was the lowest. It was shown from experimental results that the condensing HTC for R-1233zd(E) was notably affected by the change of saturation temperature outside the 3D-enhanced tube, but was less affected by the 2D fin structures.

Condensation of R134a and R22 in Shell and Tube Condensers Mounted With High-Density Low-Fin Tubes

In this work, the condensation of refrigerants on a single, high-density, low-fin tube and full-sized shell and tube condensers were investigated experimentally. The low-fin tube had an external fin density of 56 fins per inch (fpi) and fin height 1.023 mm. Another three-dimensional (3D) finned tube was also tested for comparison. The condensing heat transfer coefficient of the refrigerant R134a was first investigated outside a single horizontal tube at saturation temperature of 40 °C. The overall heat transfer coefficients of the two tubes were similar in magnitude. The condensing heat transfer coefficient of the low-fin tube was 16.3–25.2% higher than that of 3D enhanced tube. The experiments of the two condensers mounted with low-fin and 3D enhanced tubes were then conducted in centrifugal and screw chiller test rigs. It was found that chillers with the two different condensers generally had the same refrigeration capacity under the same experiment conditions. The refrigeration capacity of the screw chiller was smaller. It had fewer tube rows and elicited fewer inundation effects owing to the falling condensate. The heat transfer coefficients of the condensers with R134a in centrifugal chillers equipped with high-density low-finned tubes were higher than those in the screw chillers. The total number of tubes for low-fin tube condensers, in the two chillers, was reduced by approximately 15% compared with the use of domestic advanced condensers equipped with the 3D enhanced tubes.

Visualization Study of Steam Condensation in Rectangular Channel of Multichannel Cylinder Dryer

The phenomenon of steam condensation occurring on one surface in a rectangular horizontal channel was experimentally studied. The experiment was conducted using a visualization method with a steam quality of 0.1–0.9 and mass flux of 20–50 kg/m2 s. Four flow patterns (annular, wave, slug, and plug) were observed, and the effects of quality and mass flux on the condensing heat transfer were analyzed. The mass flux and steam quality primarily affect the condensing heat transfer coefficient in the shear-dominated flow regime. The condensing heat transfer coefficients are nearly constant only in a certain range of steam quality. This result is disparate from what has been reported in previous literatures. It was also observed that the condensing heat transfer coefficient rises with an increase in the quality. Two flow regime maps were employed to predict the flow regimes observed in this study. The result reveals that the Tandon flow regime map agrees quite well with the experimental results.