Condensation of Refrigerants 12 and 134a in Horizontal Tubes With and Without Oil

This study investigated local condensation heat transfer and pressure drop for pure R- 12, pure R-134a and R-134a/oil mixtures and examined the results based on two-phase flow patterns. Condensing conditions simulated those found in domestic refrigerator/freezers. Experiments were performed to measure internal heat transfer coefficients and pressure drops inside a 0.25 in. (6.35 mm) 00, 0.180 in. (4.57 mm) ID smooth, horizontal copper tube. Direct measurements of the temperature difference between the tube wall and the condensing fluid were made. The heat transfer coefficients and pressure drops were compared with existing prediction techniques and differences were found due primarily to differing flow patterns from those used in models and the presence of liquid entrainment in the flow. Tests with a mixture of R-134a and ester lubricant showed a slight increase in heat transfer coefficient at 1.2% concentration and a decrease at 5% concentration. Pressure drop increased with oil concentration. Heat transfer coefficients for R-134a were found to be 10% to 20% higher than for R-12 at equivalent mass flux and saturation temperature, while the difference in pressure drop was within the range of experimental error.Air Conditioning and Refrigeration Center Project 0

Experimental Evaluation of Internal Condensation of Refrigerants R-134a and R-12

Experimental and analytical work has been performed on local heat transfer for intube condensation of pure R-134a and R-12. The data were taken in a 4.57 mm (0.18 in) ill smooth copper tube of 2.90 m (9.5 ft) length. The test section was cooled by two counterflow water circuits, each covering half of the test-section length. Sight glasses of the same diameter as the test section were located at the inlet and outlet of the test section for visual flow regime observations. Data were taken with test conditions in the following ranges: mass flux, 75-500 kglm2-s (55,000-365,000 Ibm/ft2-hr), saturation temperature, 35 and 60??C (95 and 140 OF); average quality, 10-90%; heat flux, 4-15 kW/m2 (1268-4756 Btu/hr-ft2). The observed flow regimes were wavy at low mass flux and quality, progressing sequentially through the wavy-annular, annular, and mist-annular flow regimes as the mass flux and quality were increased. The data for pure refrigerants in the wavy flow regime were successfully correlated with a modified Nusselt-type approach, and exhibited no mass flux dependence. The annular flow data were successfully correlated based on an analogy between heat and momentum transfer.Air Conditioning and Refrigeration Center Project 0

Initial Condensation Comparison of R-22 With R-134a and R-321R-125

Condensation heat transfer data are reported for R-22 and two potential replacements: R-134a, and a 60%/40%, azeotropic mixture of R-32 and R-125. All condensation data were collected in an 0.18" ID (4.572 mm), smooth copper tube. The heat transfer data are compared directly with one another, as well as with heat transfer correlations developed within the ACRC for the wavy and the annular flow regimes. At constant mass flux, the heat transfer coefficients of the three refrigerants were nearly identical in both the annular and the wavy flow regimes. This agreed with predictions of the correlations. The pressure drop was highest for R-134a, followed by R-22 and R- 32/R-125. The condensation heat transfer correlations developed in the ACRC were found to fit the data quite well for each of the refrigerants.Air Conditioning and Refrigeration Center Project 0