Effect of Oil on Condensation in a Microfinned Tube

The effects of an ester oil, in concentrations up to 5% by mass, on the behavior of R -134a condensing in a microfinned tube with an 18?? helix angle were studied experimentally. The flow patterns were only minimally affected with some indication that a shift from wavy towards annular flow may be caused by the oil at the low mass fluxes. The heat transfer followed similar trends due to the presence of oil in a microfinned tube as those that occurred in a smooth tube. At low qualities there was no significant effect but, as quality increased, the heat transfer in the oil carrying refrigerant began to be depressed compared to the pure refrigerant. At some high quality the heat transfer reached a peak value. Beyond this quality the heat transfer decreased rather rapidly. The oil did not seem to have a large effect on the pressure drop in the test section. Only at the highest qualities were slight increases. measured at increased oil concentrations.Air Conditioning and Refrigeration Center Project 3

Condensation of a 50/50 Blend of R-32/R-125 in Horizontal Tubes with and Without Oil

This study examined local condensation heat transfer and pressure drop for a pure 50/50% mixture of R- 32/125 and for R-32/125 mixed with approximately 1%, 3%, and 5% concentrations of an ester oil. An apparatus was built to simulate conditions found in the condenser sections of domestic refrigerators/freezers. Experiments were performed to measure the internal heat transfer coefficients and pressure drops inside a 0.277 in. (7.0 mm) o.d. smooth, horizontal copper tube. It was observed from the oil samples that the oil concentration of the oil-refrigerant mixtures flowing through the test section changed for different mass fluxes and qualities. The data for the heat transfer coefficients were compared with existing correlations and the Dobson correlation demonstrated the best accuracy for the pure R-32/125 and predicted the performance of oil-refrigerant mixtures with less than 20% error when used with the Schlager enhancement factor. The experiments showed that oil addition degraded the heat transfer coefficient at vapor qualities greater than 50% and increased the pressure drop by as much as 25% at high mass fluxes

Condensation of a Zeotropic Refrigerant R-321R-125/R-134a (23o/al25o/al52%) in a Horizontal Tube

This experimental study examined the local heat transfer coefficients and frictional pressure gradients of a ternary zeotropic refrigerant mixture, R-32/R-125/R-134a (23%/25%/52%) condensing in a smooth, horizontal tube. The test section consisted of a 3 ft long, copper tube with a diameter of 0.277 in (7.04 mm) surrounded by a counter-flow, water-cooled annulus. Test conditions varied the average quality from 10% to 90% and the mass flux from 55 to 474 klb/ft2_hr (75 to 650 kg/m2-s) to insure that data points were taken all across the wavy and annular flow regimes. The temperature difference was held approximately constant at 5.4 OF (3.0 ??C). At mass fluxes higher than 364 klb/ft2_hr (500 kg/m2-s), the Dobson correlation consistently overpredicted the heat transfer coefficients requiring a least squares-determined factor of 0.836 to correct. As the flow regime approached wavy flow, the Dobson correlation increasingly overpredicted the heat transfer coefficient due to the dominance of zeotropic degradation. Frictional pressure gradient data showed similar trends to the Souza pressure drop correlation but were significantly lower.Air Conditioning and Refrigeration Center Project 3