Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Abstract
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
