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TWO-PHASE FLOW OF TWO HFC REFRIGERANT MIXTURES THROUGH SHORT-TUBE ORIFICES
Citation:
Payne, W. AND D. O'Neal. TWO-PHASE FLOW OF TWO HFC REFRIGERANT MIXTURES THROUGH SHORT-TUBE ORIFICES. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-95/168 (NTIS PB98-142045), 1995.
Impact/Purpose:
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Description:
The report gives results of an experimental investigation to develop an acceptable flow model for short tube orifice expansion devices used in heat pumps. The refrigerants investigated were two hydrofluorocarbon (HFC) mixtures considered hydrochlorofluorocarbon (HCFC)-22 replacements: HFC-32/HFC-125/HFC-134a (23/25/52% on a mass percentage basis) and HFC-32/HFC-125 (50/50%). Tests for both refrigerants were performed to generate data at varying operating conditions with 12 short tubes. The tests included both single- and two-phase flow conditions at the inlet of the short tube with different oil concentrations. Experimental data were presented as a function of major operating parameters and short tube diameter. Based on test results and analysis, a mass flow model was developed. The test results for both refrigerants showed that the mass flow rate was strongly dependent on upstream conditions, but slightly dependent on downstream conditions. The mass flow rate was extremely sensitive to changes in short tube diameter. The presence of oil below a concentration of approximately 2% would appear to affect the mass flow rate only slightly (less than 5%). It was found that the semi-empirical flow model estimates were in good agreement with laboratory results for both single- and two-phase flow entering the short tubes.