| Data taken at the Energy Systems Laboratory for the flow of pure refrigerants and refrigerant/oil mixtures through short tube orifices were combined with additional data taken during this work to produce a universal correlation capable of predicting the critical mass flowrate. This correlation included two-phase and single-phase flow of both pure and oil mixed refrigerants through sharp edged short tubes with length to diameter ratios ranging from 6.55 to 23.15. The data represented flow conditions that are typically seen in air-conditioning and heat pump applications. The refrigerants used in the correlation included R-12, R-134a, R-502, R-22, R-407c, and R-410a.;The correlation was developed using the Buckingham Pi theorem to generate several non-dimensional parameters. Necessary refrigerant properties were saturated liquid and vapor densities, saturated liquid viscosity, enthalpy of vaporization, critical pressure, critical temperature, and saturation pressure as a function of temperature. The length and diameter of the sharp edged orifice were also necessary for the correlation. Necessary quantities for the oil effects correlation included the mass fraction of oil, mole fraction of oil, molecular weight of the refrigerant, molecular weight of the oil, short tube length, and short tube diameter. Using this information and knowledge of the orifice upstream pressure, upstream temperature, and/or quality allows the prediction of mass flowrate. The main advantage of this correlation was that it provided a closed form equation capable of predicting mass flowrate for both two-phase and single-phase flow with the inclusion of oil mixture effects.;For single-phase conditions at the short tube entrance, the correlation predicted the flowrate with an average percent difference of 4.3% of the reading with a maximum difference of 24% and chi-squared of 9.09. Two-phase short tube conditions produced predictions with an average percent difference of 4.5% of the measured value with a maximum difference of 23% and chi-squared of 5.96. The smaller amount of oil mixture data limited the scope of the oil effects model, but data was correlated to produce an average percent difference of 3.9% with a maximum difference of 26% and chi-squared of 8.45. |
