Experimental investigation on two-phase frictional pressure drop of zeotropic mixtures of R50/R170 in a horizontal tube

In recent years, due to the environmental issues, suitable substitutes are being searched to replace the traditional chlorinated refrigerants. With zero ozone depleting potential, low global warming potential and high thermodynamic performance, the hydrocarbons are suitable selections in refrigerators and heat pump systems. As hydrocarbons, R50 and R170 are also the important parts of the natural gas and often-used components in mixture refrigerants for the low-temperature Joule-Thomson refrigerator. As the flow characteristics play important parts in the design and optimization of the heat exchangers in refrigerators and air-conditioning systems, the two-phase frictional pressure drop should be well examined and analyzed. Although there are massive experimental studies on two-phase frictional pressure drop of hydrocarbons in horizontal tubes, the published experimental investigations for zeotropic mixtures of R50/R170 are rare. Therefore, it′s desirable to conduct an experimental investigation on two-phase frictional pressure drop of zeotropic mixtures of R50/R170 in a horizontal tube and find a suitable correlation. In this paper, two-phase frictional pressure drop of R50/R170 mixtures (0.27:0.73, 0.54:0.46 and 0.7:0.3 by mole) was studied experimentally in a horizontal tube with inner diameter of 4 mm. The tests were carried out at saturation pressures from 1.5 MPa to 2.5 MPa for mass fluxes from 99 kg m−2 s−1 to 255 kg m−2 s−1, vapor qualities from 0 to 0.9. The uncertainty for the pressure drop was 40 Pa and the uncertainties for the vapor quality with a 95% confidence interval were less than 11.74% under the employed operation conditions. The effects of mass flux, saturation pressure, vapor quality and concentration on two-phase frictional pressure drop were examined and analyzed. Some conclusions can be drawn that (1) the frictional pressure drops increase with the increasing mass flux and the impact becomes more obvious when the vapor quality increases; (2) the frictional pressure drops decrease with the increasing saturation pressure and the impact enhances when the vapor quality increases; (3) the frictional pressure drops increase with the increasing vapor quality and then change to be smooth even decline at high vapor qualities. And the effect of vapor quality enhances as the mass flux increases and the saturation pressure decreases; (4) the frictional pressure drops of pure R50 are lower than that of all R50/R170 mixtures and the frictional pressure drops of the initial concentration of R50/R170 mixtures at 0.27:0.73 are also lower than that of other two initial concentrations of R50/R170 mixtures. Their differences are not obvious at low vapor qualities, while the differences enhance when the mass flux and vapor quality increase as well as the saturation pressure decreases. The influence of concentration may be mainly related to the difference of the vapor densities. In addition, the experimental data were compared with twenty well-known frictional pressure drops correlations. The comparison results showed that the Friedel correlation showed the best agreement with a mean absolute relative deviation of 19.26% and 87.45% of points in the deviation bandwidth of ±30%.