Experimental investigation on two-phase frictional pressure drop of zeotropic mixtures of R50/R170 in a horizontal tube
2017
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%.
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