Experimental investigation on flow condensation heat transfer of ethane in a horizontal tube

Abstract

In recent years, due to the environmental problems of traditional chlorinated refrigerants, it has become an urgent task to search for suitable substitutes. Hydrocarbons, with zero ozone depleting potential, low global warming potential and high thermodynamic performance, are good alternative refrigerants in refrigerators and heat pump systems. In addition, hydrocarbons also the important parts of the natural gas. As one kind of hydrocarbons, ethane and its mixtures have been widely applied in the mixed refrigerant throttling refrigeration systems and recommended to be used in the cascade refrigeration systems to replace R13 and R503. As the heat transfer characteristics of ethane play important parts in the design of the heat exchangers in refrigeration cycles, the heat transfer coefficients during condensation should be well examined and analyzed. Although there are massive experimental studies of heat transfer on flow condensation of hydrocarbons in horizontal tubes, the published experimental investigations for ethane are rare. Therefore, it’s desirable to conduct an experimental investigation on condensation heat transfer of ethane in a horizontal tube and find suitable correlations. In this paper, condensation heat transfer of ethane was studied experimentally in a horizontal tube with inner diameter of 4 mm. The heat transfer test section was a copper plate (100 mm× 20 mm× 200 mm) embedded twelve four-wire PT100 platinum resistance thermometers. Using the assumption of two-dimensional heat conduction for the copper plate, both the wall temperature and heat flux could be obtained. The tests were carried out at saturation pressures from 1.01 MPa to 2.56 MPa for mass fluxes from 100 kg/(m2 s) to 257 kg/(m2 s) and vapor qualities from 0 to 0.8. The uncertainties for the heat transfer coefficient with a 95% confidence interval were less than 3.33% under the employed operation conditions. The effects of mass flux, vapor quality and saturation pressure on condensation heat transfer coefficient were examined and analyzed. Some conclusions can be drawn that (1) in relative high mass fluxes and vapor qualities, the condensation heat transfer coefficients increased with the increasing mass flux and vapor quality while decreased with the increasing saturation pressure; (2) in relative low mass fluxes and vapor qualities, the vapor quality, mass flux and saturation pressure had a little influence on condensation heat transfer coefficients. In addition, the experimental data were compared with nine well-known correlations of condensation heat transfer coefficient. The comparison results showed that Chato (1962) correlation and Wang et al. (2002) correlation relatively agreed well with the experimental data with the mean absolute relative deviations less than 35%. The other correlations showed larger predicted results than the experimental data with the mean absolute relative deviations more than 55%. And the Chato correlation and Wang et al. correlation were both in good agreement with the relative low heat transfer coefficients rather than the relative high heat transfer coefficients.