Flow boiling characteristics of refrigerant mixture R-22/R-114 in the annulus of enhanced surface tubing

This paper presents an experimental study of flow boiling heat transfer characteristics of refrigerant mixture R-22/R-114 in the annuli of a horizontal enhanced surface tubing evaporator. The geometric parameters of the test section are: inner tube bore diameter of 17.5 mm, envelope diameter of 28.6 mm and outer smooth tube of 32.3 mm I.D. The ranges of heat flux and mass velocity covered in the tests were 5–25 kW m^?2 and 180–290 kg m^2?s^?1 respectively, at a pressure of 570 kPa. The enhanced surface tubing data showed a significant enhancement of the heat transfer compared to an equivalent smooth tube depending on the mixture's components and their concentrations. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of R-22/R-114 non-azeotropic refrigerant mixture flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition.