Analysis and experimental study of the heterogeneous nucleation process in the boiling of mixed refrigerants

The heterogeneous nucleation process is important for the study of the nucleate boiling of the mixed refrigerants. In this paper, the onset of heterogeneous bubble nucleation of non-azeotropic mixtures was analysed based on the change in the Gibbs free energy. From the calculated results, the critical radius, change in availability, onset of boiling (ONB) superheat and heat flux were determined. The results showed that the critical radius and the maximum change in the availability of the mixtures was higher than that of the corresponding pure fluids. The ONB superheat first increased and then decreased when the mole fraction of the high boiling point component was increased. In addition, experimental tests were conducted to measure the ONB temperature and heat flux of R124, R22 and R124/R22 mixtures on a copper surface at the pressure of 0.7-0.85 MPa. The ONB superheat and heat flux first increased and then decreased when the concentration of R124 was increased. Additionally, the experimental ONB superheat and heat flux were used to validate the correlations of other models as well as the model presented here. Our model shows much better agreement with the experimental data. Most of the experimental results had an error of +20% to -40%. (C) 2017 Elsevier Ltd. All rights reserved.