Vaporization of binary and ternary non-azeotropic mixtures inside channels

This study is aimed at the experimental investigation of vaporization of zeotropic mixtures inside small channels. In the recent years, the search for alternatives to high-GWP (Global Warming Potential) refrigerants is focused primarily on the use of natural fluids (hydrocarbons, ammonia, carbon dioxide) and new synthetic refrigerants having low-GWP. Unfortunately, single-component low-GWP refrigerants cannot cover all the applications unless some drawbacks, such as flammability, are accepted. A solution may be found using blends of refrigerants, to satisfy the demand for a wide range of working conditions. In the present paper, the experimental heat transfer performance of binary and ternary non-azeotropic mixtures during flow boiling is investigated. The adoption of zeotropic mixtures poses the problem of how to extend the correlations developed for pure fluids. The additional mass transfer resistance, due to the zeotrope of the mixture, leads to a degradation of the heat transfer performance, thus models developed for pure fluid vaporization cannot be directly applied. In the present paper, the contribution of the additional mass transfer resistance is assessed and the corrections needed in the model are discussed.