Comparative experimental study on flow boiling heat transfer characteristics of pure and mixed refrigerants

An experimental study is carried out to investigate the characteristics of the flow boiling heat transfer for different fluid, namely, pure refrigerant (R134a), quasi-azeotropic mixture (R410A) and zeotropic mixture (R407C). The test section is a smooth horizontal tube (7.0 mm ID) uniformly heated by the resistance heating effect. The flow boiling characteristics of the refrigerants are evaluated varying: (i) the refrigerant mass velocities within the range 100-400 kgrn(-2)s(-1); (ii) the heat fluxes within 3.0-10.0 kWm(-2); (iii) the inlet temperatures to the evaporator within 5 degrees C-9 degrees C. In this study, the effect on the heat transfer coefficient and two-phase pressure drop of vapor quality, mass velocity, imposed heat flux and fluid thermophysical properties are examined in detail. Moreover, an assessment of predictive methods is provided for local heat transfer coefficients; also a direct comparison of flow regimes visualizations for refrigerants with a flow pattern map available in the literature is presented. (C) 2014 Elsevier Ltd and IIR. All rights reserved.