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

• Experimental analysis of flow boiling in a horizontal smooth tube has been presented.
• Three refrigerants R134a, R407C and R410A are tested.
• Effects of vapor quality, heat flux and mass velocity on heat transfer coefficient and total pressure drop are considered.
• Comparisons are accomplished using the energy performance parameters.
• Experimental results are compared with some recognized correlations.

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 kgm−2s−1; (ii) the heat fluxes within 3.0–10.0 kWm−2; (iii) the inlet temperatures to the evaporator within 5°C-9°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 thermo-physical 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.