Void fractions are determined in vertical downward annular two-phase flow of R134a inside a 7 mm i.d. smooth and microfin tube. The experiments are done at average qualities ranging between 0.67–0.99. The mass fluxes are around 29 kg/m2s. The pressures are between 0.77–0.9 MPa. The experimental setup is explained elaborately. Comparisons between the void fraction determined from 35 void fraction correlations are done. According to the use of various horizontal and vertical annular flow void fraction models together with the present experimental condensation heat transfer data, similar void fraction results were obtained mostly for the microfin and smooth tube. Effect of void fraction alteration on the momentum pressure drop is also presented.

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