Abstract
This study investigates the flow pattern characteristics of R245fa in the smooth and microfin tubes under diabatic conditions. A novel electromagnetic induction system was designed to obtain visualization data in the transparent test section with a controlled heat flux. The experiments were conducted with mass fluxes of 50–240 kg/m2 s, heat fluxes of 5.65–14.87 kW/m2 and a saturation pressure Psat = 0.2 MPa. Six flow patterns were identified in both smooth and microfin tubes. The effects of the vapor quality, mass flux and heat flux on the flow patterns were analyzed. Compared with the smooth tube, the transition from intermittent to wavy-annular flow occurred at lower vapor quality in the microfin tube. Moreover, the liquid film was spread, and the shrinkage of the heated thin film was restrained in the microfin tube, so it can significantly improve the evaporation heat transfer performance. Six predictive models were compared with the present flow pattern map. The Frl = cXttn format criterion was suitable for the intermittent/wavy-annular transition of R245fa in horizontal tubes.
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