Abstract
Flow regimes and void fraction in horizontal and vertical round smooth tubes ID 7 mm with R134a in the adiabatic conditions (saturation temperature at 33 °C) and low mass flux (40–150 kg/m2 s for horizontal tubes and 65–115 kg/m2 s for vertical tubes) are presented in this paper. Flow regimes are captured by a high-speed camera while void fraction is measured by quick-closing valve method. The horizontal flow patterns are compared to Wojtan et al. (2005a) flow-regime map and some modifications based on visualization results are proposed. Void fraction results for both horizontal and vertical flows are compared to some widely used correlations. Influences of tube orientation and mass flux on void fraction are discussed. When the vapor quality keeps constant, void fraction of horizontal tubes is larger than that of vertical tubes. Higher mass flux also results in larger void fraction compared that of lower mass flux.
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