On flow boiling of R-1270 in a small horizontal tube: Flow patterns and heat transfer

An experimental study was performed to investigate both flow patterns and heat transfer during flow boiling of propylene (R-1270) at a saturation temperature of 25 degrees C in a small circular tube with an inner diameter of 1.0 mm. The heat flux was varied from 5 to 60 kW/m(2) and the mass flux ranged from 240 up to 480 kg/m(2)s, with vapor quality ranging from 0.01 to 0.99. Five flow patterns were identified: plug flow, slug flow, churn flow, wavy- and (smooth) annular flow. The influence of the heat flux, mass flux, vapor quality and flow pattern on the heat transfer coefficient are quantified and analyzed. The new experimental heat transfer coefficients were compared with predictions of correlations found in literature and recommendations are presented.