Correlation between pressure loss and heat transfer coefficient in boiling flows in printed circuit heat exchangers with semicircular and circular mini-channels

Abstract

• Boiling flow heat transfer coefficient and pressure drop were evaluated. • Printed circuit heat exchangers with semicircular and circular channels were employed. • Nucleate boiling in corners affected the heat transfer and flow resistance. • Heat transfer coefficient in semicircular channel was twice as high at low quality. • Increase in pressure drop was suppressed by effect of corners at a low quality. In this study, we investigated the correlation between the pressure loss and heat transfer coefficient for boiling flows in printed circuit heat exchangers. The effect of channel cross-sectional shapes—semicircle and circle—was evaluated. The hydraulic diameters of the semicircular and circular channels were 1.04 mm and 1.0 mm, respectively. A subcooled liquid with a subcooling temperature of 10 K was heated with hot water, and the saturation temperature was 30 °C. The refrigerant mass flux was set in a range of 100–400 kg/m 2 ·s. Consequently, despite the lower pressure drop, for low outlet quality, the heat transfer coefficient was higher for the semicircular channel than for the circular channel. The heat transfer was enhanced by the promotion of bubble nucleation in the thick liquid film at the corners, and the flow resistance was suppressed by the decrease in the vapor shear stress. However, for high outlet quality, the difference in the heat transfer coefficient decreased with an increase in the outlet quality. The experimental results were compared with the results obtained by correlation equations. The lowest mean absolute error of heat transfer coefficient and pressure drop for the semicircular mini-channel were 15.1 % and 26.7 %, respectively.