Evaluation of the heat transfer enhancement and pressure drop penalty during flow boiling inside tubes containing twisted tape insert

This paper presents experimental data for pressure drop and heat transfer coefficient for two-phase flows in tubes containing twisted-tape inserts. Based on these data, an analysis of the heat transfer enhancement and pressure drop penalty due to the use of twisted-tapes is performed. Experimental results were obtained for horizontal 12.7 and 15.9 mm ID tubes without and with twisted-tape for twist-ratios of 3, 4, 9 and 14. The experiments were performed for R134a as working fluid covering mass velocities from 75 to 200 kg/m2 s, heat fluxes of 5 and 10 kW/m2 and saturation temperatures of 5 and 15 °C. The predictive methods available in the literature were compared against the experimental data obtained in the present study. In general, it was concluded that the use of reduced twist-ratios values provide higher overall heat transfer enhancement factors for intermediary vapor quality. Additionally, it was found that the pressure drop correlation proposed by Kanizawa and Ribatski (2012) is suitable to be used as a design tool because it predicted 99% of the present database within an error band of ±30%.