A new model for flow boiling heat transfer coefficient inside horizontal tubes with twisted-tape inserts

• Review of HTC predictive methods for flow boiling in tubes with twisted tape inserts.
• Description and analysis of experimental database.
• Proposal of predictive method for dryout inception and completion vapor qualities.
• Proposal of new predictive method for heat transfer coefficient.

This paper presents a new method to predict the heat transfer coefficient during flow boiling inside horizontal tubes containing twisted tape inserts. The method was developed based on the database presented by Kanizawa et al. This database comprises flow boiling results for horizontal tubes with internal diameters of 12.7 and 15.9 mm, twisted-tape ratios of 3, 4, 9 and 14, mass velocities ranging from 75 to 200 kg m−2 s−1, heat fluxes of 5 and 10 kW m−2 and saturation temperatures of 5 and 15 °C. The method is flow-pattern based and considers flow boiling, dryout and mist flow regions. The predictive method also takes into account the physical picture of the swirl flow phenomenon by considering swirl flow effects promoted by the twisted tape insert. The proposed method provides satisfactory predictions and captures the main heat transfer trends of the data of Kanizawa et al. and also of independent data from literature.