Experimental investigation of the heat transfer coefficient during convective boiling of R134a in tubes with twisted tape insert

This paper addresses experimental results for heat transfer coefficient and flow patterns during R134a convective boiling inside horizontal tubes containing twisted tape inserts. The experimental database comprises results for twist ratios ranging from 3 to 14, tubes with internal diameters of 10.0, 12.7 and 15.9 mm, mass flux from 75 to 1000 kg/m²s, saturation temperature between 5 and 25°C, vapor quality between 0.01 and 0.95, and heat flux ranging from 5 to 250 kW/m². The influence of distinct parameters on the heat transfer coefficient is parametrically analyzed, and the data are compared with predictive methods available in the literature. The dominant heat transfer mechanisms are identified according to the operational conditions. A predictive method for the heat transfer coefficient for high heat (≥ 100 kW/m²) and mass (≥ 400 kg/m²s) fluxes is proposed.