Boiling heat transfer characteristics in a horizontal tube with internal helical threads and that with a fin-module insert

The boiling heat transfer coefficients of two horizontally installed heat transfer enhancing tubes were measured respectively. One of the tubes is with internal helical threads and the other is with a fin-module insert. The measured data were compared to those of a smooth tube for acquiring the heat transfer enhancement index (γ). The test tubes were exerted with constant surface heat flux. The evaporation temperature was in the range of − 12 to − 13 °C and the mass flux (G) of the refrigerant was in the range of 20.1–57.6 kg/m2-s. The result shows that, for the tube with internal helical threads, the image value is proportional to [(G/4.0) − 4.4]0.146; for the tube with a fin-module insert, the image value is proportional to [(G/4.0) − 4.4]0.113. The γ value of the tube with internal helical threads was found to be in the range of 1.36–1.73 and that of the tube with a fin-module insert was in the range of 1.76–2.4. The γ value tends to decrease with an increase of the G value.