LAUSR

Abstract In this paper new improved models for heat transfer calculation in inclined and vertical tubes with viscous-gravitational effects are presented. Three models, two for vertical tubes with upward and downward flow and one for inclined tubes were developed. For the validation of the models, available data of 14 different fluids, including water and organic liquids were used. The first model is valid when forced and natural convection have the same direction, obtaining a correlation adjustment with an average error of 11.6% for 77.8% of the data. The second model is valid when forced and natural convection are in opposite directions and provides a good correlation with an average error of 12.8% for 74.4% of the available experimental data. The third model is valid for inclined tubes with an angle of inclination with respect to the horizontal line between 1∘ ≤ θ ≤ 88∘, and provides a good correlation adjustment with an average error of 15.9% for 75.0% of the available experimental data. A new procedure of analysis to consider the influence of the viscous-gravitational effect on the non-isothermal laminar flow was developed, with the purpose of obtaining a better adjustment index from the experimental available data and to increase the validity range.