Incorporating the Effect of Centrifugal Force into the Correlation for Saturated Flow Boiling Heat Transfer in a Helically Coiled Tube

Abstract

The flow in a helically coiled tube exhibits a unique characteristic due to the centrifugal force acting on the fluid, which generates a secondary flow perpendicular to the main axial flow. This phenomenon is known to enhance convective heat transfer in both single- and two-phase flows. To account for this effect in a boiling heat transfer correlation, a new dimensionless number, defined by the ratio of centrifugal force to gravitational force, was introduced in a previous study. That study suggested a correlation incorporating this dimensionless number. This work aims to improve on the previous correlation. In deriving the dimensionless centrifugal force number, the pitch of the helical tube was not considered in the previous work. By properly incorporating both pitch and helical diameter into the dimensionless number, the coefficients of the heat transfer correlation must also be adjusted. The modified correlation was evaluated using 617 steam-water experimental data points for boiling heat transfer in helically coiled tubes. The results indicate that the modified correlation shows better results in comparison with the previous one and other existing correlations in terms of the root-mean-square errors of the calculated heat transfer coefficients.