Numerical investigation about radius ratio effect of helical tubes in the heat exchanger

Abstract

Enormous research has been conducted on the efficient flow and heat transfer performance of helical tube. The helical tube with a large radius ratio (ratio of curvature radius to tube radius) could not be installed when the available space is limited, and the differences in their thermal hydraulic characteristics caused by different radius ratios are rarely studied. The present study aims to use a numerical method to quantify and visualize the radius ratio effect and to determine its mechanism. The result shows that the fitness curve of the theoretical flow field and the numerical result are bell-shaped. Helical tubes with lower radius ratio have a significant improvement in flow and heat transfer performance, while higher radius ratio brings lower circumferential nonuniformity and more heat transfer area. The torsional effect or bending effect is the dominant effect when the radius ratio is low or high, respectively. The promotion of vortex generation is the mechanism of the radius ratio effect. The current study could be used as a reference for the engineering applications of helical tubes, as well as to support further research on the basic mechanism of heat and mass transfer in helical tubes.