SHAPE OPTIMIZATION OF HELICAL COIL TUBE FOR MAXIMIZING HEAT TRANSFER

Abstract

Many researchers have observed the enhancement of heat transfer in coiled tubes compared to straight tubes with the same diameter and length. It is known fact, that in a helical coil tube the maximum axial velocity shifted towards the outer wall of the pipe and imbalance between centrifugal forces and inertial loads to a secondary motion of the fluid in the cross-section of the tube. This secondary motion is responsible for improved transport of heat energy to/from the tube walls. Previous conducted Experimental and computational parametric studies show the relationship between the increased heat transfer and parameters such as pitch, coil diameter, Dean’s and Reynolds numbers subjected to different boundary conditions. The majority of these studies have focused on tubes with circular cross-sections.

In the present work, a comprehensive parametric study involving a complete set of non-dimensional parameters has been performed for laminar flow using computational fluid dynamics. The non-dimensional parameters governing the flow through the helical tube are the Reynolds number based on hydraulic diameter, Prandtl Number, the ratio of the helical coil diameter to the tube diameter, the ratio of pitch to the tube diameter, and the ratio of the tube length to the tube diameter. In a separate study, the cross-sectional shape was found to have an impact the heat transfer performance. In order to find the optimal cross-sectional shape and other geometric parameters that maximize the heat transfer performance, shape optimization was carried using a numerical optimization algorithm. 45.9% increase in heat transfer was obtained with the optimized shape, when compared to a straight tube and increase by 5% when compared to helical coiled tube with circular cross section.