Research on the thermal performance of a heat exchanger with meso-scale twisted helical tube bundles

Abstract

Heat exchangers with helical tubes are applied widely in various industrial fields and cryogenic applications. Currently, the most common ones are the spiral wound heat exchangers, which consists of many layers of spiral tubes with different coil diameters in a closed shell. Most of the fluid in the shell-side passes directly through the gap between two adjacent layers, which weakens the turbulence and the associated heat transfer coefficient. A novel twisted helical bundle geometry is proposed in this paper of which the thermal performance is explored using CFD simulation. The heat exchanger uses helium gas as the working fluid and operates between 300 K and 30 K. The curve of each tube in the bundle is generated by different 3D sinusoidal equations, and the tubes at adjacent layers are twisted together thereby producing the same end-to-end length for each tube. By simulating a spiral wound heat exchanger using different turbulent equations and comparing the results with experimental data from literature, the k-omega SST model is found to be the most suitable one to simulate this kind of geometry. Nusselt numbers and friction factors are obtained under different Re values and compared with those of standard spiral wound heat exchangers. The creative twisted geometry can improve the Nu number although also increasing the friction factor. Geometry parameters such as pitch length are being further explored to obtain an optimal thermal performance.