NUMERICAL ANALYSIS OF CONVECTIVE HEAT TRANSFER ENHANCEMENT IN SWIRL TUBES

Purpose – The aim of this paper is to investigate the convective heat transfer in swirl tubes, which are obtained by roto-translating a circular section eccentric with respect to the rotation axis. The geometry is numerically investigated with the aim of evaluating the convective heat transfer enhancement effect due to the secondary flow induced by the centrifugal force. Design/methodology/approach – The governing equations, i.e. continuity, momentum and energy equations, are integrated numerically within Comsol Multiphysicsw environment, under the assumption of incompressible Newtonian and constant properties fluid and of periodically fully developed laminar flow for what concerns both the hydrodynamic and the thermal problem under the uniform wall heat flux thermal boundary condition. Findings – The heat transfer performance of the geometry is discussed in relation to the flow pattern. In particular, the numerical results show that two different stable flow regimes may exist, according to the ratio of the Reynolds number to the dimensionless helix pitch. The Nusselt number augmentation becomes significant for high Prandtl number fluids when a critical Re/P * value, corresponding to the onset of the centrifugal forces induced secondary flow, is reached. Originality/value – The geometry here investigated represents an interesting solution to enhance the convective heat transfer in situations in which the flow, although disturbed, persists in the laminar regime. This type of enhanced tubes shows then interesting heat transfer performances (which becomes particularly significant for high Prandtl number values) by thus suggesting convenient applications also for highly viscous fluids which are often treated under the laminar flow regime.