Numerical Investigation of The Convective Heat Transfer Enhancement in Coiled Tubes

The present work is focused on the numerical analysis of forced convection in curved tubes. The study was performed by integrating the continuity, momentum and energy equations within Comsol Multiphysics 4.2a environment. The analysis was carried out under the assumptions of incompressible Newtonian, constant properties fluid and of periodically fully developed laminar flow. For the thermal problem, a uniform wall heat flux boundary condition was assumed. The main purpose was to study the influence of the curvature profile on the convective heat transfer mechanism: in order to evaluate the overall performances of the geometry the friction factor and the Nusselt Number were calculated. Moreover the flow pattern and the temperature distribution on the tube section were derived for different values of the Reynolds number. The aim was to deeply investigate the correlation between the heat transfer and friction factor enhancement and the effects of the wall curvature. In the present study, a toroidal geometry characterised by a tube diameter of 14 mm and a curvature ratio of 0.06 was considered. In addition, the numerical results were compared to the experimental values obtained on a coiled tube with the same tube diameter and the same curvature ratio. The study was performed by considering the Reynolds number range 2-100 and the Prandtl number range 25-50.