Estimation of local heat transfer coefficient in coiled tubes under inverse heat conduction problem approach

Wall curvature is a widely used technique to passively enhance convective heat transfer and it is particularly effective in the thermal processing of highly viscous fluids. These geometries produce a highly uneven convective heat flux distribution along the circumferential coordinate, impacting on the performance of the fluid thermal treatment. Although many authors have investigated the forced convective heat transfer in coiled tubes, most of them have presented the results only in terms of the Nusselt number averaged along the wall circumference. Moreover, regarding the laminar flow regime, few data about the local heat transfer coefficient are available. In this paper a procedure to estimate the local convective heat flux in coiled tubes is presented and tested: the temperature distribution maps on the external coil wall are employed as input data for the inverse heat conduction problem in the wall under a solution approach based on Tikhonov regularization method. The investigation was particularly focused on the laminar flow regime.