NONINTRUSIVE DETERMINATION OF LOCAL HEAT TRANSFER COEFFICIENT IN PIPES UNDER THE INVERSE HEAT CONDUCTION PROBLEM APPROACH

Most of passive techniques for heat transfer enhancement (e.g. rough surfaces, swirl-flow devices and coiled tubes) origins an irregular distribution of the heat transfer coefficient at the fluid wall-interface along the wall perimeter. This irregular distribution could be critical in some industrial applications but most of the available research papers presents the results only in terms of Nusselt number averaged along the wall circumference, due to the practical difficulty of locally measuring heat flux on internal wall surface of a pipe. Placing probes in a pipe is usually unfeasible because of the perturbation effects of the probes on the observed phenomenon, the geometric inaccessibility of the surface, or because of the fluid in the pipe that may destroy the sensors. The application of inverse heat conduction problem solution techniques overcomes these limitations because this approach enables to estimate the local convective heat transfer coefficient starting from the temperature distribution acquired on the external wall surface. In this work different estimation techniques were compared considering a particular problem of passive heat transfer enhancement: estimating the local convective heat transfer coefficient in coiled tubes. The comparison was performed both by synthetic and experimental data.