Heat-transfer in helically coiled tubes with laminar flow.

Research on the heat transfer coefficient for laminar flow inside a helical coil were made. In particular, the possible effect of natural convection, which was found to be very significant at low Reynolds numbers was studied. The axial temperatures show large amplitude oscillations with axial distance, which decay and damp out in the fully developed region. Consequently, the oscillatory behaviour was also present in the Nusselt number. The Nusselt number approaches an asymptotic value as the fully developed temperature field is approached. The peripherally-averaged Nusselt number, for the fully developed region, was correlated as a function of Dean Grashof, Prandtl and Reynolds numbers. The correlation developed includes the contribution of the natural effects to the Nusselt number. A better understanding of the heat transfer mechanism in helical coils was obtained. (A)