Laminar Flow Heat Transfer and Pressure Drop in a Circular Tube Having Wire-Coil and Helical Screw-Tape Inserts

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having wire-coil and helical screw-tape inserts have been presented. Peripherally and axially local temperatures on the duct outside wall have been measured. The temperature drop across the duct wall has been calculated to obtain the duct inside wall temperatures. Peripherally averaged and axially local temperatures have been used to get axially local Nusselt numbers. These axially local Nusselt numbers have been averaged over the whole length of the duct to get the mean Nusselt number. Predictive friction factor and Nusselt number correlations developed by log-regression analysis have also been presented. Nusselt number correlation takes care of the thermal development length represented by the Graetz number, swirl and inertia force due to forced convection at large Reynolds number, buoyancy force due to natural convection at low Reynolds number represented by Rayleigh number and the geometrical parameters of wire-coil and helical screw-tape inserts. The thermohydraulic performance has been evaluated. The helical screw-tape inserts in combination with wire-coil inserts perform better than the individual enhancement technique acting alone for laminar flow through a circular tube up to a certain value of fin parameter. [DOI: 10.1115/1.4007415]