Laminar flow heat transfer enhancement in a circular tube having integral transverse rib roughness and fitted with centre-cleared twisted-tape

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral transverse ribs and fitted with centre-cleared twisted-tape have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the centre-cleared twisted tapes in combination with transverse ribs perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of centre-clearance. This result is useful for the design of solar thermal heaters and heat exchangers. (C) 2012 Elsevier Inc. All rights reserved.