LAMINAR FLOW HEAT TRANSFER IN HELICAL OVAL-TWISTED TUBE FOR HEAT EXCHANGER APPLICATIONS

The heat transfer performance of a novel tube configuration that combines the swirling velocity induced by oval-twisting and secondary flow generated by a helical geometrical flow path is presented. The Nusselt number (Nu) and friction factor ( f) are compared for the laminar flow regime (Re = 250-2000) under isothermal wall conditions. Under the same flow and boundary conditions, the oval-twisted helical tube increased the Nu and slightly increased the f over the circular helical tube. The best performance with the highest Nu and lowest f occurs at the coil curvature ratio (d(h)/D) of 0.17. The quantified enhancement performance factor (eta) shows a 46 - 56% increase for the oval-twisted helical tube over the circular helical tube with d(h)/D = 0.17. Correlations for the Nu and f are developed and agreed with the numerical results: +/- 6% and +/- 5% for the Nu and f, respectively.