THERMOHYDRAULICS OF TURBULENT FLOW THROUGH SQUARE AND RECTANGULAR DUCTS WITH TRANSVERSE RIBS AND TWISTED TAPES WITH AND WITHOUT OBLIQUE TEETH

Abstract

Thermal and friction characteristics of turbulent flow through square and rectangular ducts with periodic transverse ribs and different types of twisted tapes with and without oblique teeth have been studied experimentally. Circular ducts have also been used. Correlations for predicting the friction factor and the Nusselt number have been developed and performance has been evaluated. Although both the friction factor and the Nusselt number are higher for all types of twisted tapes with oblique teeth in combination with transverse ribs, the performance evaluation has shown that the ducts with transverse ribs and regularly spaced twisted-tape elements with oblique teeth are better than those in the case without oblique teeth and this is recommended. Also, since the pressure drop in a heat exchanger is a small fraction of the total system pressure drop, the heat transfer being higher, full-length and short-length twisted tapes with oblique teeth in combination with transverse ribs can be recommended since the heat exchanging surface area requirement will be less.