Thermal and Friction Characteristics of Laminar Flow through Square and Rectangular Ducts with Transverse Ribs and Twisted Tapes with and without Oblique Teeth

Abstract

Thermal and friction characteristics of a laminar 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. Correlations for predicting the friction factor and Nusselt number have been developed and performance has been evaluated. Although both friction factor and Nusselt number are the highest for the case of 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 the best and this is recommended. However, where 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 in combination with transverse ribs can be recommended since the heat exchanging surface area requirement will be less.