Augmented Heat Transfer in Square ducts with Transverse and Inclined Ribs with and without a gap

Abstract

The effect of the rib angle orientation and influence of a gap provided in integral ribs on heat transfer and pressure drop in a square duct with two opposite in-line ribbed walls is investigated. The experimental investigation has been performed for continuous ribs (with no gap) and ribs with a gap having relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) of 0.060 and rib attack angle of 900 and 600 for Reynolds number from 5000 to 40,000. Discrete ribs with relative gap position (d/W) of 1/5 and relative gap width (g/e) of 1.0 are investigated to compare their heat transfer performance with corresponding continuous ribs (without gape). The enhancement in heat transfer and friction factor of this roughened duct is also compared with smooth duct under similar flow condition. The results show that inclined ribs performs better than transverse ribs for both the cases i.e. for continuous ribs and ribs with a gap. The 600 ribs with a gap yields about 3.8-fold enhancements in Nusselt number and about 7.4-fold increase in the friction factor compared with smooth duct and about 1.1 times and 1.2 times that of 600 continuous ribs (without gaps) for the entire range of parameters investigated. However for 900 ribs the enhancement in heat transfer and factor is very low as compared to that of corresponding 600 ribs