Thermal characteristics in a heat exchanger tube fitted with triple twisted tape inserts

In the present study, the influences of triple twisted tapes on heat transfer rate, friction factor and thermal enhancement efficiency were experimentally investigated. The triple twisted tapes were used as swirl flow generators in the test section. The investigations were conducted using the mild steel triple twisted tapes with four different twist ratios (y= 1.92, 2.88, 4.81 and 6.79) for Reynolds number ranging from 7200 to 50,200 under uniform heat flux condition. The experimental results demonstrated that the Nusselt number, friction factor and thermal enhancement efficiency increased with decreasing twist ratio. The results indicated that the presence of triple twisted tapes led to a higher increase in the heat transfer rate over the plain tube. The Nusselt number and friction factor of using the triple twisted tape inserts were found to be increased up to 3.85 and 4.2 times when compared with the plain tube, respectively. The heat transfer performance was evaluated based on the constant blower power and the performance was achieved to be 1.44 by the use of triple twisted tape inserts. Finally, correlations were developed based on the data gathered during this work for predicting the heat transfer, friction factor and thermal enhancement efficiency through a circular tube fitted with triple twisted tape inserts in terms of twist ratio (y), Reynolds number (Re) and Prandtl number (Pr). © 2013 Elsevier Ltd.