Abstract
An experimental investigation was accomplished to evaluate the performance of heat transfer for turbulent flow through a tube with helical tape inserts. The mild steel helical tape inserts with different twist ratios of 1.88, 3.13, 4.69, 6.41 and 7.81 were used in the flow field. Heat transfer and pressure drop data were prompted for a wide range of Reynolds number from 7200 to 50,000. The experimental results indicated that the Nusselt number, friction factor and thermal performance factor were increased with decreasing twist ratio. The results also showed that helical tape inserts of different geometries in a circular tube enhanced the heat transfer rate significantly with corresponding increase in friction factor. Nusselt number and friction factor for the tube with inserts were found to be increased up to 260 and 285 %, respectively, than those over the plain tube values at the comparable Reynolds number. The heat transfer performance was evaluated and found to be 44 % higher compared to the plain tube based on the constant blower power. Finally, new correlations were proposed for the twist ratios ranging from 1.88 to 7.81 for predicting the heat transfer, friction factor and thermal performance factor for turbulent flow through a circular tube fitted with helical tape inserts.
Highlights
Heat transfer augmentation techniques are frequently used in heat exchanger systems in order to enhance heat transfer and improve the thermal performance
The results obtained from present experiments on heat transfer and friction factor characteristics of the plain tube were verified in terms of Nusselt number and friction factor
This was attributed to the increase of turbulent intensity as the Reynolds number was increased, which led to an amplification of convective heat transfer
Summary
Heat transfer augmentation techniques are frequently used in heat exchanger systems in order to enhance heat transfer and improve the thermal performance. Eiamsa-ard et al [12] presented the experimental results of mean Nusselt number, friction factor and enhancement efficiency through a circular tube with short-length twisted tape inserts of several tape length ratios mounted at the entry of the test section under uniform heat flux condition. Sivashanmugam and Suresh [21, 22] evaluated the heat transfer enhancement, friction factor and thermal performance characteristics in a circular tube fitted with helical screw-tape as well as regularly spaced helical screw-tape inserts for the turbulent flow regime. The effect of swirling flow generated by the helical tape inserts on heat transfer performance and friction factor characteristics of turbulent flow through a circular tube was evaluated. It was not possible to quantify this, heat was conducted through the ends of the test section to adjacent sections
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