Analysis of Friction and Heat Transfer Characteristics of Tubes with Trapezoidal Cut Twisted Tape Inserts

Abstract

The thermo-hydraulic properties of circular tubes with a twisted tape inside (used accordingly to induce turbulence and enhance heat transfer through the tube wall) are described for Reynolds Numbers ranging from 830 to 1990. Tapes twisted with the three distinct twist ratios are considered, namely, 6, 4.4 and 3. Air is used as the working fluid in several tests. For the sake of comparison, the standard tube with no insert is also examined. It is shown that in the presence of the twisted tape, the 'frictional factor' , 'Nusselt Number' and the 'thermal performance factor' are much higher than those obtained for the plain tube. Moreover, the tapes having the lowest twist ratio, i.e., 3, are more effective than the others in terms of heat transfer augmentation. The 'thermal performance factor' is greater than one for all the twisted tapes used in the experiments, which confirms the enhanced performances of the heat exchanger and the related savings in terms of total energy.