| Given the vast numbers of heat exchangers used in the process industry for viscous fluids, substantial capital and operating cost savings can be achieved by employing twisted tapes to improve their heat transfer performance. So people are interested in the using of twisted-tape insert.A large number of researches on twisted-tape have been reported in the literature. But most of the researches were conducted with turbulent flows or laminar flows. It is evident that the correlations reported in the literature present very wide performance envelope for the predictions for any given flow condition and tape geometry. The majority of them can only be applied to the restricted range of the databases on which they have been developed. Most of the data are obtained in the condition of low temperature and normal pressure. No research about licjuid or gas flowing in the transition regime has been reported. For this regime, the heat transfer is usually predicted by the linear interpolation or extrapolation of the results of turbulent and/or laminar regimes, associated with great uncertainty in the evaluation of the performance of heat transfer.Experiment is carried out with air in tube of D=44mm with twisted-tape inserts of Y=1.88, 2.62, and 3.81. The parameters ranges are P=0.1~0.4 MPa, T=150~700癈. and Re=2400 - 45000 , covering the transition and turbulent regimes. In the experiment various mechanisms attributed to twisted tapes are identified. The increase in heat transfer coefficients and the concomitant pressure drops inserts is found to be strongly influenced by tape-induced vortex motion and higher flow velocity due to the tube blockage.. Tape twist effects are modeled by the functional relationships of Re, Pr and Y. Based on the analysis and experimental data the correlations for f and Nu for the transition and turbulent regimes are developed, respectively. The comparison between the present results and some typical correlations is also made..
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