Twisted tapes inserts

FIGURE 5.47 A circular tube with a twisted tape inserted [1],... 

R. M. Manglik, and A. E. Bergles, Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes Part I—Laminar Flows, J. Heat Transfer, (115) 881-889,1993. 

S. W. Hong, and A. E. Bergles, Augmentation of Laminar Flow Heat Transfer in Tubes by Means of Twisted-Tape Inserts, tech. rep. HTL-5, ISU-EMI-Ames 75011, Eng. Res. Inst., Iowa State University, Ames, 1974. 

Swirl-flow devices include a number of geometric arrangements or tube inserts for forced flow that create rotating and/or secondary flow inlet vortex generators, twisted-tape inserts, and axial-core inserts with a screw-type winding. 

Turbulent-flow heat transfer in uniformly heated tubes with twisted-tape inserts has been correlated by [195]... 

FIGURE 11.33 Isothermal friction factor data for twisted-tape inserts. 

FIGURE 11.34 Performance of twisted-tape inserts with air (FG-2a). 

FIGURE 11.36 Influence of twisted-tape inserts on subcooled boiling CHF of water (data from Ret 200). 

Royal and Bergles [167, 168] found that twisted-tape inserts improved heat transfer coefficients for in-tube condensation of water by 30 percent however, the pressure drop was quite high. Luu and Bergles [169,170] report similar results for R-113. The following heat transfer correlations are recommended. 

Extensive experimental work was undertaken at Babcock and Wilcox to obtain detailed heat transfer and pressure drop information as well as operating experience. Summary articles by Rhode et al. [245] and Schluderberg et al. [246] elaborate on the conclusions of this work. Heat transfer coefficients for heating were improved by as much as a factor of 10 through the addition of graphite. The suspensions were also shown to be far superior to gas coolants on the basis of pumping power requirements, especially when twisted-tape inserts... 

Rough tube wall with twisted-tape insert (Bergles et al. [354])... 

Internally finned tube with twisted-tape insert (Van Rooyen and Kroeger [356])... 

R. S. Van Rooyen and D. G. Kroeger, Laminar Flow Heat Transfer in Internally Finned Tubes With Twisted-Tape Inserts, in Heat Transfer 1978, Proceedings of the 6th International Heat Transfer Conference, vol. 2, pp. 577-581, Hemisphere, Washington, DC, 1978. 

Heat Transfer Enhancements Heat transfer enhancements increase the film heat transfer coefficient, thus improving U and consequently heat tfansfer in the exchanger. In the case of the ubiquitous ST heat exchanger, heat transfer enhancement can be achieved on the shell and/or tube sides as required. Tube-side enhancements help in improving the film heat transfer coefficient on the tube side, and are useful if the exchanger involved has lower film heat transfer coefficient on the tube side. Tube-side enhancements include, but are not limited to, twisted-tape inserts, coiled-wire inserts and internal fins. Similarly, shell-side enhancements are used to improve the heat transfer coefficient on the shell side. They include helical baffles, external fins and Expanded Metal (EM) baffles. More details on heat transfer enhancements are available in Pan et al. (2013). 

Shiralkar and Griffith (1970) determined both theoretically (for supercritical water) and experimentally (for supercritical carbon dioxide) the limits for safe operation, in terms of the maximum heat flux for a particular mass flux. Their experiments with a twisted tape inserted inside a test section showed that heat transfer was enhanced by this method. Also, they found that at high heat fluxes, DHT occurred when the bulk fluid temperature was below and the wall temperature was above the pseudocritical temperature. 

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