Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part II—Transition and Turbulent Flows

Abstract

Thermal-hydraulic design correlations are developed to predict isothermal f and Nu for in-tube, turbulent flows with twisted-tape inserts. Experimental data taken for water and ethylene glycol, with y = 3.0, 4.5, and 6.0, are analyzed, and various mechanisms attributed to twisted tapes are identified. Tube blockage and tape-induced vortex mixing are the dominant phenomena that result in increased heat transfer and pressure drop; for loose- to snug-fitting tapes, the fin effects are insignificant. The limiting case of a straight tape insert correlates with the hydraulic-diameter-based smooth tube equation. Tape twist effects are thus isolated by normalizing the data with the asymptotic predictions for y = ∞, and the swirl effects are found to correlate with Re and l/y. The validity of the final correlations is verified by comparing the predictions with previously published data, which include both gases and liquids, under heating and cooling conditions and a wide range of tape geometries, thereby establishing a very generalized applicability. Finally, correlations for laminar (presented in the companion Part I paper) and turbulent flows are combined into single, continuous equations. For isothermal f, the correlation describes most of the available data for laminar-transition-turbulent flows within ±10 percent. For Nu, however, a family of curves is needed due to the nonunique nature of laminar-turbulent transition.

Numerical investigation of heat transfer and fluid flow of water through a circular tube induced with divers' tape inserts

“…The resistance to heat flow in a heat exchanger is broken by the disturbance introduced to the flow by the twisted-tape and therefore allow more heat to be transferred [3,9,10]. The enhancement of heat transfer in a tube fitted with twisted-tape is attributed to the reduction in hydraulic diameter, the secondary motion generated by the twisted tape, and the partitioning and blockage of the tube cross section by the tape [11].…”

Review on Recent Progresses in Heat Transfer Enhancement Through the Use of Passive Vortex Generators and Its Applications in Solar Parabolic Trough Systems

“…Whitham [16] back in the 19 th century studied the effects of the twisted tapes which results in enhancement of the twisted tape inserts in fire tubes of steam boiler. The important effects induced by twisted tapes which results in enhancement of heat transfer in flow as given by Bergles [17] are a) swirl flow which improves fluid mixing, b) helical motion of the fluid flow which results in effectively longer flow path and c) blockage of the tube flow cross section which results into a higher flow velocity. Thus considering this rationale following points can be considered as responsible for the heat transfer enhancement.…”

Augmentation of Heat Transfer in a Single Phase Flow Using Simple and Modified Twisted Tape Inserts: A Review

“…As per the Manglik and Bergles [4] the mechanism of heat transfer augmentation is "due to the tube partitioning and flow blockage, longer flow path, and secondary fluid circulation and fin effect"Flow regime map for isothermal friction factors in tube flows with twisted-tape inserts gives four region namely viscous flow, thermally developed swirl flow; swirl-turbulent transition and fully developed turbulent swirl flow based on the Reynolds number. Manglik and Bergles [5] investigated that the augmentation of heat transfer coefficient and pressure loss is strong function of twisted tape induced vortex motion for turbulent flow and uniform wall temperature. They developed correlation of friction factor for combined laminar and turbulent flow and suggest that a single expression is not sufficient to describe heat transfer in transition flow region.…”