Heat transfer and pressure drop characteristics of alternating clockwise and counter clockwise twisted tape inserts in the transitional flow regime

• Published in: International journal of heat and mass transfer Vol. 133; pp. 203 - 217
• Main Authors: Abolarin, S.M., Everts, M., Meyer, J.P.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2019; Elsevier BV
• Subjects: Circular tubes; Clockwise; Copper; Counter clockwise; Enhanced; Fluid dynamics; Fluid flow; Grashof number; Heat flux; Heat transfer; Insert; Inserts; Laminar flow; Laminar heat transfer; Pressure drop; Reynolds number; Tape; Transition; Turbulent flow; Twisted; Clockwise; Tape; Counter clockwise; Enhanced; Transition; Insert; Twisted
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.12.107

•Heat transfer and pressure drop in the transitional flow regime.•Experiments with clockwise and counter clockwise twisted tape inserts.•Tape connection angle enhanced heat transfer.•Start and end of transition depended on connection angle and heat flux.•Earlier transition with increased connection angle and decreased heat flux. The purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics in a smooth circular tube with alternating clockwise and counter clockwise twisted tape (CCCTT) inserts. The CCCTT inserts were fabricated from copper plate strips with a length, width and thickness of 450 mm, 18 mm and 1 mm respectively. The strips were twisted to obtain a twist ratio of 5 and 12 strips were joined longitudinally so that a clockwise direction twisted tape insert was connected to a counter clockwise direction twisted tape. The assembling was at connection angles of 0°, 30° and 60°, to form CCCTT inserts with an overall length of 5.27 m. The CCCTT inserts were placed in a smooth circular copper tube with an inner diameter of 19 mm. Water was used as the test fluid and experiments were conducted at constant heat fluxes of 1.35, 2, 3 and 4 kW/m2 between Reynolds numbers of 300 and 11,404. This covered the laminar, transitional and turbulent flow regimes. Specific attention was given to the identification of the transitional flow regime with the CCCTT inserts and the influence of the connection angle and heat flux on the transitional flow regime. It was found that both the start and the end of the transitional flow regime were influenced by the connection angle and the heat flux. When different connection angles were compared it was found that an increase in connection angle enhanced the heat transfer in the transitional flow regime. An increase in heat flux significantly enhanced the heat transfer in the laminar flow regime and delayed transition. Heat transfer and pressure drop correlations were developed to predict the experimental data in the laminar, transitional and turbulent regimes as a function Reynolds number, modified Grashof number and connection angle.