(227aa) Heat Transfer Analysis of a Non-Newtonian Fluid Flowing through a Circular Tube Inserted with Multiple Twisted-Tapes Using CFD

Heat transfer analysis of a non-Newtonian fluid flowing through a circular tube inserted with multiple twisted-tapes using CFD

Maritza E. Cervantes-Gaxiola¹, Oscar M. Hernández-Calderón^1*, Eusiel Rubio-Castro¹, Erika Y. Rios-Iribe¹, José J. Caro-Corrales¹, Jesús R. Ortiz-del-Castillo¹

¹Chemical and Biological Sciences Department, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa 80013, Mexico.

*omhc@uas.edu.mx

Abstract

In the present work, the thermal-hydraulic behavior of non-newtonian flow through circular tubes inserted with multiple plain- and twisted-tapes mounted on a cylindrical rod is investigated using Computational Fluid Dynamic (CFD), which involves numerical solutions of the mass, momentum, and energy conservation equations. 3D numerical simulations of the heat transfer are conducted using the FLUENT^TM 6.3 software, and it is found that the inserts with multiple plain-tapes generate an axial or straight flow, and the inserts with multiple twisted-tapes induce a swirling flow. Therefore, the inserts with multiple twisted-tapes cause larger flow paths than inserts with multiple plain-tapes in the vicinity of the tube wall, this generates an enhancement in the heat transfer process is observed. Data reduction is applied to the CFD data; and for all cases, a good agreement is found between the calculated friction and Reynolds numbers, and the theoretical relationship (f = 16/Re) over the Reynolds number range of 0.2-100. The inserts with plain-tapes generate flow cores practically identical at different flow regimens, which cause the momentum and heat transfer processes to be directly dependent of the intensity of the flow regime. Meanwhile, the inserts with twisted-tapes generate flow cores whose shape and interaction with the heating surface depend strongly of the flow regime and the insert geometry, the reason for this is that the insert induces a swirling flow, which generates a centrifugal force that displaces, distorts and even destroys the flow cores  affecting both the effective surface of the momentum and heat transfer, as well as the intensity of the velocity gradients and the temperature between the tube wall and the insert. The tube inserted with multiple twisted-tapes shows superior thermal performance in contrast to the plain tube or the tube inserted with multiple plain-tapes, this is due to a swirling flow along the tube is induced. All tubes inserted with multiple twisted-tapes exhibit a maximum thermal performance of: 1.91, 1.82, 1.72 and 1.69 for 2, 3, 4 and 5 twisted-tapes, respectively. The inserts with 4 and 2 twisted-tapes lead to the best enhancements of thermal performance over the reference Reynolds number intervals of 1-50 and 50-2000, respectively. In general, the thermo-hydraulic performance depends in a complex way on the insert geometry and the flow regime.