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强化传热期刊
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ISSN 打印: 1065-5131
ISSN 在线: 1026-5511

强化传热期刊

DOI: 10.1615/JEnhHeatTransf.v10.i1.20
pages 9-20

Effects of Rib-Induced Secondary Flow on Heat Transfer Augmentation Inside a Circular Tube

Robert Kiml
Tokyo University of Agriculture and Technology, Department of Mechanical Systems Engineering, Koganei-shi,Nakacho 2-24-16,Tokyo 184-8588, Japan
Sadanari Mochizuki
Tokyo University of Agriculture and Technology, 2-24-16, Naka-cho, Koganei-shi, Tokyo 184, JAPAN
Akira Murata
Department of Mechanical Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
Virgil Stoica
Tokyo University of A&T, Department of Mechanical Systems Engineering, Koganei-shi, Nakacho 2-24-16, Tokyo 184-8588, Japan

ABSTRACT

Angled ribs were employed to induce secondary flow and to cause flow separation and reattachment. The ribs were mounted on the inner surface of a circular tube with a given interval in the direction of tube axis. The angle between the plane of each rib and the mean flow direction was 75°, 60°, and 45° for the angled ribs and 90° for the transverse ribs. The angled ribs were elliptic rings, whereas the transverse ribs were circular rings. Detailed local heat transfer measurement was conducted using as many as 350 thermocouples attached to the wall surface. Flow visualization by particle tracer method was also performed to investigate flow behaviors. It was found that the mean heat transfer coefficient for the entire tube was higher for the angled ribs than for the transverse ribs as a result of a development of the rib-induced secondary flow, which developed in the form of a pair of vortices. This secondary flow conveyed the colder and higher-momentum fluid from the tube core region toward the heated wall and consequently augmented the heat transfer. The present study clearly demonstrates the heat transfer superiority of angled ribs over conventional transverse ribs. In the case of angled ribs, the circumferential distribution of the heat transfer coefficients is the highest at the bottom of the tube as a result of the rotational direction of the secondary flow. It was confirmed that the heat transfer of the wall surface, to which the rotational direction of the secondary flow conveys fluid directly from the central core region of a tube, is augmented appreciably.


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