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International Heat Transfer Conference 12

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Heat Transfer Enhancement by Rib-Induced Secondary Flow inside a Circular Tube

Sadanari Mochizuki
Tokyo University of Agriculture and Technology, 2-24-16, Naka-cho, Koganei-shi, Tokyo 184, JAPAN

Robert Kiml
Tokyo University of Agriculture and Technology, Department of Mechanical Systems Engineering, Koganei-shi,Nakacho 2-24-16,Tokyo 184-8588, 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 the secondary flow as well as to cause the flow separation and reattachment. They 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 60-deg for the angled ribs and 90-deg 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 the 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 due to a development of the rib-induced secondary flow that develops in a form of a pair of vortices. This secondary flow conveys the colder and higher momentum fluid from the tube core region towards the heated wall and consequently augments the heat transfer. The present study clearly demonstrated 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 is to convey fluid directly from the central core region of a tube is augmented appreciably.

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