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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

VORTEX HEAT TRANSFER ENHANCEMENT BY OVAL-TRENCH DIMPLES IN NARROW CHANNELS

Get access (open in a dialog) DOI: 10.1615/IHTC16.hte.022874
pages 5259-5266

Résumé

Symmetrical and slightly asymmetrical dimples still dominate in most studies on Vortex Heat Transfer Enhancement and are characterized by low velocities of secondary flows and by high hydraulic losses. In 2003, the authors have introduced the concept of oval dimples. An oval dimple is a spherical dimple with a cylindrical insert placed between the dimple halves. Except for depth and diameter, an oval dimple has two new parameters: cylindrical insert length and orientation angle to the direction of main flow. The orientation of 45 degrees to direction of main flow was determined as optimal. Recently, authors have achieved a better understanding of governing flow mechanisms around oval dimples and introduced so-called oval-trench dimples that are characterized by much longer cylindrical insert (relative dimple length is 4-6). Results of performed calculations at the turbulent air flow over array of oval-trench dimples with relative length of 6 and relative depth of 0.3 at Re number of 10,000 indicated an over four-fold growth of heat transfer. At the same time the friction in the separation zone was increased in just four times. Flow visualization has demonstrated formation of a harness vortex structure that is shedding from the dimple edge. Thermal efficiency for evaluated channel with the oval-trench dimple has been increased by a factor of 1.66, while hydraulic losses − by 1.45 in comparison to non-dimpled channel. The paper discusses the methodology of using the VP2/3 code as well as the results of numerical studies with varied dimple geometry and flow parameters.