On the Oscillatory Instability of Closed-Loop Thermosyphons

[+] Author and Article Information
K. Chen

Department of Mechanical and Industrial Engineering, University of Utah, Salt Lake City, UT 84112

J. Heat Transfer 107(4), 826-832 (Nov 01, 1985) (7 pages) doi:10.1115/1.3247510 History: Received October 06, 1983; Online October 20, 2009


The stability of natural convection flows in single-phase closed-loop thermosyphons is investigated. The thermosyphons considered in the present analysis are fluid-filled tubes bent into rectangular shapes. The fluid is heated over the lower horizontal segment and cooled over the upper horizontal segment. Analytical and numerical solutions are presented for a range of loop aspect ratios and radii for both laminar and turbulent flows. It is found that the steady-state results for thermosyphons with different aspect ratios and radii can be expressed in terms of a single dimensionless parameter. When this parameter is less than a critical value, the flow is always stable. Above this critical point, oscillatory instability exists for a narrow range of a friction parameter. The calculated neutral stability conditions show that the flow is least stable when the aspect ratio of the loop approaches unity. The frequency of the convection-induced oscillation is slightly higher than the angular frequency of a fluid particle traveling along the loop.

Copyright © 1985 by ASME
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