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国际计算热科学期刊
ESCI SJR: 0.249 SNIP: 0.434 CiteScore™: 0.7

ISSN 打印: 1940-2503
ISSN 在线: 1940-2554

国际计算热科学期刊

DOI: 10.1615/.2014005755
pages 219-240

FLOW REVERSAL IN MIXED CONVECTION IN VERTICAL CONCENTRIC ANNULI: WHY IT OCCURS IN BUOYANCY-AIDED FLOWS

Esmail M. A. Mokheimer
Mechanical Engineering Department King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

ABSTRACT

The main purpose of this article is to shed more light on the cause of flow reversal in vertical concentric annular channels for buoyancy-aided flows under isothermal boundary conditions. The concept used to quantify the critical values of the modified buoyancy parameter (Gr/Re)critical at which the adverse pressure gradient first occurs is outlined and applied to analytically estimate these critical values. The conditions for flow reversal are also analytically obtained for buoyancy-aided and buoyancy-opposed flows. The analytical solutions show that pressure buildup takes place only for buoyancy-aided flows while flow reversal occurs for both buoyancy-aided and buoyancy-opposed flows. The analytical solutions reveal also that values of the buoyancy parameter required to initiate the pressure buildup for buoyancy-aided flows in the vertical annuli are smaller than those required to initiate the flow reversal. Thus, for buoyancy-aided flows, pressure buildup would precede the flow reversal. A numerical scheme is developed and used to simulate the development of pressure and pressure gradient in the entrance region of the vertical concentric annuli. The numerical scheme is validated by the analytical solution as well as the previously published pertinent results. Numerical results that show the pressure buildup in the developing entry region of the annuli for values of the modified buoyancy parameter (Gr/Re) greater than its critical values (Gr/Re)critical along with other flow and heat transfer parameters of importance are also presented and discussed. The locations of pressure buildup as well as those of flow reversal have been obtained and reported.


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