Title

NATURAL CONVECTION IN AN ENCLOSURE WITH DISCRETE ROUGHNESS ELEMENTS ON A VERTICAL HEATED WALL.

Document Type

Conference Proceeding

Department

Mechanical Engineering

Conference Title

Heat Transfer, Proceedings of the International Heat Transfer Conference

Location

San Francisco, CA

Date of Presentation

1-1-1986

Abstract

Natural convection flow next to a heated wall with single and repeated, two-dimensional, rectangular roughness elements is studied numerically and experimentally. The objective is to determine how these roughness elements influence heat transfer rates from the wall. Each roughness element consists of a thermally conducting, horizontal cylinder of rectangular cross section attached to the heated, isothermal wall of an enclosure. The height of roughness is on the order of the boundary layer thickness. Dye flow visualization in water confirms the numerical prediction that the steady flow over these elements does not separate. Only at high Rayleigh numbers, when the boundary layer below the roughness is unsteady, is local instantaneous flow reversal observed. Although steady flow reversals near the wall are not predicted or observed, nearly stagnant regions are formed, particularly between closely spaced cylinders. The surface heat flux in these stagnant regions is relatively low, so the total heat transfer rate may be nearly the same as for a smooth wall in spite of the increased surface area.

Volume

4

First Page

1519

Last Page

1525

DOI

10.1615/ihtc8.3080

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