Experiments are reported on initial instability, turbulence, and overall heat transfer in a porous medium heated from below. The porous medium comprises either water or a water-glycerin solution and randomly stacked glass spheres in an insulated cylinder of height:diameter ratio of 1.9. Heating is with a constant flux lower surface and a constant temperature upper surface, and the stability criterion is determined for a step heat input. The critical Rayleigh number for the onset of convection is obtained in terms of a length scale normalized to the thermal penetration depth as for . Steady convection in terms of the Nusselt and Rayleigh numbers is for . Time-averaged temperatures suggest the existence of a unicellular axisymmetric flow dominated by upflow over the central region of the heated surface. When turbulence is present, the magnitude and frequency of temperature fluctuations increase weakly with increasing Rayleigh number. Analysis of temperature fluctuations in the fluid provides an estimate of the speed of the upward moving thermals, which decreases with distance from the heated surface.
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November 2008
This article was originally published in
Journal of Heat Transfer
Research Papers
Stability and Convection in Impulsively Heated Porous Layers
M. J. Kohl,
M. J. Kohl
Mem. ASME
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455
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M. Kristoffersen,
M. Kristoffersen
Mem. ASME
Department of Mechanical Engineering,
e-mail: mkristoffersen@mmm.com
University of Minnesota
, Minneapolis, MN 55455
Search for other works by this author on:
F. A. Kulacki
F. A. Kulacki
Fellow ASME
Department of Mechanical Engineering,
e-mail: kulacki@me.umn.edu
University of Minnesota
, Minneapolis, MN 55455
Search for other works by this author on:
M. J. Kohl
Mem. ASME
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455
M. Kristoffersen
Mem. ASME
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455e-mail: mkristoffersen@mmm.com
F. A. Kulacki
Fellow ASME
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455e-mail: kulacki@me.umn.edu
J. Heat Transfer. Nov 2008, 130(11): 112601 (9 pages)
Published Online: August 28, 2008
Article history
Received:
June 21, 2007
Revised:
April 13, 2008
Published:
August 28, 2008
Citation
Kohl, M. J., Kristoffersen, M., and Kulacki, F. A. (August 28, 2008). "Stability and Convection in Impulsively Heated Porous Layers." ASME. J. Heat Transfer. November 2008; 130(11): 112601. https://doi.org/10.1115/1.2957484
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