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Transient heating in Benard convection


Nielsen, Richard Carl (1971) Transient heating in Benard convection. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/WPPS-5214.


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Experimental results are presented for a study of the effects of time-dependent heating on Benard convection, where the fluids were 5 centistoke (cs), 100 cs and 500 cs viscosity grades of silicone oil. Fluid layer depths were 0.00635m, 0.01270m and 0.01905m. For each run the heat flux at the lower surface was approximately constant, which in dimensionless units was between [...] and [...]. The study examined the effects of different heating rates on the onset of convection, the change of the Rayleigh number with time and the development of motion. Visual observations were made from shadowgraph images, which were recorded photographically.

A supplementary analytical analysis of the onset of motion was performed. The results of the work support the trends of the critical time data found in the experiments.

On the basis of the experimental results the conculsions are that as the heat flux at the lower surface is increased, the temperature difference required for the initiation of convection increases while the time to the onset of motion decreases. For the higher heating rates a "new" small closed cell pattern is observed shortly after the onset of motion. This pattern does not appear in the steady-state system. Because of the "large" (approximately greater than 100) Prandtl number, specifying the time and the heat flux at the lower surface is sufficient to characterize the state of the fluid layer.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Sabersky, Rolf H.
Thesis Committee:
  • Unknown, Unknown
Defense Date:21 May 1971
Record Number:CaltechETD:etd-10112005-093233
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4030
Deposited By: Imported from ETD-db
Deposited On:11 Oct 2005
Last Modified:21 Dec 2019 04:56

Thesis Files

PDF (Nielsen_rc_1971.pdf) - Final Version
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