Issue
EPL
Volume 86, Number 1, April 2009
Article Number 14006
Number of page(s) 6
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
DOI http://dx.doi.org/10.1209/0295-5075/86/14006
Published online 22 April 2009
EPL, 86 (2009) 14006
DOI: 10.1209/0295-5075/86/14006

Specific roles of fluid properties in non-Boussinesq thermal convection at the Rayleigh number of 2$\times$108

A. Sameen1, R. Verzicco2 and K. R. Sreenivasan3

1   Department of Aerospace Engineering, Indian Institute of Technology Madras - Chennai-600036, India
2   University of Roma "Tor Vergata" - Roma, Italy, EU
3   International Centre for Theoretical Physics - Trieste 34014, Italy, EU

krs@ictp.it

received 6 September 2008; accepted in final form 11 March 2009; published April 2009
published online 22 April 2009

Abstract
We demonstrate the specific non-Boussinesq roles played by various fluid properties in thermal convection by allowing each of them to possess, one at a time, a temperature dependence that could be either positive or negative. The negative temperature dependence of the coefficient of thermal expansion hinders effective thermal convection and reduces the Nusselt number, whereas the negative dependence of fluid density enhances the Nusselt number. Viscosity merely smears plume generation and has a marginal effect on heat transport, whether it increases or decreases with temperature. At the moderate Rayleigh number examined here, the specific heat capacity shows no appreciable effect. On the other hand, the conductivity of the fluid near the hot surface controls the heat transport from the hot plate to the fluid, which suggests that a less conducting fluid near the bottom surface will reduce the Nusselt number and the bulk temperature.

PACS
47.55.pb - Thermal convection.
47.27.te - Turbulent convective heat transfer.
47.55.P- - Buoyancy-driven flows; convection.

© EPLA 2009