We investigate the early stages of mass convection in a colloidal suspension at high solutal Rayleigh number Ra^s. From the time evolution of shadowgraph images and by assuming a diffusive growth of the boundary layers we obtain an indirect measurement of the concentration boundary layer thickness delta* at the onset of convection. We show that the dimensionless boundary layer thickness delta= delta*/d scales as Ra<sub>s</sub><sup>-p</sup>, where Ras = Ra^sdelta is a modified solutal Rayleigh number for convection which accounts for the actual density unbalance and d is the thickness of the sample layer. This scaling behavior is analogous to that reported at steady state for turbulent convection in simple fluids. We find p = 0.35, a value compatible with the exponent 1/3, reported for turbulent heat convection in simple fluids at steady state.
Scaling behavior for the onset of convection in a colloidal suspension / R. Cerbino, S. Mazzoni, A. Vailati, M. Giglio. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - 94:6(2005), pp. 064501.064501-1-064501.064501-4.
Scaling behavior for the onset of convection in a colloidal suspension
R. CerbinoPrimo
;S. MazzoniSecondo
;A. VailatiPenultimo
;M. GiglioUltimo
2005
Abstract
We investigate the early stages of mass convection in a colloidal suspension at high solutal Rayleigh number Ra^s. From the time evolution of shadowgraph images and by assuming a diffusive growth of the boundary layers we obtain an indirect measurement of the concentration boundary layer thickness delta* at the onset of convection. We show that the dimensionless boundary layer thickness delta= delta*/d scales as Ras-p, where Ras = Ra^sdelta is a modified solutal Rayleigh number for convection which accounts for the actual density unbalance and d is the thickness of the sample layer. This scaling behavior is analogous to that reported at steady state for turbulent convection in simple fluids. We find p = 0.35, a value compatible with the exponent 1/3, reported for turbulent heat convection in simple fluids at steady state.Pubblicazioni consigliate
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