Eur. Phys. J. E (2004) 15: 305-309
https://doi.org/10.1140/epje/i2004-10070-8

Transient oscillations in Soret-driven convection in a colloidal suspension

Istituto Nazionale per la Fisica della Materia and Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133, Milano, Italy

^* e-mail: stefano.mazzoni@fisica.unimi.it

Received: 11 August 2004
Accepted: 21 October 2004
Published online: 16 November 2004

Abstract

We present measurements of the transient stage of Soret-driven convective instability. The sample is a diluted colloidal suspension of silica spheres in water with an unusually large negative Soret coefficient S _T. A large temperature gradient (heating from above) is rapidly applied over the sample, while a shadowgraph imaging technique provides images of the convective flow. From the processing of the variance of the intensity of the images we are able to recover the time evolution of the overall intensity of the convective flow. A typical evolution of such signal exhibits, after a latency time, a peak followed by some damped oscillations leading to a steady-state value. Both the onset time τ_p (the temporal position of the first peak), and the oscillation period τ_osc show a power law dependence as a function of the solutal Rayleigh number R _s. The exponents found are compared with predictions from existing models.