Eur. Phys. J. E (2016) 39: 79
https://doi.org/10.1140/epje/i2016-16079-4

Regular Article

Locally induced laminar convection in liquid nitrogen and silicone oils

¹ GRASP, UR-CESAM - Physics Department B5, University of Liège, B-4000, Liège, Belgium
² Montefiore Institute B28, University of Liège, B-4000, Liège, Belgium

^* e-mail: alexis.duchesne@ulg.ac.be

Received: 8 March 2016
Revised: 21 June 2016
Accepted: 20 July 2016
Published online: 29 August 2016

Abstract

We present an experimental study of a laminar convective phenomenon induced by a centimetric heater totally immersed in a liquid pool (Rayleigh number ranging from 10⁴ to 10⁷). This local heating is observed to induce a laminar convection that differs from the classical Rayleigh-Bénard cells created by heating the whole bottom of the fluid: the convection pattern is no more periodic. In order to obtain a complete map of the velocity field, we use Particle Image Velocimetry technique. The vertical velocity between the counter-rotating convective cells is used as the relevant physical parameter to describe the phenomenon. The potential cooling applications of this problem lead us to choose liquid nitrogen as an experimental fluid. We thus compare the results obtained for various temperature gradients in liquid nitrogen with experiments performed at room temperature with silicone oils of various viscosities. The theoretical law for the maximal vertical velocity from classical Rayleigh-Bénard experiments is adapted to the specific geometry investigated by using a new definition for the characteristic wavelength. This length is studied and appears to be dependent on the liquid properties. We finally obtain a remarkable agreement between theory and experimental data.