Influence of a magnetic field on the stability of a binary fluid with Soret effect

The effect of both magnitude and orientation of a uniform magnetic field on the critical transition occurring within an electrically conducting binary fluid layer, stratified in temperature and concentration, taking into account the Soret effect, is investigated numerically. For such a configuration, the results show that the critical thresholds corresponding to an arbitrary orientated magnetic field can be derived from those obtained for a vertical magnetic field and that the axes of the marginal cells are aligned with the horizontal component of the magnetic field. Moreover, an analytical study is conducted to investigate the impact of the magnetic field on long-wavelength instabilities. The effect of the magnetic field on such instabilities reveals a new phenomenon consisting in major changes of the unstable modes that lose their unicellular nature to regain their multi-roll characteristic, as it is the case without magnetic field for psi < psi(l0) = 131Le/(34 - 131Le). For a binary fluid characterized by a Lewis number Le and a separation factor psi > psi(l0), the value of the Hartmann number Ha(l)(psi, Le) corresponding to that transition responsible for a significant change in mass and heat transfer can be determined from the analytical relations derived in this work. (C) 2015 Academie des sciences. Public par Elsevier Masson SAS. Cet article est public en Open Access sous licence CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/).