Microconvection and mass transfer near bodies in non-uniformly magnetized ferrofluid

Abstract

Introduction. Experimental observations of magnetic fluid behaviour around a grid subjected to a magnetic field shows that the presence of a temperature gradient creates a notable separation of the fluid between both sides of the grid with different temperatures [1]. Some separation of the ferrofluid occurs also without a magnetic field. Our aim here is to discuss in more detail the ferrofluid convection and subsequent separation under the action of magnetic field force resulting from the magnetic Soret effect. Understanding of the directed mass transfer in a nonuniformly magnetized ferrofluid is still insufficient, and different opinions about the role of various mechanisms are presented. Therefore, a detailed description of heat and mass transfer processes are required [2]. The heat and mass transfer processes are analysed numericaly by a two-dimensional macroscopic model in order to estimate the role of convection around micron size bodies (microconvection). Particularly, a grid consisting of large number of equidistantly spaced nonmagnetic or magnetic cylinders is considered. The example of the system is shown in Fig. 1a. Non-uniform magnetization of the ferrofluid surrounding each cylinder creates an oriented microconvection, which is the main reason for appearance of the magnetic Soret effect. Therefore, distributions of temperature, magnetic field, concentration, and velocity have to be obtained for a correct description of the microconvection.