Magnetic field effect on cooling of the magnetizable plate in magnetic fluids

V. V. Gogosov¹ - O. A. Grishanina² - A. Ya. Simonovskii²

¹ Institute of Mechanics of the M.V.Lomonosov Moscow State University, 117192, Moscow, Russia
² Academy of Stavroplol, 355014 Stavroplol, Russia

Abstract
Magnetic field magnitude effect on heat transfer near magnetizable plate cooling in magnetic fluids is investigated. The thermocouples have been mounted in six points of the surface plate along the length of the plate. The graphs showing the temperature dependence versus time in the absence of the magnetic field and in the fields 21, 40, 76 and 110 kA/m are presented. It is found that the heat transfer intensity depends significantly on the magnetic field magnitude and disposition of the thermocouples on the surface. It is found that in the magnetic field 21 kA/m the cooling in the central part of the plate occurs with the same intensity as in the absence of the field and with less intensity as compared with the other points of the plate surface. Near the ends of the plate the cooling rate is much more than that in the absence of the field. As the magnetic field magnitude increases the cooling rate in the central part of the plate decreases and becomes less than that in the absence of the field. The heat transfer dependence on the magnetic field magnitude is explained in this work by the distribution of the magnetic forces acting on the fluid surrounding the plate. These forces repulse the fluid from the plate in the central part of the plate and press the fluids against the plate in the vicinity of its ends. As a result the vapour layer thickness in the central part of the plate increases and the heat transfer decreases. In the vicinity of the ends of the plate the vapour layer thickness decreases and the heat transfer increases. However, the increment of the heat transfer with change of the magnetic field occurs nonmonotonically. In the field 40, 76 and 110 kA/m the heat transfer in some points in the neighbourhood central part of the plate occurs with much more intensity than that in the points remote from the center, where forces pressing the fluid against the plate larger and the vapour layer thickness thinner. Such nonmonotone change of the heat transfer intensity with increasing magnetic field is explained by instability of the magnetic fluid-vapour interface. Experiments on simulation of the magnetic field effect on the formation and the shape of the vapour cavity surrounded the magnetizable cooling plate are described. Figs 6, refs 9.