Control of Temperature Distribution at Cylinder Surface by Magnetic Fluid

Abstract

The present study deals with the influence of a magnetic fluid coating, held onto a circular cylinder surface by a magnetic field, on the temperature distribution at the surface of a cylinder heated by a constant heat flux. The temperature distribution over the cylinder surface in the fluid is determined by the heating power of the cylinder and the incoming flow structure. The flow structure near the cylinder can be changed by applying a magnetic fluid coating over its surface and by holding it with a magnetic field. In this case, heat from its surface to the external flow is removed by two modes. First, the heat is transferred to the external flow due to heat conduction of the magnetic fluid. Second, the heated layers of the magnetic fluid are entrained due to circulation and give up their heat to the external flow at the interface. Thus, there are two mechanisms of removing the heat inside the magnetic-fluid coating: conductive and convective. The balance of these two mechanisms is determined by the circulation intensity inside the coating and by the value of magnetic fluid thermal conductivity. A steady laminar flow of viscous fluid past a circular cylinder with magnetic fluid kept on its sur-face under a magnetic field is investigated numerically by finite-element method. A grid of 5751 nodes is used. The cases of Reynolds number Re = 10, 30, 100 are considered. The role of heat conduction ratio is determined for the meanings A = 0.1, 1, 10. The great influence of magnetic fluid coating on surface temperature distribution is discovered in the paper. The distribution can be profitably varied by the magnetic fluid properties and flow velocity: it can be nonmonotonic, and the temperature of a solid can increase in the direction opposite to the direction of fluid flow.