An experimental investigation of thermomagnetic convection in a tall enclosure subjected to progressive field gradients

An experimental setup is designed to study the recirculating flow of a magnetic fluid confined in a tall enclosure under the influence of both temperature and magnetic field gradients. The bench is instrumented with flow meters and temperature sensors positioned in strategical positions so that an average Nusselt number, Nu, can be properly measured. The magnetic field gradient is produced due to a set of three equally spaced neodymium magnets. A moving trail with the magnets is used in order to produce gradual increments of the applied magnetic field gradient under a piece of the test section by approximating the magnets to the cavity. A proper representation of the magnetic Rayleigh number, Ram, is used in order to measure how magnetic buoyancy forces affect the mean convective heat transfer coefficients. In this representation the variation of the average square of the applied field in opposite walls is used. This quantity is estimated through the analytical solution of the magnetic field produced by rectangular magnets in the free space. Our results show that it is possible to both increase or decrease the Nusselt number with respect to the intensity of magnetic field gradients, depending on the value of the gravitational Rayleigh number, Ra, in which the experiment occurs. An increase of 7% and a decrease of 9% on the average Nusselt were observed.The results are explained from a physic point of view with the aid of CFD analysis. A qualitative comparison with other experimental works is also presented.