Magneto-thermal convection of low concentration nanofluids

摘要

The main aim of this paper was to analyze possible utilization of the low concentration nanofluids and the magnetic field to enhance heat transfer. The studied fluids were based on water with an addition of copper particles (40-60 nm diameter). They belonged to the diamagnetic group of materials. As a first attempt to stated target the analysis of enclosure placed in the maximal value of square magnetic induction gradient was carried out. The maximum was in the centre of investigated cavity and it caused the most complex system of gravitational and magnetic buoyancy forces. In the lower part of cavity both forces acted in the same direction, while in the upper part they counteracted. Therefore an enhancement and attenuation of heat transfer could be observed. Due to the particle concentration and magnetic field action the character of flow was changed. In the case of 50 ppm nanofluid the flow was steady end the strong magnetic field didn’t change much in its structure except for the suppression of some vortices. In the case of 500 ppm nanofluid the flow was not steady even without magnetic field, but increasing magnetic induction caused change of its structure towards the inertial-convective regime of turbulent flow.