Non-uniform magnetic field impact on thermomagnetic convection of paramagnetic air in a permanent magnet-inserted horizontal annulus

Abstract

Heat transfer enhancement using an external magnetic field with a high level of energy economy is a promising subject. The permanent magnets with no additional electrical power consumption are adopted to produce the applied magnetic fields. The effects of the magnet assembly and magnet strength on the thermomagnetic convection of paramagnetic fluid in a horizontal annulus are studied numerically by a finite volume method. The variations of the flow pattern, thermal structure and convective heat transfer characteristics are investigated to clarify the heat transfer rate characteristics of thermomagnetic convection of paramagnetic air induced by both magnetic and gravitational buoyant forces for cases of moderate- and large-gap annuli. The results showed that the thermomagnetic convection is significantly affected by the gap width of the annulus and the magnetic field gradient induced by the permanent magnet. The average heat transfer increases more than 150% when one magnet is placed. It can be attributed to the more efficient disturbance in the boundary layer and improves heat transfer greatly. A stronger magnetic field induced better mixing in the flow which increase the Nusselt number. In addition, reducing the gap width of the annulus can effectively enhance heat transfer.