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Abstract
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In this paper, swirling flow boiling of a dilute nanofluid (water and 0.1 vol%Fe3O4) in an annulus with a twisted fin
on the outside of the inner wall in the presence of transverse magnetic gradient has been numerically investigated, using a two fluid model and a control volume technique. The results indicate that, in the boiling of swirling
flow, the rate of the heat transfer increases. This phenomenon can be attributed to the effect of centrifugal
force on the liquid phase flow and also reduction of the conductive sub-layer thickness that exists on the heated
wall. The effects of improved surface wettability induced by nanoparticle deposition during the boiling process
are accounted. The results demonstrate that the modified liquid property due to the existence of nanoparticles
in the liquid has a negligible effect on the boiling heat transfer performance with dilute nanofluids while the improved surface wettability plays an important role and leads to reduction of the void fraction and consequently,
an increase of critical heat flux. Applying a transverse magnetic field causes augmentation of the centrifugal force
and results in increased flow turbulence. Furthermore, in the presence of the magnetic field due to magnetic
force, the bubble departure diameter is reduced and bubble detachment occurs faster. Therefore, the critical
heat flux will be increased. Swirling flow boiling in the presence of magnetic field is strongly suggested in devices
requiring high heat transfer rates.
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