Film boiling of magnetic nanofluids (MNFs) over a vertical plate in presence of a uniform variable-directional magnetic field

• A closed form solution for nanoparticle distribution of MNFs at film boiling.
• Nanoparticle migration effects on heat transfer enhancement in the film.
• Anisotropic behavior of thermal conductivity induced by a magnetic field.
• The effects of orientation as well as the intensity of magnetic field on MNFs.

External magnetic fields are able to tune the thermophysical properties of magnetic nanofluids (MNFs) and control the flow and heat transfer rate. Orientation and intensity of the external magnetic field would influence the thermal conductivity of MNFs and makes it anisotropic. The motivation behind this study is the need to examine the effects of anisotropic behavior of thermal conductivity on flow field and heat transfer characteristics at film boiling of MNFs over a vertical plate in the presence of a uniform variable-directional magnetic field. The modified Buongiorno model is employed for modeling the nanofluids to observe the effects of nanoparticle migration. The results have been obtained for different parameters, including Brownian motion to thermophoretic diffusion NBT, saturation nanoparticle concentration ϕsat, Hartmann number Ha, magnetic field angle α  , and normal temperature difference γ=(Tw−Tsat)/Twγ=(Tw−Tsat)/Tw. A closed form expression for the distribution of nanoparticle volume fraction has been obtained and the effects of pertinent parameters on heat transfer rate have been investigated. It has been shown that the heat transfer rate is improved further when an external magnetic field exerts in the direction of the temperature gradient.

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