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Magnetic damping of levitated liquid droplets in AC and DC field

Magnetic damping of levitated liquid droplets in AC and DC field
Magnetic damping of levitated liquid droplets in AC and DC field
The intense AC magnetic field required to produce levitation in terrestrial conditions, along with the buoyancy and thermo-capillary forces, results in turbulent convective flow within the droplet. The use of a homogenous DC magnetic field allows the convective flow to be damped. However the turbulence properties are affected at the same time, leading to a possibility that the effective turbulent damping is considerably reduced. The MHD modified K-Omega turbulence model allows the investigation of the effect of magnetic field on the turbulence. The model incorporates free surface deformation, the temperature dependent surface tension, turbulent momentum transport, electromagnetic and gravity forces. The model is adapted to incorporate a periodic laser heating at the top of the droplet, which have been used to measure the thermal conductivity of the material by calculating the phase lag between the frequency of the laser heating and the temperature response at the bottom. The numerical simulations show that with the gradual increase of the DC field the fluid flow within the droplet is initially increasing in intensity. Only after a certain threshold magnitude of the field the flow intensity starts to decrease. In order to achieve the flow conditions close to the ‘laminar’ a D.C. magnetic field >4 Tesla is required to measure the thermal conductivity accurately. The reduction in the AC field driven flow in the main body of the drop leads to a noticeable thermo-capillary convection at the edge of the droplet. The uniform vertical DC magnetic field does not stop a translational oscillation of the droplet along the field, which is caused by the variation in total levitation force due to the time-dependent surface deformation.
Forschungszentrum Dresden-Rossendorf
Bojarevics, V.
f4e640b3-c909-4eaa-a988-44a2f5cb9b7a
Roy, A.A.
023648ec-2915-4a04-abdf-38e200a5308a
Easter, S.
e5378326-b2f3-49fb-9a91-d486ade9fc9e
Pericleous, K.
dff9eda5-84c0-41ba-b766-7115e5e6f517
Bojarevics, V.
f4e640b3-c909-4eaa-a988-44a2f5cb9b7a
Roy, A.A.
023648ec-2915-4a04-abdf-38e200a5308a
Easter, S.
e5378326-b2f3-49fb-9a91-d486ade9fc9e
Pericleous, K.
dff9eda5-84c0-41ba-b766-7115e5e6f517

Bojarevics, V., Roy, A.A., Easter, S. and Pericleous, K. (2009) Magnetic damping of levitated liquid droplets in AC and DC field. In 6th International Conference on Electromagnetic Processing of Materials: October 19 - 23, 2009, Dresden, Germany. Forschungszentrum Dresden-Rossendorf..

Record type: Conference or Workshop Item (Paper)

Abstract

The intense AC magnetic field required to produce levitation in terrestrial conditions, along with the buoyancy and thermo-capillary forces, results in turbulent convective flow within the droplet. The use of a homogenous DC magnetic field allows the convective flow to be damped. However the turbulence properties are affected at the same time, leading to a possibility that the effective turbulent damping is considerably reduced. The MHD modified K-Omega turbulence model allows the investigation of the effect of magnetic field on the turbulence. The model incorporates free surface deformation, the temperature dependent surface tension, turbulent momentum transport, electromagnetic and gravity forces. The model is adapted to incorporate a periodic laser heating at the top of the droplet, which have been used to measure the thermal conductivity of the material by calculating the phase lag between the frequency of the laser heating and the temperature response at the bottom. The numerical simulations show that with the gradual increase of the DC field the fluid flow within the droplet is initially increasing in intensity. Only after a certain threshold magnitude of the field the flow intensity starts to decrease. In order to achieve the flow conditions close to the ‘laminar’ a D.C. magnetic field >4 Tesla is required to measure the thermal conductivity accurately. The reduction in the AC field driven flow in the main body of the drop leads to a noticeable thermo-capillary convection at the edge of the droplet. The uniform vertical DC magnetic field does not stop a translational oscillation of the droplet along the field, which is caused by the variation in total levitation force due to the time-dependent surface deformation.

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Published date: October 2009
Organisations: EEE

Identifiers

Local EPrints ID: 268156
URI: https://eprints.soton.ac.uk/id/eprint/268156
PURE UUID: 7d1e2079-9812-4d21-a178-b87f7e0977c7

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Date deposited: 28 Oct 2009 18:02
Last modified: 13 Mar 2019 18:01

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