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HEAT TRANSFER TO A DROPLET TRANSLATING IN AN ELECTRIC FIELD

by SUBRAMANIAN, RAJKUMAR

Abstract (Summary)
In this thesis, the heat transfer to a spherical droplet translating in an electric field is studied. The flow is considered steady and axi-symmetric with constant thermophysical properties. The Reynolds number based on the droplet diameter is in the intermediate regime (Re_d ~ 10 to 100). The heat transfer to a droplet from surrounding immiscible medium is enhanced when an external electric field is applied. The application of electric field increases the transport rates through the electric-field-induced motion inside and outside the droplet. A steam function-vorticity formulation is adopted to numerically determine the steady flow field in the continuous and the dispersed phase. The governing equations for both phases are solved simultaneously as the flow is coupled due to the no-slip and the continuity of shear stress boundary conditions at the drop surface. Two heat transfer limits are considered. The first limit is known as the external problem where the bulk of the resistance is assumed to be in the continuous phase. The temperature distribution in the continuous phase and the corresponding Nusselt number are obtained for different flow Reynolds numbers and electric field strengths. The applied electric field is varied independently at different Reynolds numbers. Results show that the external Nusselt number increases significantly with electric field strength for all Reynolds numbers. The enhancement in heat transfer is higher with lower ratio of viscosity of the dispersed phase to the viscosity of the continuous phase. The second heat transfer limit is the internal problem where the bulk of the resistance is assumed to be in the dispersed phase. The transient temperature distribution and the transient Nusselt number variation are obtained for different flow Reynolds numbers, electric field strengths, and viscosity ratios. Results show that the transient Nusselt number initially oscillates and eventually reaches a steady value. At very low Peclet number the steady state Nusselt number is close to the conduction limit of 6.6 and increases to reach a limiting value for high Peclet number. The steady state Nusselt number for a combined electrically induced and translational flow is substantially greater than that for purely translational flow. Furthermore, for a drop moving at intermediate Reynolds number, the steady state Nusselt number is slightly greater than the corresponding Nusselt number for a purely electric field driven motion in a suspended drop.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:heat transfer enhancement electric field droplet numerical analysis

ISBN:

Date of Publication:01/01/2005

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