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Research Papers: Fundamental Issues and Canonical Flows

On the Pulsed and Transitional Behavior of an Electrified Fluid Interface

[+] Author and Article Information
Paul R. Chiarot, Sergey I. Gubarenko, Ridha Ben Mrad

Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON M5S 3G8, Canada

Pierre E. Sullivan

Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON M5S 3G8, Canadasullivan@mie.utoronto.ca

J. Fluids Eng 131(9), 091202 (Aug 17, 2009) (6 pages) doi:10.1115/1.3203203 History: Received October 17, 2008; Revised June 11, 2009; Published August 17, 2009

Transient modes of an electrified fluid interface are investigated, specifically, (a) intermittent or pulsed cone-jet mode and (b) smooth and abrupt transitions of the interface in response to a step voltage. These modes were studied experimentally by capturing the motion of the interface and measuring the emitted ion current (via electrospray) as they occur. The observed phenomena are described using an analytical model for the equilibrium of an electrified fluid interface, and the effect of operational parameters on the transient modes is discussed. Pressure, which is related to the supplied flow rate, significantly influences the behavior of the transient modes. It is useful to understand transient modes so they can be avoided in applications that require a stable electrospray. However, with improved knowledge, the modes studied here can assist in the development of specialized applications.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Quasi-equilibrium states for the interface. In all cases, the interface emits a spray.

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Figure 2

Two images of an electrified interface in “intermittent or pulse cone-jet mode.” The shape of the interface cycles back and forth between (a) and (b) at a frequency of 6 Hz. The apex angle in (b) is 63 deg.

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Figure 3

Operational domain for an electrode separation distance of 7 mm and surface tension coefficient of 27.48 mN/m. The operating point moves left and right in the domain across the critical curves between equilibrium and quasi-equilibrium.

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Figure 4

Current measurements of emitted ion current. The ion current is collected at the counterelectrode and converted to a voltage. The bulk fluid is a 100 μM solution of NaI in 90:10 MeOH:H2O. The flow rate in (a) is 2 μl/min and in (b) is 0.5 μl/min. The current peaks represent the quasi-equilibrium state of the interface.

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Figure 5

Time lapsed images of an interface undergoing an abrupt transition. The pressure difference is smoothly increased in (a) and (b), and a step voltage is discontinuously (abruptly) applied in (c). A loss of mass from the interface can be seen when the voltage is applied. (d) The stable final cone-jet.

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Figure 6

Time lapsed images of an interface undergoing a smooth transition. The voltage is applied in (a) before any fluid is present. The pressure difference smoothly changes from (b) to (d). The interface in (d) has been steady for hundreds of milliseconds. No abrupt loss of mass is seen for this smooth transition compared with the abrupt transition.

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Figure 7

Operational domain for an electrode separation distance of 10 mm and surface tension coefficient of 27.48 mN/m. The solid arrow represents the smoothly increasing pressure difference, and the dotted arrow represents a discontinuous or abrupt increase in voltage. The application of voltage is discontinuous and not smooth. The pressures at (a), (b), and (d) are known exactly. There is no pressure to report for (c) since the interface has ruptured.

Grahic Jump Location
Figure 8

Operational domain for an electrode separation distance of 10 mm and surface tension coefficient of 27.48 mN/m. The solid arrow represents smoothly increasing pressure difference, and the dashed arrow represents smooth relocations of the operating points. The transition is smooth; therefore there is no abrupt loss of mass, as seen in Fig. 5.

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