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Research Papers: Jets, Wakes, and Impingement Cooling

Application of Electrohydrodynamic Atomization to Two-Phase Impingement Heat Transfer

[+] Author and Article Information
Xin Feng

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211

James E. Bryan

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211bryanje@missouri.edu

J. Heat Transfer 130(7), 072202 (May 20, 2008) (10 pages) doi:10.1115/1.2885178 History: Received November 30, 2006; Revised July 19, 2007; Published May 20, 2008

The effect of electric fields applied to two-phase impingement heat transfer is explored for the first time. The electric field applied between a capillary tube and heated surface enhances the heat transfer by controlling the free boundary flow modes from discreet drops to jets, to sprays. Through an experimental study, the impingement heat transfer was evaluated over a range of operating conditions and geometrical parameters with subcooled ethanol used as the working fluid. The ability to change the mode of impinging mass did change the surface heat transfer. The characteristics of the impinging mass on heat transfer were dependent on flow rate, applied voltage, capillary tube to heated surface spacing, capillary tube geometry, heat flux, heater surface geometry, and capillary tube array configuration. Enhancement occurred primarily at low heat fluxes (below 30Wcm2) under ramified spray conditions where the droplet momentum promoted thin films on the heated surface resulting in 1.7 times enhancement under certain conditions. Higher heat fluxes resulted in greater vapor momentum from the surface, minimizing the effect of different impingement modes. The use of capillary tube array allowed for electrohydrodynamics atomization enhancement and higher liquid flow rates, but electrostatic repulsive forces diverted the spray from the heater surface. This reduced the mass flux to the surface, leading to premature dryout under certain conditions.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of impingement cooling system

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Figure 2

Photographs showing copper heater coupon, capillary tube fixture, and mounting surface configurations

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Figure 3

EHDA effect on two-phase impingement heat transfer at different volumetric flow rates and applied voltages: As=0.5cm2 and H=1cm on flat mounting surface

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Figure 4

Effect of applied voltage and capillary tube geometry on impingement heat transfer (hE is the average enhanced heat transfer coefficient and ho the average heat transfer coefficient obtained at 0kV with the acrylic capillary tube)

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Figure 5

Effect of height and nozzle geometry on impingement heat transfer (hE is the average enhanced heat transfer coefficient and ho the average heat transfer coefficient obtained at 0kV with the acrylic capillary tube)

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Figure 6

Effect of heat flux on impingement heat transfer (hE is the average enhanced heat transfer coefficient and ho the average heat transfer coefficient obtained at 0kV with the acrylic capillary tube)

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Figure 7

Effect of surface support structure and surface area on impingement evaporation with no applied electric field through stainless capillary tube

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Figure 8

Effect of EHDA, surface support structure, and surface area on impingement heat transfer with the stainless capillary tube (hE is the average enhanced heat transfer coefficient and ho the average heat transfer coefficient obtained at 0kV)

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Figure 9

Effect of surface structure and EHDA on impingement heat transfer (hE is the average enhanced heat transfer coefficient and ho the average heat transfer coefficient obtained at 0kV on the smooth surface)

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Figure 10

Sequence of images showing effect of electric field on capillary tube array

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Figure 11

Effect of capillary tube array on impingement heat transfer (hE is the average enhanced heat transfer coefficient and ho the average heat transfer coefficient obtained at 0kV with a single capillary tube)

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