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Research Papers: Forced Convection

Electrohydrodynamic Conduction Driven Single- and Two-Phase Flow in Microchannels With Heat Transfer

[+] Author and Article Information
Matthew R. Pearson

Thermal Fluid Sciences Department,
United Technologies Research Center,
East Hartford, CT 06108
e-mail: pearsomr@utrc.utc.com

Jamal Seyed-Yagoobi

Worcester Polytechnic Institute,
100 Institute Road,
Worcester, MA 01609
e-mail: jyagoobi@wpi.edu

Sheet resistivity is the resistivity of a material when it is printed as a thin layer of uniform thickness t. Under such a condition, the sheet resistivity is Rs = 1/(σet). The bulk resistance between opposite edges of a rectangular sheet of the material is the surface resistivity multiplied by the length-to-width ratio of the sheet (where electrical current is flowing along the length of the sheet). Thus, a square sheet has a bulk resistance R = Rs regardless of the size of the square. Since sheet resistivity and bulk resistivity are dimensionally equal, the former is often expressed as Ω/□ (read as “Ohms per square”) to distinguish it from the latter and to avoid any confusion.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received December 14, 2011; final manuscript received September 11, 2012; published online August 19, 2013. Assoc. Editor: Sujoy Kumar Saha.

J. Heat Transfer 135(10), 101701 (Aug 19, 2013) (10 pages) Paper No: HT-11-1571; doi: 10.1115/1.4007617 History: Received December 14, 2011; Revised September 11, 2012

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the microscale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The effect of these embedded electrodes on the heat transport process, flow rate, and pressure in the micro-evaporator and on the two-phase loop system is characterized. Local enhancements are found to be up to 30% at low heat fluxes. The reverse effect that phase-change has on the EHD conduction pumping phenomenon is also quantified.

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Figures

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Fig. 4

Photograph of long channel two-phase pumping module

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Fig. 5

Schematic of two-phase loop experiment

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Fig. 3

Photograph of long channel substrate (heater side) showing location of thermistors A, B, and C

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Fig. 2

Photograph of long channel substrate (electrode side)

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Fig. 1

Flow channel schematic; electrodes highlighted

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Fig. 8

Single-phase liquid pumping performance of two-phase conduction micropump (short/diabatic and long/adiabatic pump designs): EHD current

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Fig. 9

Single-phase liquid pumping performance of two-phase conduction micropump (short/diabatic and long/adiabatic pump designs): EHD power

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Fig. 6

Single-phase liquid pumping performance of two-phase conduction micropump (short/diabatic and long/adiabatic pump designs): maximum flow rate (throttling valve open) and corresponding pressure load

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Fig. 7

Single-phase liquid pumping performance of two-phase conduction micropump (short/diabatic and long/adiabatic pump designs): maximum pressure generation with zero net flow

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Fig. 14

Effect of applied heat flux on the EHD power consumption and current of the two-phase loop (750 V)

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Fig. 10

Effect of applied heat flux on the flow rate of the two-phase loop (750 V)

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Fig. 11

Effect of applied heat flux on the pressure drop across the evaporator section of the two-phase loop (750 V)

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Fig. 12

Effect of applied heat flux on the surface temperatures in the evaporator section (750 V)

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Fig. 13

Measured local heat transfer coefficients at three streamwise thermistor locations (750 V)

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