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Research Papers: Jets, Wakes, and Impingment Cooling

Thermo-Fluid Dynamics of an Array of Impinging Ionic Jets in a Crossflow

[+] Author and Article Information
Daniele Testi

e-mail: daniele.testi@ing.unipi.it

Walter Grassi

LOTHAR (LOw gravity and THermal
Advanced Research) Laboratory,
DESTEC (Department of Energy, Systems,
Territory, and Construction Engineering),
University of Pisa,
Largo Lucio Lazzarino 1,
Pisa I-56122, Italy

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received August 16, 2012; final manuscript received March 26, 2013; published online July 18, 2013. Assoc. Editor: Frank Cunha.

J. Heat Transfer 135(8), 082202 (Jul 18, 2013) (10 pages) Paper No: HT-12-1437; doi: 10.1115/1.4024280 History: Received August 16, 2012; Revised March 26, 2013

Laminar to weakly turbulent mixed convection in a square duct heated from the bottom side is highly strengthened by ionic jets generated by an array of high voltage points, opposite to the heated strip. Negative ion injection is activated within the dielectric liquid HFE-7100. Local temperatures on the heated wall are measured by liquid crystal thermography. Distributions of the Nusselt number are obtained at different forced flow rates, applied heat flows, and transiting electrical currents. In correspondence of the point emitters, higher Nusselt numbers in the impingement areas are measured and an analogy with the thermo-fluid dynamic behavior of an array of submerged impinging jets in a crossflow is drawn. The diameter of the ionic jets is evaluated and an electrohydrodynamic Reynolds number is employed for correlation and similarity purposes. Potential applications of the technique are high-efficiency compact heat exchangers and heat sinks.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Chromaticity-versus-temperature calibration curve at the center of the heated strip

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Fig. 2

Photograph of the TLCs at a uniform temperature of 23.5  °C

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Fig. 3

Drawing of a duct cross section

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Fig. 4

Drawing of the duct longitudinal section (distances are expressed in millimeters)

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Fig. 5

Schematic of the hydraulic loop

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Fig. 17

Nu* at y = 0 versus x/s at Re = 5000, HV = −10 kV, and Grh = 9.26·106, 2.32·107, and 3.71·107 for 29.6 < x/s < 32.6

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Fig. 18

Nu map on the heated wall at Re = 5000, HV = −10 kV, and Grh = 9.26·106

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Fig. 19

Nu map on the heated wall at Re = 5000, HV = −10 kV, and Grh = 2.32·107

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Fig. 20

Nu map on the heated wall at Re = 5000, HV = −10 kV, and Grh = 3.71·107

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Fig. 8

Nu* map on the heated wall at Re=10100, Grh=9.26·106, and HV = −10 kV

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Fig. 7

Nu* map on the heated wall at Re=5050, Grh=9.26·106, and HV = −10 kV

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Fig. 6

Nu* map on the heated wall at Re = 2190, Grh = 9.26·106, and HV = −10 kV

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Fig. 16

Nu* at y = 0 versus x/s at Re = 1260, Grh = 9.26·106, HV = −10 kV, and I = 0.11 and 0.25 mA for 38.2 < x/s < 39.3

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Fig. 15

Nu* at y = 0 versus x/s at Re = 1260, Grh = 9.26·106, HV = −10 kV, and I = 0.11 and 0.25 mA for 30.9 < x/s < 32.1

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Fig. 14

Schematic of upwash flow due to collision of wall jets [26]

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Fig. 13

Nu map on the heated wall at Re = 5000, HV = −10 kV, and Grh = 3.71·107 for 44.4 < x/s < 46.5 and −0.346 < y/s < 0.240

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Fig. 12

Nu map on the heated wall at Re = 5000, HV = −10 kV, and Grh = 3.71·107 for 30.6 < x/s < 32.6 and −0.346 < y/s < 0.240

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Fig. 11

Nu* at y=0 versus x/s at Grh=9.26·106, HV = −10 kV, and Re=2190, 5050, and 10,100 for 44.6 < x/s < 45.8

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Fig. 10

Nu* at y = 0 versus x/s at Grh=9.26·106, HV = −10 kV, and Re = 2190, 5050, and 10,100 for 38.2 < x/s < 39.3

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Fig. 9

Nu* at y = 0 versus x/s at Grh=9.26·106, HV = −10 kV, and Re = 2190, 5050, and 10,100 for 30.9 < x/s < 32.1

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