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Technical Briefs

On the Scalability of Liquid Microjet Array Impingement Cooling for Large Area Systems

[+] Author and Article Information
Avijit Bhunia

 Teledyne Scientific Company, 1049 Camino Dos Rios, Thousand Oaks, CA 91360abhunia@teledyne.com

C. L. Chen

 Teledyne Scientific Company, 1049 Camino Dos Rios, Thousand Oaks, CA 91360

J. Heat Transfer 133(6), 064501 (Mar 02, 2011) (7 pages) doi:10.1115/1.4003532 History: Received February 18, 2010; Revised January 10, 2011; Published March 02, 2011; Online March 02, 2011

The necessity for an efficient thermal management system covering large areas is growing rapidly with the push toward more electric systems. A significant amount of research over the past 2 decades has conclusively proved the suitability of jet, droplet, or spray impingement for high heat flux cooling. However, all these research consider small heat source areas, typically about a few cm2. Can a large array of impingement pattern, covering a much wider area, achieve similar heat flux levels? This article presents liquid microjet array impingement cooling of a heat source that is about two orders of magnitude larger than studied in the previous works. Experiments are carried out with 441 jets of de-ionized water and a dielectric liquid HFE7200, each 200μm diameter. The jets impinge on a 189cm2 area surface, in free surface and confined jet configurations. The average heat transfer coefficient values of the present experiment are compared with correlations from the literature. While some correlations show excellent agreement, others deviate significantly. The ensuing discussion suggests that the post-impingement liquid dynamics, particularly the collision between the liquid fronts on the surface created from surrounding jets, is the most important criterion dictating the average heat transfer coefficient. Thus, similar thermal performance can be achieved, irrespective of the length scale, as long as the flow dynamics are similar. These results prove the scalability of the liquid microjet array impingement technique for cooling a few cm2 area to a few hundred cm2 area.

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Copyright © 2011 by American Society of Mechanical EngineersThe United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes.
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Figures

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Figure 2

Schematic of the experimental setup including heater assembly and closed loop microjet array impingement cooling system. A microscopic image of the orifice plate and a SEM image of one sample orifice are also shown in the inset.

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Figure 3

Schematic of jet-to-jet interaction on the target surface for an array of free surface (liquid in gas) jet impingement. (a) Wall jet region and crown structure formation and (b) crown structure surrounding a single jet impingement in a large array. Drawing not to scale.

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Figure 4

Maximum base plate temperature variation (ΔT=Tbp,max−Tbp,min) with heat dissipation (QH) at various flow rates (individual jet Reynolds number, Rej, in dimensionless form) conditions for water and HFE7200. The inset shows the nine base plate temperature measurement schemes. These results are for free surface jet array. The confined jet array shows similar dependence.

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Figure 1

Schematic of liquid microjet array impingement on a target surface of area (AC). (a) Free surface jet (liquid jet in a gaseous medium) and (b) confined jet (liquid jet in the same liquid medium). Confinement is between the multi-orifice jet head and the impingement/target surface.

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Figure 5

Free surface jet array impingement—variation of the average heat transfer coefficient over the large area, expressed in dimensionless form as Nusselt number (Nuav), with flow rate (QL), nondimensionalized as Reynolds number (Rej). Comparison of current experimental data with various correlations of literature.

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Figure 6

Confined jet array impingement—variation of the average heat transfer coefficient over the large area, expressed in dimensionless form as Nusselt number (Nuav), with flow rate (QL), nondimensionalized as Reynolds number (Rej). Comparison of current experimental data with various correlations of literature for confined and submerged jets.

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