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Research Papers: Forced Convection

Experimental Study of Single Phase Heat Transfer and Pressure Loss in a Spiraling Radial Inflow Microchannel Heat Sink

[+] Author and Article Information
Maritza Ruiz

Department of Mechanical Engineering,
University of California, Berkeley,
Berkeley, CA 94720
e-mail: maritzaruiz@berkeley.edu

Van P. Carey

Professor
Department of Mechanical Engineering,
University of California, Berkeley,
Berkeley, CA 94720

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 6, 2014; final manuscript received February 2, 2015; published online March 24, 2015. Assoc. Editor: Wei Tong.

J. Heat Transfer 137(7), 071702 (Jul 01, 2015) (8 pages) Paper No: HT-14-1659; doi: 10.1115/1.4029821 History: Received October 06, 2014; Revised February 02, 2015; Online March 24, 2015

This paper presents an experimental study of the heat transfer and pressure drop characteristics of a single phase high heat flux microchannel cooling system with spiraling radial inflow. The heat sink provides enhanced heat transfer with a simple inlet and outlet design while providing uniform flow distribution. The system is heated from one conducting wall made of copper and uses water as a working fluid. The microchannel has a 1 cm radius and a 300 μm gap height. Experimental results show, on average, a 76% larger pressure drop compared to an analytic model for laminar flow in a parallel disk system with spiral radial inflow. The mean heat transfer coefficients measured are up to four times the heat transfer coefficient for unidirectional laminar fully developed flow between parallel plates with the same gap height. Flow visualization studies indicate the presence of secondary flows and the onset of turbulence at higher flow rates. Combined with the thermally developing nature of the flow, these characteristics lead to enhanced heat transfer coefficients relative to the laminar parallel plate values. Another beneficial feature of this device, for high heat flux cooling applications, is that the thermal gradients on the surface are small. The average variation in surface temperature is 18% of the total bulk fluid temperature gain across the device. The system showed promising cooling characteristics for electronics and concentrated photovoltaics applications with a heat flux of 113 W/cm2 at a surface temperature of 77 °C and a ratio of pumping power to heat rate of 0.03%.

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References

Figures

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Fig. 1

Schematic of heat sink design

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Fig. 2

Streamlines of flow in a heat sink with dimensions given in Table 1, water as a working fluid, and V· = 256 ml/min. Computed using the theoretical model formulated in Ref. [16].

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Fig. 3

Top view of the fabricated device used in this study indicating the outlet and inlet ports used to measure pressure and temperature

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Fig. 4

Locations of the TCs within the copper piece and the relative inlet orientations tested

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Fig. 5

Schematic of experimental components

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Fig. 6

Experimental results from pressure drop tests for two devices over the full range of flow rates tested in the system and compared to theoretical model described in Eq. (3) and including predicted entry and exit effects. (a) Pressure drop and (b) pumping power.

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Fig. 7

Flow visualization using dyed water injected at r = 0.75 cm; Reo = 300, 520, 830, and 1170

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Fig. 8

Average wall heat flux, q"w, of the system for two devices over a range of flow rates tested

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Fig. 9

Average Nusselt numbers of the system for two devices over the range of flow rates tested. These values are compared to a developing flow estimate of Nusselt values for laminar flow between parallel plates with a constant wall heat flux at one wall. Also shown are the values for fully developed flow between parallel flat plates with one wall insulated and both a constant wall heat flux and a constant wall temperature condition.

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Fig. 10

Wall temperature variations expressed as Θw defined in Eq. (14), and averaged over all tests. This indicates the heated wall temperature variation relative to total bulk fluid temperature gain across the surface.

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Fig. 11

Experimental values for the friction factors based on pressure drop tests at room temperature, as well as Colburn factors based on heat transfer tests over a range of heat and flow rates

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Fig. 12

Average goodness factors, j/f, averaged over all tests for each flow rate plotted against the outlet radial Reynolds number, Rer,i, defined as vr,idh/ν, and compared with developing flow and fully developed flow solutions for parallel plates under constant heat flux from one wall

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