Research Papers: Evaporation, Boiling, and Condensation

An Experimental Investigation of Pressure Drop in Expanding Microchannel Arrays

[+] Author and Article Information
Mark J. Miner

e-mail: mark.miner@asu.edu

Patrick E. Phelan

e-mail: phelan@asu.edu

Carlos A. Ortiz

Mechanical Engineering,
Arizona State University,
Tempe, AZ 85281

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 26, 2013; final manuscript received August 21, 2013; published online November 21, 2013. Assoc. Editor: W. Q. Tao.

J. Heat Transfer 136(3), 031502 (Nov 21, 2013) (9 pages) Paper No: HT-13-1046; doi: 10.1115/1.4025557 History: Received January 26, 2013; Revised August 21, 2013

The pressure effects of expanding the cross section of microchannels along the direction of flow are investigated across four rates of channel expansion in the flow boiling of R-134a. Prior investigation by the authors detailed the fabrication of four copper microchannel arrays and the pumped-loop apparatus developed to facilitate interchange of the microchannel specimens, allowing consistency across experiments. Significant beneficial pressure effects are observed to result from the expansion, including reduction by half of the pumping cost per flow rate at critical heat flux. The improvements are seen with small expansions, and greater expansion yields diminishing returns. The high pressure drops associated with microchannel evaporators are effectively reduced by expanding channel geometry, and the low-frequency system spectral response indicates that expanding channel arrays typically carry less energy in oscillations up to 2.5 Hz, suggesting amelioration of oscillatory instabilities. Results are discussed in light of a comparative force analysis, with the balance of these forces linked to the observed behavior of the pressure drop and heat flux relationship.

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Fig. 1

Microchannel turret

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Fig. 3

Juxtaposed 1 deg inlet and outlet

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Fig. 4

Cross section of apparatus (from Ref. [1])

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Fig. 5

Flow loop schematic

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Fig. 6

Pressure curves at CHF with error bars

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Fig. 7

Slopes of pressure curves at CHF with 95% fit confidence bounds

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Fig. 8

Outlet quality at CHF

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Fig. 9

Power spectral densities of pressure drop (frequency in HZ on abscissa, normalized PSD on ordinate)

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Fig. 10

Heat flux effect on pressure drop

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Fig. 11

Representative force scales in 10 mm long microchannels with 3gs R-134 a at 350kPa,x = 0.5,q· = 500 (W/cm2)




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