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Evaporation, Boiling, and Condensation

Experimental Investigation of Flow Boiling Instability in a Single Horizontal Microtube With and Without Inlet Restriction

[+] Author and Article Information
YanFeng Fan

Department of Mechanical and Industrial Engineering,  Concordia University, Montreal, QC, H3G 2W1, Canada

Ibrahim Hassan1

Department of Mechanical and Industrial Engineering,  Concordia University, Montreal, QC, H3G 2W1, Canadaibrahimh@alcor.concordia.ca

1

Corresponding author.

J. Heat Transfer 134(8), 081501 (Jun 05, 2012) (11 pages) doi:10.1115/1.4006161 History: Received August 22, 2011; Revised January 12, 2012; Published June 05, 2012; Online June 05, 2012

An experimental study is conducted to investigate the effects of inlet restriction (orifice) on flow boiling instability in a single horizontal microtube. The test-section is composed of a stainless steel tube with an inner diameter of 889 μm, and a length of 150 mm. Experiments are performed for three different orifice configurations with 20%, 35%, and 50% area ratio. Mass flux is varied from 700 to 3000 kg/m2  · s, whereas the heat flux is varied from 6 to 27 W/cm2 . The dielectric coolant FC-72 is selected as the working fluid. In the absence of an orifice at the inlet, four oscillation types are observed at the onset of flow instability; it is also noticed that the frequency of the oscillations increases with increasing heat flux, while the amplitude remains constant. The addition of an orifice at the inlet helps stabilizing the flow without generating significant pressure drop at the same operating condition as the microtube without orifice. The 20% area ratio orifice shows better performance at low mass fluxes (<1000 kg/m2  · s). Whereas, at high mass fluxes (>2000 kg/m2  · s), 50% and 35% area ratio orifices are efficient in stabilizing the flow or delaying the onset of flow instability. Therefore, selecting the area ratio of the orifice depends on the operating condition. A small area ratio orifice is preferably used at low mass fluxes, whereas a large area ratio orifice is more suitable for high mass fluxes.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The schematic of present microtube package (not to scale)

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Figure 2

The setup of facilities including the flow loop and data acquisition system

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Figure 7

The transition instability between pressure-drop and density-wave oscillations at the mass flux of 1166 kg/m2  · s

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Figure 8

The transition instability between pressure-drop and density-wave oscillations at the mass flux of 2990 kg/m2  · s

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Figure 9

The pressure-drop oscillation at the mass flux of 1546 kg/m2  · s. (a) Oscillation in a time span of 300 s (b) Oscillation in a time span of 2 s.

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Figure 10

The oscillation frequency, magnitude, and amplitude of pressure drop at onset of flow instability in the single microtube without orifice

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Figure 11

The effect of heat flux on the pressures at the mass fluxes of 977 kg/m2  · s and 1546 kg/m2  · s

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Figure 12

The comparison of inlet pressure at the onset of flow instability in microtubes with and without orifices

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Figure 3

The friction factor of liquid flow in the microtube with inner diameter of 889 μm at 1000 < Re < 7000

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Figure 4

The map of flow stability regimes in single microtube without orifice at different heat and mass fluxes (solid lines are the curve fittings of experimental data)

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Figure 5

The compound of LD at the mass flux of 763 kg/m2  · s

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Figure 6

The compound of LDP at the mass flux of 977 kg/m2  · s

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Figure 13

The heat flux at the onset of flow instability in the microtubes with different orifice sizes

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Figure 14

The magnitude of pressure drop at the onset of flow instability in the microtubes with different orifice sizes

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