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Research Papers: Evaporation, Boiling, and Condensation

Effect of Inlet Restriction on Flow Boiling Heat Transfer in a Horizontal Microtube

[+] Author and Article Information
Ibrahim Hassan

e-mail: ibrahimh@alcor.concordia.ca
Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC, H3G 2W1, Canada

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received December 12, 2011; final manuscript received August 2, 2012; published online January 3, 2013. Assoc. Editor: Louis C. Chow.

J. Heat Transfer 135(2), 021502 (Jan 03, 2013) (9 pages) Paper No: HT-11-1562; doi: 10.1115/1.4007610 History: Received December 12, 2011; Revised August 02, 2012

Flow boiling heat transfer in a horizontal microtube with inlet restriction (orifice) under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two microtubes with smaller diameters are assembled at the inlet of main microtube to achieve the restriction ratios of 50% and 20%. The experimental measurement is carried out at mass fluxes ranging from 160 to 870 kg/m2·s, heat fluxes varying from 6 to 170 kW/m2, inlet temperatures of 23 and 35 °C, and saturation pressures of 10 and 45 kPa. The effects of the orifices on two-phase pressure drop, critical heat flux (CHF), and flow boiling heat transfer coefficient are studied. The results show that the pressure drop caused by the orifice takes a considerable portion in the total pressure drop at low mass fluxes. This ratio decreases as the vapor quality or mass flux increases. The difference of normal critical heat flux in the microtubes with different orifice sizes is negligible. In the aspect of flow boiling heat transfer, the orifice is able to enhance the heat transfer at low mass flux and high saturation pressure, which indicates the contribution of orifice in the nucleate boiling dominated regime. However, the effect of orifice on flow boiling heat transfer is negligible in the forced convective boiling dominated regime.

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Figures

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Fig. 1

The package of test-section and locations of seven thermocouples (not to scale)

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Fig. 2

The experimental facility

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Fig. 3

Validation of pressure and temperature measurements: (a) friction factor and (b) local Nusselt number

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Fig. 4

The comparison of two-phase pressure drop between the experiment and proposed correlation

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Fig. 5

The comparison of two-phase pressure drop in microtubes with and without orifices at G = 160 and 550 kg/m2 · s (χ7 is the vapor quality at T7)

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Fig. 6

The comparison of saturated CHF between experiment and correlations at 160 ≤ G ≤ 550 kg/m2 · s, Psat = 10 kPa, and Tin = 23 °C

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Fig. 7

The comparison of saturated CHF in the microtubes with and without orifices

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Fig. 8

Heat transfer coefficient at the location of x = 125 mm in the microtube without orifice

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Fig. 9

Local heat transfer coefficient at G = 550 kg/m2 · s in the microtube without orifice

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Fig. 10

Comparisons of heat transfer coefficient between experiment and correlations

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Fig. 11

Heat transfer coefficient at the location of x = 125 mm: (a) G = 160 kg/m2 · s and (b) G = 420 kg/m2 · s

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