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Research Papers: Two-Phase Flow and Heat Transfer

Prediction of the Onset of Flow Instability in a Single Horizontal Microtube With an Inlet Orifice

[+] 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 21, 2012; final manuscript received August 4, 2013; published online November 7, 2013. Assoc. Editor: Ali Khounsary.

J. Heat Transfer 136(2), 022903 (Nov 07, 2013) (10 pages) Paper No: HT-12-1669; doi: 10.1115/1.4025503 History: Received December 21, 2012; Revised August 04, 2013

A methodology to predict the onset of flow instability (OFI) in a single horizontal microtube with an inlet orifice is developed based on the predication of pressure drop. The predictive methodology states, for the same flow rate, the flow instability occurs as the single-phase liquid pressure drop under no heating condition equals the two-phase pressure drop under heating condition in a single microtube. The addition of inlet orifice increases the heat flux at the onset of flow instability by increasing the upstream pressure. The present methodology is validated by comparing the predicted heat flux at the onset of flow instability with our previous experimental data in the microtubes with three sizes of inlet orifices. The results show that the present method can predict the heat flux at the onset of flow instability with a deviation of 30% and mean absolute error of 13% at mass fluxes from 700 to 3000 kg/m2 s. The effects of inlet orifice size and saturation pressure on the onset of flow instability are also studied based on the present methodology. It is found that, at mass fluxes from 100 to 2000 kg/m2 s, the area ratio less than 15% eliminates the flow instability completely before the critical heat flux occurs.

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Figures

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Fig. 1

Schematic of the prediction of onset of flow instability. The horizontal dashed line represents the pressure drop in (a); the horizontal dot dash line represents the pressure drop in (b); the solid line represents the pressure drop in (c).

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Fig. 2

Comparison of single-phase pressure drop under no heating condition and two-phase pressure drop under heating condition at the onset of flow instability

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Fig. 3

Schematic of pressure distribution between inlet and outlet measurement locations

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Fig. 4

The iteration process for searching the saturation pressure at x = Lh,e

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Fig. 5

Comparisons of pressure drops between the prediction and experiment for four mass fluxes in the microtube without an inlet orifice (a) G = 160 kg/m2 s, (b) G = 295 kg/m2 s, (c) G = 420 kg/m2 s, (d) G = 550 kg/m2 s

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Fig. 6

Comparisons of pressure drops between the prediction and experiment at four mass fluxes in the microtube with a 20% inlet orifice (a) G = 160 kg/m2 s, (b) G = 295 kg/m2 s, (c) G = 420 kg/m2 s, (d) G = 550 kg/m2 s

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Fig. 7

Comparison of pressure drop between the prediction and experiment

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Fig. 8

Comparisons of onset of flow instability between the prediction and experiment in the microtubes with and without inlet orifices

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Fig. 9

Pressure drop ratio in the microtube with and without an inlet orifice under no heating condition

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Fig. 10

Comparison of the onset of flow instability between the experiment and prediction

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Fig. 11

Effect of area ratio on the onset of flow instability

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Fig. 12

Pressure drop at G = 500 kg/m2 s under two saturation pressures

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Fig. 13

Effect of saturation pressure on the onset of flow instability

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Fig. 14

The critical area ratio at different mass fluxes

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