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Research Papers

Passive Control of Two-Phase Flow Thermal Instabilities in a Vertical Tube Evaporator

[+] Author and Article Information
Ghazali Mebarki

Faculty of Technology,
LESEI Laboratory,
Department of Mechanical Engineering,
University of Batna 2,
Avenue Chahid Boukhlouf Mohamed Elhadi,
Batna 05000, Algeria
e-mails: g.mebarki@yahoo.fr;
ghazali.mebarki@univ-batna.dz

Samir Rahal

Faculty of Technology,
LESEI Laboratory,
Department of Mechanical Engineering,
University of Batna 2,
Avenue Chahid Boukhlouf Mohamed Elhadi,
Batna 05000, Algeria
e-mail: samir.rahal@lycos.com

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received October 6, 2015; final manuscript received June 15, 2016; published online August 2, 2016. Assoc. Editor: Wei Li.

J. Thermal Sci. Eng. Appl 8(4), 041008 (Aug 02, 2016) (9 pages) Paper No: TSEA-15-1286; doi: 10.1115/1.4034092 History: Received October 06, 2015; Revised June 15, 2016

Passive heat transfer techniques are considered to be one of the most important means to enhance heat transfer in heat exchangers that allow also reducing their size and manufacturing cost. Moreover, this passive technique can also be used to control the thermal instabilities caused by the two-phase flow in the evaporators. The thermal instabilities are undesirable because they can lead to a tube failure. For this purpose, a numerical study of the two-phase flow with evaporation in a vertical tube has been performed in this work. The volume of fluid (VOF) multiphase flow method has been used to model the water vapor–liquid two-phase flow in the tube. A phase-change model, for which source terms have been added in the continuity and energy equation, has been used to model the vaporization. The numerical simulation procedure was validated by comparing the obtained results with those given in the literature. The passive control technique used here is a ring element with square cross section, acting as a vortex generator, which is attached to the tube wall at various positions along the tube. Instabilities of temperature and void fraction at the tube wall have been analyzed using fast Fourier transforms (FFTs). The results show that the attachment of the control element has a significant influence on the value and distribution of the void fraction. Higher positions of the control element along the tube allow reducing the magnitude of void fraction oscillations.

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References

Figures

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Fig. 1

Geometric reconstruction scheme: (a) real interface and (b) PLIC method

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Fig. 2

Geometry and boundary conditions of the evaporator

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Fig. 3

Variation of the void fraction along the inner tube wall for four grids

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Fig. 13

Contours of the temperature without and with control element at 400 mm, for t = 100 s and Re = 6381

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Fig. 14

(a) Temperature contours at different positions of the ring, for t = 100 s and Re = 6381: control element at 20 mm and (b) temperature contours at different positions of the ring, for t = 100 s and Re = 6381: control element at 200 mm

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Fig. 15

(a) Vapor fraction contours at different positions of the ring, Re = 6381 and t = 100 s: control element at 20 mm and (b) vapor fraction contours at different positions of the ring, Re = 6381 and t = 100 s: control element at 200 mm

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Fig. 16

Void fraction variation versus the control element location at y = 450 mm, for various Reynolds numbers and t = 100 s

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Fig. 12

Contour plots of the vapor volume fraction without and with control element at 400 mm, for t = 100 s and Re = 6381

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Fig. 11

FFTs of the temperature at y = 450 mm, for various positions of the control element, Re = 6381

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Fig. 10

Time variation of temperature at y = 450 mm and for various positions of the control element, Re = 6381

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Fig. 9

Time variation of the void fraction at y = 450 mm and for various positions of the control element, Re = 6381

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Fig. 8

FFTs of the temperature at y = 450 mm and for various Reynolds numbers. Control element at 400 mm.

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Fig. 7

Temperature variation for various Reynolds numbers at y = 450 mm. Control element at 400 mm.

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Fig. 6

Time variation of the void fraction at y = 450 mm and for various Reynolds numbers. Control element at 400 mm.

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Fig. 5

Vapor fraction calculated numerically compared to that obtained using literature correlations, Re = 480

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Fig. 4

Heat transfer rate calculated numerically compared to that obtained by Kandlikar correlation [28], Re = 480

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