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Technical Brief

Numerical Research of Film Boiling Heat Transfer Around a Vertical Short Cylinder With Flat or Hemispherical Ends

[+] Author and Article Information
Rubén Arévalo

Mechanical Engineering Department,
UNET,
San Cristóbal 5001, Venezuela

Alberto Abánades, Luis Rebollo

ETSII/Universidad Politécnica de Madrid,
J. Gutiérrez Abascal,
Madrid 2-28006, Spain

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 16, 2015; final manuscript received March 8, 2016; published online April 12, 2016. Editor: Portonovo S. Ayyaswamy.

J. Heat Transfer 138(7), 074502 (Apr 12, 2016) (7 pages) Paper No: HT-15-1197; doi: 10.1115/1.4033094 History: Received March 16, 2015; Revised March 08, 2016

Film boiling is a heat transfer mechanism that might appear in different processes, such as cryogenics, metallurgical, and nuclear reactors during abnormal operating conditions, as happens during a loss of coolant accident. In this research, film boiling around a finite vertical cylinder was studied by means of computational fluid dynamics (CFD) simulations, considering six cases that include three different levels of surface temperature and two different shapes of the cylinder ends: flat and hemispherical ends. Volume of fluid (VOF) method for the treatment of multiphase flow was used, and a user-defined function was programed to consider the exchange of mass and energy between the phases. The simulations were performed with a vertical cylinder of 32 mm in diameter and 32 or 64 mm in high for flat ends or hemispherical ends, respectively, placed in a two-dimensional axisymmetric domain of 0.125 m × 0.25 m. Results obtained for the heat flux show a periodic fluctuating behavior in time as a consequence of periodical variations in the thickness of the vapor film around the cylinder. A wavy liquid–vapor interface is observed as is reported in the experimental works. The simulations results are compared with the experimental values reported in literature as well as with values obtained from correlations. The results show that the computational code used captures reasonably well the physics involved in the film boiling, being obtained that average heat flux to the case of hemispherical ends is 15.6% higher than for the case of flat ends, versus 15.2% showing experiments and 1.6% calculated combining correlations for the individual surfaces. It shows that use of correlations in this way is not appropriate in film boiling because it does not take into account the interactions between the different surfaces.

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Figures

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Fig. 1

Simulated cylinders: flat ends (left) and hemispherical ends (right)

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Fig. 2

Computational domains and boundary conditions

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Fig. 3

A 12,000 elements grid for hemispherical end cylinder cases

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Fig. 4

Evolution of the liquid–vapor interface for case 1 (Ts = 300 °C) during the formation of the first vapor slug from 0.01 to 0.08 s at intervals of 0.01 s (vapor in black)

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Fig. 5

Evolution of the liquid–vapor interface for case 4 (Ts = 300 °C) during the formation of the first vapor slug from 0.01 to 0.06 s at intervals of 0.01 s (vapor in black)

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Fig. 6

Comparison of simulations images with photographs reported by Momoki et al. [15], Shigechi et al. [16], Yamada [17], and Yamada et al. [18]

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Fig. 7

Simulation result for area-averaged heat flux for case 3

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Fig. 8

Simulation result for area-averaged heat flux for case 4

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Fig. 9

Area and temporal averaged heat flux behavior with surface temperature for cylinders with flat ends

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Fig. 10

Area and temporal averaged heat flux behavior with surface temperature for cylinders with hemispherical ends

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Fig. 11

Local heat flux behavior (case 4, t = 0.03 s)

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