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Technical Brief

Eulerian–Eulerian Modeling of Convective Heat Transfer Enhancement in Upward Vertical Channel Flows by Gas Injection

[+] Author and Article Information
Deify Law

Department of Mechanical Engineering,
California State University, Fresno,
2320 E. San Ramon Avenue, M/S EE94,
Fresno, CA 93740-8030
e-mail: dlaw@csufresno.edu

Haden Hinkle

Department of Mechanical Engineering,
California State University,
Fresno, 1320 E. San Ramon Avenue, M/S EE94,
Fresno, CA 93740-8030

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received March 29, 2017; final manuscript received July 13, 2017; published online September 13, 2017. Assoc. Editor: Wei Li.

J. Thermal Sci. Eng. Appl 10(2), 024501 (Sep 13, 2017) (5 pages) Paper No: TSEA-17-1097; doi: 10.1115/1.4037650 History: Received March 29, 2017; Revised July 13, 2017

Two-phase bubbly flows by gas injection had been shown to enhance convective heat transfer in channel flows as compared with that of single-phase flows. The present work explores the effect of gas phase distribution such as inlet air volume fraction and bubble size on the convective heat transfer in upward vertical channel flows numerically. A two-dimensional (2D) channel flow of 10 cm wide × 100 cm high at 0.2 and 1.0 m/s inlet water and air superficial velocities in churn-turbulent flow regime, respectively, is simulated. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS fluent. The bubble size is characterized by the Eötvös number. The inlet air volume fraction is fixed at 10%, whereas the Eötvös number is maintained at 1.0 to perform parametric studies, respectively, in order to investigate the effect of gas phase distribution on average Nusselt number of the two-phase flows. All simulations are compared with a single-phase flow condition. To enhance heat transfer, it is determined that the optimum Eötvös number for the channel with a 10% inlet air volume fraction has an Eötvös number of 0.2, which is equivalent to a bubble diameter of 1.219 mm. Likewise, it is determined that the optimum volume fraction peaks at 30% inlet air volume fraction using an Eötvös number of 1.0.

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Figures

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Fig. 1

Schematic of the 2D channel

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Fig. 2

Comparison of CFD and experimental data [18] for wall heat transfer coefficient of a 0.385 m diameter bubble column at 82.3 cm above the column inlet at several inlet gas superficial velocities

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Fig. 3

Grid-resolution study for space-averaged water axial velocity profile of case 2 between channel heights of 20 and 80 cm at 40 s

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Fig. 4

Grid-resolution study for space-averaged water static temperature profile of case 2 between channel heights of 20 and 80 cm at 40 s

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Fig. 5

Comparison of average Nusselt number at a given Eötvös number with a 10% inlet air volume fraction between channel heights of 20 and 80 cm

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Fig. 6

Comparison of average Nusselt number at a given inlet air volume fraction with Eötvös number of 1.0 between channel heights of 20 and 80 cm

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