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Research Papers: Natural and Mixed Convection

A Numerical Study of Turbulent Mixed Convection in a Smooth Horizontal Pipe

[+] Author and Article Information
Ahmed Faheem

School of Civil Engineering,
The University of Sydney,
Building J05,
New South Wales 2006, Australia
e-mail: ahmed.faheem@sydney.edu.au

Gianluca Ranzi

Associate Professor
School of Civil Engineering,
The University of Sydney,
Building J05,
New South Wales 2006, Australia
e-mail: gianluca.ranzi@sydney.edu.au

Francesco Fiorito

Faculty of Architecture, Design & Planning,
The University of Sydney,
Building G04,
New South Wales 2006, Australia
e-mail: francesco.fiorito@sydney.edu.au

Chengwang Lei

School of Civil Engineering,
The University of Sydney,
Building J05,
New South Wales 2006, Australia
e-mail: chengwang.lei@sydney.edu.au

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 12, 2015; final manuscript received June 22, 2015; published online August 11, 2015. Assoc. Editor: Antonio Barletta.

J. Heat Transfer 138(1), 012501 (Aug 11, 2015) (11 pages) Paper No: HT-15-1191; doi: 10.1115/1.4031112 History: Received March 12, 2015

This paper presents a numerical study aimed at identifying a suitable turbulence model to describe the fully developed turbulent mixed convention of air in smooth horizontal pipes. The flow characteristics considered here are relevant to those typically observed in ventilated hollow core slab (VHCS) applications and, because of this, the adopted geometry and boundary conditions are represented by the Reynolds number and Richardson number of about 23,000 and 1.04, respectively. Empirical expressions available in the literature are used as reference to evaluate the accuracy of different turbulence models in predicting the dimensionless velocity (u+) and temperature (T+) profiles as well as the Nusselt number (Nu). Among the turbulence models considered, the standard and realizable k-ε models provide the best overall predictions of u+, T+, and Nu in the fully developed flow, and the former is recommended for the modeling of VHCS systems as it gives slightly better estimates of the Nu values.

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References

Figures

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Fig. 2

Cross sections showing three grid arrangements: (a) G1, (b) G2, and (c) G3

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Fig. 1

Geometry and boundary conditions of a horizontal pipe

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Fig. 3

Grid sensitivity test results: (a) cross section showing points of temperature, shear stress, and velocity measurements in the fully developed region at z/d = 61.1, (b) grid sensitivity test results for the STDkε model, and (c) grid sensitivity test results for the SSTkω model

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Fig. 5

Comparisons between NuT values obtained from empirical correlations C1–C6 (Table 4) and experiments

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Fig. 8

Comparisons between the numerical and empirical T+ profiles in the fully developed region at z/d = 61.1 on the radius at (a) φ = 180 deg (lower half of the vertical diameter) and (b) φ = 0 deg (upper half of the vertical diameter)

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Fig. 4

Representative flow patterns in the fully developed region at z/d = 61.1: (a) secondary velocity vectors, (b) isotherms, (c) axial velocity contours, and (d) axial velocity profiles along the vertical diameter

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Fig. 6

Comparisons between numerical and empirical u+ profiles in the fully developed region at z/d = 61.1 on the radius at (a) φ = 180 deg (lower half of the vertical diameter) and (b) φ = 0 deg (upper half of the vertical diameter)

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Fig. 7

Average errors associated with the numerical u+ profiles in the fully developed region at z/d = 61.1 for different angles  φ considering (a) the inner region, (b) the outer region, and (c) the complete boundary layer

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Fig. 9

Average errors associated with the numerical T+ profiles in the fully developed region at z/d = 61.1 for different angles  φ considering (a) the inner region, (b) the outer region, and (c) the complete boundary layer

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Fig. 10

(a) Comparisons of the numerically predicted Nusselt numbers against the empirical correlation—Eq. (5), in the fully developed region at z/d = 61.1. (b) Errors associated with the numerical predictions of Nu at different angles  φ.

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