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Research Papers: Natural and Mixed Convection

# Experimental Investigation of Transitional Natural Convection in a Cube Using Particle Image Velocimetry—Part I: Fluid Flow and Thermal Fields

[+] Author and Article Information
Marios D. Georgiou

Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: georgiou@illinois.edu

Aristides M. Bonanos

Energy, Environment and Water Center,
The Cyprus Institute,
Nicosia, Cyprus
e-mail: a.bonanos@cyi.ac.cy

Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: georgia@illinois.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 28, 2016; final manuscript received June 23, 2016; published online September 20, 2016. Assoc. Editor: Andrey Kuznetsov.

J. Heat Transfer 139(1), 012502 (Sep 20, 2016) (9 pages) Paper No: HT-16-1314; doi: 10.1115/1.4034166 History: Received May 28, 2016; Revised June 23, 2016

## Abstract

An experimental investigation of transitional natural convection in an air filled cube was conducted in this research. The characteristic dimension of the enclosure is 0.35 m, and data were collected in the middle plane of the cavity. The Rayleigh number range examined is $5.0×107≤Ra≤3.4×108$. This was achieved by varying the temperature on the hot and cold walls. The velocity field in the middle plane is measured using particle image velocimetry (PIV). Temperature measurements in the core of the enclosure indicate a linear profile. The average Nu number is also presented and compared against other correlations in the literature. This study attempts to close the gap of available experimental data in literature and provide experimental benchmark data that can be used to validate computational fluid dynamics (CFD) codes since the estimated error from PIV measurements is within 1–2%.

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## Figures

Fig. 1

Schematic of the experimental setup: the main components of the experiment are the test cavity and the 2D-PIV system

Fig. 2

Top view of the enclosure: the profile probes were inserted through the top cavity wall. Location 1 and 3 were on the symmetry plane between the hot and the cold wall and location 2 was on the symmetry plane between the nonheated walls.

Fig. 3

Ensemble average velocity 〈U〉 in the horizontal direction: (a) Ra = 5.08 × 107, (b) Ra = 1.50 × 108, and (c) Ra = 3.40 × 108

Fig. 4

Ensemble average velocity 〈V〉 in the horizontal direction: (a) Ra = 5.08 × 107, (b) Ra = 1.50 × 108, and (c) Ra = 3.40 × 108

Fig. 5

Velocity profile lines: (a) Mean velocity curves 〈U〉 in the horizontal direction and (b) Mean velocity curves 〈V〉 in the vertical direction

Fig. 6

Velocity magnitude |〈U〉| in the enclosures: (a) Ra = 5.08 × 107, (b) Ra = 1.50 × 108, and (c) Ra = 3.40 × 108

Fig. 7

Gradient of the third velocity component (w): we observe that values for the derivative fluctuate between −0.0005 and 0.0005: (a) Ra = 5.08 × 107, (b) Ra = 1.50 × 108, and (c) Ra = 3.40 × 108

Fig. 8

Temperature measurements as a function of height in the core at locations 1 and 3. The filled symbols correspond to the profile probe in location 1, whereas the hollow symbols correspond to the probe in location 3.

Fig. 9

Nusslet number as a function of Ra over the range examined in the present work

Fig. 10

Cube: surface 1 is the hot side, surface 2 is the cold side, and surface 3 is the four Plexiglass sides

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