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Experiments in Single-Phase Natural Circulation Miniloops With Different Working Fluids and Geometries

[+] Author and Article Information
Pietro Garibaldi

Dipartimento di Ingegneria della Produzione, Termoenergetica e Modelli Matematici DIPTEM-Tec, University of Genoa, Via all’Opera Pia 15a, 16145 Genova, Italy

Mario Misale

Dipartimento di Ingegneria della Produzione, Termoenergetica e Modelli Matematici DIPTEM-Tec, University of Genoa, Via all’Opera Pia 15a, 16145 Genova, Italymisale@diptem.unige.it

J. Heat Transfer 130(10), 104506 (Aug 14, 2008) (5 pages) doi:10.1115/1.2948393 History: Received September 13, 2007; Revised February 25, 2008; Published August 14, 2008

The aim of this work is to analyze experimentally the influence of geometrical parameters and fluid properties on the thermal performances of rectangular single-phase natural circulation miniloops, which could be used for cooling of electronic devices. The present paper analyzes two experimental campaigns performed on two rectangular miniloops (ML1 and ML2), characterized by different heights, when two working fluids (water and FC43) are employed. The temperature trends are measured for different combinations of miniloop inclination and power, and the associated fluid velocities are calculated by means of an enthalpy balance. The experimental data are compared with Vijayan’s model, developed for large scale loops in steady-state conditions, corrected with a parameter that takes into account the loop inclination. The dynamical behavior is always stable. The time of the initial transient is long at high miniloop inclination (close to horizontal) and at low power, while the temperature overshoot grows up with increasing power and inclination. Results show that at the same power the velocity of FC43 is almost twice than that of water, but the thermal performances are worse because FC43 is characterized by low specific heat. Moreover, the velocities of the tallest miniloop are the lowest, probably because the enhancement of shear stresses overcomes the increase in buoyancy forces. For both fluids, the velocity grows almost linearly with power. Experimental data show a good agreement with the modified Vijayan’s model.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scheme of the miniloops

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Figure 2

Transient behaviors of ΔTh for α=0deg

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Figure 3

Transient behaviors of ΔTh for α=30deg

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Figure 4

Transient behaviors of ΔTh for α=75deg

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Figure 5

Steady-state fluid velocities

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Figure 6

Comparison between experimental data and Vijayan’s correlation

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