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Research Papers

Effects of Ultrasounds on the Heat Transfer Enhancement From a Circular Cylinder to Distilled Water in Subcooled Boiling

[+] Author and Article Information
Federica Baffigi

Department of Energetics “L.Poggi,” University of Pisa, Via Diotisalvi 2, Pisa 56126, Italy

Carlo Bartoli

Department of Energetics “L.Poggi,” University of Pisa, Via Diotisalvi 2, Pisa 56126, Italyc.bartoli@ing.unipi.it

J. Thermal Sci. Eng. Appl 3(1), 011001 (Mar 01, 2011) (7 pages) doi:10.1115/1.4003510 History: Received November 08, 2010; Revised January 17, 2011; Published March 01, 2011; Online March 01, 2011

The main aim of this work is to investigate experimentally the influence of ultrasonic waves, on the heat transfer enhancement, from a stainless steel circular cylinder to distilled water, in subcooled boiling conditions. This study has carried on for a few years at the Department of Energetics “L.Poggi.” The effect was observed since the 1960s: Different authors had investigated the cooling effect due to the ultrasonic waves at different heat transfer regimes, especially from a thin platinum wire to water. They had found out that the highest heat transfer coefficient enhancement was in subcooled boiling conditions. So this paper has the purpose to clarify the physical phenomenon and optimize a large range of variables involved in the mechanism. It reports the experimental results obtained with ultrasound at the frequency of 38 kHz, at two different subcooling degrees, ΔTsub=25°C and 35°C. The heat fluxes applied on the cylinder, the ultrasonic generator power Pgen, and also the placement of the heater inside the ultrasonic generator tank were varied. The ultrasonic waves seem to be very useful for a practical application in the last generation electronic components’ cooling: They need dissipating huge heat fluxes and avoiding high temperatures (150°C), after that they could damage themselves.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental apparatus: (1) ultrasonic generator, (2) dc power supply, (3–5) digital multimeters, and (6) calibrated resistance

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Figure 2

Section of the circular cylinder immersed in the ultrasonic generator tank: (1) ultrasonic generator tank, (2) circular cylinder, (3 sliding thermocouple inside the cylinder, and (4) thermocouple for the water temperature

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Figure 3

Experimental apparatus: the circular cylinder and the copper coil inside the ultrasonic tank

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Figure 4

The circular cylinder

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Figure 5

((a) and (b)) Schematic representation of the two parameters, L and H

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Figure 6

Trend of the heat transfer coefficient h versus q″ without ultrasonic waves, at ΔTsub=35°C, with the superior and inferior range of error of the measured values

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Figure 7

Trend of the heat transfer coefficient h versus q″ without and with ultrasonic waves, at ΔTsub=35°C, L=45 mm, H=25 mm, and Pgen=400 W and 500 W

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Figure 8

Trend of the heat transfer coefficient h versus q″ without and with ultrasonic waves, at ΔTsub=25°C, L=45 mm, H=25 mm, and Pgen=300 W, 400 W, and 500 W

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Figure 9

Trend of the heat transfer coefficient h versus (Twall−TH2O) without and with ultrasonic waves, at ΔTsub=25°C, L=45 mm, H=25 mm, and Pgen=300 W, 400 W, and 500 W

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Figure 10

Trend of the q″ versus Twall−TH2O without and with ultrasonic waves, at ΔTsub=25°C, L=45 mm, H=25 mm, and Pgen=300 W, 400 W, and 500 W

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Figure 11

Trend of the q″ versus Twall−TH2O without and with ultrasonic waves, at ΔTsub=35°C, L=45 mm, H=25 mm, and Pgen=400 W and 500 W

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Figure 12

Trend of h versus q″ without and with ultrasonic waves, at ΔTsub=25°C, Pgen=500 W, H=25 mm, and L=40 mm, 45 mm, and 50 mm

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Figure 13

Trend of h versus q″ without and with ultrasonic waves, at ΔTsub=25°C, Pgen=500 W, L=50 mm, and H=15 mm, 25 mm, and 35 mm

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