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Research Papers

Forced Convection Cooling of Low-Power Handheld Devices Using a Vibrating Cantilever Beam

[+] Author and Article Information
Jangwoo Kim

Samsung Electronics,
Giheung, South Korea
e-mail: jangwooo@gmail.com

Paul I. Ro

Mechanical and Aerospace
Engineering Department,
North Carolina State University,
Raleigh, NC 27695-7910
e-mail: ro@ncsu.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received June 3, 2013; final manuscript received January 13, 2015; published online February 10, 2015. Assoc. Editor: Mark North.

J. Thermal Sci. Eng. Appl 7(2), 021010 (Jun 01, 2015) (11 pages) Paper No: TSEA-13-1095; doi: 10.1115/1.4029677 History: Received June 03, 2013; Revised January 13, 2015; Online February 10, 2015

In this study, a convection cooling technique for handheld electronic devices is proposed and investigated. The technique uses bulk airflows generated by a vibrating cantilever beam actuated by a rotating imbalance motor. Analytic coupled physics modeling using an approximate integral method within laminar-flow boundary layers was used to analyze the proposed cooling technique. The cantilever beam and enclosure were designed based on the form factors of a typical handheld device. The bulk airflow cooling performances at various probe locations were investigated experimentally for low and high heating loads and numerically verified. The results indicate that a higher heating load of the heat source results in a larger temperature drop at the same convection rate. Also, for the probe locations away from the heat source and closer to the beam, the resulting temperature drops were relatively small despite a stronger velocity field generated by the beam. This is due first to the heat generated by the vibrating beam itself and second to a circulation of the air heated by the heat source to the rest of the regions in the enclosure. In general, a good agreement between experimental and numerical results was attained, even though a slight difference between two results exists. Overall, significant cooling was achieved by the proposed system. With a beam tip deflection of ±4 mm, nearly an 18-fold increase in the cooling performance was achieved compared to a natural convection case. Furthermore, the cooling performance continues to increase as the tip deflection of the cantilever beam increases. Thus, a cooling system using the bulk airflow generated by a vibrating cantilever beam has much potential as a feasible solution for electronic handheld devices.

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Figures

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Fig. 1

A proposed convection cooling system using a fixed-free vibrating cantilever beam

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Fig. 2

Schematic cross-sectional views of the proposed cooling system

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Fig. 3

A schematic of laminar-flow boundary layers with an unheated starting length,x0, in the enclosure

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Fig. 4

A schematic sketch of a cantilever beam (fixed-free beam) subjected to a transverse harmonic force by a vibration motor

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Fig. 5

Resonance frequencies as a function of the length of the beam for different thicknesses of the beam: (a) first resonant frequency and (b) second resonant frequency

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Fig. 6

Maximum tip deflections of the beam for different beam thicknesses when the force acts at (a) the free end, (b) 10 mm from the free end, and (c) 20 mm from the free end of the beam

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Fig. 7

Harmonic response of the 0.6 mm thick beam with force applied at 10 mm from the free end

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Fig. 8

Effects of opening configurations on airflow in the enclosure with the beam at its maximum deflection to the right: (a) case 1: no opening near the beam and no opening near the heat source, (b) case 2: no opening near the beam and two openings near the heat source, (c) case 3: one opening near the beam and two openings near the heat source, (d) case 4: no opening near the beam and three Openings near the heat source, and (e) case 5: one opening near the beam and three openings near the heat source

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Fig. 9

Steady velocity fields at a point over the heat source for five different opening configurations

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Fig. 10

A schematic of experimental setup for measuring cooling performance

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Fig. 11

Probe locations for measuring the temperature variations

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Fig. 12

Temperature variations obtained at the reference point (over the center of heat source) when the fan is turned on

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Fig. 13

Temperature drops at various locations for 50 °C and 90 °C of the heat source

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Fig. 14

Transient temperature variations at the reference point for (a) 50 °C and (b) 90 °C at the heat source when the fan is turned on

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Fig. 15

Transient velocity variation at the reference point (a) before and after the fan is turned on and (b) in the first 5 s after the fan is turned on

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Fig. 16

Thickness variation of the (a) hydrodynamic and (b) thermal boundary layers

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Fig. 17

Comparisons of temperature drops at the reference point

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Fig. 18

Effect of a tip deflection of the vibrating beam on the Nusselt number

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