Research Papers: Jets, Wakes, and Impingment Cooling

Numerical and Experimental Analysis of Impinging Synthetic Jets for Cooling a Point-Like Heat Source

[+] Author and Article Information
Robert Glowienko

Institute of Fluid Mechanics,
FAU Erlangen-Nuremberg,
Ingolstadt 85053, Germany
e-mail: robert.glowienko@audi.de

Hans Derlien

Institute of Fluid Mechanics,
FAU Erlangen-Nuremberg,
Ingolstadt 85053, Germany

Oezguer Ertunc

Mechanical Engineering Department,
Ozyegin University Istanbul,
Istanbul 34794, Turkey

Antonio Delgado

Institute of Fluid Mechanics,
FAU Erlangen-Nuremberg,
Ingolstadt 85053, Germany

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 3, 2017; final manuscript received October 13, 2017; published online February 21, 2018. Assoc. Editor: Amy Fleischer.

J. Heat Transfer 140(5), 052201 (Feb 21, 2018) (8 pages) Paper No: HT-17-1001; doi: 10.1115/1.4038547 History: Received January 03, 2017; Revised October 13, 2017

High power light emitting diodes (LEDs) being used for low and high beam in automotive lighting need active cooling of their heat sinks by radial or axial fans. But the moving elements of the fan cause abrasion, noise, and high energy consumption. Synthetic jets can replace conventional fans with their disadvantages and allow the directed cooling of LEDs. Therefore, in this paper, flow and heat transfer characteristics of impinging synthetic jets are investigated numerically and experimentally as an alternative to cooling LEDs with fans. It is shown that the impact plate brings forward the laminar-turbulent transition of the jets temporally and spatially. The impact plate itself should not be positioned in the region of the free jet's transition height. Increasing the frequency of the synthetic jet has a greater influence on the heat transfer compared to an increase in amplitude. The maximum cooling performance is achieved for all jet configurations with moderate distances between the orifice and the impact plate. In this case, the jet reaches its highest mass flow and impulse and its lowest temperature.

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Fig. 1

Formation of a synthetic jet and boundary conditions of the computational fluid dynamics (CFD) model

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Fig. 2

Housing of the jet ejector with diaphragm [13]

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Fig. 3

Housing of the jet ejector with diaphragm and measured stroke of the oscillating diaphragm inside the cavity [13]

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Fig. 4

Visualization of an impinging jet at a distance H = 10 d and Ta = Ths = 23 °C (4 V 50 Hz, Re = 1078) [13]

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Fig. 5

Transition area of an impact jet brought forward at a distance H = 20 d and Ta = Ths = 23 °C (3 V 35 Hz, Re = 892) [13]

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Fig. 6

Increased swirl of an impact jet at distance H = 25 d and Ta = Ths = 23 °C (3 V 50 Hz, U0=7.15  m/s)

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Fig. 7

Comparison of the normalized jet mass flows (left) and the normalized jet temperatures (right) for all distances H in the 30th cycle (1 V 10 Hz, Ta = 23 °C, U0=1.4  m/s)

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Fig. 8

Comparison of the normalized jet velocities for all distances H in the 30th cycle (1 V 10 Hz, Ta = 23 °C, U0=1.4  m/s)

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Fig. 9

Displacement of the impact jet by lateral inflow of an impact vortex at H = 50 d and t/TM = 0.569 (205 deg)/24 cycle (1 V 10 Hz, Ta = 23 °C, U0=1.4 m/s)

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Fig. 10

Comparison of Nusselt numbers from measurement and simulation (1 V 10 Hz, Ta = 23 °C, U0=1.4  m/s)



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