Development of heat sink with ionic wind for LED cooling

https://doi.org/10.1016/j.ijheatmasstransfer.2015.10.029Get rights and content

Highlights

  • A heat sink with the ionic wind was developed using the CFD technique.

  • The ionic wind showed the best behavior when the wire was placed near the rear corner.

  • The ratio of the number of fins to the fin width (n/W) had the optimum value of 1.

  • The ratio of the fin height to the spacing between the fin and the wire (H/S) had the optimum value of 2.

  • The prototype had the enhanced cooling performance of 150% compared with the natural convection.

Abstract

A heat sink with ionic wind has been developed in this study for a new cooling device of a Light Emitting Diode (LED). The characteristics of the ionic wind using wire to parallel-plate-electrodes were analyzed using the Computational Fluid Dynamics (CFD) technique suggested in this study. Also, the cooling performance of the heat sink applied by the impinging flow of the ionic wind was investigated by parametric studies. The CFD results were verified from the experimental results of the ionic wind velocity and temperature. A developed prototype of the heat sink with the ionic wind was then manufactured and tested for its cooling performance. Finally, the advantages of the heat sink with the ionic wind for cooling the LED were confirmed.

Introduction

The Light Emitting Diode (LED) has attracted attention as an energy saving device since it has the highest energy efficiency among existing lighting devices. Thus, many studies on a cooling device for the LED have been performed. The heat dissipation rates of LED devices have increased, and the demand for efficient cooling systems therefore now exceeds the current technology. In accordance with the increasing demand for a compact size, the cooling system should also become smaller and lighter. A heat sink is the most common cooling device for all electronics because of its high productivity. However, the cooling performance of the heat sink is proportional to its size and weight in general since the heat transfer by natural convection is strongly affected by the surface area of the heat sink. Thus, it is natural that the heat sink is becoming larger and heavier in accordance with increasing power of a LED. However, too large and heavy heat sink is not applicable in industrial and commercial fields. Although market share of the LED lighting is now starting to include high-power LEDs, there still is a problem for the lack of a proper cooling technology. Nevertheless, very few studies have been performed for the high-power LED over than 150 W up to date [1], [2], [3]. For the high-power LED greater than 150 W, natural convection with the heat sink has a limit for the application as a lighting device because of its size and weight. Thus, research about optimization of the heat sink using a fan for the LED cooling have been published in these days for enhancing the cooling performance of the heat sink, and at the same time, minimizing the system compared to the heat sink without the fan [4], [5], [6], [7]. The LED lighting used in the room, however, requires silence and vibrationless characteristics of the cooling device. Therefore, the studies for a piezoelectric fan [8], [9] or an ionic wind blower [10], [11], [12] have a great attention for the cooling device of the LED recently.

Thus, a heat sink using ionic wind is suggested for a new cooling device for the LED in this study to overcome the disadvantages of other cooling devices. This new cooling system does not need any mechanical moving parts to create a flow. Because an impinging jet is made using a single wire, the required compact size of the device can be achieved. Also, it does not have any vibration that can cause noise and wear.

Although study on the impinging flow of a synthetic jet on the heat sink is very new, a few researchers such as Chaudhari [13], [14], [15] and Lasance [16] have already carried out many tests and proved its relatively high value due to the heat transfer performances. The impinging ionic wind has been proven to have a higher heat transfer augmentation to natural convection and many advantages compared with fan cooling [17], [18], [19], [20]. Moreover, most recently, Chen [12] analyzed the effect of ionic wind and demonstrated its advantages for cooling the LED. However, no report on the practical development of the heat sink with the ionic wind has been presented. Thus, in this study, the parametric study of the heat sink with the ionic wind was conducted using Computational Fluid Dynamics (CFD). Also, a performance test of the prototype was carried out experimentally. The results presented in this paper can be used practically in the industrial field for the optimum design of an ionic wind generator with the heat sink. The results of the impinging ionic wind with the developed heat sink are expected to have practical utility.

Section snippets

Generation of ionic wind

If the threshold electric field is applied between a wire (a discharge electrode) and a plate electrode (collecting electrodes), a corona discharge occurs at the wire. From this local discharge at the wire, air molecules are ionized into ions and electrons. The charged ions and electrons then move in opposite directions due to their polarity as space charges. Positive ions moved to the plate electrode after positive voltage was applied on the wire in this study. During this travel, heavy ions

Testing method

The measurement tests of the velocity and temperature were conducted to verify the CFD results in this study. The ionic wind generator with the wire between the parallel plates, and the hot plate made of a copper block were installed as shown in Fig. 1, Fig. 2. The wire and the plate-electrodes were made of nickel alloys. In addition, the specific dimensions of the test materials are listed in Table 1.

The nichrome wire was attached under the hot plate using a thermally conductive adhesive, and T

Verification of CFD results

Fig. 3 shows the CFD result of the space charge density. The size of the calculation domain was 1 × 2 × 3 cm3. Although the figures in the Section 4.1 showed two-dimensional geometries because of the symmetric arrangement of the wire to parallel plate electrodes, the depth of 1 cm was considered. The white hole in the center area represents the cross sectional view of the wire and both sides of the figure show the plate-electrodes. High space charge density was formed near the wire and a uniform

Conclusion

A heat sink with ionic wind for LED cooling was developed in this study. The characteristics of the ionic wind impinging on the heat sink were investigated using CFD, and were verified from the experimental data for the velocity and temperature. Thus, the optimum position of the wire in the case of the wire to parallel-plates was obtained. In addition, the parametric study for the design of the heat sink under the impinging flow was accomplished. Finally, the prototype for the heat sink with

Conflict of interest

None declared.

Acknowledgement

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Korean government (MEST) (NRF-2013R1A2A2A01068653).

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