Oscillating flow in a heat sink with parallel micro channels

Author(s):  
Yiwu Kuang ◽  
Wen Wang ◽  
Rui Zhuan
Author(s):  
Guillermo E. Valencia ◽  
Jose D. Aldana ◽  
Miguel A. Ramos ◽  
Antonio J. Bula

The Bootstrap Statistical method is applied for estimating the accuracy of the convective heat transfer non linear correlation of AL2O3 nanofluid working as cooling fluid. The flow experiment considers laminar and turbulent regimen through an array of aluminum microchannels and millichannels heat sink, taking into account the Volume Fractions, Reynolds, Peclet and Prandtl numbers. The β’s parameters are estimated with nonlinear least square approach. StatGraphics® was used, considering the Gauss-Newton algorithm with Levenberg-Marquardt modifications for global convergence. Correlation for Nusselt number is presented and suggestions for future experimentation are presented in order to improve the accuracy of the regression.


Author(s):  
Liang-Han Chien ◽  
Han-Yang Liu ◽  
Wun-Rong Liao

A heat sink integrating micro-channels with multiple jets was designed to achieve better heat transfer performance for chip cooling. Dielectric fluid FC-72 was the working fluid. The heat sink contained 11 micro-channels, and each channel was 0.8 mm high, 0.6 mm wide, and 12 mm in length. There were 3 or 5 pores on each micro-channel. The pore diameters were either 0.24 or 0.4 mm, and the pore spacing ranged from 1.5 to 3 mm. In the tests, the saturation temperature of cooling device was set at 30 and 50°C, and the volume flow rate ranged from 9.1 to 73.6 ml/min per channel (total flow rate = 100∼810 ml/min). The experimental result showed that heat transfer performance increased with increasing flow rate for single phase heat transfer. For heat flux between 20 and 100 kW/m2, the wall superheat decreases with increasing flow rate at a fixed heat flux. However, the influence of the flow rate diminished when the channels are in two phase heat transfer regime. Except for the lowest flow rate (9.1 ml/min), the heat transfer performance increased with increasing jet diameter/spacing ratios. The best surface had three nozzles of 0.4 mm diameter in 3.0 mm jet spacing. It had the lowest thermal resistance of 0.0611 K / W in the range of 200 ∼ 240 W heat input.


Author(s):  
H. Chiba ◽  
T. Ogushi ◽  
H. Nakajima

In recent years, since heat dissipation rates and high frequency electronic devices have been increasing, a heat sink with high heat transfer performance is required to cool these devices. Heat sink utilizing micro-channels with several ten microns are expected to provide an excellent cooling performance because of their high heat transfer capacities due to small channel. Therefore, various porous materials such as cellular metals have been investigated for heat sink applications. However, heat sink using conventional porous materials has a high pressure drop because the cooling fluid flow through the pores is complex. Among the described porous materials, a lotus-type porous metal with straight pores is preferable for heat sinks due to the small pressured drop. In present work, cooling performance of the lotus copper heat sink for air cooling and water cooling is introduced. The experimental data for air cooling show 13.2 times higher than that for the conventional groove fins. And, the data for the water cooling show 1.7 times higher than that for the micro-channels. It is concluded that lotus copper heat sink is the most prospective candidate for high power electronics devices.


Author(s):  
Ruixian Fang ◽  
Jamil Khan

Two-phase flow instabilities in micro-channel exhibit pressure and temperature fluctuations with different frequencies and amplitudes. An active way to suppress the dynamic instabilities in the boiling micro-channels is to introduce synthetic jets into the channel fluid. Thus the bubbles can be condensed before they clog the channel and expand upstream causing flow reversal. The present work experimentally investigated the effect of synthetic jets on the suppression of flow boiling instabilities exhibited in a micro-channel heat sink. The heat sink is consisted of five parallel rectangular microchannels measured 500 μm wide, 500 μm deep each. An array of synthetic jets was placed right above the micro-channels with each channel corresponds to 8 jet orifices. The strength and frequency of the jets are controlled by changing the driving voltage and frequency of the piezoelectric driven synthetic jet actuator. Tests were performed with synthetic jets operating at 80 Hz and 150 Hz respectively. It is found that the bubbles were effectively condensed inside the jet cavity. The boiling flow reversals were notably delayed by the synthetic jets. Meanwhile, the pressure fluctuation amplitudes were substantially reduced. Test results were analyzed and discussed in detail.


2013 ◽  
Vol 479-480 ◽  
pp. 192-196
Author(s):  
Tzer Ming Jeng ◽  
Sheng Chung Tzeng ◽  
Wei Ting Hsu ◽  
Guan Wei Xu

This work experimentally investigated the effect of the oscillating flow on the heat transfer enhancement of the finned heat sink with top bypass clearance. The cooling system of the finned heat sink usually employs the steady flow with fixed flow rate to complete the objective of forced convection. This work designed and manufactured a device to oscillate air flow. The experimental results indicate that it would obtain 10~34% heat-transfer increment for the oscillating-flow cases with sufficiently small bypass clearance. It demonstrates that the oscillating flow does promote the cooling performance of finned heat sink.


2016 ◽  
Vol 819 ◽  
pp. 171-175
Author(s):  
Husain Zaidan ◽  
Normah Mohd Ghazali ◽  
Robiah Ahmad

During the last three decades the concept of the traditional cooling systems was modified to include single, double, and multi-layer micro channels. The new studies, applications, fabrication, and research focus on four main areas: the geometrical shape of the micro channels, the number of stacked layers, the type of the coolants, and the heat performance optimization. The previous studies have shown a significant reduction in the power consumption as the optimization is accomplished. In this paper, a semi-review for the previous works is provided, an attempt to interpret the nature of the work done, and show another trial for optimization. In this study, water was used as coolant, stacked multi-channel was adopted, and thermal resistance network was calculated. The heat sink under consideration is a rectangle of width W and length L. The thickness Hsub of the base of the micro-channel is 100 [μ m] while the depth Hc of the micro-channel is 500[μ m], both kept constant for all future optimization cases.


Author(s):  
Stephen A. Solovitz ◽  
Thomas E. Conder

Modern advancements in transistor technology have pushed thermal dissipations from power electronics near the edge of the capability of single-phase micro-channel designs. To alleviate this problem, researchers have begun investigating enhancements to these designs, using methods such as pin fins, turbulators, and impinging jets. These techniques can potentially enhance the convective thermal performance by a factor of 2 to 3, although they do incur a similar magnitude pressure penalty. However, because of the requirements of electrical isolation and mechanical assembly, much of this benefit is tempered, as the convective thermal resistance is only a small fraction of the total resistance. This limitation can be removed through the use of an integral package design where the heat sink passages are fashioned in the electrical stack, which can reduce the conductive resistance until convective enhancements are significant again. These methods include fabrication of micro-channels directly into the active metal braze substrate and potentially even the electrical insulation layer. Thus, while a traditional, non-integral design only experiences a 5% overall benefit when the convective resistance is reduced by 50%, an integral package can have a 20 to 30% improvement for the same enhancement. To examine this capability, a series of computational fluid dynamics studies were conducted to study the performance of several integral micro-channel heat sink configurations. These simulations determined the response for a range of coolants, flowrates, device power dissipations, and operating conditions. These results will serve as a baseline for further development of enhanced, integral micro-channel designs.


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