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Ionic wind is induced by corona discharge caused by extremely inhomogeneous electric field between two electrodes. Due to its compact size, energy saving, flexible design, and easy integration, ionic wind technique exhibits great potential to improve hotspot cooling, especially for compact electronic devices. However, the heat removal capability towards high power density is relatively low due to the limited heat transfer area and low air thermal conductivity. The principle and designs are still lacking for local hotspot cooling. Here, an ionic wind generator with a novel architecture coupled with porous medium is conceived to enhance cooling performance. It is demonstrated that when a porous medium block is coupled, heat transfer can be significantly boosted due to the modified heat and mass transfer in the porous block. It is also found that electrode configuration significantly influences the device performance. There is a trade-off between heat transfer area and airflow impediment in the device. The geometry and property parameters of the porous block are critical for the cooling performance, which is attributed to the modified flow field by changing porous structure. Based on this principle, another ionic wind generator improved by a coupled heat sink with porous fins is proposed, whose performance can be further enhanced by optimizing its design parameters. The optimized heat sink structure can maintain the max temperature of the cooling surface below 83.2 °C at a heat flux of 90 kW/m2. This study provides a promising way for air-side thermal management of hotspot. The findings are helpful for understanding EHD-induced airflow heat transfer in porous medium and shed new light on designing ionic wind generators with better performance. [ABSTRACT FROM AUTHOR]

Conventional double-layered microchannel heat sink (DL-MCHS) significantly improves temperature uniformity on the bottom wall due to temperature compensation between the two layers through conduction. However, temperature of the top coolant is always higher than that of the bottom coolant in the inlet region of bottom channels, which inevitably leads to a heating effect of the top coolant on the bottom coolant. To prevent the heating effect, a new DL-MCHS with truncated top channels was proposed in our previous study. To further enhance the cooling performance of the new design, multi-parameter optimizations are performed at various fixed pumping powers Ω and fixed coolant volumetric flow rates Q v , respectively. The optimization algorithm is composed of a three-dimensional solid–fluid conjugate heat sink model and a simplified conjugate-gradient method. Overall heat resistance R is the objective function to be minimized with channel number N , channel height H c , channel width W c , and the dimensionless truncation length of top channels l as search variables. With a constant heat flux of 100 W cm −2 applied to the bottom wall, and a constant Ω of 0.05 W, the optimal design has N = 55, W c = 0.116 mm, H c = 0.525 mm, l = 0.28, and R = 0.102 K W −1 . However, with a constant Q v = 200 ml min −1 , the optimal design has N = 79, W c = 0.026 mm, H c = 0.175 mm, l = 0.38, and R = 0.093 K W −1 . The improvements of cooling performance for constant Ω and constant Q v are all attributed to the enhancement of cooling effect and/or the reduction of heating effect. Finally, the design directions of the four search variables are given at various Ω and Q v . [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional solid–fluid conjugate model coupled with a simplified conjugate-gradient method was employed to optimize the performance of double-layered microchannel heat sinks. Channel number, channel width, bottom channel height, and bottom coolant inlet velocity were selected as search variables to achieve the optimal heat sink performance. Firstly, two single-objective optimizations based on different objective functions (one is the maximum temperature change on the bottom wall Δ T w,b and the other is the overall thermal resistance R ) were performed at a constant pumping power. Subsequently, the effects of total pumping power on the optimal Δ T w,b and R were analyzed, and the optimal search variables at various pumping powers were obtained. For single-objective optimization with the objective function of Δ T w,b , Δ T w,b is respectively decreased by 6.01, 5.29, and 2.99 K when compared with three original designs. For the objective function of R , however, R is respectively decreased by 36.51%, 15.10%, and 16.67%. The results also indicate that R and Δ T w,b cannot achieve their optimal values simultaneously by the two single-objective optimizations. Thus, a multi-objective optimization was carried out, which demonstrates that when a set of desirable values of Δ T w,b and R is required by designers, the present multi-objective optimization could meet this requirement. [ABSTRACT FROM AUTHOR]

Abstract Microchannel heat sinks have provided an efficient solution in the thermal management of high-power density devices. In general, however, they cannot exhibit high thermal performance and lower pressure drop simultaneously. In this work, an improved design of microchannel heat sinks possessing a combination of high thermal performance and low pressure drop is proposed, where the superiority of double-layered concept and the advantage of porous-ribs design are taken into account. In the improved design, two layers of rectangular channels are stacked one atop another with porous ribs utilized in the upper layer while solid ribs employed in the lower layer. The thermal performance and the flow characteristics of the improved design are numerically studied using a three-dimensional solid-fluid conjugate model. Four other heat sinks with different structure (solid-ribs single-layered, porous-ribs single-layered, solid-ribs double-layered, and porous-ribs double-layered) are designed for performance comparison. The results demonstrate that the improved design yields the lowest thermal resistance and the best temperature uniformity on the bottom wall among all the five designs whether at an identical Reynolds number or at a fixed pumping power. The appropriate combination of better thermal conductivity of solid ribs and lower pressure drop of porous ribs in a double-layered heat sink is responsible for the performance improvement. Highlights • An improved double-layered microchannel heat sink is proposed. • Porous ribs are employed in the upper layer with solid ribs in the lower layer. • Thermal performance and pumping power both reduce for the improved design. [ABSTRACT FROM AUTHOR]

Microchannel heat sink (MCHS) is regarded as a promising cooling scheme for high power microelectronic devices. To further enhance its cooling capacity and improve the temperature uniformity, the investigation of the MCHS employing transcritical CO 2 as coolant was conducted in this work for the first time. A three-dimensional solid–fluid conjugated model is developed to investigate the performance of CO 2 -cooled MCHS. Sufficiently changed thermophysical properties of the transcritical CO 2 is taken into account in the model. The results demonstrate that, with the same pumping power of 0.03 W, the thermal resistance ( R ) of the CO 2 -cooled MCHS is reduced by 23.34–34.62% in the inlet temperature range of 285–305 K, as compared with the water-cooled MCHS. Likewise, the maximum temperature drop (Δ T b,max ) on the bottom surface is decreased by 24.18–48.75%. The improved performance is attributed to the lower viscosity and higher specific heat of the transcritical CO 2 . Moreover, as compared with the water-cooled MCHS, R and Δ T b,max for the CO 2 -cooled MCHS exhibit a more significant reduction when the MCHS has a larger number of channels, a larger channel aspect ratio, or a smaller channel width to pitch ratio. For a given inlet pressure p in of CO 2 , the optimal inlet temperature should be appropriately lower than the pseudocritical temperature at the given p in to ensure the larger specific heat for CO 2 flowing in microchannels. [ABSTRACT FROM AUTHOR]