Flow dynamics and heat transfer in partially porous microchannel heat sinks

Significance 

Currently, the thriving digital economy is a consequence of the ‘electronic revolution’ and has been supported by the development of many electrical appliances. This economy has a unique characteristic, particularly with regard to electronic devices in that the demand for slimmer and smaller devices is ever on the rise. The performance of such high-powered cutting-edge miniature electronic devices depends on the heat dissipation efficiency, since heat generation in such small devices is the most problematic issue, and failing to control it renders the application of such devices economically untenable. Device creators have developed various approaches to circumvent this shortfall where the use of microchannel heat sinks (MCHS) has shown great promise. MCHS devices are advantageous in that they possess a high surface-to-volume ratio, portability and low coolant requirements. To further increase the available surface for heat transfer, MCHS with built-in porous media have been used. Research has further shown that the use of pin-based MCHS increases the heat dissipation efficiency of MCHS by increasing the surface area for heat transfer. Further, published studies have reported that partially filled porous channels have less pressure drop as the coolant can flow through the porous medium as well as around it.

Overall, the hydrodynamic behavior of partially filled pin-based MCHS is very complex as there are various flow regimes in the system. In fact, it has been demonstrated that such intricacy can lead to unpredictable behavior in terms of heat removal performance. Therefore, to address this, researchers from the Schulich School of Engineering at University of Calgary in Canada: Dr. Mohammad Zargartalebi and Professor Jalel Azaiez studied carefully the effects of porous medium size on both heat transfer and flow patterns in a partially filled MCHS. In addition, they also focused on examining if recently published results regarding the pin configuration for fully filled microchannels could be extended to partially filled ones. Their work is currently published in Journal of Fluid Mechanics.

In their approach, the lattice Boltzmann method was used to analyze the physics of the partially filled pin-based MCHS system in addition to the effects of the flow, pin configuration, size and porous medium height. Due to the hydrodynamic response of the pins, the flow geometry as well as the energy removal performance were shown to be complicated.

The authors revealed that unlike the fully filled pin-based MCHS, there was no unique behavior for the pin configuration effects and the performance of partially filled pin-based MCHS depended on the porous medium size and structure as well as the inertial forces in the flow. In particular, the two scientists reported that there were hydrodynamic and thermal-based critical porous medium heights at which the best performance in terms of heat removal switches from the inline to the staggered configuration.

In summary, the study by Dr. Mohammad Zargartalebi and Professor Jalel Azaiez presented an in-depth assessment of the hydrodynamic and energy removal efficiencies in partially filled pin-based MCHS for both inline and staggered pin configurations. The study revealed that at the critical porous medium height, the friction ratio of the staggered over the inline configuration increased abruptly indicating that the coolant was forced to flow through the porous medium. In an interview with Advances in Engineering, Dr. Mohammad Zargartalebi further highlighted that the critical hydrodynamic and thermal parameters were inevitable in such systems, where there exists a competition between high- and low-resistivity flow passes in terms of flow rate, and that the critical values depended on the porous medium properties.

Advances-in-Engineering-Flow-dynamics-heat-transfer-in-partially-porous-microchannel-heat-sinks
figure shows the temperature distribution in a staggered structure along with the particle tracking analysis revealing the flow pattern

Reference

Mohammad Zargartalebi, Jalel Azaiez. Flow dynamics and heat transfer in partially porous microchannel heat sinks. Journal of Fluid Mechanics (2019), vol. 875, pp. 1035–1057.

Go To Journal of Fluid Mechanics

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