Experimental Achievements in Mini- and Micro- Channel Cooling

There are a significant number of cooling techniques for micro- and mini-sized devices. One of them is mini-channel cooling. In this review, a large amount of experimental work on mini-channel cooling by various liquids is conceptually considered, in which the threshold in the removal of specific heat flux of >1 MW/m2 has been reached. A comparison of mini-channel cooling with other cooling techniques is performed. It was established that 1) micro-channel cooling has practically no thermophysical advantages over macro- or mini-channel one; 2) single-phase cooling in mini-channels gives comparable results compared to two-phase cooling; 3) only a small set of conceptual techniques allows the mini-channel heat exchanger to overcome the limit of 10 MW/m2 or to reach the heat transfer coefficient larger than 0.2 MW/(m2*K).

Cooling of High Powered GPUs Using Liquid Nitrogen Cold Plates Made With Additive Manufacturing

Processor energy density is exceeding the capabilities of conventional air-cooling technology, but two-phase cooling has the potential to manage these resulting heat fluxes at reliable temperatures and higher electrical efficiency. When two-phase cooling is used in tandem with overclocking, data center footprints are reduced as individual chip processing power can be set at limits well beyond the manufacturer’s Thermal Design Power (TDP) or nominal operating condition. This study examines how Liquid Nitrogen (LN2) can be used with Additive Manufacturing (AM) and overclocking to increase the computational performance of a commercially available GPU. The power consumption and frequency relationship were established for both the cryogenically cooled solution and a comparative air-cooled solution. The cryogenic solution saw up to a 17.4% increase in compute efficiency and an 18.1% improvement in compute speed with comparable power efficiency at an equivalent performance level to the air-cooled solution. This study considers the computational performance and efficiency gains that can be acquired through cryogenic cooling on an individual graphics card, which can be replicated on a larger scale in data center applications.

An Assessment of Effects of Nanofluids on Heat Transfer Performance of Two-Phase Cooling Systems

The recent increase in complexity of computations and the expansion of edge computing have led to the emergence of high power density data centers with an urgent demand for more advanced thermal management systems. Two-phase passive cooling systems such as thermosyphons and heat pipes have been widely used in industry to maintain the temperature of the servers below the threshold of failure and carry away a large quantity of heat from a small area. Such systems are economically viable and sustainable since they have no moving parts and consume lower power. However, an upgrade to these cooling systems is imminent due to the ever-increasing power densities of the data centers and more challenging thermal management issues faced by the industry. Nanofluids have emerged recently as a new class of cooling liquids claiming to enhance the heat transfer performance in single and two-phase cooling systems. As per several studies presented in this paper, the thermal performance of thermosyphons is shown to be enhanced by employing nanofluids. In this paper, a comprehensive review is presented on the effect of nanofluids in improving the Critical Heat Flux (CHF) and Heat Transfer Coefficient (HTC) in two-phase cooling systems. The boiling phenomenon and working principles of thermosyphons will be discussed to understand the underlying mechanisms affecting heat transfer in the evaporator region, where the heat is absorbed from the source. The impact of nanoparticle features, concentration, and deposition pattern on HTC enhancement will also be studied. Additionally, estimates of the heat dissipation improvement by using nanofluids along with the bottlenecks and challenges faced in applying such fluids practically are reviewed as well. In conclusion, recommendations are made for future research needed to overcome the risks and commercialize the nanofluids in two-phase cooling systems for providing significant improvement in heat transfer performance as compared to conventional working fluids.