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Abstract In recent years there has been a phenomenal development in cloud computing, networking, virtualization, and storage, which has increased the demand for high performance data centers. The demand for higher CPU (Central Processing Unit) performance and increasing Thermal Design Power (TDP) trends in the industry needs advanced methods of cooling systems that offer high heat transfer capabilities. Maintaining the CPU temperature within the specified limitation with air-cooled servers becomes a challenge after a certain TDP threshold. Among the equipments used in data centers, energy consumption of a cooling system is significantly large and is typically estimated to be over 40% of the total energy consumed. Advancements in Dual In-line Memory Modules (DIMMs) and the CPU compatibility led to overall higher server power consumption. Recent trends show DIMMs consume up to or above 20W each and each CPU can support up to 12 DIMM channels. Therefore, in a data center where high-power dense compute systems are packed together, it demands efficient cooling for the overall server components. In single-phase immersion cooling technology, electronic components or servers are typically submerged in a thermally conductive dielectric fluid allowing it to dissipate heat from all the electronics. The broader focus of this research is to investigate the heat transfer and flow behavior in a 1U air cooled spread core configuration server with heat sinks compared to cold plates attached in series in an immersion environment. Cold plates have extremely low thermal resistance compared to standard air cooled heatsinks. Generally, immersion fluids are dielectric, and fluids used in cold plates are electrically conductive which exposes several problems. In this study, we focus only on understanding the thermal and flow behavior, but it is important to address the challenges associated with it. The coolant used for cold plate is 25% Propylene Glycol water mixture and the fluid used in the tank is a commercially available synthetic dielectric fluid EC-100. A Computational Fluid Dynamics (CFD) model is built in such a way that only the CPUs are cooled using cold plates and the auxiliary electronic components are cooled by the immersion fluid. A baseline CFD model using an air-cooled server with heat sinks is compared to the immersion cold server with cold plates attached to the CPU. The server model has a compact model for cold plate representing thermal resistance and pressure drop. Results of the study discuss the impact on CPU temperatures for various fluid inlet conditions and predict the cooling capability of the integrated cold plate in immersion environment. 

Abstract The increasing demand for high-performance computing in applications such as the Internet of Things, Deep Learning, Big data for crypto-mining, virtual reality, healthcare research on genomic sequencing, cancer treatment, etc. have led to the growth of hyperscale data centers. To meet the cooling energy demands of HPC datacenters efficient cooling technologies must be adopted. Traditional air cooling, direct-to-chip liquid cooling, and immersion are some of those methods. Among all, Liquid cooling is superior compared to various air-cooling methods in terms of energy consumption. Direct on-chip cooling using cold plate technology is one such method used in removing heat from high-power electronic components such as CPUs and GPUs in a broader sense. Over the years Thermal Design Power (TDP) is rapidly increasing and will continue to increase in the coming years for not only CPUs and GPUs but also associated electronic components like DRAMs, Platform Control Hub (PCH), and other I/O chipsets on a typical server board. Therefore, unlike air hybrid cooling which uses liquid for cold plates and air as the secondary medium of cooling the associated electronics, we foresee using immersion-based fluids to cool the rest of the electronics in the server. The broader focus of this research is to study the effects of adopting immersion cooling, with integrated cold plates for high-performance systems. Although there are several other factors involved in the study, the focus of this paper will be the optimization of cold plate microchannels for immersion-based fluids in an immersion-cooled environment. Since immersion fluids are dielectric and the fluids used in cold plates are conductive, it exposes us to a major risk of leakage into the tank and short-circuiting the electronics. Therefore, we propose using the immersed fluid to pump into the cold plate. However, it leads to a suspicion of poor thermal performance and associated pumping power due to the difference in viscosity and other fluid properties. To address the thermal and flow performance, the objective is to optimize the cold plate microchannel fin parameters based on thermal and flow performance by evaluating thermal resistance and pressure drop across the cold plate. The detailed CFD model and optimization of the cold plate were done using Ansys Icepak and Ansys OptiSLang respectively. 

Abstract With more development in electronics system capable of having larger functional densities, power density is increasing. Immersion cooling demonstrates the highest power usage efficiency (PUE) among all cooling techniques for data centers and there is still interest in optimizing immersion cooling to use it to its full potential. The aim of this paper is to present the effect of inclination and thermal shadowing on two-phase immersion cooling using FC-72. For simulation of boiling, the RPI (Rensselaer Polytechnic Institute) wall boiling model has been used. Also, two empirical models were used for calculation of bubble departure diameter and nucleate site density. The boundary condition was assumed to be constant heat flux and the bath temperature was kept at boiling temperature of FC-72 and the container pressure is assumed to be atmospheric. this study showed that due to the thermal shadowing, boiling boundary layer can lay over the top chipset and increases vapor volume fraction over top chipsets. This ultimately causes increase in maximum temperature of second chip. The other main observation is with higher inclination angle of chip, maximum temperature on the chip decreases up to 3°C.