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The variety of new electronic packaging technologies has grown significantly over the last 20 years as a result of market demands for higher device performance at lower costs and in less space. Those demands have pushed for heterogeneous packaging, where computer chips with different stack heights are closely packed, creating nonuniform heat flux and temperature and additional challenges for thermal management. Without implementing an appropriate thermal management strategy for heterogeneous packages, large temperature gradients can be observed within the package, which would increase the thermal stresses on the chip and raise reliability issues. To mimic this real-life scenario of such packaging, an experimental setup was designed and built. The design of the new experimental setup consists of four identical 1.2 cm × 1.2 cm ceramic heaters, each of which is connected to a separate power supply and can reach a heat flux of 140 W/cm2. Accordingly, this mock package is capable of delivering different power levels to mimic different multicore microprocessor conditions. To give the heater the ability to move precisely in the x-, y-, and z-directions, each heater is mounted to an XYZ linear stage. Deionized water (DI) was used as the working fluid, and a pin-fin heat sink was used to run the initial steady-state tests on the experimental rig. The tests showed how different flow rates at a constant fluid temperature and input power affect the temperatures of the heaters and the thermohydraulic performance of the heat sink. In addition, a three-dimensional numerical model has been developed and validated with experimental data in terms of heat sink pressure drop and the temperatures of the heaters. 

In the design of high-performance heat and mass transfer devices such as liquid-cooled heat sinks, catalytic reactors, and catalytic convertors, parallel mini/microchannels are favored owing to their special potentials. Offering low pressure drop, providing high transfer surface area to volume ratio, and being easy to manufacture and optimize have been drawing thermal and chemical engineers attention to parallel channels for past decades. When working with parallel channels, the challenge of flow maldistribution is commonly faced which decreases their efficiency significantly. System total pressure drop and flow uniformity are two parameters that determine the system performance. In the present study, a variety of practical ideas, aiming to enhance parallel channels performance, are studied numerically. Inventive manifold designs with high hydraulic performance are created through the course of this study. The results of these designs are compared with basic conventional designs which show substantial enhancement. Analyzing less successful designs lead us to deep understanding of fluid dynamics in parallel channel heat and mass transfer devices. 

The ability of traditional room-conditioning systems to accommodate expanding information technology loads is limited in contemporary data centers (DCs), where the storage, storing, and processing of data have grown quickly as a result of evolving technological trends and rising demand for online services, which has led to an increase in the amount of waste heat generated by IT equipment. Through the implementation of hybrid air and liquid cooling technologies, targeted, on-demand cooling is made possible by employing a variety of techniques, which include but are not limited to in-row, overhead, and rear door heat exchanger (HX) cooling systems. One of the most common liquid cooling techniques will be examined in this study based on different conditions for high-power density racks (+50 kW). This paper investigates the cooling performance of a liquid-to-air in-row coolant distribution unit (CDU) in test racks containing seven thermal test vehicles (TTVs) under various conditions, focusing on cooling capacity and HX effectiveness under different supply air temperatures (SAT). This test rig has the necessary instruments to monitor and analyze the experiments on both the liquid coolant and the air sides. Moreover, another experiment is conducted to assess the performance of the CDU that runs under different control fan schemes, as well as how the change of the control type will affect the supply fluid temperature and the TTV case temperatures at 10%, 50%, and 100% of the total power. Finally, suggestions for the best control fan scheme to use for these systems and units are provided at the conclusion of the study. 

This study explores the latent thermal energy storage potential of an organic phase change material with porous copper foam and its applicability in electronic cooling under varying heat load conditions. The organic phase change material, n-eicosane, is known for its inherently low thermal conductivity of 0.15 W/mK, rendering it vulnerable during power spikes despite its abundant latent heat energy for phase transition from solid to liquid. Porous copper foams are often integrated into n-eicosane to enhance the composite’s thermal conductivity. However, the volume fraction of the phase change material in the porous foam that optimally improves the thermal performance can be dependent on the boundary condition, the cut-off temperature, and the thickness. A finite difference numerical model was developed and utilized to ascertain the energy consumption for the composite of n-eicosane with two kinds of porous copper foam with varying porosity under different heat rates, cut-off temperatures, and thickness. In addition, the results are compared with a metallic phase change material (gallium), a material chosen with a similar melting point but significantly high thermal conductivity and volumetric latent heat. For validation of the numerical model and to experimentally verify the effect of boundary condition (heat rate), experimental investigation was performed for n-eicosane and high porosity copper foam composite at varying heat rates to observe its melting and solidification behaviors during continuous operation until a cut-off temperature of 70 ◦C is reached. Experiments reveal that heat rate influences the amount of latent energy storage capability until a cutoff temperature is reached. For broad comparison, the numerical model was used to obtain the accessed energy and power density and generate thermal Ragone plots to compare and characterize pure gallium and n-eicosane - porous foam composite with varying volume fractions, cutoff temperature, and thickness under volumetric and gravimetric constraints. Overall, the proposed framework in the form of thermal Ragone plots effectively delineates the optimal points for various combinations of heat rate, cutoff point, and aspect ratio, affirming its utility for comprehensive design guidelines for PCM-based composites for electronic cooling applications 

The increasing prevalence of high-performance computing data centers necessitates the adoption of cutting-edge cooling technologies to ensure the safe and reliable operation of their powerful microprocessors. Two-phase cooling schemes are well-suited for high heat flux scenarios because of their high heat transfer coefficients and their ability to enhance chip temperature uniformity. In this study, we perform experimental characterization and deep learning driven optimization of a commercial two-phase cold plate. The initial working design of the cold plate comprises a fin height of 3mm, fin thickness of 0.1 mm, and a channel width of 0.1 mm.A dielectric coolant, Novec /HFE 7000, was impinged into microchannel fins through impinging jets. A copper block simulated an electronic chip with a surface area of 1˝ × 1˝. The experiment was conducted with three different coolant inlet temperatures of 25◦ C, 36◦ C, and 48◦ C with varying heat flux levels ranging from 7.5 to 73.5 W cm2. The effects of coolant inlet temperatures and flow rate on the thermo-hydraulic performance of the cold plate were explored. In two-phase flow, increasing coolant inlet temperature results in more nucleation sites and improved thermal performance consequently. Thermal resistance drops with flow rate in single-phase flow while it is not affected by flow rate in nucleate boiling region. An improvement in the design of the cold plate was carried out, with the goal of increasing the number of bubble sites and flow velocity at the root fins, by cutting the original fins and creating channels perpendicular to the original channels. Three design parameters, fin height, width of machined channels, and height of short fins preserved through machined channels, were defined. It was observed that widening the machined channels and cutting fins to some point can improve the thermal performance of the cold plate. However, removing fins excessively adversely affects the thermal performance of the cold plate because of loss of heat transfer surface area. Moreover, preserving the short fins through the machined channels decreases thermal resistance as they increase heat transfer surface area and nucleation sites. Furthermore, a deep learning-based compact model is demonstrated for the two-phase cold plate design in the specific range of geometry and flow conditions. The developed compact model is utilized to drive the single and multi-objective optimization to arrive at global optimal results. 

Owing to the dramatic increase in IT power density and energy consumption, the data center (DC) sector has started adopting thermally- and energy-efficient liquid cooling methods. This study examines a single-phase direct-to-chip liquid cooling approach for three high-heat-density racks, utilizing two liquid-to-air (L2A) cooled coolant distribution units (CDUs) and a combined total heat load of 128 kW. An experimental setup was developed to test different types of CDUs, cooling loops, and thermal testing vehicles (TTVs) for different operating conditions. IR images and the collected data were used to investigate the effect of air recirculation between cold and hot aisle containments on the CDU’s performance and stability of supply air temperature (SAT). Three different types of cooling loops (X, Y, and Z) were characterized thermally and hydraulically. Results show that Type Y has the lowest cold plate thermal resistance and pressure drop, among others. In a later test that included a single rack at a heat load of 53 kW and a single CDU, the heat capture ratio for fluid was found to be 94%. Experiments show that using blanking panels on the back of the racks limits hot air recirculation and maintains a steady SAT in the cold aisle. Finally, the CDU performance was evaluated at a high heat load for the three racks at 128 kW, and the average cooling capacity of the units is 58.6 kW, and the effectiveness values for CDU 1 and CDU 2 are 0.83 and 0.82, respectively. 

As the online frameworks and services are growing rapidly with the evolution of web-based Artificial Intelligence (AI) applications, server rooms are upgrading in computational capacity and size to keep up with these demands. Enterprise companies with their limited capacity server rooms struggle to keep up with these increasing computational demands. Hence, some of them end up outsourcing their servers to co-located facilities (Co-Lo) and the others choose to upgrade their existing server rooms. Correspondingly, the thermal load associated with such upgrades is typically tremendous. Approximately around 40% of the power consumed by datacentres is dissipated as heat. Conventional HVAC systems fail to satisfy the requirements of such server capacities. Not only do they struggle to fulfil the cooling load, but their maldistribution of cool air into the server room forms a major cause for hotspots formation. To tackle this issue, Liquid-to-Air (L2A) Coolant Distribution Units (CDUs) are being used as a liquid-based cooling solution for rack-level cooling. This type of CDUs provide efficient cooling for servers through liquid coolant that is distributed into cooling loops mounted on top of each server board. The generated heat is curried away using this liquid coolant back to the CDU, which then dissipates it into the surrounding air using dedicated pumps, fans, and heat exchanger, hence the name Liquid-to-Air. In the present work, one of the most popular liquid cooling strategies is explored based on various scenarios. the performance of a 24-kW liquid to Air (L2A) CDU is judged based on cooling effect, stability, and reliability. The study is curried out experimentally, in which a test rack with three thermal test vehicles (TTVs) are used to investigate various operation scenarios. Both liquid coolant and air sides of this experimental setup are equipped with the required instrumentations to monitor and analyse the tests. All test cases were taken in a room with limited air conditioning to resemble the environment of upgraded server rooms with conventional AC systems. Moreover, the impact of using such high-power density cooling unit on the server room environment with restricted HVAC system is also brought to light. Environmental and human comfort parameters such as noise, air velocity, and ambient temperature are measured under various operation conditions and benchmarked against their ranges for human comfort as listed in ASHREE standards. At the end of this research, recommendations for best practice are provided along with areas of enhancement for the selected system. 

The electronics packaging community strongly believes that Moore’s law will continue for another few years due to recent technological efforts to build heterogeneously integrated packages. Heterogeneous integration (HI) can be at the chip level (a single chip with multiple hotspots), in multi-chip modules, or in vertically stacked three-dimensional (3D) integrated circuits. Flux values have increased exponentially with a simultaneous reduction in chip size and a significant increase in performance, leading to increased heat dissipation. The electronics industry and the academic research community have examined various solutions to tackle skyrocketing thermal-management challenges. Embedded cooling eliminates most sequential conduction resistance from the chip to the ambient, unlike separable cold plates/ heat sinks. Although embedding the cooling solution onto an electronic chip results in a high heat transfer potential, technological risks and complexity are still associated with the implementation of these technologies and with uncertainty regarding which technologies will be adopted. This manuscript discusses recent advances in embedded cooling, fluid selection considerations, and conventional, immersion, and additive manufacturing-based embedded cooling technologies. 

Semiconductor thermal management is becoming a bottleneck challenge that restricts further development in the electronics industry. Compromising processor thermal requirements will impact the processor performance and reliability. Heat sinks are designed to increase the available surface area of an electronic component and allow for more heat to be easily dissipated. As a result, the thermal characterization of the heat sinks plays a critical role in electronics thermal management. In this study, a flexible experimental apparatus is designed, built, and assembled to characterize and test various electronics components in different aerodynamics and thermal conditions. This novel experimental apparatus allows for controlled characterization of the various heat sinks with different heights as well as realistic scenarios with air bypass at server level. Moreover, a general guideline on precise experimental procedure to characterize air cooled heat sinks is developed. The results show that introduced method reduces the experimental error by 26%. 

As the demand for faster and more reliable data processing is increasing in our daily lives, the power consumption of electronics and, correspondingly, Data Centers (DCs), also increases. It has been estimated that about 40% of this DCs power consumption is merely consumed by the cooling systems. A responsive and efficient cooling system would not only save energy and space but would also protect electronic devices and help enhance their performance. Although air cooling offers a simple and convenient solution for Electronic Thermal Management (ETM), it lacks the capacity to overcome higher heat flux rates. Liquid cooling techniques, on the other hand, have gained high attention due to their potential in overcoming higher thermal loads generated by small chip sizes. In the present work, one of the most commonly used liquid cooling techniques is investigated based on various conditions. The performance of liquid-to-liquid heat exchange is studied under multi-leveled thermal loads. Coolant Supply Temperature (CST) stability and case temperature uniformity on the Thermal Test Vehicles (TTVs) are the target indicators of the system performance in this study. This study was carried out experimentally using a rack-mount Coolant Distribution Unit (CDU) attached to primary and secondary cooling loops in a multi-server rack. The effect of various selected control settings on the aforementioned indicators is presented. Results show that the most impactful PID parameter when it comes to fluctuation reduction is the integral (reset) coefficient (IC). It is also concluded that fluctuation with amplitudes lower than 1 ᵒC is converged into higher amplitudes