Scott N. Schiffres

A novel in-situ method to indirectly sense changing thermal properties of the TIM (thermal interface material) without using any onboard temperature sensors is demonstrated. The technique can detect the average junction temperature at specific computational elements (CPU, GPU) by the temperature dependent power consumption of these elements that have a periodically applied software stressor. The technique was demonstrated on a commercial system on chip (SOC) development kit. The temperature response for frequency modulated heating depends on thermal conductivity, density, and specific heat of layers making up the test package. By selecting the modulation frequency, the thermal penetration depth can be varied to probe individual layers in the build-up of the electronic package. The total power consumption is used to sense a spatially localized computational element's temperature (e.g. specific core) by way of temperature-dependent leakage current in transistors. Simulations using different thermal conductivities for the TIM show the sensitivity of this technique to TIM layer degradation. This technique's temperature measurements are validated against the chip's onboard temperature with good agreement (within 1K for ~25sqmm section in ~100sqmm SOC). Measurements by this technique make averaged measurements and can complement onboard temperature sensors, often located at periphery of the sensed unit. We found this SOC increases energy consumption with junction temperature by ~0.5% per K over large temperature rise and ~4% per K at around 333 K (60 °C), having implications for computational energy efficiency versus chip temperature considering advanced nodes have larger leakage current.

The rapid growth of digitization and data-driven technologies is driving large-scale deployment of data centers worldwide. As societies become increasingly inference-hungry, the energy consumption of data centers continues to rise at an unprecedented rate, with a significant fraction of this energy being expended on thermal management and cooling infrastructure. Improving cooling efficiency has therefore become a critical challenge for the thermal management community, directly impacting both the sustainability and scalability of future computing systems. In this paper, we demonstrate an energy-efficient cooling solution based on chip-integrated two-phase cooling, which leverages liquid-to-vapor phase-change heat transfer to achieve high heat-flux dissipation at reduced pumping power and thermal resistance. This paper investigates an aggressive cooling architecture utilizing direct-on-die two-phase jet impingement on an NVIDIA Tesla V100 GPU without any thermal enhancement structures. By eliminating thermal interface material (TIM) and impinging the working fluid R1233zd(E), a low-global warming potential (GWP) (<1) refrigerant, directly onto the silicon backside, the primary thermal bottleneck is removed. Experimental results demonstrate a junction-to-coolant thermal resistance of 0.056 °C/W and a theoretical pumping power of only 0.172 W versus the conventional air-cooled cold plate of 0.1709 °C/W and a fan power of 39.9 W. Furthermore, the reliability of the direct-on-die cooling technique was validated through 200 h of continuous, stable operation. This study positions direct jet impingement as a highly efficient, compact, and sustainable solution for next-generation high-performance computing environments.

More than ever before, data centers must deploy robust thermal solutions to adequately host the high-density and high-performance computing that is in high demand. The newer generation of central processing units (CPUs) and graphics processing units (GPUs) has substantially higher thermal power densities than previous generations. In recent years, more data centers rely on liquid cooling for the high-heat processors inside the servers and air cooling for the remaining low-heat information technology equipment. This hybrid cooling approach creates a smaller and more efficient data center. The deployment of direct-to-chip cold plate liquid cooling is one of the mainstream approaches to providing concentrated cooling to targeted processors. In this study, a processor-level experimental setup was developed to evaluate the cooling performance of a novel computer numerical control (CNC) machined nickel-plated impinging cold plate on a 1 in. × 1 in. mock heater that represents a functional processing unit. The pressure drop and thermal resistance performance curves of the electroless nickel-plated cold plate are compared to those of a pure copper cold plate. A temperature uniformity analysis is done using compuational fluid dynamics and compared to the actual test data. Finally, the CNC machined pure copper one is compared to other reported cold plates to demonstrate its superiority of the design with respect to the cooling performance.

The miniaturization of microelectronic devices and an increasing demand for clock speed result in high heat flux systems. By adopting direct liquid cooling, the high heat flux and high-power demands can be met, while the reliability of the electronic devices is greatly improved. In this paper, thermo-hydraulic performance of a commercial hybrid micro-channel/slot-jet heat sink with

The interaction of graphene with water molecules under an applied electric field is not thoroughly understood, yet this interaction is important to many thermal, fluidic, and electrical applications of graphene. In this work, the effect of electrical doping of graphene on water adsorption is studied through adsorption isotherms and current–voltage (IV) characterizations as a function of the Fermi level. The water adsorption onto graphene increases by ≈15% and the doping levels increase by a factor of three with a gate‐to‐graphene voltage of +20 or −20 V compared to 0 V for sub‐monolayer adsorption. This change in uptake is attributed to the increase in density of state of graphene upon electrical‐doping, which changes the Coulombic and van der Waals interactions. The water adsorption onto graphene is either n‐ or p‐doping depending on the applied gate‐to‐graphene voltage. The ambi‐doping nature of water onto graphene is due to the polar nature of water molecules, so the doping depends on the orientation of the water molecules.

The interaction of graphene with water molecules under an applied electric field is not thoroughly understood, yet this interaction is important to many thermal, fluidic, and electrical applications of graphene. In this work, the effect of electrical doping of graphene on water adsorption was studied through adsorption isotherms and current-voltage (IV) characterizations as a function of the Fermi level. The water adsorption onto graphene increased ~15% and the doping levels increased by a factor of three with a gate-to-graphene voltage of +20 or –20V compared to 0V for sub-monolayer adsorption. This change in uptake is attributed to the increase in density of state of graphene upon electrical-doping, which changes the Coulombic and van der Waals interactions. The water adsorption onto graphene is either n- or p-doping depending on the applied gate-to-graphene voltage. The ambi-doping nature of water onto graphene is due to the polar nature of water molecules, so the doping depends on the orientation of the water molecules.

The goal of this study is to evaluate the filtration efficiency and breathability of improvised filtration and commonly available mask materials, as well as to assess their reusability. Materials readily available to the general public such as cotton, fragrance and additive-free dry baby cleaning wipes, and those abundantly available in the hospital setting, such as sterilization wraps, were chosen for testing, amongst others. In the COVID-important 2–5 µm particle range, two-layers of cotton provided filtration efficiency between 34%–66%. Amongst potential filter materials, 300-weight sterilization wraps provided approximately 80% filtration efficiency and are readily available in the healthcare setting. The addition of sterilization wrap to cotton fabrics brought the filtration efficiency to above that of the sterilization wrap (80%–90%) at the expense of added pressure drop. Four-layers of dry baby wipes performed very well with a filtration efficiency of 85% and a reasonable pressure drop (1/3 of procedure mask). Since the material is advertised as pure spunlace polypropylene and designed to contact the skin during cleaning, it would appear generally safe as a filter insert. Of improvised filters, polypropylene electrostatic HVAC filters performed the best with filtration efficiencies of >99%, but are not recommended due to the risk of confusion with glass-based HVAC filters and uncertainty regarding trace materials used in the filter. The filtration efficiency of two-layers of cotton fabrics with one-layer of sterilization wrap slightly improved over 10 laundry cycles, while the performance of other non-wovens, like dry baby wipes, degraded more rapidly and should be considered disposable. In summary, we found that two-layers of cotton fabric can provide a comfortable, breathable and reusable option. The addition of a sterilization wrap or four-layers of pure spunlace fragrance free dry baby wipes can significantly improve filtration and block expiratory aerosols at the expense of an added pressure drop. Copyright © 2021 American Association for Aerosol Research