A Meta-study on the Thermal Properties of Carbon Nanotubes in Thermal Interface Materials

Computer Integrated Circuit (IC) microprocessors are becoming more powerful and densely packed while cooling mechanisms are seeing an equivalent improvement to compensate. A significant limit to cooling performance is thermal transfer between die and heatsink. In this meta study we evaluate carbon nanotube (CNT) thermal interface materials (TIMs) in order to determine how to maximise thermal transfer efficiency. We gathered information from over 15 articles focused on the thermodynamic parameters of CNT TIMs from databases such as Scopus, IEEE Xplore and ScienceDirect. Articles were filtered by key words including ‘carbon nanotubes’ and ‘thermal interface materials’ to identify scientific articles relevant to our research on TIMs. From our meta study we have found that enhancing CNTs will provide the best improvement in TIMs. The parameters analysed to determine TIM performance included thermal resistance, thermal conductivity and the effect of CNT concentration on computer operation time. Through our investigation we understood that increasing the concentration of CNT from 0 to 2 wt % increases the operation time from 75 seconds at 66°C to 200s at 63°C as well as increasing the thermal conductivity by 1.82 times for the AS5 thermal paste with 2 wt % CNT. Furthermore, CNT TIM pastes with less thickness have a lower thermal resistance of 0.4 K/W. However not all these parameters have been tested with computer chips. This means that in order to increase current heat transfer efficiency limit, we must integrate these parameters into experimental models. Keywords: Thermal Interface Material; Thermal Paste; Carbon Nanotubes; Thermal Transfer Efficiency; Integrated Circuit; Heat Sink; Heat Dissipation

Investigation of liquid cooling on M9506A high density Keysight AXIE chassis

2021 Fall.Includes bibliographical references.Forced convection air-cooled heat sinks are the dominant cooling method used in the electronics industry, accounting for 86% of high-density cooling in data centers. However, the continual performance increases of electronics equipment are pushing these air-cooled methods to their limit. Fundamental limitations such as acoustics, cooling power consumption, and heat transfer coefficient are being reached while processor power consumption is steadily rising. In this study, a 4U, 5-slot, high density computing box is studied to determine the maximum heat dissipation in its form factor while operating at an ambient air temperature of 50°C. Two liquid cooling technologies were analyzed in this effort and compared against current state-of-the-art air-cooled systems. A new configuration proposed using return jet impingement with dielectric fluid FC72 directly on the integrated circuit die shows up to a 44% reduction in thermal resistance as compared to current microchannel liquid cooled systems, 0.08 K W-1, vs 0.144 K W-1, respectively. In addition, at high ambient temperatures (~45°C), the radiator of the liquid cooled system accounts for two thirds of the thermal resistance from ambient to junction temperature, indicating that a larger heat exchanger outside the current form factor could increase performance further. The efficiency of the chips was modeled with efficiency predictions based on their junction temperature. On a system level, the model showed that by keeping the chassis at 25°C ambient, the overall power consumption was significantly lower by 500W. Furthermore, the failure rate was accounted for when the chip junction temperature was beyond 75°C. FC72 jet impingement on the die showed the best performance to meet the system cooling requirements and kept the chips below 75°C for the highest ambient temperatures but consumed the most pumping power of all of the fluids and configurations investigated. The configuration with microchannels bypassing TIM 2 showed near the same performance as jet impingement with water on the lid and reduced the junction temperature difference by 5°C when compared to baseline. When the fluid was switched from water to a water glycol 50/50 mixture, an additional thermal resistance of 0.010 K W-1 was recorded at the heat sink level and a higher mass flow rate was required for the GC50/50 heat exchanger to achieve its minimum thermal resistance

Topical Workshop on Electronics for Particle Physics

The purpose of the workshop was to present results and original concepts for electronics research and development relevant to particle physics experiments as well as accelerator and beam instrumentation at future facilities; to review the status of electronics for the LHC experiments; to identify and encourage common efforts for the development of electronics; and to promote information exchange and collaboration in the relevant engineering and physics communities

Modelling and Simulation for Power Distribution Grids of 3D Tiled Computing Arrays

This thesis presents modelling and simulation developments for power distribution grids of 3D tiled computing arrays (TCAs), a novel type of paradigm for HPC systems, and tests the feasibility of such systems for HPC systems domains. The exploration of a complex power-grid such as those found in the TCA concept requires detailed simulations of systems with hundreds and possibly thousands of modular nodes, each contributing to the collective behaviour of the system. In particular power, voltage, and current behaviours are critically important observations. To facilitate this investigation, and test the hypothesis, which seeks to understand if scalability is feasible for such systems, a bespoke simulation platform has been developed, and (importantly) validated against hardware prototypes of small systems. A number of systems are simulated, including systems consisting of arrays of ’balls’. Balls are collections of modular tiles that form a ball-like modular unit, and can then themselves be tiled into large scale systems. Evaluations typically involved simulation of cubic arrays of sizes ranging from 2x2x2 balls up to 10x10x10. Larger systems require extended simulation times. Therefore models are developed to extrapolate system behaviours for higher-orders of systems and to gauge the ultimate scalability of such TCA systems. It is found that systems of 40x40x40 are quite feasible with appropriate configurations. Data connectivity is explored to a lesser degree, but comparisons were made between TCA systems and well known comparable HPC systems, and it is concluded that TCA systems can be built with comparable data-flow and scalability, and that the electrical and engineering challenges associated with the novelty of 3D tiled systems can be met with practical solutions

Detecting High-Energy Cosmic Ray Electrons With CREST (the Cosmic Ray Electron Synchrotron Telescope).

The Cosmic Ray Electron Synchrotron Telescope (CREST) was a balloon-borne detector designed to measure the high-energy cosmic ray all-electron energy spectrum. It utilized a novel indirect technique proposed in 1983 by Stephens and Balasubrahmanyan to detect electrons by means of the synchrotron radiation they produce while interacting with the Earth’s magnetic field. CREST took data during a 10-day circum-anti-polar flight originating near McMurdo Station, Antarctica from December 2011-January 2012. In this work I describe the instrument’s design, assembly, operation, detection scheme, launch, flight and recovery, as well as my original work on displaying and analyzing the flight data. In particular I describe a novel detection method combining direct detection of the primary electron and indirect detection of the electron’s secondary synchrotron photons. Further I characterize CREST’s ability to determine the momentum direction of signal electrons, and outline a method for determining the charge of primary leptons making use of that pointing capability. I also propose an improved detector surface configuration suitable for future CREST-like detectors which greatly reduces sensitivity to the ubiquitous charged particle background.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113331/1/jgennaro_1.pd