Thomas Brunschwiler

Bio: Thomas Brunschwiler is an academic researcher from IBM. The author has contributed to research in topics: Thermal resistance & Heat transfer. The author has an hindex of 21, co-authored 170 publications receiving 1580 citations.

Variable flow computer cooling system for a data center and method of operation

Abstract: Disclosed herein is a data center having a plurality of liquid cooled computer systems. The computer systems each include a processor coupled with a cold plate that allows direct liquid cooling of the processor. The cold plate is further arranged to provide adapted flow of coolant to different portions of the processor whereby higher temperature regions receive a larger flow rate of coolant. The flow is variably adjusted to reflect different levels of activity. By maximizing the coolant temperature exiting the computer systems, the system may utilize the free cooling temperature of the ambient air and eliminate the need for a chiller. A data center is further provided that is coupled with a district heating system and heat is extracted from the computer systems is used to offset carbon emissions and reduce the total cost of ownership of the data center.

Microvortex-enhanced heat transfer in 3D-integrated liquid cooling of electronic chip stacks

Abstract: The cooling of three-dimensional electronic chip assemblies (stacks) is one of the most serious challenges facing the electronics industry as it moves toward fabrication approaches combining speed with energy efficiency. Here we show that by generating vortical microscale flows taking advantage of the inherent presence of Through Silicon Vias (TSV) in 3D integrated liquid (water) cooling of chip stacks, both large heat transfer enhancement as well as significantly better temperature uniformity can be accomplished. The approach is demonstrated experimentally in heat sinks consisting of a microcavity confining micropin fin arrays, mimicking TSV. Flow fluctuations and vortex shedding were triggered at specific Reynolds numbers, which are functions of the pin geometries and level of confinement. The resulting heat transfer enhancement due to the vortex-induced fluctuations and mixing, yields local Nusselt number increases up to 230% thereby reducing the chip temperature non-uniformity almost by a factor of three. The vortex shedding also induces a pressure drop increase. Remarkably, the effective improvement in the thermal performance due to vortex shedding, even after factoring in the rise in pumping power, reaches a peak value of 190%. Analysis of instantaneous liquid temperature signatures of shed microvortices using micron-resolution laser-induced fluorescence (μLIF), proved them to be the reason for both the elimination of liquid hotspots and the exceptional augmentation in heat transfer. These findings have important implications in the design of the new generation of integrated, out of plane electronics cooling with liquids.

Experimental investigation into vortex structure and pressure drop across microcavities in 3D integrated electronics

Abstract: Hydrodynamics in microcavities with cylindrical micropin fin arrays simulating a single layer of a water-cooled electronic chip stack is investigated experimentally. Both inline and staggered pin arrangements are investigated using pressure drop and microparticle image velocimetry (μPIV) measurements. The pressure drop across the cavity shows a flow transition at pin diameter–based Reynolds numbers (Re d ) ~200. Instantaneous μPIV, performed using a pH-controlled high seeding density of tracer microspheres, helps visualize vortex structure unreported till date in microscale geometries. The post-transition flow field shows vortex shedding and flow impingement onto the pins explaining the pressure drop increase. The flow fluctuations start at the chip outlet and shift upstream with increasing Re d . No fluctuations are observed for a cavity with pin height-to-diameter ratio h/d = 1 up to Re d ~330; however, its pressure drop was higher than for a cavity with h/d = 2 due to pronounced influence of cavity walls.

Nocturnal Cough and Snore Detection in Noisy Environments Using Smartphone-Microphones

Abstract: The reporting on nocturnal sounds like cough and snore is not only relevant to follow the progress of respiratory diseases of patients but also to assess the quality of sleep of subjects. In this study, we discuss an audio analysis approach to count individual cough events and the duration of snore sounds in presence of air-conditioner noise through recordings of a smartphone and computationally efficient classifiers. A new audio data set of cough and snore sounds was acquired from 26 subjects. Energy threshold-based segmentation was applied to identify cough or snore events in the original low noise dataset. A k-nearest neighbor classifier was trained to merge cough phases belonging to the same cough event, to derive the proper ground-truth labeling. The original audio signal was augmented by the superposition of air-conditioner noise, with a signal-to-noise ratio of -40dB to 40dB, to enrich the training set of the binary classifier. Nine out of 40 mel-frequency cepstral coefficients in combination with the logarithm of energy from an entire cough or snore event were computed. Various classifiers, such as k-nearest neighbor (k-NN), rule-based classifier, decision tree, random forest, naive Bayes, and support vector machine were benchmarked against each other. The k-NN classifier with k=1 resulted in the highest F_ 1 scores of.85 and.88 in the binary classification task using generalized and personalized models, respectively, considering noise augmented samples. These results underline the potential of smartphones to objectively report on patient symptoms through audio recordings at night.

Study of non-isothermal liquid evaporation in synthetic micro-pore structures with hybrid lattice Boltzmann model

Abstract: Non-isothermal liquid evaporation in micro-pore structures is studied experimentally and numerically using the lattice Boltzmann method. A hybrid thermal entropic multiple-relaxation-time multiphase lattice Boltzmann model (T-EMRT-MP LBM) is implemented and validated with experiments of droplet evaporation on a heated hydrophobic substrate. Then liquid evaporation is investigated in two specific pore structures, i.e. spiral-shaped and gradient-shaped micro-pillar cavities, referred to as SMS and GMS, respectively. In SMS, the liquid receding front follows the spiral pattern; while in GMS, the receding front moves layer by layer from the pillar rows with large pitch to the rows with small one. Both simulations agree well with experiments. Moreover, evaporative cooling effects in liquid and vapour are observed and explained with simulation results. Quantitatively, in both SMS and GMS, the change of liquid mass with time coincides with experimental measurements. The evaporation rate generally decreases slightly with time mainly because of the reduction of liquid–vapour interface. Isolated liquid films in SMS increase the evaporation rate temporarily resulting in local peaks in evaporation rate. Reynolds and capillary numbers show that the liquid internal flow is laminar and that the capillary forces are dominant resulting in menisci pinned to the pillars. Similar Peclet number is found in simulations and experiments, indicating a diffusive type of heat, liquid and vapour transport. Our numerical and experimental studies indicate a method for controlling liquid evaporation paths in micro-pore structures and maintaining high evaporation rate by specific geometry designs.

Emerging challenges and materials for thermal management of electronics

Abstract: The rapid development of faster, cheaper, and more powerful computing has led to some of the most important technological and societal advances in modern history. However, the physical means associated with enhancing computing capabilities at the device and die levels have also created a very challenging set of circumstances for keeping electronic devices cool, a critical factor in determining their speed, efficiency, and reliability. With advances in nanoelectronics and the emergence of new application areas such as three-dimensional chip stack architectures and flexible electronics, now more than ever there are both needs and opportunities for novel materials to help address some of these pressing thermal management challenges. In this paper a number of cubic crystals, two-dimensional layered materials, nanostructure networks and composites, molecular layers and surface functionalization, and aligned polymer structures are examined for potential applications as heat spreading layers and substrates, thermal interface materials, and underfill materials in future-generation electronics.

Power Electronics Converters Applications And Design

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Light emitting diodes reliability review

Abstract: The increasing demand for light emitting diodes (LEDs) has been driven by a number of application categories, including display backlighting, communications, medical services, signage, and general illumination. The construction of LEDs is somewhat similar to microelectronics, but there are functional requirements, materials, and interfaces in LEDs that make their failure modes and mechanisms unique. This paper presents a comprehensive review for industry and academic research on LED failure mechanisms and reliability to help LED developers and end-product manufacturers focus resources in an effective manner. The focus is on the reliability of LEDs at the die and package levels. The reliability information provided by the LED manufacturers is not at a mature enough stage to be useful to most consumers and end-product manufacturers. This paper provides the groundwork for an understanding of the reliability issues of LEDs across the supply chain. We provide an introduction to LEDs and present the key industries that use LEDs and LED applications. The construction details and fabrication steps of LEDs as they relate to failure mechanisms and reliability are discussed next. We then categorize LED failures into thirteen different groups related to semiconductor, interconnect, and package reliability issues. We then identify the relationships between failure causes and their associated mechanisms, issues in thermal standardization, and critical areas of investigation and development in LED technology and reliability.

State of the Art of High Heat Flux Cooling Technologies

Abstract: The purpose of this literature review is to compare different cooling technologies currently in development in research laboratories that are competing to solve the challenge of cooling the next generation of high heat flux computer chips. Today, most development efforts are focused on three technologies: liquid cooling in copper or silicon micro-geometry heat dissipation elements, impingement of liquid jets directly on the silicon surface of the chip, and two-phase flow boiling in copper heat dissipation elements or plates with numerous microchannels. The principal challenge is to dissipate the high heat fluxes (current objective is 300 W/cm2) while maintaining the chip temperature below the targeted temperature of 85°C, while of second importance is how to predict the heat transfer coefficients and pressure drops of the cooling process. In this study, the state of the art of these three technologies from recent experimental articles (since 2003) is analyzed and a comparison of the respective merits and ...