Amy S. Fleischer

• Villanova University

The use of Organic Rankine Cycles (ORCs) for waste heat recovery can reduce energy consumption in data centers, which in turn benefits the environment through the reduction of carbon-based fuels. However, data center applications exist in the ultra-low temperature range (40 - 80℃), making efficient and economical operation challenging. The operatin...

The Organic Rankine Cycle (ORC) is a promising technology for waste heat recovery in data centers due to its low-cost production of electricity, which can be used elsewhere in the data center. In this paper, an analysis is presented which assesses the effectiveness of ORC systems in repurposing data center waste heat energy from both thermodynamic...

The growing demand for data center utilization and the resulting increases in energy requirements are creating significant challenges for data center operators and for thermal designers. Design options which can cool the servers efficiently while also reducing electricity usage are thus of considerable interest. One potential technique is the use o...

For nearly two decades, research groups have attempted to increase the thermal conductivity of bulk materials by saturating them with different concentrations and types of nanoparticles. However, optimal enhancements in the thermal conductivity of these materials continue to go unrealized, primarily due to interfacial phenomena that impede phonon p...

Molecular dynamics (MD) simulation of yttria/scandia-stabilized zirconia (SSZ) with variably distributed Y/Sc dopant ions shows that energy is minimized when the dopants are uniformly spread apart, provided that the lattice maintains cubic fluorite symmetry. In contrast, highly clustered dopants are found to destabilize the cubic phase due to the p...

Presently, engineers are unable to fully utilize the high thermal energy storage capacities of paraffin-based phase change materials (PCMs) in electronics cooling and waste heat recovery applications due to their inherently low thermal conductivities, which result in slow melting and solidification rates. In order to increase the paraffin’s thermal...

Solid-liquid phase change materials (PCMs) are attractive candidates for thermal energy storage and electronics cooling applications, but have limited applicability in state-of-the-art technologies due to their low intrinsic thermal conductivities. Recent efforts to incorporate graphene and multilayer graphene into PCMs have led to the development...

Our theoretical studies showed that absorption refrigeration (AR) system and organic Rankine cycle (ORC) are the most promising technology candidates in utilizing the waste heat dissipated by data centers. Since both candidates work with heat of temperatures not less than 65°C, this study is limited to water-cooled and hybrid two-phase cooled data...

Nanoparticles are expected to significantly enhance future thermal energy generation systems, thermal energy storage materials, thermal interface materials and electronic devices. However, very few of these technologies are able to take full advantage of the unique thermal properties of nanoparticles, primarily due to the unusual transport phenomen...

The depletion of the world0s limited reservoirs of fossil fuels, the worldwide impact of global warming and the high cost of energy are among the primary issues driving a renewed interest in the capture and reuse of waste energy. A major source of waste energy is being created by data centers through the increasing demand for cloud based connectivi...

The stability of the fast ion conducting cubic phase of zirconia has been investigated using atomistic molecular dynamics to determine the effect of clustering of dopant ions for zirconia containing 11 mol% of yttria or scandia stabilizing additive. Large clusters of dopant ions entrap vacancies within the dopant cluster, which increases the averag...

One of the few remaining opportunities to increase heat dissipation in IC circuitry is to sub-stantially decrease the thermal interface resistance between solid–solid contacts from source to sink. In this study, heterogeneous nanostructured mats (1–100 lm thick, ran-domly oriented networks of nanostructures) are synthesized for use as thermal inter...

Characteristics of the annealed state of yttria and scandia stabilized zirconia have been investigated using molecular dynamics simulations. A genetic algorithm was used to find the minimal energy configuration of dopant ions to simulate the effects of annealing for compositions of 8 mol% Y2O3 in ZrO2, and compositions with 9, 10 and 11 mol% Sc2O3...

The fast oxygen-conducting cubic phase of zirconia is commonly stabilized by the substitution of group III cations such as yttrium and scandium, which creates vacancies in the oxygen sublattice. While scandia stabilized zirconia can achieve higher conductivity in freshly prepared specimens, it has previously been shown that yttria provides better s...

Phase change materials (PCMs) are promising candidates for thermal energy storage due to their intrinsically high values of latent heat. However, PCMs are unable to effectively utilize all of their energy storage capacities due to their poor thermophysical properties. In this study, the effect of graphite nanofibers (diameter = 2 to 1000 nm, length...

Paraffin phase change material (PCM) is enhanced with suspended graphite nanofibers at high loading levels. The loading levels reach in excess of 10% by weight. The thermal effects of the nanofiber loading level, the PCM module design, and the applied power density on the transient thermal response of the system are examined. A strong effect of nan...

Graphite nanofibers (GNFs) embedded in paraffin phase change material are found to settle to the bottom of the sample when subjected to repeated thermal cycling. The majority of this settling is found to occur over the first heating/cooling cycle. A method is developed to prevent GNF settling by creating a shape stabilized phase change material usi...

This work presents the results of an effort to create and thermally characterize sub-ambient phase change materials enhanced with graphite nanofibers. Several samples were created using a paraffin based phase change material with 10% by weight suspended graphite nanofibers. This material has a melting point of 21°C, slightly below standard ambient...

In this work, the effect of infiltration method on the saturation rate of paraffin phase change material within graphite foams is experimentally investigated. Graphite foams infiltrated with paraffin have been found to be effective for energy storage, but it is difficult to completely saturate the foam with paraffin. In this work, two methods are u...

The passive nature of energy storage through phase transition makes phase change materials (PCMs) a reliable choice for many applications. Shape-stabilized phase change materials (PCMs) mix liquid PCM with a molten polymer to create a material in which the PCM is fully contained even above the melt temperature of the PCM. Since the energy storage i...

The thermal management of high density power electronics can be extremely challenging due to high power loads paired with small device footprints. When these power electron-ics are used in systems, which require extremely high reliability, the design of the thermal abatement system takes on increasing importance. In this study, the thermal response...

The thermal management of high density power electronics can be extremely challenging due to high power loads paired with small device footprints. When these power electronics are used in systems, which require extremely high reliability, the design of the thermal abatement system takes on increasing importance. In this study, the thermal response...

The thermal performance and energy storage capabilities of a 54 °C organic paraffin wax is be tested and directly compared using three common different thermal conductivity enhancement methods (TCE). These include the use of graphite foam with infiltrated PCM, aluminum foam with infiltrated PCM, and PCM with 10 wt% graphite nanofibers. The applied...

Phase change materials (PCMs) are known to be excellent candidates for thermal energy storage in transient applications. However, enhancement of the thermal conductivity of a paraffin-based PCM is required for effective performance, particularly during solidification where diffusion is the dominant heat transfer mode. This study experimentally exam...

The thermal management of power electronics presents a significant challenge to thermal engineers due to high power loads coupled with small footprints. Inadequate thermal dissipation of these loads can lead to excessively high equipment temperatures and sub-sequent system failure. In this study, a unique power electronics-based transformer, called...

The use of high surface area foamed metals in heat sink design is desirable to improve thermal performance and there have been a number of studies which investigated the heat transfer aspects of jet impingement on foamed metals. However, an understanding of the fluid dynamics is also crucial to optimize the convective flow and heat transfer perform...

Cyclically utilized electronics provide an interesting challenge for thermal management. Phase Change Materials (PCM) are ideal for cyclic operations due to their high capacity to store heat, however, many phase change materials do not exhibit sufficient conductivity to be effective in larger sizes. Conductivity enhancement can be done in a number...

This study analyzes the use of a carbon fiber epoxy heat sink for evaporator surface enhancement in a FC-72 thermosyphon. The pin-fin heat sink features 945 small-cross-section (1.27 mm by 0.965 mm) fins fabricated with an integral base plate. These fins have a high thermal conductivity (500 W/m K) along the length of the fin. The influence of heat...

High-conductivity graphite foam is investigated for use as a surface enhancement for improved thermal performance in both pool boiling and an FC-72 thermosyphon. The influences of heat load and fluid level on the overall system thermal performance including surface superheat, effective heat transfer coefficient, and thermal resistance are examined....

The addition of phase change material (PCM) to a transparent polyester panel is used to create an energy absorbing building material that can be used for daylighting. One of the key development needs of this energy efficient material is the identification of the thermal properties. Without a clear understanding of the thermal properties and thermal...

The high surface area of foamed metals makes them an attractive choice for impingement heat sinks. If the jet can effectively penetrate the foam, the high surface area will lead to enhanced thermal performance. However, if the jet fails to effectively penetrate the foam, the surface enhancement effect will be reduced. Previous studies have suggeste...

Phase Change Materials (PCMs) are used for thermal management and are ideal for cyclic operations due to their high capacity to store heat. Most PCMs do not exhibit sufficient conductivity to be effective at larger sizes. Enhancing conductivity can be done in a number of ways including carbon foam. It is not widely known how well PCMs penetrate ins...

As the use of alternative energy sources increases globally, there exists a need for a smart grid system to handle the increased power capacity. As part of this new power grid, a new type of intelligent universal transformer (IUT) has been developed to enhance power quality, throughput and efficiency to tackle green initiatives and enable distribut...

This paper explores the thermal behavior of a 69kV/3000A Solid State Current Limiter in various transient fault cases. The system has been thermally analyzed in steady-state conditions and the authors have found an acceptable cooling strategy in the case of 864kW of waste heat in a three phase system. It is desired, now, to numerically model two di...

Smoke-wire flow visualization is employed to investigate the behavior of a round jet issuing from a straight tube and impinging on a cylindrical pedestal mounted on a flat plate. Velocity and turbulence intensity measurements at the jet exit show correlation with the formation of visualized structures near the impingement surface. The effects of je...

Phase change materials (PCMs) exhibit excellent thermal storage capacity due to their high latent heat of transformation and have been successfully utilized in small volumes for transient thermal management of electronics. However, their low thermal conductivity makes it difficult to utilize large volumes of PCMs for transient thermal management of...

To improve the thermal performance of phase change materials (PCMs), graphite nanofibers were embedded into a paraffin PCM. The thermal effects of graphite fiber loading levels (0-5 wt %) and graphite fiber type (herringbone, ribbon, or platelet) during the melting process were examined for a 131 cm3 volume system with power loads between 3 W and 7...

This paper presents the results of thermal modeling of a unique 69 kV 3000A Solid State Fault Current Limiter (SSFCL) developed by Silicon Power of Malvern, PA with support of EPRI. The development of the Solid State Fault Current Limiter is expected to modernize power distribution systems through the use of small-scale solid-state power devices. T...

This paper outlines the thermal performance of a unique liquid-cooled 15 kV/4000 A Solid State Fault Current Limiter (SSFCL) developed by Silicon Power of Malvern, PA with support of EPRI. The design features an extremely high power system which consumes 96 kW of power in a one phase configuration. The system is submerged in mineral oil coolant and...

The localized thermal interactions between adjacent devices on vertically orientated circuit boards in natural convection are predicted using experimentally validated computational fluid dynamics models. The effects of power density, device proximity, device geometry, circuit board material, board packing density and board separation distance on th...

The purpose of this study is to examine the thermal interactions through both conduction and convection between two unequally powered discrete heat sources in free convection on a vertical plate. The sources are positioned at steadily increasing separation distances. The role of the thermal wake from the downstream component is quantified and is fo...

This paper analyzes the thermal design of an RF High Power amplifier. The device, with a maximum dimension of only .4 mm, has a high power density, dissipating up to 4 W. There is concern about the impacts of device proximity on thermal performance due to desired packaging density. The devices are numerically modeled and the effects of device proxi...

The presence of voids in the die bond region is known to adversely affect the thermal resistance of the packaged chip-level device. Unfortunately, such voids are easily formed in the solder layer during manufacturing, and are found to nucleate, grow and coalesce with thermal cycling. Although the relationship between package thermal resistance and...

The vertical coupling of active InP based ring resonators and passive feeding waveguides necessitates the use of a waferbonding technology in the fabrication process. The required bond material (BCB) has a low thermal conductivity and will strongly influence the operating temperature and thus the performance of the ring resonator through its insula...

The on-going trend towards increasing device performance while shrinking device size often results in escalating power densities and high operating temperatures. High operating temperatures may lead to reduced reliability and induced thermal stresses. Therefore, it is necessary to employ new and innovative thermal management techniques to maintain...

Phase change materials (PCMs) exhibit excellent thermal storage capacity due to their high latent heat of transformation and have been successfully utilized in small volumes for transient thermal management of electronics. However, their low thermal diffusivity makes it difficult to utilize large volumes of PCMs for transient thermal management of...

An electrochemical technique is used to study local mass transfer coefficients on surfaces of inclined enclosures over the range 1.1×104 < Ra H < 1.4×1010 for a nominal Schmidt number of 2280. Scaling with gcosθ instead of g in the Rayleigh number correlates the data well at low angles of inclination; however, as either the aspect ratio or the angl...

The performance enhancements and footprint decreases of advanced electronic devices result in soaring power densities which may in turn lead to elevated operating temperatures. As elevated device temperatures lead to decreased device reliability and increased thermal stresses, it is necessary to employ aggressive thermal management techniques to ma...

The influence of a protruding pedestal on impinging jet heat transfer is investigated. A discretely heated portion of a protruding pedestal is exposed to a single circular impinging air jet with Re=10,000–30,000. Jet exit diameters of 3.5, 9.5 and 21 mm are positioned at jet exit-to-surface distances of 2–5 diameters. The nondimensional heat transf...

Natural convection and passive heat rejection from two independent heat sources maintained at different temperatures (60degreesC and 100degreesC above ambient) on single circuit boards (FR4 and copper clad FR4) are experimentally studied. The effect of heat source location on maximum power dissipation is presented for both horizontal and vertical o...

An experimental investigation to understand the influence of the impingement surface geometry on the heat transfer from a discretely heated surface to a single round impinging jet is conducted. In this study, heat transfer at the stagnation region of a discretely heated pedestal protruding into an air stream is compared to the heat transfer on a di...

Active microring optical devices are promising candidates for use in next generation optical signal processing and sensor products. In this design, an InP based microring laser is vertically coupled to a passive feeding waveguides using a waferbonding technology. The vertical coupling is expected to detrimentally affect the operating temperature an...

Liquid crystals are used to investigate the effect of high relative curvature on surface heat transfer for a round air jet impinging perpendicularly on a semicylindrical convex surface. The relative curvature, (d/D), is varied by changing the jet tube diameter for the same surface diameter. Relative curvature varies from 0.18–0.38. The effects of r...

Smoke–wire flow visualization is used to investigate the behavior of a round jet issuing from a straight tube and impinging on a convex surface. Video analysis of the impinging jet shows the initiation and growth of ring vortices in the jet shear layer and their interaction with the cylindrical surfaces. Effects of relative curvature, nozzle-to-sur...

Thesis (Ph. D.)--University of Minnesota, 2000. Includes bibliographical references (leaves 65-67).

Smoke wire flow visualization is used to investigate the behavior of a round jet issuing from a straight tube and impinging on concave and convex surfaces with high relative curvature values. Local velocity and turbulence intensity measurements of the free jet are correlated to the formation of the visualized ordered-flow structures. Visualization...

Smoke-wire visualization provides insight into the flow structure of round jets issuing from straight tubes and impinging on concave and convex surfaces with high relative curvature values. The technique provides a crosssectional view of the jet, allowing the imaging of the initiation and growth of ring vortices in the jet shear layer and their sub...