Rapid Transient Cooling Utilizing Flash Boiling and Desorption on Graphitic Foams

Transient thermal systems present significant challenges. Neglecting the time constant

Exploration of Graphene-like 2D Materials for Energy Management and Interface Enhancement Applications

Ever since the discovery of graphene in 2004, graphene-like 2D materials and their derivatives have attracted extensive investigations because of their exceptional physical and chemical properties. At present, the study of graphene-like 2D materials is at a stage where most of their outstanding physical and chemical properties have been discovered, but the technology for incorporating them into practical commercial products is rarely revealed. For the potential practical industrial applications of graphene-like 2D materials, energy management and interface enhancement are two of the most promising areas. So far, the behavior of the commercialized graphene-like 2D material products is far from their theoretical performance and expectations as a result of defects and π-π agglomeration, etc. In this regard, there is plenty of research room at the bottom for exploring their practical industrial applications. At present, surface modification is the most widely used strategy to cope with agglomerations. While to be widespread in market, developing low-cost, uniform, and high-quality preparation technology, and encountering the intrinsic agglomeration issues of graphene-like 2D materials are two of the main challenges. To focus on the above two issues, we developed the functionalization method for graphene-like 2D materials, including graphene and hexagonal boron nitride, and explored their potential industrial applications in energy management and interface enhancement. Further, mass production technology and industrial demonstration for graphene and hexagonal boron nitride were explored in some chapters. The main scientific conclusions and innovations of this thesis are listed as below:At first, Chapter 2 presents the experimental research study on using graphene-like 2D materials for energy management, especially in heat dissipation. With the rapid development of microelectronics and 5G communications, efficient heat dissipation is severely demanded for future electronics. To improve heat dissipation efficiency of electronics, based on the ultrahigh thermal conductivity of graphene-like 2D materials, this chapter explored two experimental works, including lightweight and high-performance graphene enhanced heat pipe and hexagonal boron nitride enhanced thermally conductive and electrically insulation heat spreader. (1) Graphene Enhanced Heat PipeIn this work, a unique lightweight and high thermal performance graphene heat pipe were firstly designed and developed. At first, the inner structures of graphene enhanced heat pipe were optimized, including the wicker structures, the filling volume of working fluids and the preparation of high thermal conductivity graphene film. Compared to the conventional copper-based heat pipe, our graphene enhanced heat pipe improves the specific cooling capacity more than 3 times. Further, COMSOL Multiphysics was used to establish the cooling model for graphene enhanced heat pipe. And the equation for quantifying the contribution factor from container and phase change was established. Finally, a graphene/copper composite heat pipe was studied to further improve reliability and mechanical strength. (2) Hexagonal Boron Nitride Enhanced Heat SpreaderIn this work, a hexagonal boron nitride based heat spreader was prepared by electrospinning with polyvinylpyrrolidone. After electrospun, the hexagonal boron nitride nanosheets are aligned along the fiber, and thus increasing the thermal conductivity. At first, the exfoliation technology was investigated. The result shows that a mixture of water and isopropanol (Vwater:VIPA=1:3) shows the highest exfoliation efficiency. With the optimized hexagonal boron nitride particle geometry and loading, the in-plane thermal conductivity of hexagonal boron nitride based heat spreader reaches 22 W m-1 K-1, this value is comparable to most of the reported work. Particularly, such electrospinning process is constant and scalable, showing high potential for mass-production.Chapter 3 still focuses on the application of utilizing graphene-like 2D materials for energy management but specifically in energy storage. Based on the ultrahigh electric mobility, large surface area, flexible, lightweight properties, graphene is an attractive option for energy storage. Therefore, graphene was investigated for electrical double layer capacitors and in-plane micro-supercapacitors in this chapter.(1) Graphene Enhanced Electric Double-layer CapacitorIn this work, a scalable soft template strategy was developed to prepare graphene foam with high electrochemical performance as electrode for supercapacitors. The specific surface areas and wettability of graphene foam is tailored by doping. Further, density functional theory simulation reveals why increasing the polarity of graphene largely improves its wettability. Afterwards, the unique porous structure, low ohm resistance, and high electrical conductivity largely improve the electrochemical performance of graphene foam electrodes and thus achieve ultrahigh specific ca pa city (550 F g-1), cycling sta bility ( 96.1% ca pa city retention after 10 000 cycles at a high current density of 10 A g-1), and outstanding rate capability (308 \ua0\ua0F \ua0\ua0g-1 a \ua0t 100 \ua0\ua0A \ua0\ua0g-1). (2) Graphene Based In-plane Micro-supercapacitorIn this work, graphene assembled film was used to replace the conventional silicon wafer for fabricating flexible and high thermal performance micro-supercapacitors. The result shows that such replacement decreases the surface temperature of micro-supercapacitors by 4 \ub0C, and the graphene based micro-supercapacitor present a similar electrochemical behavior with the referenced silicon based micro-supercapacitor. In addition, the graphene assembled film substrate can work as heat spreader for micro-supercapacitor, thus saving spaces and optimizing the following packaging procedures. This work paves the way for utilizing graphene assembled film in semiconductors.Chapter 4 presents the application of using functional graphene-like 2D materials for interface enhancements due to their high Young’s module, large surface area, anti-friction, etc. Graphene-like 2D materials enhanced composites and bio-application are two of the main categories for the commercialization of interface enhancement. However, the graphene-like 2D materials suffer from π-π agglomeration, which leads to poor dispersibility in solvents and matrix. As a result, graphene-like 2D materials enhanced composites exhibit lower property than their theoretical expectations. At present, surface functionalization is the most effective strategy to encounter the π-π agglomeration. Therefore, this chapter explored the application of using functional graphene-like 2D materials in composites, including graphene enhanced water-borne epoxy coatings and hexagonal boron nitride enhanced cement repair materials.(1) Graphene Enhanced Water-borne Epoxy CoatingGraphene was used to lower the coefficient of friction and extend the lifetime of the water-borne epoxy coating in this work. To improve the dispersibility and the compatibility with epoxy, p-hydroxybenzene diazonium salt was prepared to functional graphene. With the optimized geometry and loading, 30 times less coefficient of friction than graphene-free coatings were achieved. And the wear-out time is more than 2 times longer than the three commercial graphene oxide enhanced coatings. This result is confirmed by Applied Nanosurface AB, Sweden. Besides, mass production technology up to 300 g per batch was developed for the functional graphene. The geometry of graphene was optimized, and the result shows that with the same functional groups, the larger graphene sheets show higher tribological performance than their smaller encounters. Finally, this functionalization strategy was further developed to improve the dispersibility of carbon nanotubes too. (2) Hexagonal Boron Nitride Enhanced Cement Repair MaterialThis work explored the application of using hexagonal boron nitride to enhance cement repair materials. To improve the dispersibility in cement repair materials and the adhesion with substrates, hexagonal boron nitride was functionalized by carboxymethyl cellulose. After functionalization, the surface zeta potential of hexagonal boron nitride decrease from -5.61 mV to -55.07 mV, and thus largely improves its dispersibility. Results show the incorporation of hexagonal boron nitride improve mechanical strength of cement repair materials by contributing to forming alite. Besides, for the repair material containing h-BN, most of the failure happened at the interface repair material/concrete, while the failure is mainly happening in the concrete for the sample containing FBN. Cooperated with a local cement company (Lanark AB), this work has demonstrated the commercial application as repair materials for walls.Besides, we studied the functional graphene quantum dots for mRNA based drug delivery platform. After complexed with mRNA, the transfection efficiency of the graphene quantum dots based drug delivery platform is 25% with a formation concentration as 4000 ng mL-1. A comparable transfection efficiency could be achieved at much lower doses if the ratio between the carrier and the cargo is optimized. This graphene quantum dots based drug delivery platform exhibits excellent processability. This work describes a potentially strategy for prepare stable and effective mRNA delivery systems

Experimental and Numerical Analysis of a Commercial Phase Change Material Melting at Different Inclinations

The study of various phase change materials (PCM), experimentally and numerically, have been completed over the past several years to address their feasibility and potential when used in latent heat thermal energy storage (LHTES) systems for a variety of potential applications. Previous studies have investigated changes into the type of PCM used in the system as well as the system configuration, ranging from boundary conditions to internal and external geometries and orientations of the system. The present study focused on conducting experiments at different inclination angles and isothermal wall temperatures with the organic PCM PureTemp37, and continued with a numerical investigation into the mushy-zone constant with respect to the aforementioned changes to system parameters. For the experiments, an acrylic enclosure was used in conjunction with a constant temperature bath that transferred heat via an aluminum heat spreader. Data collection was completed via imaging at a set interval, and these were used to determine the solid/liquid percentage of PCM in the enclosure at a specific point in time during the melt. The experiments along with a series of material properties tests were used to complete and validate numerical simulations of an identical system. To ensure numerical accuracy a variety of meshes were studied to confirm mesh independence, and methods for the simulations were selected based on standards that have been established for the field. Using the experiments as a benchmark, the numerical data returned differing trends in inclination angle and isothermal wall temperature with respect to the mushy-zone constant depending on the fineness of the constructed mesh. This led to the conclusion that more care is needed when completing mesh independence studies as false correlations of the mushy-zone constant at differing system parameters appear with more coarse models

Heat-Driven Self-Cooling System Based On Thermoelectric Generation Effect

This research entails the first comprehensive and systematic study on a heat-driven, self-cooling application based on the thermoelectric generation effect. The system was studied using the first and second laws of thermodynamics to provide a solid and basic understanding of the physical principles governing the system. Multiphysics equations that relate heat transfer, fluid dynamics and thermoelectric generation are derived. The equations are developed with increasing complexity, from the basic Carnot heat engine to externally and internally irreversible engines. A computational algorithm to systematically use the fundamental equations has been presented and computer code is implemented based on the algorithm. Experiments were conducted to analyze the geometric and system parameters affecting the application of thermoelectric based self-cooling in devices. Experimental results show that for the highest heat input studied, the temperature of the device has been reduced by 20-40% as compared to the natural convection case. In addition, it has been found that in the self-cooling cases studied, convection thermal resistance could account for up to 60% of the total thermal resistance. A general numerical methodology was developed to predict steady as well as transient thermal and electrical behavior of a thermoelectric generation-based self-cooling system. The methodology is implemented by using equation modeling capabilities to capture the thermo-electric coupled interaction in TEG elements, enabling the simulation of major heating effects as well as temperature and spatial dependent properties. An alternative methodology was also presented, which integrates specialized ANSI-C code to integrate thermoelectric effects, temperature-dependent properties and transient boundary conditions. It has been shown that the computational model is able to predict the experimental data with good accuracy (within 5% error). A parametric study has been done using the model to study the effect of heat sink geometry on device temperature and power produced by TEG arrays. In addition, a dynamic model suited for integration in control systems is developed. Therefore, the study has shown the potential for a heat driven self-cooling system and provides a comprehensive set of tools for analysis and design of thermoelectric generation

VECSEL systems for quantum information processing with trapped beryllium ions

Two vertical-external-cavity surface-emitting laser (VECSEL) systems producing ultraviolet (UV) radiation at 235 nm and 313 nm are demonstrated. The systems are suitable for quantum information processing applications with trapped beryllium ions. Each system consists of a compact, single-frequency, continuous-wave VECSEL producing high-power near-infrared light, tunable over tens of nanometers. One system generates 2.4 W at 940 nm, using a gain mirror based on GaInAs/GaAs quantum wells, which is converted to 54 mW of 235 nm light for photoionization of neutral beryllium atoms. The other system uses a novel gain mirror based on GaInNAs/GaAs quantum-wells, enabling wavelength extension with manageable strain in the GaAs lattice. This system generates 1.6 W at 1252 nm, which is converted to 41 mW of 313 nm light that is used to laser cool trapped $^{9}$Be$^{+}$ ions and to implement quantum state preparation and detection. The 313 nm system is also suitable for implementing high-fidelity quantum gates, and more broadly, our results extend the capabilities of VECSEL systems for applications in atomic, molecular, and optical physics.Comment: 8 pages, 7 figure

Experimental analysis and transient numerical simulation of a large diameter pulsating heat pipe in microgravity conditions

A multi-parametric transient numerical simulation of the start-up of a large diameter Pulsating Heat Pipe (PHP) specially designed for future experiments on the International Space Station (ISS) are compared to the results obtained during a parabolic flight campaign supported by the European Space Agency. Since the channel diameter is larger than the capillary limit in normal gravity, such a device behaves as a loop thermosyphon on ground and as a PHP in weightless conditions; therefore, the microgravity environment is mandatory for pulsating mode. Because of a short duration of microgravity during a parabolic flight, the data concerns only the transient start-up behavior of the device. One of the most comprehensive models in the literature, namely the in-house 1-D transient code CASCO (French acronym for Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in English), has been configured in terms of geometry, topology, material properties and thermal boundary conditions to model the experimental device. The comparison between numerical and experimental results is performed simultaneously on the temporal evolution of multiple parameters: tube wall temperature, pressure and, wherever possible, velocity of liquid plugs, their length and temperature distribution within them. The simulation results agree with the experiment for different input powers. Temperatures are predicted with a maximum deviation of 7%. Pressure variation trend is qualitatively captured as well as the liquid plug velocity, length and temperature distribution. The model also shows the ability of capturing the instant when the fluid pressure begins to oscillate after the heat load is supplied, which is a fundamental information for the correct design of the engineering model that will be tested on the ISS. We also reveal the existence of strong liquid temperature gradients near the ends of liquid plugs both experimentally and by simulation. Finally, a theoretical prediction of the stable functioning of a large diameter PHP in microgravity is given. Results show that the system provided with an input power of 185W should be able to reach the steady state after 1min and maintain a stable operation from then on

Graphene and other Two-dimensional Materials in Nanoelectronics and Optoelectronics

Graphene is probably the most fascinating material discovered in this century. A group of 2D materials can be called graphene derivatives, and these have attracted tremendous interest. This includes materials that are one or a few atoms thick. They have outstanding optical/electrical properties, and, most importantly, they are flat and thin—they can be processed with existing semiconductor technologies. Therefore, they have great potential in nanoelectronics and optoelectronics, playing a revolutionary role in these fields via their integration with other bulk materials. Of course, there are still challenges, such as large-scale production, as well as the mechanical transfer of these atomically thin sheets. These are the fields where scientists are now actively doing research. In this book, some leading scientists in the area share their most recent results on the material growth, device physics/processing, and system integration of 2D materials and devices. This book can serve as a starting point for young students to get familiar with the field, and should also be valuable to established device physicists and engineers who would like to explore the potential applications of 2D materials in electronics