Current concentrated solar technologies are not cost-effective means of generating electricity and would benefit greatly from higher operating temperatures. To reach these temperatures at high efficiencies, a novel receiver design should be used in the plant. As a first step in the design of such a receiver, a sensitivity analysis is useful to determine what parameters most affect the performance of a generic cavity receiver. The results of this sensitivity analysis can be used to develop an optimized cavity receiver geometry intended to operate at a high efficiency (>80%) at extreme temperatures (1,350°C). It was found that limiting re-radiation and convection through the cavity aperture most improve the performance of the receiver; at the same time, the receiver must be designed in such a way as to minimize thermal stresses. Descriptions of many experimental components that have been developed to allow for a successful test of a laboratory scale receiver are also included in this thesis. Additionally, presented here are the results of some initial experiments intended to validate the simulations used to perform the aforementioned sensitivity analysis. Finally, some remarks are proffered detailing additional steps and considerations necessary to scale up the receiver design to an industrial scale.

Hydrogen separation membranes could be an enabling technology in a hydrogen economy. A comprehensive microkinetic model for hydrogen permeation was developed to expand the ability to predict hydrogen flux through various potential dense metal (solid and liquid) membrane candidates over a wide range of operating conditions. The molecular steps in the assumed mechanism, i.e., surface adsorption, dissociation, infiltration, and bulk diffusion, are adopted from the literature. The limiting assumptions made normally in the literature models, however, were avoided to develop a more comprehensive and rigorous model while still being computationally accessible. The use of an electric circuit analogy to model the molecular permeation step network allowed individual steps to be analyzed insightfully and in identifying which are rate-limiting steps under various conditions and which may be considered to be at quasi-equilibrium. The model was validated using experimental flux data available in the literature, and involving kinetic and thermodynamic parameters derived from theoretical and experimental sources, for the conventional solid palladium and palladium- silver membranes. In order to extend the model to evaluate the efficacy of a sandwiched liquid metal membrane (SLiMM), a novel membrane under development in this laboratory, the molecular step kinetic and thermodynamic parameters must first be determined. Experimental as well as theoretical work was thus performed to determine these parameters for liquid gallium (Ga) and liquid indium (In), two potential SLiMM candidates. A semi-theoretical approach termed the Pauling Bond Valence-Modified Morse Potential (PBV-MMP) method was used to determine activation energies as well as pre-exponential factors for the steps involved in hydrogen permeation in a liquid metal. Experimentally, absorption isotherms as well as adsorption and diffusion kinetics were measured using a Sieverts apparatus that operates by measuring the pressure difference when a valve is opened between an evacuated sample chamber of known volume and another chamber charged to an initial pressure of hydrogen gas. Based on the hence theoretically and experimentally determined parameters, the microkinetic model was extended to SLiMM and conditions identified when different steps are rate-limiting or at quasi-equilibrium. The model was compared to experimental data for permeation of hydrogen in liquid Ga and liquid In membranes, giving a reasonable first prediction of the hydrogen flux through each metal membrane, and confirming their potential as hydrogen membranes.

Hydrogen (H2) and fuel cells applications are central to the realization of a global hydrogen economy. In this scenario, H2 may be produced from renewable biofuels via steam reforming and by solar powered water electrolysis. The purification required for fuel cell grade H2, whether in tandem or in situ within a catalytic reformer operating at 500 oC or above, would be greatly facilitated by the availability a cheaper and more robust option to palladium (Pd) dense metal membrane, currently the leading candidate. Here we describe our results on the feasibility of a completely novel membrane for hydrogen separation: Sandwiched Liquid Metal Membrane, or SLiMM, comprising of a low-melting, non-precious metal (e.g., Sn, In, Ga) film held between two porous substrates. Gallium was selected for this feasibility study to prove of the concept of SLiMM. It is molten at essentially room temperature, is non-toxic, and is much cheaper and more abundant than Pd. Our experimental and theoretical results indicate that the Ga SLiMM at 500 oC has a permeability 35 times higher than Pd, and substantially exceeds the 2015 DOE target for dense metal membranes. For developing a fundamental understanding of the thermodynamics and transport in liquid metals, a Pauling Bond Valence-Modified Morse Potential (PBV-MMP) model was developed. Based on little input, the PBV-MPP model accurately predicts liquid metal self-diffusion, viscosity, surface tension, as well as thermodynamic and energetic properties of hydrogen solution and diffusion in a liquid metal such as heat of dissociative adsorption, heat of solution, and activation energy of diffusion. The concept of SLiMM proved here opens up avenues for development practical H2 membranes, For this, improving the physical stability of the membrane is a key goal. Consequently, a thermodynamic theory was developed to better understand the change in liquid metal surface tension and contact angle as a function of temperature, pressure and gas-phase composition.

No description available.

Introduction Low melting point metals are often encapsulated in a hermetic container, irradiated and the container transferred to hot-cell for material removal and processing. An important process of this kind is the production of 82Sr from rubidium (melting point: 39.5 °C.) This new concept departures completely form the encapsulated targets approach and allows an almost continues production by the irradiation of the bulk metal. As well, eliminated is the target transfer. By placing the target material dissolution chamber right in the target station, only the dissolution product is pumped to the hotcell for further processing. Material and Methods Some of the disadvantages of the encapsulated target are: 1. Complicated transfer system that is ex-pensive to install, slow and prone to failures. 2. Complex and expensive encapsulation procedure. 3. Loss of production time during the lengthy target changing. 4. Capsule geometry is constrained by the encapsulating process and transfer demands compromising heat transfer and beam power. To avoid the difficulties of liquid metal handling, metal salts are often used instead (rubidium chloride is one example). This creates other problems and limits the beam currents and production yields. In the system described, the liquid metal is transferred (by gravity) from a bulk container to an irradiation chamber. The chamber, made out of nickel-plated silver, holds the correct quantity of rubidium for one irradiation run. Because of the geometry of the chamber and the efficient cooling, up to 40KW of beam power can be delivered to the target. The chamber is equipped with thermocouples and a liquid-metal level detector and is entirely of welded/brazed construction. The alloy foil that forms the beam window is electron-beam welded to the chamber front ring. At the end of irradiation the irradiated liquid metal is gravity fed into a reaction chamber situ-ated below the irradiation chamber, and a new load of fresh rubidium released into the irradia-tion chamber. The liquid-metal transfer and the irradiation components are shown on FIG. 1, and the sectional view on FIG. 2. Appropriate chemicals (n-butanol in the case of rubidium) are delivered to the reaction chamber and the irradiated metal dissolved. The liquid dissolution product is transferred back to the hotcell. Since all steps of the reaction involve liquids, only small diameter tubes connect the target station with the hotcell. The transfer is fast and simple. The bulk liquid-metal storage container can be constructed to hold enough material for 10 or more runs. When empty, it is replaced with a pre-loaded one. The container is connected to the target system with one coupling and the exchange takes a short time. A robotic bottle exchange can be implemented if desired. The station is equipped with its own vacuum system, beam diagnostic (consisting of a four-sector mask) and a collimation. The target chamber and each of the beam intercepting components are electrically insulated to allow beam current monitoring. Constructed entirely out of metal and ceramic the target core assembly does not suffer from radiation damage. The use of aluminum, silver and alumina reduce component activation. Results and Conclusion A large part of the station design is based on the well proven construction of high current solid target system and is using the same, or similar components. Test was performed to optimize the liquid-metal transfer and the chamber filling with the correct volume, while leaving some room for expansion. A process for niobium coating of sliver is investi-gated. Niobium is known to provide good corro-sion resistance against liquid metals. Thermal modelling of the target and flow analysis of the cooling geometry is under way.

Thesis (M.S.)--University of Michigan, 1957.

Thesis (M.S.)--University of Michigan, 1958.

Thesis (M.A.)--Monterey Institute of International Studies, 2002. / Translation of: Avariĭnye i perekhodnye prot︠s︡essy v bystrykh reaktorakh.

Soft electronics have become increasingly necessary for the implementation and integration of novel technologies in a variety of environments including aerospace, robotics, and healthcare. In order to develop these soft electronic devices, materials and manufacturing strategies are required for these soft, stretchable, and flexible systems. Further, the ability to effectively tune not only these mechanical properties but also their thermal and electrical properties is key to developing multifunctional materials for soft electronic applications. In this thesis, we present a method of printing highly tunable flexible and stretchable composites consisting of elastomers with liquid metal (LM) inclusions. We analyze the mechanical and functional behaviors and highlight the anisotropic properties that can be created via our printing system, and we apply this understanding to the development of a multiphase material with a programmable crack propagation path. Throughout this work we describe the process by which we use Direct Ink Write (DIW) technology, a type of additive manufacturing, to print 2D and 3D LM composites with tunable properties. The design map used to control LM microstructure in-situ is first outlined in Chapter 2. This tuning ability is used to print materials with varied LM microstructures and study the impact on mechanical, thermal, and electrical properties (Chapter 2, Chapter 3). We further study the elongated LM droplet inclusions for how their orientation with respect to loading may impact mechanical properties (Chapter 3). We further utilize these findings to control crack propagation along a specified path using only variations in printing parameters (Chapter 3). We provide concluding statements and outlooks on future work in Chapter 4. We then summarize our findings and detail the implications for the soft electronics field (Chapter 5). / Master of Science / Soft electronics have become increasingly necessary for the successful implementation and integration of novel technologies in a variety of environments including the spaces of aerospace, robotics, and healthcare. In order to develop these soft electronic devices, a new class of materials with soft, stretchable, and flexible properties is critical. Further, the ability to effectively tune not only these mechanical properties but also their thermal and electrical properties is key to developing high-functioning materials for soft electronic applications. In this thesis, we present a method of printing highly tunable flexible and stretchable materials with liquid metal (LM), known as liquid metal embedded elastomers (LMEEs). We analyze the mechanical properties and their direction-dependent nature that can be tuned via our printing system, and we apply this understanding to the development of a 2D material with a programmable path along which the material will tear. Throughout this work we describe the process by which we use Direct Ink Write (DIW) technology, a type of additive manufacturing, to print 2D and 3D LMEE structures with tunable properties. The design map used to control the LM microstructure in-situ is first outlined in Chapter 2. This tuning ability is used to print materials with varied LM microstructures and study the impact on mechanical, thermal, and electrical properties (Chapter 2, Chapter 3). We further study the elongated LM droplet inclusions for how their orientation with respect to loading may impact mechanical failure (Chapter 3). We further utilize these findings to control crack propagation along a specified path using only variations in printing parameters (Chapter 3). We provide concluding statements and outlooks on future work in Chapter 4. We then summarize our findings and detail the implications for the soft electronics field (Chapter 5)

Thesis (doctoral)--Delft University of Technology, 2007. / "Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft." Includes bibliographical references (p. 120-128) and index.