No description available.

Recent studies have shown that thermophotovoltaic (TPV) technology is a promising source of high power density generation. Enhanced TPV systems can theoretically provide power densities of up to 100 W/cm2. The inherent ineffiencies in the system dictate that up to 90% of that energy is not converted to electrical power, and must be removed as waste heat to ensure that the components are maintained at a reasonable operating temperature. The present study addresses this issue by investigating the suitability of using spray cooling techniques to remove heat generated by power densities of up to 100 W/cm2. A simple, scaleable experiment was designed using low-cost commercially available components to study the effects that spray mass flux and droplet size have on the heat removal capacity of the system. A series of nozzles were used so that mass flux and droplet size could be studied independently, giving high resolution to the data so that predictive correlations could be developed over the range of parameters varied in the study. / US Naval Reserve (USNR) author.

Research was performed on the development of metal-supported solid oxide fuel cell (SOFC) electrolytes by suspension and solution precursor plasma spraying (SPS and SPPS). Experiments were conducted to understand the effects of many plasma-, feedstock-, and substrate-related process parameters on the microstructure, permeability, and conductivity of the resulting coatings. Most work was performed with yttria-stabilized zirconia (YSZ), but samaria-doped ceria (SDC) was also considered. The plasma-to-substrate heat flux behaviour of the process is particularly relevant for producing dense electrolytes with low segmentation cracking. Heat flux profiles for various processing conditions were experimentally determined and then used to model temperature distributions in the electrolyte and substrate during deposition. The results showed a strong correlation between segmentation crack severity and the peak temperature difference between the electrolyte surface and the metal support during deposition. Building on these findings, two strategies were developed for improving electrolyte performance. The first strategy is to use a bi-layer electrolyte structure, in which one layer is dense but has segmentation cracks and the other layer is more porous but contains relatively few segmentation cracks. A cell with a bi-layer electrolyte achieved a peak power density of 0.718 W cm-2 at 750 °C using hydrogen as fuel. The second strategy involves reducing the thickness and roughness of the electrode on which the electrolyte is deposited, which first required the development of improved metal supports. A thinner electrode reduces the thermal stresses that drive segmentation cracking and a smoother surface minimizes the formation of concentrated porosity. A cell with a 16 μm thick anode and a 21 μm thick electrolyte achieved an open circuit voltage (OCV) of 1.053 V, a series resistance of 0.284 Ω cm2, and a peak power density of 0.548 W cm-2 at 750 °C using hydrogen as fuel. A separate cell with a 28 μm thick electrolyte achieved an OCV of 1.068 V. At the end of the thesis, cell performance is compared to that of state-of-the-art cells produced in other facilities and using other production methods.

The algorithm of arc spraying process simulation was created, which allow to make prognosis of arc spraying jet configuration and flying particles parameters. This scientific research shows the dependence between the arc spraying technological parameters and mechanical and physical properties of the obtained coatings. It was established, how by change of the spraying parameters the coatings with the best exploiting parameters can by received. The performed research shows the influence of the kind of the sprayed material on morphology of the formed jet particles and on technical and structural characteristics of the formed coatings. On basis of obtained results made suggestions how to improve the creation of thermal spraying coatings making new products or making restoration.

The algorithm of arc spraying process simulation was created, which allow to make prognosis of arc spraying jet configuration and flying particles parameters. This scientific research shows the dependence between the arc spraying technological parameters and mechanical and physical properties of the obtained coatings. It was established, how by change of the spraying parameters the coatings with the best exploiting parameters can by received. The performed research shows the influence of the kind of the sprayed material on morphology of the formed jet particles and on technical and structural characteristics of the formed coatings. On basis of obtained results made suggestions how to improve the creation of thermal spraying coatings making new products or making restoration.

Research was performed on the development of metal-supported solid oxide fuel cell (SOFC) electrolytes by suspension and solution precursor plasma spraying (SPS and SPPS). Experiments were conducted to understand the effects of many plasma-, feedstock-, and substrate-related process parameters on the microstructure, permeability, and conductivity of the resulting coatings. Most work was performed with yttria-stabilized zirconia (YSZ), but samaria-doped ceria (SDC) was also considered. The plasma-to-substrate heat flux behaviour of the process is particularly relevant for producing dense electrolytes with low segmentation cracking. Heat flux profiles for various processing conditions were experimentally determined and then used to model temperature distributions in the electrolyte and substrate during deposition. The results showed a strong correlation between segmentation crack severity and the peak temperature difference between the electrolyte surface and the metal support during deposition. Building on these findings, two strategies were developed for improving electrolyte performance. The first strategy is to use a bi-layer electrolyte structure, in which one layer is dense but has segmentation cracks and the other layer is more porous but contains relatively few segmentation cracks. A cell with a bi-layer electrolyte achieved a peak power density of 0.718 W cm-2 at 750 °C using hydrogen as fuel. The second strategy involves reducing the thickness and roughness of the electrode on which the electrolyte is deposited, which first required the development of improved metal supports. A thinner electrode reduces the thermal stresses that drive segmentation cracking and a smoother surface minimizes the formation of concentrated porosity. A cell with a 16 μm thick anode and a 21 μm thick electrolyte achieved an open circuit voltage (OCV) of 1.053 V, a series resistance of 0.284 Ω cm2, and a peak power density of 0.548 W cm-2 at 750 °C using hydrogen as fuel. A separate cell with a 28 μm thick electrolyte achieved an OCV of 1.068 V. At the end of the thesis, cell performance is compared to that of state-of-the-art cells produced in other facilities and using other production methods.

No description available.

Spray-forming is a newly developed industrial metal forming process in which a cylindrical metal billet is produced by the incremental deposition and solidification of an atomised metal spray on a moving substrate. A mathematical model is developed to describe billet growth and heat flow within spray-formed aluminium alloy billets. In the first part of the thesis, growth dynamics of the billet are considered. Conservation of mass at the billet surface yields a single first order quasi-linear partial differential equation for the movement of the billet surface; the nonlinearity arising from the possibility of surface shadowing. The existence of two distinctly different timescales, amongst the process motions governing billet growth, prompts the use of an averaging method. The resulting averaged equations permit analysis and are shown to provide a valid asymptotic approximation to the billet surface motion on the timescale 1/∊, for a suitably defined class of billet surfaces. The parameter ∊ ≪ 1 is the ratio of the two process timescales. Conditions under which the crown profile of the cylindrical billet becomes steady are analysed, through the averaged equations, and the stability of such profiles is examined. Computed examples of single and multiple steady state crown profiles are given. The averaged equations are also solved numerically to provide a model for transient billet growth on a "slow" timescale; results are presented. The second part of the thesis considers heat flow within the growing billet. Phase change is incorporated using an enthalpy formulation of the energy equation. The resulting equation is a nonlinear heat equation that must be solved in an expanding domain, the boundary of which is determined by solution of the billet growth model equations. Conduction on the billet length-scale takes place only on the slow timescale, with more rapid heat flow taking place only close to the billet surface. Accordingly, billet heat flow is analysed through the assumption that there is a thermal boundary layer close to the billet surface, which is driven by the "rapid" timescale spray deposition, with heat flow in the remainder of the billet driven by the time-averaged growth. The boundary layer equation is a one dimensional nonlinear advection-diffusion equation, with a nonlinear boundary condition that incorporates the intermittent deposition from the spray in the form of an irregular pulse. This equation is solved numerically using an implicit finite difference method. The slow-time heat flow is two dimensional, (assuming axisymmetric slow-time billet growth), and must also be solved numerically. For this an implicit predictor-corrector method is used. The predictor stage uses a "splitting" method, adapted from the fully implicit L.O.D. method to take account of the expanding domain. The method appears to be stable and consistent. Various numerical results are presented. The model provides significant new understanding of the dynamics of billet growth and succeeds in providing a useful framework within which the transient heat flow that occurs during spray deposition, on a number of different timescales and length-scales, can be understood. Comparison of computed model predictions with real sprayed billets confirms the validity of the model. The thesis is concluded with a summary of results and a look at possible future directions for research in this area.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1978. / Bibliography: leaves 193-205. / Microfiche. / xv, 205 leaves ill. 28 cm

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1972. / Bibliography: leaves [160]-168. / xii, 168 l illus. tables