Browsing by Subject "Gas dynamics"
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Item Electrodynamics of a hypervelocity surface conversion process using electromagnetic accelerators(2003) Zowarka, Raymond Charles; Driga, Mircea D.The U.S. Government and commercial entities are dependent on chemical plating and coating processes to replace worn or eroded material on damaged parts. Logistics Centers have been forced to consider replacement materials for repair operations due to tightening of government regulations on the use of toxic and hazardous materials. Existing state of the art thermal spray processes (HVOF, D-gun, Plasma Spray) are limited to powder velocities of about 1 km/s because they rely on the thermodynamic expansion of gases. Because these methods rely on the mechani- cal bonding of the powder to the substrate the coatings and their bonds are a frac- tion of the parent material strength. To make full use of this repair process the coating has to bond to substrate with near parent material strength and coating has to build with good strength layer to layer. A new thermal spray process using electromagnetic forces can accelerate powder particles to a final velocity in ex- cess of 2 km/s. At this velocity powder particles have sufficient kinetic energy to melt their own mass and an equivalent substrate mass on impact. The kinetic en- ergy of the process allows fusion bonding of greater strength than that created by low velocity processes as well as improved coating density. This dissertation describes the invention of the Electromagnetic Powder Deposition (EPD) process. The railgun process is combined with a gas dynamic mechanism, called a snowplow, to produce controllable bursts of gas with the speed and duration required to accelerate finite segments of dispersed powder to the conditions required for plating purposes. The physics of the railgun and snow- plow process are presented and proof of principle experiments is described. A method to start a planar arc in repetitive fashion had to be developed. An added complexity was that the source had to be stable at atmospheric pressure. A repeti- tive discharge power supply, instrumentation and control system had to be devel- oped. To industrialize the process it had to be demonstrated that the process could build multiple layers with good bond strength layer to layer.Item Experimental study of the hydrodynamics of high Mach number blast waves(2005) Edens, Aaron Douglas; Ditmire, Todd R.We have performed a series of experiments examining the properties of high Mach number blast waves. Preliminary experiments were conducted on the Janus laser at Lawrence Livermore National Laboratory while the majority of experiments were carried out on the Z-Beamlet laser at Sandia National Laboratories. We created blast waves in the laboratory by using 10 J- 1000 J laser pulses to illuminate millimeter scale solid targets immersed in gas. The experimental results can be grouped into three categories. Firstly, we confirmed the importance of line radiation on the evolution of the blast wave and that this importance increased with the atomic number of the gas used. This was determined through three measurements: Interferometric measurements of the size of the radiative precursor preceding the blast front, measurements of the blast wave trajectory, and measurements of the size of additional blast waves created by the radiation ablating material in the blast wave path. The second set of experiments examined the effect of the passage of a laser pulse on the subsequent evolution of the created blast wave. We find that the laser’s passage creates a warm channel of gas where a blast wave travels at higher velocity than it does through unperturbed gas. This creates a bulge-like feature on the blast wave surface. This effect is magnified in higher atomic number gases where multi-photon ionization is more prevalent, causing additional energy to be deposited in the gas. The final set of experiments studied the validity of theories forwarded to explain the dynamics of perturbations on astrophysical blast waves. These experiments consisted of a systematic scan of the decay rates of perturbations of known primary mode number induced on the surface of blast waves by means of a regularly spaced wire array. The amplitude of the induced perturbations relative to the radius of the blast wave was tracked and fit to a power law in time. Measurements were taken for a number of different mode numbers and background gasses and the results show qualitative agreement with previously published theories for the hydrodynamics of thin shell blast wave.Item Measuring void fraction in bubbly air-water mixtures with ultrasonic extinctions(1995-08) Maher, Thomas Francis, 1957-; Not availableItem The removal of an airborne low-volatility heavy metal from exhaust gases through condensation onto sorbent particles(2001-08) Rodriguez, Alexander; Hall, M. J. (Matthew John)The removal of a low volatility heavy metal through condensation was investigated experimentally. The unfavorable volatilization behavior of a low volatility metal was altered using chlorine gas and an inorganic sulfur compound. Using such compounds the speciation of the heavy metal during combustion was modified, which caused a different volatilization and condensation behavior. Condensation sites included predistributed sorbent and soot particles. In addition to condensation rate, other processes, such as nucleation and coagulation influencing the particle size distribution and capture efficiency were investigated experimentally using particle size segregation, atomic absorption analysis, atomic emission analysis, nitrogen porosimetry, X-ray diffraction analysis and scanning electron microscopy. Using these techniques, a set of parameters promoting condensation capture was developed. Parameters under investigation were temperature, rate of temperature drop, equivalence ratio, concentrations of heavy metal, sorbent, chlorine gas and sulfur. After investigating the condensation behavior experimentally, a numerical model BAEROSOL was developed. BAEROSOL contains only condensation, nucleation and Brownian coagulation, neglecting the impact of other physical and chemical particle evolution processes. The experimental findings were compared to the model. The model BAEROSOL was used to investigate the pertinent mechanisms. The model proved to be a useful tool to estimate the general trend of the particle size evolution and its dependence on the investigated parameters. Without chlorine, typical values for the recovered fraction of the low volatility heavy metal ranged from 15% to 25%. Chlorine proved to be a suitable agent to improve the particle size distribution and the overall capture efficiency. Efficiencies could be increased up to 73% in the presence of chlorine. Sulfur did not exhibit a positive influence on the particle size distribution or capture efficiency.