Browsing by Subject "Gas dynamics"
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Item Behavior of fluidized beds with variable gas velocity(Texas Tech University, 1983-12) Wolfe, Steven DeanThe objective of this study was to investigate how gas generating within a fluidized bed affects the bed behavior. A special experimental system was designed and constructed for this investigation. The system was a simple modification of a two-dimensional fluidized bed used previously by numerous researchers. The gas generation was simulated by introducing uniformly an air stream throughout the back wall of the bed. Trends and characteristics of fluidized beds with gas generation were identified. A relationship between the overall bed void fraction and gas generation rate was found to be linear. This linear relationship was experimentally verified only in the range in which the ratio of Lf/Lp^f was less than 1.20. Above this range the bed was too turbulent to measure the void fraction accurately. A correlation between bubble size and bubble velocity with and without generation was derived. The scattering of the data was large such that both a linear and parabolic relationship would be acceptable. It was observed that as gas generation increased, the bubble size slightly increased, and this in turn resulted in a slight increase in bubble velocity. Three simplified, idealized cases were examined to explain the observed bed expansion and bubble velocities: a) All generated gas passes through the bed in the form of new bubbles of equal size identical to that of the existing bubbles, b) All generated gas penetrates existing bubbles and passes through the bed. c) All generated gas passes through the bed in the emulsion phase while the existing bubbles remain unaffected. The model most consistent with experimental data was that the generation gas penetrates the existing bubbles and passes through the bed.Item Compressible Fluid Flow Through an Orifice(Texas Tech University, 1973-05) Waller, Herschel NathanielNot Available.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 Investigation of the use of horizontal baffles in a gas-liquid agitated tank(Texas Tech University, 1990-05) Forster, Charles CThe objective of this investigation was to study horizontal baffle parameters and determine their effect on the mixing performance of a gas-sparged agitated contactor and compare to contactors of standard design. Unlike standard baffle design, horizontal baffles are located at the dispersion surface. The following horizontal baffle parameters were investigated; the number of horizontal baffles and the inclination of each baffle. The performance criterion to be examined was the mass transfer coefficient for a given power input. The experiments were conducted on a 7.5-gallon lab-scale agitated tank. The sodium sulfite method was used to determine the mass transfer coefficient. The primary independent variables were the impeller speed and the air injection rate. The impeller speed and air injection rate were varied from 500 to 1500 RPM and 160 to 1280 cm3/s, respectively. The number of horizontal baffles and their inclination had little effect on mixing performance. For a gas injection rate of 160 cm^/s, contactors equipped with horizontal baffles showed only a 25% improvement in the mass transfer coefficient compared to a contactor of standard design. At larger gas injection rates there is little or no difference in mixing performance for contactors of different baffle design. Results of this investigation were compared to previous research and it was found that the design of the tank (specifically, the horizontal baffles) is a crucial factor for improving the performance of a contactor equipped with horizontal baffles.Item The removal of an airborne low-volatility heavy metal from exhaust gases through condensation onto sorbent particles(2001-08) Rodriguez, Alexander; Hall, Matthew JohnThe 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.