Development And Tests Of A Dust Combustion Shock Tube

Dust explosion hazards in areas where combustible dusts are found have caused loss of life and halted business operations in some instances. The elimination of secondary dust explosion hazards, i.e. reducing dust dispersion, can be characterized in shock-tubes to understand shock-dust interactions. For this reason, a new shock-tube test section was developed and integrated into an existing shock-tube facility. The test section has large windows to allow for the use of the shadowgraph technique to track dust-layer growth behind a passing normal shock wave, and it is designed to handle an incident shock wave up to Mach 2 to impersonate real-industry scenarios. The characterization experiments presented herein demonstrate the advantages of the authors' test techniques toward providing new physical insights over a wider range of data than what have been available heretofore in the literature. First, the effect of shock strength on the dust entrainment process was explored by subjecting limestone dust to Mach numbers ranging from 1.10 to 1.60. Also, the effect of dust-layer thickness on the entrainment process was observed by performing tests with two different layer depths, namely 3.2- and 12.7-mm thicknesses. New data were collected to develop correlations between the shock strength and the dust entrainment height as a function of time for each layer depth. The longer observation time and higher camera framing rates led to the discovery of trends not previously observed by earlier studies, such as a clear transition time between the early, linear growth regime and a much-slower, average growth regime. This second regime is however accompanied by surface instabilities that can lead to a much larger variation in the edge of the dust layer than seen in the early growth regime. In addition, for the linear growth regime, there was no significant difference in the dust-layer height growth between the two layer thicknesses; however, the larger thickness led to higher growth rates and much larger surface instabilities at later times. Next, we conducted experiments to elucidate the effect of particle size and size polydispersity on dust cloud formation phenomena behind blast waves. Through systematic modification of the span of the particle size distribution, the striking effect of polydispersity on the entrainment process was demonstrated. Moreover, correlations between linear dust rise rate and particle size and size polydispersity have been developed. Finally, recommendations for numerical modelers of this field and NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids are provided for developing a better dust explosion hazard assessment tool. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155415

To ensure safety regarding dust explosion hazards, it is important to study the dust lifting process experimentally and identify important parameters that will be valuable for development and validation of numerical predictions of this phenomenon. A new shock tube test section was developed and integrated into an existing shock tube facility. The test section allows for shadowgraph or laser scattering techniques to track dust layer particle motion. The test section is designed to handle an initial pressure of 1 atm with an incident shock wave velocity up to Mach 2 to mimic real world conditions. The test section features an easily removable dust pan and inserts to allow for adjustment of dust layer thickness. The design allows for the changing of experimental variables including initial pressure, Mach number, dust layer thickness and characteristics of the dust itself. A separate vacuum manifold was designed to protect existing equipment from negative side effects of the dust. A study was performed to demonstrate the capabilities of the new facility and to compare results with experimental trends formerly established in the literature. Forty-micron limestone dust with a layer thickness of 3.2 mm was subjected to Mach 1.22 and 1.38 shock waves, and a high-speed shadowgraph was used for flow visualization. Dust layer rise height was graphed with respect to shock wave propagation. Dust particles subjected to a Mach 1.38 shock wave rose more rapidly and to a greater height with respect to shock wave propagation than particles subjected to a Mach 1.22 shock wave. These results are in agreement with trends found in the literature, and a new area of investigation was identified. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151046

In all the diverse industries-from food and agriculture to plastics- where combustibledust exists, the possibility of an explosion looms as an ever-present threat. Gathering awealth of practical , theoretical , and experimental data, this important work provides a‘state-of-the-art study of the Development and Control of Dust Explosions, promotingimproved control over such hazards.Comprehensive in scope, this single-source reference presents invaluable guidelines for awide variety of planning and operational activities , including calcu lation of explosionpressure and vent area required to minimize explosion damage . . . the development ofmathematical mode ls used in the evaluation of explosion phenomena . .. determinationof the effect of numerous factors on explosion development ... and control and preventionof the ignition of dust by eliminating the fines in a product.With this outstanding book, industrial, safety , mechanical , manufacturing, loss prevention, fire protection, and chemical engineers; as well as plant managers, operators, anddesigners ; and all other specialists concerned with the possibility of dust exp losions nowhave an authoritative reference. The book also serves as the basis for further research inthis important field. In addition , the unique range of data included makes th is volumeideal for in-house training programs, professional seminars, and college-level coursesstudying explosion safety and safety engineering .

Shock tubes utilize a difference in pressures between gases separated by a diaphragm to create a shock wave when the diaphragm ruptures. The AFIT 2- inch shock tube was reassembled and tested to ensure proper and safe operation. A high-speed data acquisition system was configured to take data at 2 MS/s. This research showed that the Mach number of the shock waves produced in this shQCk tube fall within 7% of theoretical values at speeds under Mach 3 and within 9% at higher speeds. The peak velocity of each shock wave was shown to occur at approximately 3 meters from the diaphragm. The second portion of the research focused on the testing of sensors used to evaluate the performance of the pulse detonation engine (PDE) for research and developmental purposes. Two alternatives were developed to standard sensors to withstand the heat of the engine: coat the sensors with an insulating, 0.6 mm thick silicone that protects it from the heat and use spark plugs as ion sensors to detect the ions in the combustion inside the PDE tubes. This researched proved that no degradation in response time, rise time, or sensitivity results from coating the pressure transducers with silicone. The research also found that the ion sensors are unable to consistently detect ions created by a Mach 8 shock wave through air.

Unfortunately, dust explosions are common and costly in a wide array of industries such as petrochemical, food, paper and pharmaceutical. It is imperative that practical and theoretical knowledge of the origin, development, prevention and mitigation of dust explosions is imparted to the responsible safety manager. The material in this book offers an up to date evaluation of prevalent activities, testing methods, design measures and safe operating techniques. Also provided is a detailed and comprehensive critique of all the significant phases relating to the hazard and control of a dust explosion. An invaluable reference work for industry, safety consultants and students. A completely new chapter on design of electrical equipment to be used in areas containing combustible/explosible dust A substantially extended and re-organized final review chapter, containing nearly 400 new literature references from the years 1997-2002 Extensive cross-referencing from the original chapters 1-7 to the corresponding sections of the expanded review chapter