MKOPSC Theses and Dissertations
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Browsing MKOPSC Theses and Dissertations by Subject "aerosol"
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Item High Flash-point Fluid Flow System Aerosol Flammability Study and Combustion Mechanism Analysis(2013-12-02) Huang, Szu-Ying; Mannan, M. Sam; Holste, James C; Cheng, Zhengdong; Petersen, Eric LThe existence of flammable aerosols creates fire and explosion hazards in the process industry. Due to the operation condition of high pressure circumstances, heat transfer fluids tend to form aerosols when accidental leaking occurs on pipelines or storage vessels. An aerosol system is a complicated reactive system; there are neither systematic flammability data similar to the case with pure gases, nor clearly described ignition-to-combustion process of a droplet-air mixture system. The flammable regions of three main, widely-used commercial heat transfer fluids: Paratherm NF (P-NF); Dowtherm-600 (D-600); and Plate Heat Exchange Fluid (PHE), were analyzed by electro-spray generation with laser diffraction particle analysis method. The aerosol ignition behavior depends on the droplet size and concentration of the aerosol. From the adjustment of differently applied electro-spray voltages (7-10 kV) and various liquid feeding rates, a flammable condition distribution was obtained by comparison of droplet size and concentration. All of the fundamental study results are to be applied to practical cases with fire hazards analysis, pressurized liquid handling, and mitigation system design once there is a better understanding of aerosols formed by high-flash point materials. On the other hand, the process of combustion from initial stage to global flame formation was simulated with COMSOL-multi-physics in terms of heat transfer, droplet evaporation, and fluid dynamics of liquid-air interaction. The local temperature change through time, as an indicator of luminous flame appearance, was analyzed to describe the flame development and ignition delay time of aerosols. We have conducted a series of simulation regarding physical formula in description of this combustion process, and will conclude with how temperature distribution influenced the appearance of luminous flames, which was the symbol of successful ignition of aerosol. The mitigation implementing timing and location can be characterized with further understanding of this combustion process. The potential application of the ignition delay will be beneficial to the mitigation timing and detector sensor setting of facilities to prevent aerosol cloud fires. Finally, the scientific method of aerosol flammability study was discussed for its potential impacts on experimental results. A modeling point of view was introduced, with the analysis of electric field application on fuel droplets, and the related fundamental study of the ignition phenomenon on aerosol system. Existing charges from electrospray is beneficial for the monodispersity and control of aerosols for fundamental study. However, the additional charges accumulated on the droplet surfaces are likely to have impacts on flammability due to the excess energy they applied to the aerosols system and droplet-droplet distraction or turbulences. This is a re-visit of aerosol flammability study method, with a conclusion that charges did have positive impact on droplets’ ignition concentration range with a balancing effect on turbulence increase to reduce the ignition chance.Item Laminar Flame Speeds of Nano-Aluminum/Methane Hybrid Mixtures(2014-12-12) Sikes, Travis; Petersen, Eric L; Mannan, M. Sam; Staack, David A.An existing flame speed bomb, which uses optical techniques to measure laminar flame speed, was employed to study the fundamental phenomena of flame propagation through a uniformly dispersed aerosol. In a previous thesis by Andrew Vissotski, the groundwork was laid to begin studies of hybrid flames. Beginning from these preliminary findings, the facility was upgraded to disperse dust into the test chamber through a strong burst of gas. This aerosol was then allowed to settle for a minimum of 45 seconds to ensure that the conditions inside the test chamber were quiescent and that the dust was uniformly distributed. Extinction of laser light through the resulting aerosol was measured through the large optical access with a 632.8-nm, 5-mW HeNe laser so that the mass of suspended nano-particles could be determined as a function of time up until combustion has occurred. The particles used in these experiments were aluminum nano-particles with a manufacturer-stated average fundamental particle size of 100 nm. To properly quantify the particle distribution inside of the vessel, a scanning mobility particle sizer was employed to characterize the aluminum, resulting in an average particle size of 446.1 nm. With a calibrated extinction measurement, experimental suspended mass of aluminum was measured up to 90 mg. A hybrid mixture of Al/CH4 was chosen to serve as the combustion medium and to provide a well-characterized parent fuel to measure the contribution of nano-aluminum on combustion. Two series of experiments were performed, both at stoichiometric conditions: one with the mixture in air and the second with the mixture in a 70/30 N2/O2 mix. The results herein show a maximum decrease in flame speed, 5-7% from the neat mixture, when nano-aluminum is introduced. In the 70/30 N2/O2 mixture, the addition of aluminum results in a maximum decrease of 5 cm/s from the neat flame speed of 80.5 cm/s and in the air mixture, a 2 cm/s maximum decrease from 35.3 cm/s. A preliminary spectroscopic analysis was performed but was inconclusive. It was also found that the addition of nanoparticles cause the flame to become unstable faster when compared to the neat mixture of CH4/air.Item Measurement and prediction of aerosol formation for the safe utilization of industrial fluids(Texas A&M University, 2004-09-30) Krishna, Kiran; Mannan, M. Sam; Hall, Kenneth R.; Kihm, Kenneth D.; West, Harry H.Mist or aerosol explosions present a serious hazard to process industries. Heat transfer fluids are widely used in the chemical process industry, are flammable above their flash points, and can cause aerosol explosions. Though the possibility of aerosol explosions has been widely documented, knowledge about their explosive potential is limited. Studying the formation of such aerosols by emulating leaks in process equipment will help define a source term for aerosol dispersions and aid in characterizing their explosion hazards. Analysis of the problem of aerosol explosions reveals three major steps: source term calculations, dispersion modeling, and explosion analysis. The explosion analysis, consisting of ignition and combustion, is largely affected by the droplet size distribution of the dispersed aerosol. The droplet size distribution of the dispersed aerosol is a function of the droplet size distribution of the aerosol formed from the leak. Existing methods of dealing with the problem of aerosol explosions are limited to enhancing the dispersion to prevent flammable concentrations and use of explosion suppression mechanisms. Insufficient data and theory on the flammability limits of aerosols renders such method speculative at best. Preventing the formation of aerosol upon leaking will provide an inherently safer solution to the problem. The research involves the non-intrusive measurement of heat transfer fluid aerosol sprays using a Malvern Diffraction Particle Analyzer. The aerosol is generated by plain orifice atomization to simulate the formation and dispersion of heat transfer fluid aerosols through leaks in process equipment. Predictive correlations relating aerosol droplet sizes to bulk liquid pressures, temperatures, thermal and fluid properties, leak sizes, and ambient conditions are presented. These correlations will be used to predict the conditions under which leaks will result in the formation of aerosols and will ultimately help in estimating the explosion hazards of heat transfer fluid aerosols. Heat transfer fluid selection can be based on liquids that are less likely to form aerosols. Design criteria also can incorporate the data to arrive at operating conditions that are less likely to produce aerosols. The goal is to provide information that will reduce the hazards of aerosol explosions thereby improving safety in process industries.