Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains xii, 91 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 76-78).

No description available.

Thesis PlanB (M.S.)--University of Wisconsin--Stout, 2009. / Includes bibliographical references.

Thesis (M.S. in biological systems engineering)--Washington State University, December 2007. / Includes bibliographical references (p. 41-45).

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 7, 2007) Includes bibliographical references.

Thesis (M.Sc. (Engineering))--University of the Witwatersrand, Faculty of Engineering, 1987.

ABSTRACT Asbestos has been extensively used to insulate boilers and associated heated pipe work throughout the world. Managing human health risks posed by asbestos during the removal of lagging poses many challenges. For this reason, acquiring a better understanding of factors that lead work tasks to produce high airborne fibre concentrations is important for the development of improved control methods. Aim: The aim of this study was to link observed work tasks and work practices with measured airborne concentrations of fibres in order to identify those factors contributing to high airborne concentrations generated during boiler de-lagging. The investigation was based on a study of two employees working on a boiler de-lagging contract lasting twenty-one days and resulting in a total of 79 measurements of airborne asbestos fibres. The primary form of asbestos dust control for the duration of the contract was the application of non-amended water. Objectives: To definitively identify the presence and type of asbestos lagging as well as quantify airborne fibre concentrations for two work tasks i.e. Stripping (removing lagging) and Bagging (placing removed lagging into bags as well as cleaning spills), in order to demonstrate how they may influence airborne fibre concentrations. Methodology: The type of asbestos was confirmed by Scanning Electron Microscopy. Phase Contrast Microscopy (PCM) was selected as the primary measure of airborne asbestos fibres. A Work Practice Checklist was developed to link observed daily Work Tasks and Work Practices with the concurrent airborne fibre concentrations. The geometric mean was a useful measure of central tendency for the data since it was highly skewed to the right (positively skewed). However, for public health purposes the arithmetic mean was also considered because it provides some idea of health risk where the human respiratory system is assumed to accumulate fibres linearly with concentration. Results: Bulk sample analysis confirmed the presence of both chrysotile and amosite asbestos lagging. Work Practices such as Wetting, Stripping and Bagging asbestos, were undertaken in a relatively uncontrolled manner during the first three days of the project resulting in mean airborne fibre concentrations of 1.171 f/ml for the Stripper, ranging from 0.612 to 1.236 f/ml and 0.315 f/ml for the Bagger, ranging from 0.107 to 0.631f/ml. These means were 4.5 times and 2.3 times respectively, greater than the means calculated for the entire project. The overall mean fibre concentration was approximately five times greater for personal samples, 0.198 f/ml (± 1.647) than for the concurrent static samples, 0.039 f/ml (± 0.129). The analysis of log transformed data revealed several strong tendencies for airborne fibre concentrations when related to Work Tasks and Work Practices. The difference between stripping asbestos in small manageable as opposed to larger unmanageable pieces was highly significant (p < 0.001). Smaller manageable pieces resulted in much lowerconcentrations. The manner with which asbestos was bagged was also highly significant (p < 0.001). Bagging in an uncontrolled manner resulted in much higher airborne concentrations. Surprisingly, the degree of wetting was not as important as expected: working dry did not generate significantly more fibres than working with saturated insulation but did generate significantly more fibres (p < 0.005) than working with partially wet insulation (which lead to the highest concentrations). A limitation to interpreting the Wetting work practice was the low number of samples taken within the dry category (n = 5). The difference in mean sample concentrations between personal and static samples for this study demonstrates the importance of spatial and temporal proximity as a determinant for airborne fibre concentrations. It also showed clear associations between what can be described as rushed, reckless Work Practices, and the resulting high levels of airborne fibre concentrations (exceeding the OEL). Within the context of this project, these findings demonstrate the utmost importance of providing the appropriate training and supervision of employees, not only for protecting themselves against airborne asbestos fibres, but for removing asbestos in manner that results in the generation of the least amount of airborne fibres possible

Yau Yat Man. / Bibliography: leaves 124-129 / Thesis (M.Phil.) -- Chinese University of Hong Kong, 1983

Dust control is a very significant issue in underground coal mining. The benefits of reducing dust levels will be a lesser risk of lung disease to coal miners, improved working conditions and a reduced risk of dust explosions. Coal dust is commonly suppressed by water sprays but suppression efficiency is not high because dust tends to travel in the air flow round the water droplets rather than being captured by them. If water sprays are electrostatically charged, then a significant improvement in dust suppression efficiency may be achieved. Of the three principal droplet charging mechanisms, i.e. corona charging, induction charging and contact charging, corona charging is the most widely used in many industrial fields including dust suppression, However, it requires a high applied voltage, ranging from thousands to more than a hundred thousand volts, depending on the geometry of the charging equipment. Induction charging has been used in agricultural spraying since Law (1978) developed an embedded-electrode induction charging spraying nozzle. This nozzle provides a compact, inexpensively fabricated droplet charger and, reduces design requirements on size and output voltage (of the order of 1000 volts). It also reduces the potential for mechanical damage, misalignment and personnel hazard. In order to evaluate the effectiveness of dust suppression, either the charge on individual droplets or the charge-to-mass ratio of water sprays needs to be known. However, the parameters which control the charge applied to water and the charging rate have been unsolved theoretically for any charging mechanism. The existing theories for the induction-charged and air-atomising a liquid jet have been found to be inadequate. And there is no theory available for corona charging of the droplets produced with a pneumatic nozzle in order to predict the spray charge level or the spray charge-to-mass ratio. In view of this situation, mathematical models have been developed in this thesis for both the corona and induction charging mechanisms. During the development of the theories, it has been assumed that for corona charging, that the jet is disintegrated into droplets and the droplets are then charged; for induction charging, that the jet is first charged and the charged jet is then disintegrated into charged droplets. The Sauter mean diameter of the sprays, D32 , plays an important role in linking the individual droplet charge to the spray charge-to-mass ratio for both charging mechanisms. The developed theories are general models suitable for any liquid with both corona and induction charging. Theoretical calculations for the spray charge-to-mass ratio, individual droplet charge and the ratio of droplet charge to the Rayleigh charge limit have been presented for almost all of the influencing electrical and mechanical parameters such as applied voltage, air flowrate, liquid flowrate, liquid conductivity, liquid dielectric constant, nozzle dimensions, cylindrical electrode dimensions, and fluid parameters, for example, density, viscosity and surface tension. In the calculation for corona charging of droplets, the effect of the droplets on corona current and corona-onset voltage has been assessed for first time. The introduction of the Sauter mean diameter of the sprays, D32 , makes the assessment possible. Theoretical calculations for induction charging of liquid jets have shown that provided liquids have a conductivity value higher than the critical value, s = - 10 4 S/m, then they can be charged satisfactorily by the induction charging method. Among all of the influencing parameters, the electrical and mechanical parameters determine the charging rate and the water spray charge level. The suitability of employing these two charging mechanisms to dust suppression in coal mine has been evaluated based on the spray charge level, safety issues and the simplicity or otherwise of the equipment. The induction charging method was considered to have advantages over its corona charging counterpart, and has been chosen for charging the water sprays in the experiment program. Water has a conductivity of s = - 10 2 S/m, higher than the critical value, s = - 10 4 S/m. Based upon theoretical considerations, it is concluded that water is an appropriate liquid for corona charging, based on its dielectric constant, and for induction charging, based on its conductivity. In order to facilitate the testing of electrostatically charged water spray cloud parameters, a spray charger/collector was designed and constructed by others and a computerised data acquisition system has been employed. According to the theory developed for induction charging, the optimum length of the charging electrode has been analysed based upon the assumption that water jet is first charged and then the charged jet is disintegrated into charged droplets by the high pressure air. An experimental program examined the dependence of spray current upon four parameters: air flowrate, water flowrate, applied voltage and jet diameter. The experiments have shown that the induction-charged air-atomising nozzle used in the experiment is able to impart a significant charge into the water sprays. The spray charge-to-mass ratio calculated based upon the measured spray current demonstrates the same characteristics as predicted by theory: increasing with air flowrate, decreasing with water flowrate, increasing with applied voltage to a peak value then decreasing with further increase in the voltage, and increasing with jet diameter. A successful interpretation of an important phenomenon in the inductioncharged air-atomising a water jet, that spray charge-to-mass ratio and spray current increase with air pressure (or air flowrate) and decrease with increasing water flowrate, has been achieved based on the theories developed in this thesis. This phenomenon occurs because increasing air flowrate and/or decreasing water flowrate leads to a higher velocity of jet flowing through the induction electrode. However, when water flowrate becomes very small, a decrease in spray current with increasing air pressure (or flowrate) may be caused both by jet breakup inside the electrode and by contraction of the jet. In order to verify the theory, a preliminary comparison of experimental data with theoretical predictions employing a constant kic in the air-jet interaction coefficient a which was assumed to be 0.7 has shown a general agreement. However, the value of kic appears to be related to jet diameter, air/water mass ratio and applied voltage. An empirical equation for kic has then been formulated based on the experimental data for the spray charge-to-mass ratio. Finally a comparison of experimental results with theoretical predictions using the formulated kic shows an improved agreement. It is concluded that the induction-charged air-atomising nozzle has a potential application in dust suppression in coal mines, as the voltage required to charge water sprays is only 1000 ~ 1200 volts, and that the theory developed for induction charging of water sprays can be used to guide laboratory investigations and design processes for dust suppression and other industrial applications which might employ the electrostatic charging of liquid sprays.

No description available.