The effect of particle size distribution (PSD) on the performance of a fluidized bed reactor was investigated using the ozone decomposition reaction, combined with the study of hydrodynamics, for fresh and spent fluid cracking catalysts, each having three particle size distributions - wide, narrow and bimodal - all with nearly the same mean diameter (60 µm), the same particle density and the same BET surface area. The superficial gas velocity was varied from 0.1 to 1.8 m/s to include the bubbling, slugging, turbulent and fast fluidization regimes. The catalytic rate constant, based on the volume of the particles, ranged from 2 to10 s⁻¹, while the static bed height was varied from 0.15 m to 1 m. Four different multi-orifice gas distributors with different hole diameters (2.2 to 5.1 mm) and hole numbers (4 and 21) were also tested to evaluate the influence of gas distributor on the performance of fluidized bed reactors. The particle size distribution was found to play a larger role at higher gas velocities than at lower velocities. At low gas velocities (Uf ≤ 0.2 m/s), the reaction conversion was not greatly affected by the PSD. However, with an increase in gas velocity the PSD effect became larger. The wide size distribution gave the highest reactor efficiency, defined as the ratio of the volume of catalyst required in a plug flow reactor to that required in the fluidized bed reactor to achieve the same conversion, while the narrow blend gave the lowest. The differences are not solely a function of the "fines content". The influence of particle size distribution on the hydrodynamics of fluidization was evaluated by measuring particle concentrations in voids, bubble sizes, and dense phase expansion. When the superficial gas velocity exceeded 0.1 m/s, the bed with the wide size distribution usually gave the highest particle concentration inside the voids, the smallest bubble size and the greatest dense phase expansion at the same operating conditions. There is evidence that there is a greater proportion of "fines" present in the voids than in the overall particle size distribution. This has been explained in terms of the throughflow velocity inside bubbles being of the same order as the terminal velocity of typical "fines", causing these particles to spend longer periods of time inside the voids. The effect of the PSD on the fluidization regime and its transitions was determined by measuring pressure fluctuations along the column. The earliest transition from bubbling or slugging to turbulent fluidization occurred in the bed of wide size distribution, while the latest corresponded to the narrow PSD. For particles of wide size distribution, higher conversion was achieved for the turbulent and fast fluidization regimes than for the bubbling fluidization regime under otherwise identical conditions, while for particles of narrow size distribution, the dependence of conversion on regime was small. Hence, for reactors of wide PSD, the performance can be improved significantly by operating in the turbulent or fast fluidization regime, while for particles of narrow size distribution, the benefit of operating at high gas velocity is slight at best. The PSD influence should be considered in modelling fluidized bed reactors. The "Two-Phase Bubbling Bed Model" has been modified to account for PSD effects. For the reactor of wide particle size distribution operated at high gas velocities, a single-phase axial dispersion model with closed inlet and open outlet boundary conditions appears to be suitable to predict the performance. It was also found that a high pressure drop across the gas distributor was not sufficient to maintain good performance of the distributor. The reactor efficiency in the entry region was higher for a distributor with a greater number of orifices, even though it had a lower pressure drop, than for a distributor plate with fewer larger holes. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

In gas-solid fluidized bed reactors, such as those employed for polyethylene production, the generation of electrostatic charge is almost unavoidable. Electrostatic charges are generated due to the continuous contacts between particles and particles and the reactor wall. In such processes, accumulation of electrostatic charge causes a layer of particles to adhere to the reactor wall, a problem known as “sheeting” in polyolefin industry. Sheeting results in frequent reactor shutdowns for clean-up and in turn significant economic loss. The overall focus of this research is to better understand the underlying mechanisms of charge generation in gas-solid fluidized beds to ultimately be able to find means to reduce or eliminate this problem. The specific objective of this thesis is to determine the effect of fluidizing particle size on the degree of bed electrification and reactor wall coating. The experimental program involved the fluidization of polyethylene resins received directly from commercial reactors (i.e., having a wide size distribution of 20-1500 micron), as well as mono-sized large particles (600-710 micron) and binary mixture of small particles (200-300 micron and 300-425 micron with fractions up to 20 wt%) and large particles (600-710 micron). Experiments were carried out under atmospheric conditions in 3D fluidization columns housing two Faraday Cups for electrostatic charge measurement. For all conditions, the charge, mass and size distribution of particles fouled on the reactor wall as well as the layer thickness were measured and compared. Fluidization of the resins as received resulted in a certain size of particles (400 µm and smaller) to adhere to the column wall. For binary mixtures, the particles layer formed on the reactor wall mainly consisted of the smaller particles. Although the extent of wall coating declined as the amount of the smaller particles increased, but the smaller particles had a much higher net specific charge and thus replaced the large particles within the wall coating. Such high charge of small particles accumulated on the column wall in turn prevented the wall coating growth due to repelling the oppositely charged particles to the bulk of the bed. Regardless of the charge polarity of the bulk and wall particles, the wall fouling formation mechanism was found to be similar. Between the two sizes of small particles tested, the 212-300 micron particles gained a higher net specific charge than 300-425 micron particles. Bipolar charging due to small and large particles contacts was detected within the bulk of the bed and the wall coating.

The world is experiencing a growing demand for miniaturised products. Micro-milling, using carbide micro tools has the potential for direct, economical manufacture of micro parts from a wide range of workpiece materials. However, in previous studies several critical issues have been identified that preclude the direct application of macro machining knowledge in the micro domain through simple dimensional analysis. The research presented in this thesis focused on some of the areas that require development of the scientific knowledge base to enable determining improved microscale cutting performance. In the mechanical micro machining of coarse grained materials, the programmed undeformed chip thickness can be lower than the length scale of the workpiece grains. Moreover, when the microstructure of such materials is composed of more than one phase, the micro cutting process can be undertaken at a length scale where this heterogeneity has to be considered. Driven by this challenge, the material microstructure 'size effect' on micro-machinability of coarse grain steel materials was investigated in this PhD. In this regard, a predominantly single phase ferritic workpiece steel material and another workpiece material with near balanced ferrite/pearlite volume fractions was studied over a range of feedrates. The results suggested that for micro machined parts, differential elastic recovery between phases leads to higher surface roughness when the surface quality of micro machined multiphase phase material is compared to that of single phase material. On the other hand, for single phase predominantly ferritic materials, reducing burr size and tool wear are major challenges. In micro machining the so called 'size effect' has been identified as critical in defining the process performance. However, an extensive literature search had indicated that there was no clear reported evidence on the effect of process variables on driving this size effect phenomenon. It is often assumed in literature that the un-deformed chip thickness was the main factor driving the size effect. This limit manufactures to only altering the feedrate to try and influence size effect. To explore the significance of a range of inputs variables and specifically, cutting variables on the size effect, micro cutting tests were conducted on Inconel 718 nickel alloy. Taguchi methodology along with signal processing techniques were applied to micro milling acoustic emission signals to identify frequency/energy bands and hence size effect specific process mechanism. The dominant cutting parameters for size effect characteristics were determined by analysis of variance. These findings show that despite most literature focussing on chip thickness as the dominant parameter on size effect, the cutting velocity is a dominant factor on size effect related process performance. This suggests that manipulating the cutting speed can also be a very effective strategy in optimising surface finish in micro machining and in breaking the lower limit of micro machining.In micro machining the lower limit of the process window is set by the minimum chip thickness. Identifying this limit is thus important for establishing the process window. Process windows are valuable guidelines for industrial selection of cutting conditions. Additionally, understanding factors that influence the value of minimum chip thickness is even more important for progressing micro machining capability to the nano-scale machining regime. For this reason, in this PhD study, acoustic emission signatures emanating from microscale milling of six different workpiece materials were characterised to identify the rubbing mode and this enabled the identification of the threshold conditions for occurrence of minimum chip thickness. The minimum chip thickness predicted by this novel approach compares reasonably well to the values that exist in published literature. Additionally, the decomposition of raw acoustic signal allowed the determination of energy levels corresponding to deformation mechanisms. The PhD work provides significant and new knowledge on the utility and importance of acoustic emission signals in characterising chip formation in micro machining. A novel method for determining the minimum chip thickness was developed, micro machining chip formation mechanisms were identified and the machinability of coarse grained multiphase material is presented.

To improve upon the understanding and efficiency of the crushing/ i screening process, the Brenda Mines Limited secondary crushing plant was simulated. The plant consists of two stages of crushing, with a single stage of screening employed in closed circuit with the latter crushing stage. Acquisition of plant data was carried out according to full or modified factorial designs intended to cover normal operating ranges. The units sampled include a Symons Nordberg 7 - foot standard cone crusher, a Symons Nordberg 7 - foot short-head cone crusher and two Allis-Chalmers 8ft.x20ft. double deck virbrating screens. Sampling was carried out under conditions as close to steady state as was possible. All samples were screened at the plant using a standarized procedure. Raw data obtained around the screens was later adjusted by means of a least squares technique that assumes all measured values are in error. The models developed to describe both crushing operations are modifications of those used at Mt. Isa Mines Limited. The model parameters were empirically fitted to the observed data. Both models gave satisfactory performance. The model proposed for the vibrating screens was derived from small particle statistics. It is continuous over all size ranges and was judged to perform satisfactorily. Models for the short-head crushers and the screens can be extrapolated approximately twenty percent beyond their fitted data ranges. The fitted models were combined to enable a steady-state simulation of the complete secondary crushing plant. A study of the simulation was performed in accordance with a full factorial design modified to include intermediate ranges. Operating variables whose values were generated during the simulation remained within their fitted ranges, with the exception of the short-head crusher feedrate. Preliminary analysis of the simulation output shows that the results conform to expected and observed plant behavior. Further analysis with respect to short-head crusher power draw indicates that it may be possible to increase plant capacity under some conditions. The economic advantage of a digital simulation is demonstrated by the fact that the average cost for one computer run is approximately twenty cents. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

As a byproduct of incomplete combustion, soot attracts increasing attentions as extensive researches exploring serious health and environmental effects from soot particles. Soot emission reduction requires a comprehensive understanding of the mechanism for polycyclic aromatic hydrocarbons and of soot formation and aging processes. Therefore, advanced experimental techniques and numerical simulations have been conducted to investigate this procedure. In order to investigate the effects of dimethyl ether (DME) mixing on soot particle size distribution functions (PSDFs), DME was mixed in premixed ethylene/oxygen/argon at flames at the equivalence ratio of 2.0 with a range of mixing ratio from 0% to 30% of the total carbon fed. Two series of atmospheric pressure flames were tested in which cold gas velocity was varied to obtain different flame temperatures. The evolution of PSDFs along the centerline of the flame was determined by burner stabilized stagnation probe and scanning mobility particle sizer (SMPS) techniques, yielding the PSDFs for various separation distances above the burner surface. Meanwhile, the flame temperature profiles were carefully measured by a thermocouple and the comparison to that of simulated laminar premixed burner-stabilized stagnation flame was satisfactory. Additionally, to understand the chemical role of DME mixing in soot properties, characterization measurements were conducted on soot samples using thermo-gravimetric analysis (TGA) and elemental analysis (EA). Results of the evolution of PSDFs and soot volume fraction showed that adding DME into ethylene flame could reduce soot yield significantly. The addition of DME led to the decrease of both the soot nucleation rate and the particle mass growth rate. To explain the possible mechanism for the observation, numerical simulations were performed. Although DME addition resulted in the slight increase of methyl radicals from pyrolysis, the decrease in acetylene and propargyl radicals inhibited the production of polycyclic aromatic hydrocarbons. At the same time, the addition of DME gave rise to the increase of the flame temperatures, which favored the production of OH radicals. The incremental concentration of OH radicals promoted the oxidation rate of soot particles. Additionally, soot samples from flames with higher DME mixing ratios showed higher O/C, H/C mass ratios and thus better oxidation characteristics. In summary, the addition of DME reduces soot emission in two ways: on the one hand, it inhibits soot nucleation and mass/size growth, then the production of soot particles decreases; on the other hand, it promotes soot oxidation process by increasing the concentration of OH radicals and improving the oxidation behavior of the soot particles, then more particles are oxidized. Both of them are responsible for the reduction of soot emissions at the presence of DME.

We examine the hypothesis that firm size affects the sensitivity of bank term loan maturity to its underlying determinants. As borrower size increases, negotiating power with the lender and information transparency increase, while the lender is able to spread the fixed costs of loan production across a larger dollar value of the loan. We find strong evidence of firm size dependency in the determinants of bank term loan maturity and show that this is unrelated to syndication. Only large borrowers can manipulate bank loan contract terms so as to increase firm value.

The purpose of this study was to explore the impact of class size reduction (CSR) on student performance while implementing Common Core State Standards (CCSS). The researcher sought to examine test scores specifically in 1st grade classrooms during the 1st year implementation of CCSS. Additionally, the researcher wanted to assist school leaders in identifying ways to motivate teachers to perform at the highest level and focus on student outcomes. The results indicated that students in the CSR classes had higher scores than the students in the non-CSR classes in some subjects. The findings from this study were consistent with the studies in the literature. There was a difference in the pre-test scores and the post-test scores of the CSR and non-CSR. The post-test scores were higher for the students enrolled in the reduction classes. School leaders should consider reducing class size and find a balance between CCSS and the Mississippi frameworks. This challenge will require the support and understanding of the entire learning community and other key members of the educational community. School leaders will be primarily responsible for ensuring this new initiative is put into practice at a high level of rigor to ensure that students are prepared for college and/or a career.

There is renewed interest in cotton performance grown using various row spacings and plantings patterns in the Midsouth. Cotton seed size has been reduced compared to sixty years ago. Planting smaller seeds is concerning due to having less energy for emergence as well as complicating the ginning process. Two row spacings, two planting patterns, and two cotton varieties were evaluated over eight site years from 2019-2020. The solid planting pattern produced a higher yield on a land area basis. In addition, two varieties, each with three seed counts, were planted at three seeding rates and evaluated over six site years from 2019-2020. Greater seedcotton yields were observed from larger seed sizes and higher seeding rates. Row spacing had no impact on yield but depending on input cost, a 2x1 skip pattern could be beneficial. Also, higher seeding rates and larger seeds maximized yields.

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