David S. Nobes

Mixing characteristics of axisymmetric free jets from a contoured nozzle, an orifice plate and a pipe

The differences in mixing performance between axisymmetric turbulent jets issuing from three common types of nozzle, viz. a contoured (or smooth contraction) nozzle, a sharpedged orifice and a long pipe, are investigated. The investigation is carried out using both qualitative flow visualizations and quantitative measurements of the centerline passive temperature. It is revealed that the jet issuing from an orifice plate provides the greatest rate of mixing with ambient fluid, while the pipe jet has the lowest rate. Physical insight into the differences is explored using a planar imaging technique and measurements of power spectra of the fluctuating velocity

Measurement and prediction of NOx emissions from unconfined propane flames from turbulent-jet, bluff-body, swirl, and precessing jet burners

The relationships among flame radiation, NOx emissions, and residence time are explored for unconfined propane turbulent diffusion flames with widely dissimilar mixing characteristics. Variations in mixing of a turbulent-jet were achieved at constant initial conditions using coaxial air through swirl and bluff-body burners and using a precessing jet burner to allow the separate effects of jet Froude number and flame temperature to be explored. A wide range of flame types were produced, from the strongly radiating and sooting flame of the precessing jet burner, which is buoyancy dominated, through recirculation-zone-dominated bluff-body and swirl flames, for which partial quenching of the reactions occurs. It was found that the radiant fraction scales with residence time for all the flames, suggesting a relationship between Froude number and global flame temperature. The importance of flame temperature, and hence thermal NOx, in all flames is demonstrated. The NOx emission indices from these flames are well correlated with the residence time and non-adiabatic flame temperature, demonstrating that the role of flame radiation is significant. Departure from purely thermal NOx predictions for high-temperature recirculation-zone-dominated flames is attributed to the poor correlation of the reaction-zone volume with the flame volume of this class of flames. Departure for the most radiant, and hence lowest temperature, flames is attributed to increased relative significance of the prompt mechanism.

Investigation into the selection of viewing configurations for three-component planar Doppler velocimetry measurements

A method for the calculation of three orthogonal velocity components in planar Doppler velocimetry (PDV) using four or more measured velocity components (to the three typically used) is presented. The advantages and disadvantages are assessed by use of a Monte Carlo simulation and experimental measurements of the velocity field of a rotating disk. The addition of a fourth velocity component has been shown to lead to reductions in the final errors of up to 25%. The selection of viewing configurations for experiments is discussed by simulation of the level of errors in measured velocity components and investigation of the final level of errors in the orthogonal velocity components. Experimental measurements of the velocity field of a rotating disk are presented, demonstrating the effect of the viewing configuration on the final level of error.

Two-frequency planar Doppler velocimetry (2ν-PDV)

A planar Doppler velocimetry (PDV) system has been designed which is able to generate two beams from a single source separated in frequency by 690 MHz. This allows a common-path imaging head to be constructed, using a single imaging camera instead of the usual camera pair. Both illumination beams can be derived from a single laser and a set of acousto-optic modulators used to affect the frequency shifts. One illumination frequency lies on an absorption line of gaseous iodine, and the other in a region of zero absorption. The beams sequentially illuminate a plane within a seeded flow and Doppler-shifted scattered light passes through an iodine vapor cell onto the camera. The reference beam that lies in a zero absorption region is unaffected by passage through the cell, and provides a reference image. The signal beam, the frequency of which coincides with an absorption line, encodes the velocity information as a variation in transmission dependent upon the Doppler shift. Images of the flow under both illumi...

Bioconversion of coal: new insights from a core flooding study

A pressurized core flooding experiment was performed to better understand in situ coal bioconversion processes. The core flooding experiment was conducted using a biaxial core holder packed with subbituminous coal particles (250–150 μm grain size) obtained from the Highvale mine in Alberta, Canada. The coal pack was inoculated with a methanogenic microbial culture enriched from coal and was continuously flooded with mineral salt medium and an organic carbon/nitrogen nutrient supplement (tryptone). The changes in the physical properties of the coal pack during the core flooding suggested coal bioconversion to methane under the experimental conditions. Colonization and bioconversion of coal by microbes was evident from the change in core permeability and presence of metabolites and gas (CH4 and CO2) in the effluent. A total of 1.52 μmol of CH4 was produced per gram of coal during the 90 days experiment at 22 °C. Signature metabolites consistent with anaerobic biodegradation of hydrocarbons, e.g., carboxylic acids, were identified in effluent samples throughout incubation. The transient nature of metabolites in effluent samples supports fermentation of coal constituents and nutrient supplement to simple molecules such as acetic acid, which served as a substrate for methanogenesis during the bioconversion process. Accumulation of carboxylic acids such as succinic acid in the effluent also demonstrates that the coal bioconversion process may be used for extraction of other value-added products apart from CH4 generation. Importantly, results presented here suggest that coal bioconversion by biostimulation under reservoir conditions is a scalable technology with potential for energy generation and for overall reduction of greenhouse gas emissions.

Determination of view vectors from image warping mapping functions

The measurands of several reported laser-based measurement techniques are sensitive to both the propagation direction of the laser and the viewing direction from the region of interest to the detector. For such imaging techniques, the view vector must be determined uniquely for each pixel in the detector array. The bulk view vector is often physically measured and a simple model used to determine the view vector for each pixel. This, however, has limitations where access is limited, the distances involved are small, or the optical system employed introduces errors. We describe a procedure to determine the unique view vector from a planar region to the detector (CCD camera) for each element in a 2-D array based on a reference target aligned with the planar region of interest. Determination of the view vector is based on the spatial distribution of the mapping function used to dewarp the view. No physical measurement of the view vector is required. Good agreement is achieved when the procedure is compared to a simple pin-hole camera model of the view using a computed test target.

An investigation into the mechanical characteristics of select self-ligated brackets at a series of clinically relevant maximum torquing angles: loading and unloading curves and bracket deformation

Edgewise orthodontic treatment utilizes a force couple in order to achieve labial-lingual tooth angulation. Two self-ligating brackets (Damon Q and Speed) were examined across a range of clinically relevant torques in order to assess the loading and unloading curves and bracket deformation. A previously developed torquing and load measurement system was utilized to rotate a 0.199 × 0.25 in stainless steel wire in a fixed bracket slot to the following angles: 16, 20, 24, 28, 32, and 40 degrees. The torque on the bracket was measured during both wire loading and unloading cycles. The torque play for the Damon brackets was determined to increase by less than 0.4 degrees when torqued to 70 Nmm, whereas the increase for the Speed brackets was 2.1 degrees at the same torque magnitude. The deformation curves for the Damon and Speed brackets were found to be different for loading and unloading. Speed brackets were found to start to plastically deform when torqued to 24 degrees (26 Nmm of torque), while Damon brackets did not plastically deform until 28 degrees (38 Nmm of torque). Damon brackets were found not to plastically deform as easily and to have a smaller increase in torque play than Speed brackets. Both the Damon and the Speed brackets demonstrated minimal effect of plastic deformation and torque play at maximum angles of twist less than 20 degrees. Torque measured in the brackets was different for loading and unloading.

Measurement of Orthodontic Bracket Tie Wing Elastic and Plastic Deformation by Arch Wire Torque Expression Utilizing an Optical Image Correlation Technique

Orthodontic lingual root movement (torque) is an important aspect of treatment biomechanics and is typically achieved by torsion of a rectangular wire within the orthodontic bracket slot which introduces a force couple. The magnitude of the force moment achieved by wire torsion may be influenced by deformation of the orthodontic bracket. A device utilizing an optical image correlation technique has been developed to accurately quantify bracket slot dimensional changes during application of wire torsion. Simultaneous torque moment magnitude, degrees of wire twist, and bracket slot dimension data can be gathered. Bracket tie wing elastic deformation when loaded was demonstrated and plastic deformation was also observed with a single rotation of the wire.

Analysis of the Particle Formation Process of Structured Microparticles

The particle formation process for microparticles of cellulose acetate butyrate dried from an acetone solution was investigated experimentally and theoretically. A monodisperse droplet chain was used to produce solution microdroplets in a size range of 55-70 μm with solution concentrations of 0.37 and 10 mg/mL. As the droplets dried in a laminar air flow with a temperature of 30, 40, or 55 °C, the particle formation process was recorded by two independent optical methods. Dried particles in a size range of 10-30 μm were collected for morphology analysis, showing hollow, elongated particles whose structure was dependent on the drying gas temperature and initial solution concentration. The setup allowed comprehensive measurements of the particle formation process to be made, including the period after initial shell formation. The early particle formation process for this system was controlled by the diffusion of cellulose acetate butyrate in the liquid phase, whereas later stages of the process were dominated by shell buckling and folding.

Orthodontic Bracket Manufacturing Tolerances and Dimensional Differences between Select Self-Ligating Brackets

In all manufacturing processes there are tolerances; however, orthodontic bracket manufacturers seldom state the slot dimensional tolerances. This experiment develops a novel method of analyzing slot profile dimensions using photographs of the slot. Five points are selected along each wall, and lines are fitted to define a trapezoidal slot shape. This investigation measures slot height at the slots top and bottom, angles between walls, slot taper, and the linearity of each wall. Slot dimensions for 30 upper right central incisor self-ligating stainless steel brackets from three manufacturers were evaluated. Speed brackets have a slot height 2% smaller than the nominal 0.559 mm size and have a slightly convergent taper. In-Ovation brackets have a divergent taper at an average angle of 1.47 degrees. In-Ovation is closest to the nominal value of slot height at the slot base and has the smallest manufacturing tolerances. Damon Q brackets are the most rectangular in shape, with nearly 90-degree corners between the slot bottom and walls. Damon slot height is on average 3% oversized.