Yes / To date, mixing design practice in anaerobic digestion has focussed on biogas production, but no adequate consideration has been given to energy efficiency. A coherent, comprehensive and generalized strategy based on computational fluid dynamics (CFD) modelling is proposed to improve mixing efficiency of a full-scale, unconfined gas-mixed digester for wastewater treatment. The model consists of an Euler-Lagrange (EL) model where biogas bubbles are modelled as the Eulerian dispersed phase, and non-Newtonian sludge as the Lagrangian continuous phase. Robustness tests show that mixing predictions are independent of bubble size. The CFD strategy comprises the assessment of different mixing geometries and a range of input gas flow rates. Quantitative results show that simple retrofitting measures are able to achieve a significant improvement in the degree of mixing with reduced mixing times, and consequently recommendations for best mixing geometry and gas flow rate are given. A generalization to a generic digester is discussed in a form that is readily usable by professionals and consultants.

An experimental study of an aerodynamic ramp (aeroramp) injector was conducted at Virginia Tech. The aeroramp consisted of an array of two rows with two columns of flush-wall holes that induce vorticity and enhance mixing. For comparison, a single-hole circular injector with the same area angled downstream at 30 degrees was also examined. Test conditions involved sonic injection of helium heated to 313 K, to safely simulate hydrogen into a Mach 4 air cross-stream with average Reynolds number 5.77 e+7 per meter at a jet to freestream momentum flux ratio of 2.1. Sampling probe measurements were utilized to determine the local helium concentration. Pitot and cone-static pressure probes and a diffuser thermocouple probe were employed to document the flow. The main results of this work was that the mixing efficiency value of this aeroramp design which was optimized at Mach 2.4 for hydrocarbon fuel was only slightly higher than that of the single-hole injector at these flow conditions and the mass-averaged total pressure loss parameter showed that the aero-ramp and single-hole injectors had the same overall losses. The natural extension of the investigation was then to look in detail at two major physical phenomena that occurs in a complex injector design such the Aeroramp: the jet-shock interaction and the interaction of the vortical structures produced by the jets injection into a supersonic cross flow. Experimental studies were performed to investigate the effects of impinging shocks on injection of heated helium into a Mach 4 crossflow. It was found that the addition of a shock behind gaseous injection into a Mach 4 crossflow enhances mixing only if the shock is closer to the injection point where the counter-rotating vortex pair (always associated with transverse injection in a crossflow) is not yet formed, and the deposition of baroclinic generated of vorticity is the highest. The final investigation concerned with the interaction of the usual vortex structure produced by jet injection into a supersonic crossflow and an additional axial vortex typical of those that might be produced by the inlet of a scramjet or the forebody of a vehicle to be controlled by jet interaction phenomena. The additional axial vortices were generated by a strut-mounted, diamond cross-section wing mounted upstream of the injection location. The wing was designed to produce a tip vortex of a strength comparable to that of one of the typical counter-rotating vortex pair (CVP) found in the plume of a jet in a crossflow. The profound interaction of supersonic vortices supported by a quantitative description and characterization of the flowfield has been demonstrated. / Ph. D.

A method is developed for experiments with mixtures where the mixture components are categorized (acids, bases, etc.), and each category of components contributes a fixed proportion to the total mixture. The number of categories of mixture components is general and each category will be represented in every mixture by one or more of its member components. The purpose of this paper is to show how standard response surface designs and polynomial models can be used for estimating the response to mixtures of the k mixture components. The experimentation is concentrated in an ellipsoidal region chosen by the experimenter, subject to the constraints placed on the components. The selection of this region, the region of interest, permits the exclusion of work in areas not of direct interest. The transformation from a set of linearly dependent mixture components to a set of linearly independent design variables is shown. This transformation is accomplished with the use of an orthogonal matrix. Since we want the properties of the predictor ŷ at a point w to be invariant to the arbitrary elements of the transformation matrix, we choose to use rotatable designs. Frequently, there are underlying sources of variation in the experimental program whose effects can be measured by dividing the experimentation into stages, that is, blocking the observations. With the use of orthogonal contrasts of the observations, it is shown how these effects can be measured. This concept of dividing the program of experiments into stages is extended to include second degree designs. The radius of the largest sphere, in the metric of the design variables, that will fit inside the factor space is derived. This sphere provides an upper bound on the size of an experimental design. This is important when one desires to use a design to minimize the average variance of ŷ only for a first-degree model. It is also shown with an example how with the use of the largest sphere, one can cover almost all combinations of the mixture components, subject to the constraints. / Ph. D.

An attempt has been made to find a new mixing-length model which will account for the effects of compressibility on the turbulence. Through an analysis of the Reynolds-stress formula and following the ideas of Prandtl’s original mixing-length hypothesis, the effort has essentially been directed to classes of compressible flow problems where there exist large changes of density and Mach number. The new mixing-length model which has been found here is a generalization to include gradients of Mach number, pressure and density; and the local parameters values, such as speed of sound, density, Mach number, ratio of specific heats and a new parameter S which is introduced in the new turbulent transport formula. The new parameter S acts like an effective turbulent Schmidt Number for mixtures of gases or a turbulent Prandtl Number for a homogeneous gas. The new turbulent model and Prandtl’s original model are both applied to six test cases including: tangential slot injection problems, the very complex cases of shock-wave/turbulent shear-layer and boundary-layer interactions, and high Mach number turbulent boundary layer flows over a flat plate. The effective numerical method of flux-splitting with Roe’s scheme has been adopted in the present work. The results are all compared with experimental data. The predictions with the new mixing-length model are generally in good agreement with the measured data. The predictions with Prandtl’s original model have some discrepancies, especially for heated injection and higher Mach number turbulent boundary layers. The inability of Prandtl's model to predict the spreading rate of the free shear layer in slot injection into supersonic flows and higher Mach number turbulent boundary layer flows is due to the occurrence of large density changes which are not accounted for in the original Prandtl model. The new mixing-length model obtained here is the first to explicitly include these effects, and the results obtained show that these effects are important. / Ph. D.

An experimental investigation of a flush-wall, diamond-shaped injector was conducted in the Virginia Tech supersonic wind tunnel. The diamond injector was elongated in the streamwise direction and is aimed downstream angled up at 60° from the wall. Test conditions involved sonic injection of helium heated to approximately 313 K into a nominal Mach 4.0 crossstream airflow. These conditions are typical of a scramjet engine for a Mach 10 flight, and heated helium was used to safely simulate hydrogen fuel. The injector was tested at two different injectant conditions. First, it was investigated at a baseline mass flow rate of 3.4 g/s corresponding to an effective radius of 3.54 mm and a jet-to-freestream momentum flux ratio of 1.04. Second, a lower mass flow rate of 1.5 g/s corresponding to an effective ratio of 2.35 mm and a jet-to-freestream momentum flux ratio of 0.49 was studied. The diamond injector was tested both aligned with the freestream and at a 15° yaw angle for the baseline mass flow rate and aligned with the freestream at the lower mass flow rate. For comparison, round injectors angled up at 30° from the wall were also examined at both flow rates. A smaller round injector was used at the lower mass flow rate such that the jet-to-freestream momentum flux ratio was 1.75 for both cases. A concentration sampling probe and gas analyzer were used to determine the local helium concentration, while Pitot, cone-static and total temperature probes were used to determine the flow properties. The results of the investigation can be summarized as follows. For the baseline case, the aligned diamond injector penetrated 44% higher into the crossflow than did the round injector. The addition of yaw angle increased the crossflow penetration to 53% higher than the round injector. The aligned diamond injector produced a 34% wider jet than the round injector, while the addition of yaw angle somewhat reduced this widening effect to 26% wider than the round injector. The aligned and yawed diamond injectors exhibited 10% and 15% lower mixing efficiency than the round injector, respectively. The total pressure loss parameter of the aligned diamond was 22% lower than the round injector, while the addition of yaw angle improved the total pressure loss parameter to 34% lower than the round injector. For the lower mass flow (and momentum flux ratio) case, the diamond injector demonstrated 52% higher penetration and a 39% wider plume than the round injector. The mixing efficiency was nearly identical between the two injectors with just a 4% lower mixing efficiency for the diamond injector. The total pressure loss parameter of the diamond injector was 32% lower than round injector. These results confirm the conclusions of earlier, lower free stream Mach number and higher molecular weight injectant, studies that a slender diamond injector provides significant benefits for crossflow penetration and lower total pressure losses. / Master of Science

Yes / When compounding polymers with additives to develop materials at specifications (colouring plastics is the simplest example), the difficulties is in getting the formulation right the first time. Also, when developing completely new materials such as in nanotechnology applications, there is a need to do the initial trials safely and with as small quantities as possible to enable a wide range of experimentation. Wiith traditional applications, often the initial compounding formulation is done using small single or twin screw extruders but with machines that have a fair output to instruct the large scale operation. This step is costly in material wastage and time but more importantly it often does not provide the right formulation which in turn results in bigger wastage cost at the industrial scale before the right formulation is eventually obtained. With the very new material formulations, any reduction in cost of development is always essential. With these aims in mind, we have developed a new minimixer capable of handling tiny quantities of order 10-100g but the minimixer is capable of reproducing the very high mixing conditions experienced in large machines. This invention provides a new opportunity to develop new products quickly, safely and cheaply. The application is not restricted to polymers and can be extended to other soft materials. It has also other spin-offs as a research tool for studying mixing and developing new, more efficient, mixing flows. In this paper we explain the principle of operation we have engineered to produce such intense mixing. Basically, the device is based on combining two opposing flows: a single screw extruder circulation flow with a twin screw extruder mixing flow. The mixing is carried out as a batch but on its completion, the single screw extruder flow is reversed and becomes co-current with the twin extruder flow to enable the discharging of the batch through a die. In the paper we present mixing data obtained with various polymer-additive combinations tested in the minimixer under various conditions of screw speeds, mixing times and temperatures and at the larger scale to underpin the operation of this novel mixer. The quality of mixing of the extrudate was measured using a variety of methods depending on applications: using image analysis of microtome sections of the extrudate or of blown film samples produced from the formulations or measuring electrical properties.

Cyanobacteria are a naturally occurring component of reservoir aquatic ecosystems. Given that some species possess the ability to control their depth within the water column, they have a competitive advantage over other species of photosynthetic organisms. This leads to the potential for cyanobacteria blooms, and because of taste and odor problems, as well as possible toxin production associated with certain species of cyanobacteria, these organisms can cause major problems in drinking water production. The Western Virginia Water Authority installed a solar-powered circulator in Falling Creek Reservoir, located in Bedford County, Virginia, in an attempt to limit the growth of these organisms through limiting light exposure by circulating them deeper within the reservoir. Experiments were performed during the summer of 2008 to quantify the effect of the circulator on the reservoir. Temperature, dissolved oxygen, water velocity, and photosynthetic yield were monitored before and during operation of the unit. The overall effect of the mixer was limited to the first 10 m immediately adjacent to the unit during the afternoon. The effect was stronger during the morning when the difference in density between the intake water and the surface of the reservoir was smaller, allowing the water to travel up to 80 m away from the unit. Although the circulator was only intended to mix and possibly deepen the epilimnion, the entire reservoir became mixed about two weeks after the circulator was put into operation. The reservoir is quite shallow, leading to a weak stratification that is easily disrupted by the operation of the circulator. / Master of Science

A four unit helical conveyor type mixer with cut and folded elements built by L. C. Peery at Virginia Polytechnic Institute in 1939 was tested. Preliminary investigations, made before tests to obtain pertinent data were begun, showed the advisability of straightening these folds. The purpose of this was to prevent all of the mixing action from occurring in the first unit and to show an incomplete picture of the mixer operation. These preliminary investigations also showed the maximum particle size usable in the mixer without obtaining excessive size reduction during mixing. In addition to the above, the investigations showed that in tests where a difference in the density of these materials existed as well as a difference in their crystalline structure, irregularities in the mixing data obtained under these conditions could be attributed more to the difference in density than to the difference in the crystalline structure of the materials. On this basis, tests made on the screw conveyor mixer with the available materials were titled as studies of the effect of a difference in density on mixing. The first tests on the mixer were made with chert and copper sulfate to determine the effect of speed of elements, feed rate, feed proportions, and particle size on mixing efficiency. These materials were relatively inexpensive and the copper sulfate was readily leached from the samples to form a basis for weight analysis of samples. In the tests to determine the effect of a difference in density on mixing efficiency the materials used were barytes, andalusite and chert with copper sulfate, which is the only soluble material of the four listed. The procedure followed is as follows: the particle size, density, and weight of the two materials to be used were recorded. These materials were fed into the mixer and at given time intervals samples were taken at the sampling ports and discharge opening. The feed time, time of the run, rpm. of the mixer elements, average time between samples and weight of material in the system were taken. These samples were analyzed and families of curves drawn to show the relationship of variations in the variable factors to mixing efficiency. Results show that a mixing element speed up to 56 rpm. and above 108 rpm. gave the most efficient mixing with feed rates below three cubic feet per hour and above nine cubic feet per hour. The optimum particle size was in the range from twenty to fifty mesh with feeds of approximately equal percentages by weight of the two materials showing the best mixing efficiency at 108 rpm. At a speed of 56 rpm. the relationship of feed proportions to mixing efficiency was not definitely established. The efficiency of mixing varied inversely with the difference in density at a speed of 108 rpm. and showed the apparent reverse of this at 56 rpm, but dispersion of the materials in each other at this speed was very poor. With materials of 16 mesh size, the size reduction taking place during mixing is negligible, but with materials of 4 mesh size there is an appreciable amount of size reduction taking place. Equations, holding within specified limits and showing the effect of each variable factor on mixing efficiency, were derived. / Master of Science

Stroboskoptiska sirener använder en kombination av ljus och ljudsignalerför att förmedla information till användaren om en viss situation eller före-liggande fara. Produkten kan kommunicera information med hjälp av ljusmed ett antal olika färger, skapat av LED-dioder. Genom ökande av an-talet färger kan även mängden information som produkten kan förmedlaöka. Med LED-dioder av färgerna RGB (Röd-Grön-Blå) möjliggörs ska-pandet av alla nyanser inom det synliga spektrumet. Metoden kallas föradditiv färgblandning och används vanligen inom belysningsindustrin. Medmetoden kommer utmaningar. Dioderna måste placeras med ett exceptio-nellt kort avstånd jämte varandra för att blanda ljusstrålarna och skapaen homogen ljusbild. Det korta avståndet är kostsamt att uppnå, vilketresulterar i att yttre områden i ljusbilden har individuellt synliga färger.Dessa genomträngande färger, färgskuggor, ger upphov till ett inhomogentljus. Speciellt är detta synligt när alla tre färger lyser för att skapa vitt ljus.Det finns olika metoder för att underlätta den additiva färgblandningenfrån LED-dioder för att öka homogeniteten i ljuset. Exempel på meto-der för att uppnå homogenitet är med optiska geometriska linser, materialmed Scattered photon extraction technique (SPE) och reflektorer. Studienomfattar framtagning, testning och utvärdering av koncept från dessa tremetodkategorier. Lösningarna är testade och utvärderade utifrån påverkanpå synlig ljusbild, påverkan på ljusintensitet mätt med luxmätning och på-verkan på färgbilden med navigering i CIE-diagram. Studien visade att enavsevärd minskning av färgskuggor uppnåddes med två lager av SPE ma-terial. Liknande resultat uppnåddes med reflektorer, däremot minskade dåden upplysta arean. Två lager SPE material påverkade ljusintensiteten ne-gativt emedan reflektorer ökade ljusintensiteten. Geometriska linser gav ettmindre fördelaktigt resultat. De uppvisande tydlig dispersion av färgernaoch uppkomst av rutmönster i ljusbilderna

無 / The purpose of this study is; to review literature on bilingual speech and advertising and summarize the functions of the use of English in advertising; and conduct a content analysis to study the functions in print advertisements in two Taiwanese magazines (ViVi and Business Weekly) as well as to find correlations between advertisement attributes (country-of-origin, parts of an ad, product categories, and advertising appeals) and the functions. First, past literature in advertising and linguistics are reviewed. In summary, there are six code-mixing functions of the use of English in advertising in linguistic aspects, which include: 1) Referential Function, 2) Poetic Function, 3) Direct Quotation Function, 4) Reiteration Function, 5) Ease of Expression Function, and 6) Euphemism Function. Then, print advertisements in two Taiwanese magazines (ViVi and Business Weekly) will be analyzed in the content analysis. There are five research questions: 1) To what extent are the functions of the use of English present in print ads in magazines?, 2) Are there any correlations between country-of-origin and the functions?, 3) Are there any correlations between the parts of an ad and the functions?, 4) Are there any correlations between product categories and the functions?, 5) Are there any correlations between advertising appeals and the functions? The content analysis showed that all six functions were present in print advertising in Taiwan, with Ease of Expression Function to be the most frequent one, and Euphemism to be the least. The results also showed that there are correlations between the parts of an ad (slogan, headlines and subheadlines, and body copy) and the functions, but no correlations were found between country-of-origin and the functions, or between advertising appeals and the functions.