This thesis presents a comprehensive study of the ice particle production process through experimentation and numerical methods using computational fluid dynamics (CFD) that can be used to produce ice particles with controlled temperature and hardness for use in ice jet (IJ) process for industrial applications. The analytical and numerical modeling for the heat exchanger system are developed that could predict the heat, mass and momentum exchange between the cold gas and water droplets. Further, the feasibility study of the deployment of ice particles produced from the ice jet system for possible cleaning and blasting applications are analyzed numerically. Although the use of Abrasive Water Jet (AWJ) technology in cutting, cleaning, machining and surface processing is a very successful industrial process, a considerable amount of secondary particle waste and contamination impingement by abrasive materials has been an important issue in AWJ process. Some alternate cryogenic jet methods involving vanishing abrasive materials, such as plain liquid nitrogen or carbon dioxide have been tried for these applications, but they also suffer from certain drawbacks relating to the quality, safety, process control and materials handling. The use of ice jet process involving minute ice particles has received relatively little attention in industrial applications. Some researches have concentrated on the studies of effects of Ice Jet outlet parameters of the nozzle and focus tube for machining soft and brittle materials. Most of the work in this area is qualitative and researchers have paid a cursory attention to the ice particles temperature and the efficiency of production of these particles. An extensive investigation to gain insight knowledge into the formulation of ice formation process parameters is required in arriving at a deeper understanding of the entire ice jet process for production application. Experimental investigations were focussed on the measurement of ice particle temperature, phase transitions, ice particle diameter, coalescence and hardness test. The change in ice particle diameter from the inlet conditions to the exit point of the heat exchanger wasinvestigated using the experimental results. These observations were extended to numerical analysis of temperature variations of ice particles at different planes inside the custom built heat exchanger. The numerical predictions were carried out with the aid of visualization studies and temperature measurement results from experiments. The numerical models were further analysed to find out the behaviour of ice particles in the transportation stage, the mixing chamber of the nozzle and focus tube. This was done to find out whether the methodology used in this research is feasible and if it can be used in applications such as cleaning, blasting, drilling and perhaps cutting. The results of the empirical studies show that ice particles of desired temperature and hardness could be produced successfully with the current novel design of the heat exchanger. At the optimum parameters, ice particles could be produced below -60�C, with hardness of particles comparable to gypsum (Moh�s hardness of 1.5 to 3). The visualization studies of the process assisted in observation of the phases of ice at various points along the heat exchanger. The results of numerical analysis were found to agree well with the experiments and were supported by the statistical model assessments. Numerical analyses also show the survival of ice particles at the nozzle exit even with high-pressure, high-velocity water/air mixture.

An analytical dispersion model has been derived to determine the distribution of velocities and concentrations of a tracer in a two-dimensional jet in a coflowing ambient fluid. The particular novelty of this model is that it bridges the gap between near-field (where initial momentum dominates behaviour) and far-field (where ambient turbulence is more important) domains. We describe this domain as the ???intermediate field???. In a literature review of coflowing jets we find several laboratory studies and models which can predict the velocities (and in some cases concentrations) in a 2D jet, however they all have shortcomings. None could fully account for ambient turbulence, and all were strictly near-field, i.e. they are unable to describe behaviour when ambient turbulence dominates the initial shear. A brief review of analytical far-field models was also undertaken. There are standard solutions for the dispersion of a 2D continuous source but none that allow for an initial source momentum or non-uniform velocity. As opposed to the near-field coflow approach used by other researchers we start from the far-field, modifying the simple diffusion models by perturbing the governing equations to allow for the initial momentum. Models are developed for both along-stream velocity and the concentration field of a tracer. From the velocity model, a comparison is made with experimental data available from one researcher (Wang, 1996) and an existing near-field coflow model PJCMERG (Davidson, 1989). The initial conditions (width and excess velocity) for our model are determined by Gaussian curve fitting to an arbitrary point in the near-field. The diffusivity parameter is used to adjust (tune) the model until the centreline velocity profile matches. We can always achieve this match and to a much closer degree than PJCMERG. There are no available laboratory or field data for concentrations of a tracer in a 2D coflowing jet although the near-field model PJCMERG does have a tracer component. We demonstrate how PJCMERG cannot converge to any far-field model, while our model provides a neat transition between the near-field and far-field. We have started the extension of the 2D model to the more common 3D situation although we have yet to carry out any comparisons with other models or data. The model development is included in an appendix for other researchers to pick up.

An analytical dispersion model has been derived to determine the distribution of velocities and concentrations of a tracer in a two-dimensional jet in a coflowing ambient fluid. The particular novelty of this model is that it bridges the gap between near-field (where initial momentum dominates behaviour) and far-field (where ambient turbulence is more important) domains. We describe this domain as the ???intermediate field???. In a literature review of coflowing jets we find several laboratory studies and models which can predict the velocities (and in some cases concentrations) in a 2D jet, however they all have shortcomings. None could fully account for ambient turbulence, and all were strictly near-field, i.e. they are unable to describe behaviour when ambient turbulence dominates the initial shear. A brief review of analytical far-field models was also undertaken. There are standard solutions for the dispersion of a 2D continuous source but none that allow for an initial source momentum or non-uniform velocity. As opposed to the near-field coflow approach used by other researchers we start from the far-field, modifying the simple diffusion models by perturbing the governing equations to allow for the initial momentum. Models are developed for both along-stream velocity and the concentration field of a tracer. From the velocity model, a comparison is made with experimental data available from one researcher (Wang, 1996) and an existing near-field coflow model PJCMERG (Davidson, 1989). The initial conditions (width and excess velocity) for our model are determined by Gaussian curve fitting to an arbitrary point in the near-field. The diffusivity parameter is used to adjust (tune) the model until the centreline velocity profile matches. We can always achieve this match and to a much closer degree than PJCMERG. There are no available laboratory or field data for concentrations of a tracer in a 2D coflowing jet although the near-field model PJCMERG does have a tracer component. We demonstrate how PJCMERG cannot converge to any far-field model, while our model provides a neat transition between the near-field and far-field. We have started the extension of the 2D model to the more common 3D situation although we have yet to carry out any comparisons with other models or data. The model development is included in an appendix for other researchers to pick up.

<p>Since the mid-1990s there has been an active effort to develop hydrocarbon-fueled power generation and propulsion systems on the scale of centimeters or smaller. This effort led to the creation and expansion of a field of research focused around the design and reduction to practice of Power MEMS (microelectromechanical systems) devices, beginning first with microscale jet engines and a generation later more broadly encompassing MEMS devices which generate power or pump heat. Due to small device scale and fabrication techniques, design constraints are highly coupled and conventional solutions for device requirements may not be practicable. </p><p>This thesis describes the experimental investigation, modeling and potential applications for two classes of microscale jet pumps: jet ejectors and jet injectors. These components pump fluids with no moving parts and can be integrated into Power MEMS devices to satisfy pumping requirements by supplementing or replacing existing solutions. This thesis presents models developed from first principles which predict losses experienced at small length scales and agree well with experimental results. The models further predict maximum achievable power densities at the onset of detrimental viscous losses.</p> / Dissertation

The atomization problem of high speed viscous jets has many applications in industrial processes and machines. In all these applications, it is required that the droplets have high surface area/volume ratio meaning that the droplets should be as small as possible. This can be achieved with high rates of turbulence and mixing of the flow. In order to constitute a foresight of geometry eects on droplet size, experimental investigation and the determination of flow characteristics in near and far fields of a low-speed air jet have been performed. In order to fulfill this task, three components of instantaneous velocity are measured, using a triple sensor Constant Temperature Anemometer (CTA) system. Through these measurements, mean velocity, Reynolds stress, velocity decay, spreading rate, turbulent kinetic energy, vorticity, and mass entrainment rate values are obtained. Stress-Strain relationship is also observed. Measurements are obtained for a baseline circular nozzle (round jet) as well as for an equilateral triangular and a square nozzle. On the basis of these measurements, the equilateral triangular jet is found to be the best option in order to get highest turbulence and mixing level with smallest core length.

Shaped charges are explosive devices with a high penetration capability and are used for both civilian and military purposes. In civilian applications shaped charge devices are used in demolition works, oil drilling and mining. In the military applications, shaped charges are used against different kinds of armors, primarily as anti-tank devices. This thesis work involves the modeling and simulation of shaped charge devices, with the focus being on anti-tank warhead design. Both numerical simulation and analytical calculation methods are used to predict shaped charge performance / in the aspects of jet formation, breakup and penetration. The results are compared within themselves and with the data available in the literature. AUTODYN software is used for the numerical simulations. Different solver and modeling alternatives of AUTODYN are evaluated for jet formation and penetration problems. AUTODYN&rsquo / s Euler solver is used to understand how the jet formation is affected by the mesh size and shape and the presence of air as the surrounding medium. Jetting option in the AUTODYN-Euler simulations are used to simulate jet formation as an alternative to simulations performed using AUTODYN&rsquo / s Euler solver. In the jetting option liner elements are modeled as Lagrangian shell elements, rather than Eulerian elements. Analytical codes are written to study the jet formation, breakup and penetration processes. Many alternative formulas that can be used in the analytical calculations are listed and discussed. Parameters of these formulas are varied to investigate their effects on the results. Necessary constants for the analytical formulas are obtained using the results of AUTODYN simulations.

This experiment is to investigate the effects of fluid with and without mass injection through a slit on the vortex shedding from a single cylinder. We research Reynolds Numbers on ranges from 800 to 4000. We used four kinds of ways which contain no mass injection, steady blowing, steady suction and oscillatory jet to study of the wake behind a circular cylinder under excitation in this experiment. No mass injection is measured for the sake of its reliability and comparability of experiment. Steady blowing and suction are applied to influence the wake flow. An oscillatory jet is used to influence the wake flow with varying frequencies and amplitudes. The experiment looks forward to use the results of this experiment so as to research into the effects on the wake flow, including the velocity values of fluctuation and turbulence intensity of the vortices structure, the dominant frequency in the flow pattern on a single cylinder. The main parameters in the study are the frequency, momentum and the location of the blowing and suction jet, which are a steady jet or unsteady oscillatory jet. Flow visualization has been carried out to investigate the interaction of steady or unsteady fluid perturbation and the vortex shedding of a cylinder.

The jet-in-crossflow problem has been extensively studied, mainly because of its applications in film cooling and injector designs. It has been established that in low-speed flows, pulsing the jet significantly enhances mixing and jet penetration. This work investigates the effects of pulsing on mixing and jet trajectory in high speed (compressible) flow, using Large Eddy Simulation. Jets with different density ratios, velocity ratios and momentum ratios are pulsed from an injector into a crossflow. Density ratios used are 0.55 (CH4/air), 1.0 (air/air) and 1.5 (CO2/air). Results are compared with the low speed cases studied in the past and then analyzed for high speed scaling. The simulations show that the lower density jet develops faster than a higher density jet. This results in more jet spread for the lower density jet. Scaling for jet spread and the decay of centerline jet concentration for these cases are established, and variable density scaling law is developed and used to predict jet penetration in the far field. In most non-premixed combustor systems, the fuel and air being mixed are at different initial temperatures and densities. To account for these effects, heated jets at temperatures equal to 540K and 3000K have been run. It has been observed that, in addition to the lower density of heated jets, the higher kinematic viscosity effects the jet penetration. This effect has been included and validated in the scaling law for the heated jet trajectory.

Two active flow control methods are investigated numerically to understand the mechanism by which they control aerodynamics in the presence of severe flow separation on an airfoil. In particular, synthetic jets are applied to separated flows generated by additional surface feature (the actuators) near the trailing edge to obtain Coanda-like effects, and an impulse jet is used to control a stalled flow over an airfoil. A moving-grid scheme is developed, verified and validated to support simulations of external flow over moving bodies. Turbulent flow is modeled using detached eddy simulation (DES) turbulence models in the CFD code CDP (34) developed by Lopez (54). Synthetic jet actuation enhances turbulent mixing in flow separation regions, reduces the size of the separation, deflects stream lines closer to the surface and changes pressure distributions on the surface, all of which lead to bi-directional changes in the aerodynamic lift and moment. The external flow responds to actuation within about one convective time, which is significantly faster than for conventional control surfaces. Simulation of pitching airfoils shows that high-frequency synthetic jet affects the flow independently of the baseline frequencies associated with vortex shedding and airfoil dynamics. These unique features of synthetic jets are studied on a dynamically maneuvering airfoil with a closed-loop control system, which represents the response of the airfoil in wind-tunnel experiments and examines the controller for a rapidly maneuvering free-flight airfoil. An impulse jet, which is applied upstream of a nominal flow separation point, generates vortices that convect downstream, interact with the separating shear layer, dismantle the layer and allow following vortices to propagate along the surface in the separation region. These following vortices delay the separation point reattaching the boundary layer, which returns slowly to its initial stall condition, as observed in wind-tunnel experiments. A simple model of the impulse jet actuator used herein is found to be sufficient to represent the global effects of the jet on the stalled flow because it correctly represents the momentum injected into the flow. / text

Characterization of jet fuels obtained from sources other than crude oil is a modern area of research that is developing continuously to replace available petroleum-based fuels with ‘drop-in’ alternative fuels. Therefore, reliable composition-property relations are developed to correlate the hydrocarbon compositions of formulated synthetic fuels with their properties to be certified for aviation commercial use. Intensive studies have been initiated at Texas A&M University Qatar in collaboration with industry and academia to study synthetic jet fuels derived from natural gas. These studies are being implemented at its Fuel Characterization Lab where the most advanced testing equipment is used and strict Quality Management and safety systems are followed. This study is divided into two tracks. The first track is focused on conducting experimental investigations using in-house formulated synthetic jet fuels derived from natural gas via Gas-to-Liquid technology and Fischer-Tropsch chemistry. Throughout this research work, these fuels will be referred to as Synthetic Paraffinic Kerosene (SPK). These experimental investigations activities are composed of three phases: the first phase focuses on the influence of SPK building blocks (paraffinic hydrocarbons) on fuels’ properties, the second phase concerns evaluating the role of aromatics and cyclo-paraffins on properties, and the third phase studies the influence of mixing SPK with conventional Jet A-1 derived from crude oil. All of the aforementioned experimental investigations are aimed at building an experimental data bank to assist the efforts of the formulation of new generations of SPKs that meet aviation industry standards. On the other hand, the second track is directed towards the development of mathematical correlations for four properties of high importance to SPK certification. These correlations aim at optimizing fuel composition whereby major physical/chemical properties of ASTM D1655 are met at the lowest cost of composed fuel. The primary findings of this study showed that GTL derived SPK paraffinic constituents can improve certain properties while affecting others negatively, and emphasizing the necessity of aromatics in improving specific properties. Further studies compensating the absence of aromatics and sulfur through blended Jet A-1 revealed a practical solution through jet fuels optimization based on cost and technical effective manners.