No description available.

No description available.

The jet mixing of water in crude oil pipelines by single nozzle and multi-nozzle mixers was studied by dividing the mixing domain into to three regions. the penetration. near field and farfield regions. At the penetration region the quantitative experimental data were aided by a flow visualisation study in an attempt to to form fundamental semi-empirical correlations to estimate the entrainment rate of stratified water from the bottom and the Sauter mean diameter of the entrained water droplets for a single nozzle jet mixer. The flow field diagnostics into the near field region. defined as the region where high level of swirl and mixing is occuring. were conducted theoretically using computational fluid dynamic code "Phoenics" and experimentally through LOA measurements and flow visualisation. The entrainment rate found in penetration region was treated as a source term for theoretical analysis. Experimental analysis of this region was conducted in single phase flow for two mixer nozzles i) Single nozzle mixer and ii). Existing multi-nozzle mixer. Experimental results have revealed that the swirl velocities decay faster for higher velocity ratios and their dependence on Reynolds number (in the range 27600 to 48400) is weak. Higher velocity ratios would generate and dissipate higher levels of energy, therefore break up water droplets to smaller sizes and increase the eddy viscosity. The dispersion strength due to swirl decays faster and the gravity settling begins earlier. As the flow reaches downstream. approximately four diameters. the distribution of velocities (mean and RMS) flattens out and their magnitude begins to close up for the two mixers. when their momentum ratios are equal. It was also shown that the swirl velocities (at axis) die away. approximately at the same axial point for both of the nozzles. The multi-nozzle mixer is shown to be better in two characteristics; i). The mixing is faster and ii) The jet energy is more evenly distributed in the vicinity of the injection cross section. hence improving the quality of the droplet size distribution. Besides providing information to aid understanding of the complex flow in the mixer zone. the experimental data is believed to be of sufficient quality and quantity to improve the present simple modelling procedures as well as to be used as test cases for assessment of the predictive accuracy of more elaborate computational models. Comparision with computational results (of low velocity ratios) shows the agreement with swirl velocities is reasonable. but not always acceptable for mean axial velocities. However. the computational model predicts the near field jet trajectory reasonably well. The flow visualisation of dispersion of passive contaminant agrees qualitatively with the contours of the passive contaminant. In the far field region. where the swirl has decayed. the flow behaves two dimensionally. Therefore. an exact solution was obtained for two dimensional water conservation equation. The boundary conditions were specified by using sticking probability constants. A relationship was obtained to specify eddy viscosity through turbulent kinetic energy. The turbulent kinetic energy and swirl decay were estimated from LDA experimental data. This solution can be used to study the developing characteristics of water concentration profiles along the far field region of the pipeline.

Successful characterization of vortex structures in unsteady flow fields depend crucially upon an adequate choice of a reference frame. Vortex detection approaches in flow visualization aspire to be objective, i.e., invariant under time-dependent rotations and translations of the input reference frame. However, objectivity by itself does not guarantee good results as different specific approaches lead to different results. Moreover, recent more generic approaches to objectivity still require parameters to be specified beforehand which can significantly influence the resulting vortex detection, depending on the complexity and characteristics of the input flow field. With the assumption that human intervention is unavoidable to some extent, we tackle the problem of specifying parameters for vortex detection from a human-centered perspective. In this work, we present a novel system that enables users to interactively explore the parameter space of a flexible objective method, while jointly computing and visualizing the resulting vortex structures. We build on the computation of an objective field of reference frames and enable users to interactively change computation parameters as well as choose different observers, compute vortex structures on-the-fly during exploration, and visualize the flow field from the viewpoint of the chosen observers. Overall, we illustrate that such an interactive approach can be of significant value to the user for analyzing vortex structures visually and understanding why a computational method has detected a specific structure as a vortex.

No description available.

Overend et al [68] designed a viscometer to measure the viscosity of slurries that have a tendency to settle. This viscometer consists of a rotating ribbed rotor surrounded by a stationary slotted sleeve; this system is then placed eccentrically within an inclined rotating bowl. It, is claimed that this overcomes most of the difficulties encountered when attempting to obtain accurate measurements for these types of mixtures. If the mixture being sheared within the annulus does not represent the true composition of the slurry being, tested then the results are expected to be inaccurate. The presence of sediment at the bottom of the rotor or the formation of large masses of particles within the flow domain will affect the accuracy of the measurements obtained. This dissertation studies the amount of flow through the slotted sleeve and the region, or regions, of low shear rate within the flow domain. Assuming that end-effects are unimportant and that the slurries can be replaced by a single-phase fluid, three two-dimensional models are proposed. These models are designed to capture the large-slot construction of the sleeve and the, approximate, non-Newtonian behaviour of the slurries. The first two models solve analytically (using a regular perturbation scheme) and numerically (using a finite volume method) the moderate-and large-Reynolds-number flow, and the third model uses a finite volume method to study the flow patterns developed by pseudoplastic fluids. The results show that the mixing of the slurry is expected to be enhanced by moving the concentric system (i.e., the rotor and the slotted sleeve) close to the rotating bowl and using low to moderate speeds for the rotor and bowl. In addition, when the cylinders rotate in the same directions, two (counter-rotating) eddies are present within the flow domain; whereas, only one eddy (rotating counter-clockwise) is ++ / present when the cylinders rotate in opposite directions. The presence of eddies in the former situation inhibits the flow through the sleeve; while, for moderate rotorspeeds, the flow through the sleeve is enhanced in the latter. When the slurry assumed pseudoplastic, we observe a region of low shear rate located near the dividing streamline present within the flow field. The distribution of shear rate within the flow field is shown to be affected by factors such as the rate of diffusion of the apparent viscosity and the value of the power law index. Therefore, this study suggests that for certain types of slurries, concentrations of particles exist within the domain and that the mixing of slurries can be impeded by the presence of eddies within the main flow field.

In polymer electrolyte membrane (PEM) fuel cells one of the most important components is the flow field. The flow field distributes reactant gasses to the active area and also delivers electrons from the outer circuit so that the electrochemical reaction may be completed. Optimizing flow field design is extremely important in order to increase the overall power density of the fuel cell. It is particularly important to understand the ways in which the different portions of the flow field, namely the land and channel sections, interact with the gas diffusion layer (GDL), catalyst layer and membrane; this study focuses on those interactions. The most common type of flow field design currently used in PEM fuel cells is the serpentine flow field. It is used for its simplicity of design, its effectiveness in distributing reactants and its water removal capabilities. The knowledge about where current density is higher, under the land or the channel, is critical for flow field design and optimization. Yet, no direct measurement data are available for serpentine flow fields. In this study a fuel cell with a single channel serpentine flow field is used to separately measure the current density under the land and channel, which is either catalyzed or insulated on the cathode. In this manner, a systematic study is conducted under a wide variety of conditions and a series of comparisons are made between land and channel current density. Results show that under most operating conditions, current density is higher under the land than that under the channel. However, at low voltage, a rapid drop off in current density occurs under the land due to concentration losses. The mechanisms for the direct measurement results and general guidelines for serpentine flow field design and optimizations are provided. In addition the same technique is utilized to separately measure current density under the land and channel on a variety of serpentine flow field geometries. Each flow field is tested under a wide variety of operating conditions thereby providing guidance for the optimum design geometry. Experimental results show that generally flow fields with both thinner lands and thinner channels provide better overall performance. However, the optimal flow field designs are highly dependent on fuel cell operating parameters. Finally, it is critical not only to know where the current density is greater, under the land or under the channel, but to understand the fundamental mechanisms driving these differences. Resistance was measured, ex-situ, between the GDE and flow plate under the land of the flow field and under the channel separately. The contact resistance between the gas diffusion electrode (GDE) and the graphite flow plate were measured using an ex-situ technique. The resistance was measured under different land and channel widths. Cyclic Voltammetry tests were also conducted in order to determine if there is any different in electrochemically active area(ECA) under the land and under the channel and what the cause of this difference might be. Results show that the compression of the gas diffusion electrode not only affects the electronic resistance but the ECA as well and that these are key factors in current density variations under the land and channel.

No description available.

Engine designers continually push the combustor exit temperature higher to produce more power from gas turbine engines. These high turbine inlet temperatures, coupled with high turbulence levels and flow field non-uniformities, make turbine vane and endwall cooling a very critical issue in engine design. To appropriately cool these surfaces, knowledge of the passage flow field and endwall temperature distribution at representative engine conditions is necessary. A combustor test section was used to simulate realistic turbine inlet profiles of turbulence, normalized temperature, normalized total pressure, and normalized streamwise velocity to study the flow field in a turbine vane passage and the adiabatic temperature distribution on the endwall. The combustor liner film-cooling and exit slot flows were varied independently to determine their relative effect on endwall cooling in the downstream turbine vane. Flow field measurements revealed the presence of a previously unmeasured third vortex in the vane passage. The tertiary vortex was located above the passage vortex and had rotation opposite to the passage vortex. Increasing the amount of slot flow reduced the size and strength of the nearwall vortices, while increasing the size and strength of the tertiary vortex. Adiabatic endwall temperature measurements revealed higher temperatures surrounding the base of the vane. The endwall measurements also showed that the exit slot flow was effective at cooling only a region of the endwall near the vane leading edge on the suction side. Increasing slot flow was found to have a larger thermal benefit to the endwall relative to increasing combustor liner film-cooling. / Master of Science

In this thesis biomimetic design is applied to the redesign of a PEM fuel cell flow field. A number of designs inspired by biological phenomena were developed to address the problem of attaining a uniform current density distribution across a PEM fuel cell. These designs are evaluated using a numerical model. One design, inspired by Murray’s law of branching in plants and animals, is further evaluated using and a physical model and comparing it to a commercial triple serpentine flow field. Improvements in pressure drop were seen for the Murray’s law inspired flow field, however, it was found to be prone to flooding. If this flow field design were to be applied to high temperature membrane materials, materials that can operate above 100 °C where water is always in the vapor state, the mass transfer and reduced pressure drop advantages of the Murray flow field could be fully achieved.