The influence of particle shape of coating pigments on theirpacking ability and on the flow properties of coating colourshas been investigated. The particle shapes considered werespherical, flaky and acicular (needle-shaped). In the case ofsuspensions containing monodisperse spherical polystyreneparticles, a concentration gradient appeared in the filter cakeforming during filtration under static conditions. Such agradient, monitoredby non-destructive magnetic resonanceimaging (MRI), is not accounted for in the traditionalfiltration theory used in coating technology. Good agreementwas found between a literature model describing filtrationthrough a compressible filter cake and the concentrationgradients measured by MRI. According to this model, the scaledconcentration gradient was the same at all times. For flaky (mainly kaolin) and acicular (aragonite)particles, a rapid method was evaluated to estimate a shapefactor of the pigment particle. Generalised mathematical modelsof oblate and prolate spheroids were applied to reduce thethree geometrical dimensions of the particle to two, the majoraxis and the minor axis. The shape factor, which is mass-based,was derived from a comparison between the results obtained bytwo different size-assessment instruments, viz. the Sedigraphand an instrument using light scattering. This yields a shapefactor distribution as a function of equivalent sphericalparticle size, but the results are uncertain for small particlediameters, below 0.2 µm. Good agreement was obtainedbetween the shape factor and a mass-based aspect ratio obtainedby image analysis, but the rapid method is generally moreaccurate for flaky than for acicular particles. Results obtained by capillary viscometry showed that therewas a relationship between the viscosity at high shear rates(&gt;105s-1) and the shape factor, but that it was notsufficient to use the median value of the shape factor toachieve proper information. A more complete evaluation requiresknowledge of the shape factor distribution, which is also givenin part by the method mentioned above. However, a large medianshape factor was related to a high high-shear viscosity.Non-Newtonian entrance pressure losses were sometimessignificant in capillary viscometry, indicating that it wasinappropriate to measure the shear viscosity with only onecapillary. Such effects were however relatively much morepronounced in slit die viscometry, especially in the case ofacicular particles, where the aspect ratio was a crucialparameter. The influence of the shape factor of kaolinparticles on the non-Newtonian entrance pressure losses over aslit die was surprisingly small. The high-shear viscosity ofcoating suspensions based on different pigments correlated withthe median pore size of the corresponding coating layer ratherthan with the porosity. <b>Keywords</b>: Aspect ratio, capillary viscometry, coatingcolour, filtration, particle packing, pigment, pore structure,rheology, shape factor, slit die viscometry, spheroid.

Numerical study of laminar convective cooling of ribs in a parallel plate channel is investigated. Single rib mounted on one channel wall in forced, mixed and free convection is analyzed. Furthermore, the series ribs array with in-line and staggered mounted on channel walls are considered. Through the use of a stream function vorticity transformation, solution of the transformed governing equations for the system is obtained using the control volume method with non-uniform grid. The effects of the Reynolds number, thermal conductivity ratio of rib to fluid and rib¡¦s profile area on heat transfer rate of single rib and rib array are presented. In addition, the effects of the length from inlet to the first rib and the space between ribs for rib array are carried out. A correlation for single and rib array in forced convection is presented to estimate the optimum aspect ratio of rib with various Reynolds number, thermal conductivity ratio of rib to fluid, rib¡¦s profile area. Furthermore, the results of different Gr/Re2 and various channel inclination angle in mixed convection are also examined numerically. The results indicate that both in forced and mixed convection, the optimum aspect ratio of a rib corresponding to the rib with maximum heat transfer rate increases with increasing Re but decreases with K for a fixed rib profile area. In forced convection the optimum aspect ratio of rib array increases with rib¡¦s space but decreases with the length from inlet to the first rib of channel. Then, numerical correlations to predict the optimum aspect ratio of single rib and rib array are developed for fixed rib¡¦s area with various Re, K and rib number. In mixed convection, the optimum aspect ratios of single rib and staggered rib array increase with not only the inclination angle but also Gr/Re2.

Heat transfer and fluid flow are studied numerically for a repeating microchannel array with water as the circulating fluid. Generalized transport equations are discretized and solved in three dimensions for velocities, pressure, and temperature. The SIMPLE algorithm is used to link pressure and velocity fields, and a thermally repeated boundary condition is applied along the repeating direction to model the repeating nature of the geometry. The computational domain includes solid silicon and fluid regions. The fluid region consists of a microchannel with a hydraulic diameter of 85.58μm. Independent parameters that were varied in this study are channel aspect ratio and Reynolds number. The aspect ratios range from 0.10 to 1.0 and Reynolds number ranges from 50 to 400. A constant heat flux of 90 W/cm2 is applied to the northern face of the computational domain, which simulates thermal energy generation from an integrated circuit. A simplified model is validated against analytical fully developed flow results and a grid independence study is performed for the complete model. The numerical results for apparent friction coefficient and convective thermal resistance at the channel inlet and exit for the 0.317 aspect ratio are compared with the experimental data. The numerical results closely match the experimental data. This close matching lends credibility to this method for predicting flows and temperatures of water and the silicon substrate in microchannels. Apparent friction coefficients linearly increase with Reynolds number, which is explained by increased entry length for higher Reynolds number flows. The mean temperature of water in the microchannels also linearly increases with channel length after a short thermal entry region. Inlet and outlet thermal resistance values monotonically decrease with increasing Reynolds number and increase with increasing aspect ratio. Thermal and friction coefficient results for large aspect ratios (1 and 0.75) do not differ significantly, but results for small aspect ratios (0.1 and 0.25) notably differ from results of other aspect ratios.

Microchannels have been studied extensively for electronic cooling applications ever since they were found to be effective in removing high heat flux from small areas. The rate of heat removed using microchannels depends on many factors including the geometry shape, solid and fluid materials used, and surface roughness, among others. Many configurations of microchannels have been studied with various materials and compared for their effectiveness in heat removal. However, there is little research done so far in using Phase Change Material (PCM) fluids and pin fins in microchannels to enhance the heat transfer. PCM fluids exhibit greater heat transfer when the phase change material undergoes liquid-to-solid transformation. Staggered pins in microchannels have also shown higher heat removal characteristics because of the continuous breaking and formation of the thermal and hydrodynamic boundary layer; they also exhibit higher pressure drop because pins act as flow obstructers. This paper presents numerical results of circular, square, straight rectangular microchannels with various aspect ratios (1:2, 1:4 and 1:8), and rectangular microchannels with two characteristic staggered pins (square and circular, fixed height with no variation in aspect ratio). The heat transfer performance of a single phase fluid and PCM fluid in all of these microchannels and the corresponding pressure drop characteristics are also presented. An effective specific heat capacity model was used to account for the phase change process of PCM fluid. Comparison of heat transfer characteristics of single phase fluid and PCM fluid are presented for all the geometries considered. Among the straight microchannels, 1:8 geometry was found to have the highest Nusselt number. The use of PCM fluid in straight microchannels increased the Nusselt number by 3-7 percent compared to the single phase fluids. Among the staggered pin microchannels, circular pins were found to be more effective in terms of heat transfer by exhibiting higher Nusselt number. Circular pin microchannels were also found to have lower pressure drop compared to the square pin microchannels. Overall, for all the geometries considered, it was found that the PCM fluid enhances the heat transfer compared to the SPF fluid.

The frequency of on-site systems for treatment of domestic wastewater is increasing with new residential development in both rural and low-density suburban areas. Subsurface flow constructed wetlands (SFCW) have emerged as a viable option to achieve advanced or secondary treatment of domestic wastewater. The pollutant removal efficiency in SFCW depends on design parameters. Many of these factors have been investigated while others such as aspect ratio, design of water inlet structure and method of dosing the wetland have yet to be fully examined. This study examined the effect of aspect ratio and header design on BOD5 removal efficiency as well as the impact of flow rate on flow distribution in a SFCW. An aspect ratio of 4:1 achieved 10% greater removal of organic matter than a 1:1 ratio. Tracer studies demonstrated that wetlands loaded at a constant rate of 3.8 L/min and 7.6 L/min experienced preferential flow. In addition, tracer studies showed wetlands with leaching chambers as headers failed to achieve equal flow distribution. An improvement in effluent water quality was achieved by replacing the leaching chamber for a perforated manifold as the inlet structure. This study demonstrated the importance of the careful selection of aspect ratio and means by which water is introduced to the wetland in the design of SFCW.

Pattern geometry plays a major role in determining oil recovery during waterflooding and enhanced oil recovery operations. Although simulation is an important tool for design and evaluation, the first step often involves rough calculations based upon areal sweep efficiencies of displacements in homogeneous, two-dimensional, scaled, physical models. These results are available as a function of the displacement pattern and the mobility ratio M. In this research I studied the effect of mobility ratios on five-spot and staggered waterflood patterns behavior for areal (2D) displacement in a reservoir that is homogeneous and isotropic containing no initial gas saturation. Simulation was performed using Eclipse 100 simulator. Simulation results are presented as graphs of areal sweep efficiency at breakthrough versus Craig mobility ratio for various staggered line drive aspect ratios. The main results of the study are presented in the form of a graph of areal sweep efficiency at breakthrough as a function of staggered line drive aspect ratio. This should enable engineers to utilize the results in a convenient manner.

Luminescent emission of partially conjugated homopolymers was successfully demonstrated as light emitting diodes (LEDs). A series of coil-like heterocyclic aromatic poly(2,2¡¦-phenyl-5,5¡¦-bibenzimiazole) (Pbi) was synthesized and derivatized with alkyl pendants for changing the band gap to form different electroluminescence (EL) emissions. Because of the entropy and van der Waals' interaction, multi-wall carbon nanotube (MWNT) tends to aggregate. In this investigation, chemical synthesis was applied to functionalize the MWNT. MWNT was esterificated by incorporating the functional group (-COOC10H21) to reduce its aspect ratio to facilitate its dispersion in the Pbi solution. MWNT-COOC10H21 was analyzed using Fourier transform infrared, elemental analysis, Raman spectrum and thermogravimetric analysis. In the polymer light emitting devices, Pbi mixed with MWNT-COOC10H21 would decrease threshold voltage for about 2 V, and the device emission current was increased 5~10 times of magnitude than those of devices without MWNT- COOC10H21. Pbi was in-situ polymerized with acidified multi-wall carbon nanotube (MWNT- COOH) for polymer LED fabrication. The emission current of these devices was still increased 10~15 times but no threshold voltage decrease compared to those of Pbi polymer solution-mixed with MWNT-COOC10H21. The polymer LED Commission International del'Eclairage chromatic indices were about the same for Pbi mixed with MWNT-COOC10H21 or in-situ polymerized with MWNT-COOH.

This study is focused on the technique for fabrication of high aspect ratio nanostructures by combining both the advantages of maskless patterning of focused ion beam (FIB) and anisotropic etching of inductively coupled plasma etcher (ICP) in CF4 atmosphere. The materials contain p-type (100) single crystal silicon and thermal silicon dioxide. The study details include¡G (1) The reliability of AFM when scanning isotropic and anisotropic nanostructures with high aspect ratio tip in tapping mode. (2) FIB direct writing test. (3) The influences of ICP parameters including ICP power, bias power, content of oxygen, and process pressure. After completion of above-mentioned items, an optimized condition is used to get the anisotropic Si-based high aspect ratio nanostructures of holes array, gratings and cylinder under 100nm. The smallest line width of single crystal silicon gratings is 48nm, and aspect ratio up to 2.36. The smallest line width of silicon dioxide gratings is about 100nm, height is 410nm and aspect ratio up to 2.36 measured by SEM. By combining both advantages of different systems, we can provide another simple and rapid method for nanofabrication.

<p>The influence of particle shape of coating pigments on theirpacking ability and on the flow properties of coating colourshas been investigated. The particle shapes considered werespherical, flaky and acicular (needle-shaped). In the case ofsuspensions containing monodisperse spherical polystyreneparticles, a concentration gradient appeared in the filter cakeforming during filtration under static conditions. Such agradient, monitoredby non-destructive magnetic resonanceimaging (MRI), is not accounted for in the traditionalfiltration theory used in coating technology. Good agreementwas found between a literature model describing filtrationthrough a compressible filter cake and the concentrationgradients measured by MRI. According to this model, the scaledconcentration gradient was the same at all times.</p><p>For flaky (mainly kaolin) and acicular (aragonite)particles, a rapid method was evaluated to estimate a shapefactor of the pigment particle. Generalised mathematical modelsof oblate and prolate spheroids were applied to reduce thethree geometrical dimensions of the particle to two, the majoraxis and the minor axis. The shape factor, which is mass-based,was derived from a comparison between the results obtained bytwo different size-assessment instruments, viz. the Sedigraphand an instrument using light scattering. This yields a shapefactor distribution as a function of equivalent sphericalparticle size, but the results are uncertain for small particlediameters, below 0.2 µm. Good agreement was obtainedbetween the shape factor and a mass-based aspect ratio obtainedby image analysis, but the rapid method is generally moreaccurate for flaky than for acicular particles.</p><p>Results obtained by capillary viscometry showed that therewas a relationship between the viscosity at high shear rates(>10⁵s^-1) and the shape factor, but that it was notsufficient to use the median value of the shape factor toachieve proper information. A more complete evaluation requiresknowledge of the shape factor distribution, which is also givenin part by the method mentioned above. However, a large medianshape factor was related to a high high-shear viscosity.Non-Newtonian entrance pressure losses were sometimessignificant in capillary viscometry, indicating that it wasinappropriate to measure the shear viscosity with only onecapillary. Such effects were however relatively much morepronounced in slit die viscometry, especially in the case ofacicular particles, where the aspect ratio was a crucialparameter. The influence of the shape factor of kaolinparticles on the non-Newtonian entrance pressure losses over aslit die was surprisingly small. The high-shear viscosity ofcoating suspensions based on different pigments correlated withthe median pore size of the corresponding coating layer ratherthan with the porosity.</p><p><b>Keywords</b>: Aspect ratio, capillary viscometry, coatingcolour, filtration, particle packing, pigment, pore structure,rheology, shape factor, slit die viscometry, spheroid.</p>

One of the most important, but often ignored, factors affecting the transport and the seismic properties of hydrocarbon reservoir is pore shape. Transport properties depend on the dimensions, geometry, and distribution of pores and cracks. Knowledge of pore shape distribution is needed to explain the often-encountered complex interrelationship between seismic parameters (e.g. seismic velocity) and the independent physical properties (e.g. porosity) of hydrocarbon reservoirs. However, our knowledge of reservoir pore shape distribution is very limited. This dissertation employs a pore structure parameter via a rock physics model to characterize mean reservoir pore shape. The parameter was used to develop a new physical concept of critical clay content in the context of pore compressibility as a function of pore aspect ratio for a better understanding of seismic velocity as a function of porosity. This study makes use of well log dataset from offshore Norway and from North Viking Graben in the North Sea. In the studied North Sea reservoir, porosity and measured horizontal permeability was found to increase with increasing pore aspect ratio (PAR). PAR is relatively constant at 0.23 for volumes of clay (V_cl) less than 32% with a significant decrease to 0.04 for V_cl above 32%. The point of inflexion at 32% in the PAR –V_cl plane is defined as the critical clay volume. Much of the scatters in the compressional velocity-porosity cross-plots are observed where V_cl is above this critical value. For clay content higher than the critical value, Hertz-Mindlin (HM) contact theory over-predicts compressional velocity (V_p) by about 69%. This was reduced to 4% when PAR distribution was accounted for in the original HM formulation. The pore structure parameter was also used to study a fractured carbonate reservoir in the Sichuan basin, China. Using the parameter, the reservoir interval can be distinguished from those with no fracture. The former has a pore structure parameter value that is ≥ 3.8 whereas it was < 3.8 for the latter. This finding was consistent with the result of fracture analysis, which was based on FMI image. The results from this dissertation will find application in reservoir characterization as the industry target more complex, deeper, and unconventional reservoirs.