Dispersion of solid particles in turbulant flow through pipe expansions

Studies of the effects upon gas-liquid two-phase flows of pipefittings such as expansions, contractions, bends, and valveshave usually concentrated upon pressuredrop correlations andhave not attempted to determine changes in the distributionsof the gas and liquid phases caused by the fitting. However,it is known that such information is important if, for example,flow separators, which divide the gas and liquid phases in avariety of industrial processes, are to function efficiently.It is therefore important to gain an understanding of the influenceupon phase distributions of the common pipe fittings mentionedabove, which will be found in almost any industrial pipeworksystem. As a first step, the dispersion of solid particles carriedby turbulent gas flows through a pipe expansion has been modellednumerically. The commercial fluid-flow code CFDS-FLOW{smalltilde}hDas been used to model the gas flow, together with aneddy interaction model for determination of the motion of thesolid particles. Mean particle velocities and root-mean-squarevalues of the particle velocity fluctuations, as well as particleconcentrations, are evaluated and compared with recent experimentalresults. The influence of different eddy-length and eddy-lifetimespecifications upon the dispersion of particles of various sizesis investigated. It is found that the different eddy characteristicshave little effect on predicted mean particle velocities, whereasfluctuations in particle velocities and particle concentrationare sensitive to the changes made. By comparing the resultswith experimental data, it is possible to draw conclusions aboutthe relative merits of the different eddy specifications.     

The Minimal Branch of Solutions of an Equation Arising in Thermal Combustion Theory

Although the steady-state equation of thermal combustion theoryoften has multiple solutions, it is usually the minimal positivesolution which has most physical significance. For instance,an exothermically reacting system will approach this minimalsteady state if the initial temperature is not too high. Theoccurrence of discontinuities in the minimal solution branchas the parameters governing the reaction are varied often signifiesdrastic changes in the behaviour of the evolving system, andindeed this phenomenon has been equated with the onset of explosion.In this paper, it is shown that the presence of such discontinuitiesis equivalent, under quite general conditions, to the existenceof values of the thermal parameters at which multiplicity ofsolutions gives way to uniqueness.     

The Application of Site-Specific Natural Isotope Fractionation-Nuclear Magnetic Resonance (SNIF-NMR) to the Analysis of Alcoholic Beverages

The relative deuterium concentration and specific deuterium-site locations in a molecule can be determined using Site-Specific Natural Isotope Fractionation-Nuclear Magnetic Resonance (SNIF-NMR). For a given compound (e.g., ethanol) SNIF-NMR can provide information about the chemical pathway of formation and, in some cases, information about the geographic origin of a sample can also be discerned. SNIF-NMR has been applied to the analysis of wines and other alcoholic beverages. In this work, data were collected on samples of apple brandy, tequila, rum, potato vodka, cognac, and synthetic ethanol. Signal-to-noise considerations limit the samples that can be studied without preconcentration to those with relatively high alcohol contents.     

The effect of buoyancy on upper-branch Tollmien-Schlichting waves

We investigate the effect of buoyancy on the upper-branch linearstability characteristics of an accelerating boundary-layerflow. The presence of a large thermal buoyancy force significantlyalters the stability structure. As the factor G (which is relatedto the Grashof number of the flow, and defined in Section 2)becomes large and positive, the flow structure becomes two layeredand disturbances are governed by the Taylor-Goldstein equation.The resulting inviscid modes are unstable for a large componentof the wavenumber spectrum, with the result that buoyancy isstrongly destabilizing. Restabilization is encountered at sufficientlylarge wavenumbers. For G large and negative the flow structureis again two layered Disturbances to the basic flow are nowgoverned by the steady Taylor—Goldstein equation in themajority of the boundary layer, coupled with a viscous walllayer. The resulting eigenvalue problem is identical to thatfound for the corresponding case of lower-branch Tollmien—Schlichtingwaves, thus suggesting that the neutral curve eventually becomesclosed in this limit.     

Electro-Optic Polymer Integrated Optic Devices and Future Applications

Recent developments in electro-optic polymer materials and devices have led to new opportunities for integrated optic devices in numerous applications. The results of numerous tests have indicated that polymer materials have many properties that are suitable for use in high-speed communications systems, various sensor systems, and space applications. These results, coupled with recent advances in device and material technology, will allow very large bandwidth modulators and switches with low drive voltages, improved loss, long-term stability, and integration with other microelectronic devices such as MEMS. Low drive voltage devices are very important for space applications where power consumption scales as the square of the modulator half-wave voltage. In addition, we have demonstrated novel dual polymer modulators for mixing RF signals to produce sum and difference frequency modulation on an optical beam. This novel approach allows the suppression of the modulation at the two input RF signals, and only the mixing signals remain superposed on the optical beam. The dual modulator can be used for various encoding/decoding and frequency conversion schemes that are frequently used for both terrestrial and space communications. Another application of polymer integrated optics is in the field of optical sensing for high-frequency (GHz) electric fields.     

New families of exact solutions for finitely deformed incompressible elastic materials

The governing partial differential equations for static deformationsof homogeneous isotropic incompressible elastic materials arehighly nonlinear, and consequently only a few exact solutionsare known. For these materials, only one general solution involvinga single arbitrary function is presently known, which is forplane deformations and is applicable to the so-called Vargastrain-energy function. In this paper, new families of exactsolutions are derived for plane and axially symmetric deformationsof perfectly elastic materials. In the case of plane deformations,a different formulation of the known general solution for theVarga strain-energy function is presented, from which numerousnew solutions may be obtained. In the case of axially symmetricdeformations, the Varga material again arises as the privilegedstrain-energy function, and this constitutes the main resultof the paper. For this material, a number of new simple exactsolutions are derived for axially symmetric deformations. Finally,all the solutions obtained here are shown to also apply to amodified Varga strain-energy function involving the reciprocalsof the principal stretches.     

Cylindrical and spherical inflation in compressible finite elasticity

Murphy (1992) examined cylindrical and spherical inflation ofcompressible perfectly elastic materials having three specialforms of the strain-energy function. In this paper a generalprocedure for handling such problems for any strainenergy functionis proposed. This procedure is used to confirm some of the resultsby Murphy as well as to deduce new solutions. One solution obtainedby that author for cylindrical inflation is found to be incorrect.     

The structure of fully nonlinear Taylor vortices

The structure of nonlinear short-wavelength Taylor vorticesin the flow between rotating concentric cylinders is considered.In the short-wavelength limit, the nonlinear vortex motion isgoverned by a mean-flow-first-harmonic interaction problem.The initial structure of the nonlinear vortex state is shownto be governed by a multilayer structure in which the vortexis constrained to lie between the inner cylinder and a positioninternal to the flow regime. This position is dependent uponthe Taylor number and it is found that there is a critical valueof the Taylor number at which the vortex first impinges on theouter boundary. The vortex field then develops a double boundarylayer structure at both the inner and outer boundary as theTaylor number is increased past this critical Taylor number.