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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 276 (1998), S. 1019-1023 
    ISSN: 1435-1536
    Keywords: Key words Hydroxypropylmethylcellulose ; emulsions ; particle size ; active laser scanning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Emulsions stabilized with hydroxypropylmethylcellulose were characterized with respect to their particle size and their flow behavior. This part of the study focuses on the former. Active laser scanning revealed that the particle size is independent of the hydroxymethylcellulose content. The critical density of the surface film was determined to be ≤0.01 g/m2. This is the basis for the interpretation of the flow behavior, which is described in detail in part II of this contribution.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 276 (1998), S. 1024-1031 
    ISSN: 1435-1536
    Keywords: Key words Hydroxypropylmethylcellulose ; emulsions ; stabilization ; flow behavior ; rheometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Emulsions stabilized with hydroxypropylmethylcellulose were characterized with respect to their particle size and their flow behavior. This part of the study focuses on the latter. During shear experiments an increase in viscosity was detected with increasing phase volume fraction. After a critical phase volume fraction, φ, of 0.6 had been exceeded, yield stresses of between 7 and 17 Pa were exhibited. In the emulsions without yield stress the relative emulsion viscosities were examined against the relevant theories, which resulted in good agreement being found with the predictions of Krieger and Dougherty. Using the extrapolated maximum phase volume fraction, it was thus possible to calculate the thickness of the adsorbate layer as approximately 60 nm. In the dynamic measurements, a maximum was determined for the material functions. This was attributed to shear-induced restructuring processes in the emulsions. The dynamic measurements in the linear viscoelastic range showed that, in spite of increasing phase volume fraction, the critical relaxation time decreased, whereas the values of the moduli rose at small oscillation frequencies. Time-dependent measurements showed that thixotropy was detected for emulsions with a phase volume fraction of φ≥0.7. Creep tests showed that the compliance fell with increasing phase volume fraction. The zero shear modulus and the relative elastic compliance were calculated for the emulsions that exhibited yield stresses. Good agreement was found between the zero shear modulus and the values for the storage modulus determined in dynamic measurements.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 6 (1986), S. 395-401 
    ISSN: 0271-2091
    Keywords: Computer Extended Series ; Gas Centrifuge Theory ; MACSYMA ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Linearized, multidimensional, thermally driven flow in a gas centrifuge can be approximately described in regions away from the ends by Onsager's homogeneous pancake equation.1 Upon reformulation of the general problem, we find a new, simple and rigorous closed form, analytical solution by assuming a special separable solution and replacing the usual Ekman end cap boundary conditions with idealized impermeable, free slip boundary conditions. Then the flow may be described by an ordinary differential equation with solutions in terms of simple, classical functions. By identifying a small parameter, say ∊, defining the semi-long bowl approximation, and assuming a power series expansion in ∊, a sequence of asymptotic approximations to the master potential is obtained. Not surprisingly, the leading order term involves the well known ‘long bowl’ solution. Using the so-called ‘solving’ property of the 1-D pancake Green's function,2 we determine the next higher order solution. This recursive process is carried out on the computer to find all the terms up to O(∊4).Consequently, the solution of some complex rotating, viscous, heat conducting flow problems that normally require large mainframe computers can be better understood.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 2 (1982), S. 1-23 
    ISSN: 0271-2091
    Keywords: Transition ; Boundary Layers ; Models of Turbulence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A computational procedure for compressible axisymmetric boundary layers, on bodies of revolution, in transition from laminar to turbulent flow, is introduced. The procedure is an extension of a former method, due to Patankar and Spalding.The flow field is computed by solution of four simultaneous equations for the momentum, the thermal energy, the turbulence energy amplitude and the turbulent scale.The results show good agreement with existing theoretical and experimental data.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0271-2091
    Keywords: Finite Element Method ; Rotating Fluid Mechanics ; Slip Flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Linearized multidimensional flow in a gas centrifuge can be described away from the ends by Onsager's pancake equation. However a rotating annulus results in a slightly different set of boundary conditions from the usual symmetry at the axis of rotation. The problem on an annulus becomes ill-posed and requires some special attention. Herein we treat axially linear inner and outer rotor temperature distributions and velocity slip. An existence condition for a class of non-trivial, one-dimensional solutions is given. New exact solutions in the infinite bowl approximation have been derived containing terms that are important at finite gap width and non-vanishing velocity slip. The usual one-dimensional, axially symmetric solution is obtained as a limit. Our previously reported finite element algorithm has been extended to treat this new class of problems. Effects of gap width, temperature and slip conditions are illustrated. Lastly, we report on the compressible, finite length, circular Couette flow for the first time.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 0271-2091
    Keywords: Computer Extended Series ; Rotating Fluid Mechanics ; MACSYMA ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We have reformulated the general problem of internal flow in a modern, high speed gas centrifuge with sources and sinks in such a way as to obtain new, simple, rigorous closed form analytical solutions. Both symmetric and antisymmetric drives lead us to an ordinary differential equation in place of the usual inhomogeneous Onsager partial differential equation. Owing to the difficulties of exactly solving this sixth order, inhomogeneous, variable coefficient ordinary differential equation we appeal to the power of perturbation theory and techniques. Two extreme parameter regimes are identified, the so-called semi-long bowl approximation and a new short bowl approximation. Only the former class of problems is treated here. The long bowl solution for axial drive is the correct leading order term, just as for pure thermal drive. New O(1) results are derived for radial, drag and heat drives in two dimensions. Then regular asymptotic, even ordered power series expansions for the flow field are carried out on the computer to O(ε4) using MACSYMA. These approximations are valid for values of ε near unity. In the spirit of Van Dyke, one can carry out this expansion process, in theory, to apparently arbitrary order for arbitrary but finite decay length ratio. Curiously, the flows induced by axial and radial forces are proportional for asymptotically large source scale heights, x*. Corresponding isotope separation integral parameters will be given in a companion paper.
    Additional Material: 2 Ill.
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