Homogeneous material systems

In an earlier little recognized study Schwartzberg and Treybal [497] determined the fluid motion in baffled tanks with turbine stirrers by visualizing it using streak photography. They found that outside the stirrer discharge zone the fluctuating velocities u were described by the proportionality 

Detailed evaluation of the test results gave the following  

From this it followed that u increased proportionally to n and that w /u 1-13. Through the following reasoning the authors came to an interesting proposition  

This expression was very close to that of equation (1.17). From this it was concluded that if P/V = idem, approximately the same local flow velocities will occur in tanks of different sizes. 

Thomae [544] measured the turbulent flow field in an unbaffled stirred tank of V = 1.6 m by determining the vector of the momentary flow velocity by point for point determination with a constant temperature hot-film anemometer. From these paths of equal flow velocity, so-called isotachs, and paths of equal turbulence, so-called isotarachs, were derived for the turbine and for the propeller stirrer. It was also found that u and u increased linearly with Re up to Re = 4 x 10 u cc u oc nd. However, relatively low values were found for the ratio u /u 0.18 for the turbine stirrer and ca. 0.09 for the propeller stirrer. 

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In dispersing of L/L systems, the same power characteristics apply as with mixing in homogeneous material systems, if for the liquid density the average density of the dispersion... 

Colloidal System, a (macro)-homogeneous material system containing colloidal... 

With the assumption that a fibrous medium impregnated with incompressible resin forms a macroscopically homogeneous material system for heat transfer analysis, the three-dimensional energy equation for a moving composites lay-up in a pultrusion die may be written as ... 

The general picture of the relative merits of homogeneous and heterogeneous processes has not yet emerged clearly. The homogeneous catalyst system may offer advantages in chemical efficiency but lead to difficulties of catalyst separation and recovery, or catalysts may tend to plate out in the reactor due to slight instability. Materials of construction may have to be different for the two rival plants. All these factors will have to be considered in an economic assessment and detailed studies made of the complete process networks in both cases. 

If a material system experiences a continuous action, or a complete cycle of operations, of a perfectly reversible kind, the quantities of heat which it takes in at different temperatures are subject to a homogeneous linear equation, of which the coefficients are the reciprocals of these temperatures. If Qr be... 

Gy PM (1992) Sampling of heterogeneous and dynamic material systems - theories of heterogeneity, sampling and homogenizing. Elsevier, Amsterdam... 

In homogeneous catalytic systems we witnessed a new process for the production of acetic acid from methanol and carbon monoxide using a transition metal complex, thus displacing the earlier process employing ethylene as the starting material. The use of immobilized enzymes makes possible the commercial conversion of glucose into fructose. 

Poly(methyl methacrylate) (PMMA) is a classical one-component, positive resist system. PMMA is a single, homogeneous material that combines the properties of excellent film-forming characteristics, resistance to chemical etchants and intrinsic radiation sensitivity. 

Mixing time 6 necessary to achieve a molecular homogeneity of a liquid mixture—normally measured by decolorization methods in material systems without differences in density and viscosity depends on only four parameters, stirrer diameter d, density p, dynamic viscosity / , and rotational speed k ... 

Phase - A physically homogeneous, mechanically separable portion of a material system. 

The incorporation of high amount of niobium results in the formation of an additional pore system and the achievement of an incoherent structure. A stirring with water (at RT, for 8 h) leads to the well ordered homogeneous material, confirmed by the adsorption/desorption isotherm and the pore size distribution (Figure 1 A). 

The quantity ( D) is the average effective diffusivity, which describes the overall diffusion in the system. The diffusion in the system therefore behaves macroscopically as if bulk diffusion were occurring in a homogeneous material possessing a uniform diffusivity given by Eq. 9.4. The situation is illustrated schematically in Fig. 9.4a, and experimental data for diffusion of this type are shown in Fig. 9.5. This diffusion regime is called the multiple-boundary diffusion regime since the diffusion field... 

The free-energy density should not depend on the choice of coordinate system [i.e., /( , VO should not depend on the gradient s direction] and therefore L = 0 and K will be a symmetric tensor.5 Furthermore, if the homogeneous material is isotropic... 

In what follows frequent reference will be made to acceptors and donors. Acceptors are test samples of the expl subjected to shocks and donors are the shock generating systems. Unless otherwise specified, liq expls and single crystals of solid expl will be considered as homogeneous materials, and all poured , pressed or cast solid expls will be considered as heterogenous materials. As will become apparent, there are pro-nouced differences in the shock behavior of homogeneous and heterogenous expls... 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

Gy, PM. (Ed.) Sampling of Heterogeneous and Dynamic Material Systems. Theories of Heterogeneity, Sampling and Homogenizing Data Handling in Science and Technology, Elsevier, Amsterdam, 1992... 

Ecotoxicological considerations and the effort to achieve an increasingly accurate description of the state of the environment challenge analytical chemists who need to determine increasingly lower concentrations of various analytes in samples that have complex and even non-homogenous matrices. The newly coined expression "analytics" emphasizes the interdisciplinary nature of available methods for obtaining information about material systems, with many methods that exceed the strict definition of analytical chemistry. Drawing on the disciplines of chemistry, physics, computer science, electronics, material science, and chemometrics, this book provides in depth information on the most important problems in analytics of samples from aquatic ecosystems. 

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