Hydrodynamic aspects

The geometrical shape of the temperature profiles can be controlled in relation to the thermal dependence of the dielectric properties, and moreover, the absence of warming walls, as in classical heating, gives new dimensions to microwave heating. These two characteristics can make it possible to obtain specific and promising hydrodynamic effects as a result of thermal treatment of liquids. 

The possibility of the tie rods vibrating in the complex flow pattern has been the subject of considerable analysis and study as the reactor design developed. This study and analysis divided naturally into two parts, one which considered the hydrodynamic aspects of possible tie rod oscillations and one which determined the vibration deflections and stresses of the tie rods under the influence of the possible exciting forces. The following paragraphs describe the results of these analyses and studies. 

The primary conclusion is that in the unlikely event that the tie rods vibrate in resonance with maximum possible excitation the stresses and deflections in the tie rods will be sufficiently small that there is no possibility of fatigue failure. In the actual case, the tie rods are not expected to be in resonance with the exciting force because the maximum local cross flow velocity will probably be less than 7 ft s. Furthermore, at high Reynolds numbers, there are experimental indications that the exciting forces will be aperiodic and that the combination of parallel and cross flow will decrease the stability of the flow 

The velocity distributions normal and parallel to the tie rods, respectively, were obtained from potential flow analogue studies of a two-dimensional model of the lower plenum. A wake of highly turbulent, but essentially stagnant fluid, was assumed to exist, protruding downwards into the plenum from the lower edge of the core barrel. The extent of the wake was adjusted to give consistency with the experimentally observed flow non-uniformity at the lower core plate. 

A maximum cross flow velocity of 7 ft s occurs just above the middle of the tie rod. Below this point, the velocity decreases to less than 0.5 ft s at one-third of the distance between the casting and the core plate. 

The velocity parallel to the rod decreases from 12 ft s at a position two-thirds of the distance between the casting and core plate to less than 1 ft s at the mid-point of the tie rods. 

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Recently, hydrodynamic aspects of multiphase applications have been studied in detail for the cocurrent and countercurrent flow regimes. Useful correlations were determined and it was found that foams combine high rates and low pressure drop, proving their high potential in multiphase applications [9, 107, 108]. 

Because the bubble population increases with heat flux, a point of peak flux may be reached in nucleate boiling where the outgoing bubbles jam the path of the incoming liquid. This phenomenon can be analyzed by the criterion of a Hemholtz instability (Zuber, 1958) and thus serves to predict the incipience of the boiling crisis (to be discussed in Sec. 2.4.4). Another hydrodynamic aspect of the boiling crisis, the incipience of stable film boiling, may be analyzed from the criterion for a Taylor instability (Zuber, 1961). 

In Chapter 3 the steady-state hydrodynamic aspects of two-phase flow were discussed and reference was made to their potential for instabilities. The instability of a system may be either static or dynamic. A flow is subject to a static instability if, when the flow conditions change by a small step from the original steady-state ones, another steady state is not possible in the vicinity of the original state. The cause of the phenomenon lies in the steady-state laws hence, the threshold of the instability can be predicted only by using steady-state laws. A static instability can lead either to a different steady-state condition or to a periodic behavior (Boure et al., 1973). A flow is subject to a dynamic instability when the inertia and other feedback effects have an essential part in the process. The system behaves like a servomechanism, and knowledge of the steady-state laws is not sufficient even for the threshold prediction. The steady-state may be a solution of the equations of the system, but is not the only solution. The above-mentioned fluctuations in a steady flow may be sufficient to start the instability. Three conditions are required for a system to possess a potential for oscillating instabilities ... 

Dijkman, F. J. M., 1969, Some Hydrodynamic Aspects of a Boiling Water Channel. Thesis Technische Hogeschool to Eindhover, the Netherlands. 

Thorgerson, E. J., 1969, Hydrodynamic Aspects of the Critical Heat Flux in Subcooled Convection Boiling, Ph.D. thesis, University of South Carolina, Columbia, SC. (5)... 

Nuclear Soc., ANS 1966 Annual Meeting, American Nuclear Society, LaGrange Park, IL. (6) Zuber, N., 1958, On Stability of Boiling Heat Transfer, Trans. ASME, J. Heat Transfer 50 711-720. (2) Zuber, N., 1959, Hydrodynamic Aspects of Boiling Heat Transfer, USAEC Rep. AECU-4439, Ph.D. 

During the dissolution test, the hydrodynamic aspects of the fluid flow in the vessel have a major influence on the dissolution rate (1). Therefore, the working condition of the equipment is of critical importance. In this chapter, the qualification and calibration of the equipment referred to in the two USP General Chapters related to dissolution, < 711 > Dissolution and < 724 > Drug Release (2), will be discussed. Sources of error when performing dissolution... 

AN Skouloudis H M Kottowski, "Hydrodynamic Aspects of Venting for - Vessels Containing Viscous Fluids", Plant/Operations Prog, 10 (2), 107-114,... 

Tulin MP (1966) Hydrodynamic aspects of macromolecular solutions Proceed 6th Symp on Naval Hydrodynamics, ONR CR-136, p 3, Washington... 

Heiszwolf JJ, Engelvaart LB, Gvd Eijnden M, Kreutzer MT, Kapteijn F, Moulijn JA. Hydrodynamic aspects of the monolithic loop reactor. Chem Eng Sci 2001 56 805-812. 

The work leading up to the 1968 conference produced a volume of target boundary-layer data. A eommittee headed by D. Coles surveyed over 100 experiments and selected 33 flows for inclusion in this volume. The data of each experiment were carefully reanalyzed and recomputed for placement in a standard form critiques were solicited from the experimenters and all this was documented in a tidy manner by E. Hirst and D. Coles (S3). These data now stand as a classic base of comparison for turbulent boundary-layer prediction methods. Only the hydrodynamic aspects of these layers... 

The hydrodynamic aspects of chromatography play a major role in selecting the appropriate particle size. In contemporary HPLC, flow rates higher than the optimum on the H-u plots predicted by Eq. (1.10) or Eq. (1.11) are used to allow shorter separation times without significant loss of resolution. The minimum velocity, Mmm, for the H u plots described by the van Deemter equation (1.10) can be calculated from Eq. (1.12) [12] ... 

A re dew of thermal and hydrodynamic aspects of heat-exchanger fouling appears in Refs. Minimization of fouling through operational and design factors is addressed in... 

While the chemical aspects of catalyst performance (resistance to poisoning, activity, and selectivity) are being continually improved, only little has been done to date to improve the hydrodynamic aspects (heat transfer and mass transfer rates, pressure drop, and uniformity of distribution of concentration, temperature, and velocity) of heterogeneous contacting. 

Baldyga J, Orciuch W. Some hydrodynamic aspects of precipitation. Powder Technol2001 121 9-19. 

The hydrodynamic aspects of cell design have been studied using a rotating electrode setup.25 As the electrode rotation speed is increased, the potential required to sustain constant-current deposition increases. The hydrodynamics increase the rate of oligomer transport away from the electrode and therefore prevent polymer deposition. 

The optimization of an electrochemical reactor calls for a full description of the process to accomplish the specific objective of the mass and the energy balances together with heat transfer considerations and thermodynamic and enthalpy changes that are related to the unit cell and the whole stack [1,2]. A full description of the kinetics of both processes, the electric properties of the cell components, and the hydrodynamic aspects of the entire cell is also required. 

Especially the chapters by Ives on rate theories (pp. 37-61) and by L. A. Spielman on hydrodynamic aspects of flocculation (pp. 63-88) are recommended. An extensive and detailed treatment is in... 

This especially stresses the hydrodynamic aspects of aggregation and coalescence. An overview of fractal aggregation is... 

Hydrodynamic aspects of the operation include the minimum impeller speed needed to ensure complete dispersion of one liquid phase la the other, and the size of droplets produced under a given nst of conditions, preferably during the process of mass transfer. 

N. Zuber, Hydrodynamic Aspects of Boiling Heat Transfer, Report AECU-4439, Atomic Energy Commission (US), 1958. 

The appeal of fluorescence spectroscopy in the study of biomolecular systems lies in the characteristic time scale of the emission process, the sensitivity of the technique, and its ability to accommodate rapid and facile changes in the solvent milieu under conditions corresponding to thermodynamic equilibrium. The time scale of the emission process invites exploitation in two related manners. First, information on hydrodynamic aspects of the system is available from steady-state or time-resolved measurements. Second, detailed information on local dynamic processes within the biomolecular matrix may be derived. Information on hydrodynamic aspects of a macromolecular system may be used to study binding processes, that is, the association of small ligands with macromolecules or macromolecule-macromolecule interactions. In this chapter we focus on the latter applications of polarization or anisotropy data. We shall also try to clarify aspects of this area that our experience has shown to be occasionally misunderstood by initiates. 

Chapters 26—29 all discuss hydrodynamic aspects of emulsified systems. The contribution by Danov, Kralchevsky, and Ivanov presents a very fundamental and thorough survey of different phenomena in emulsions related to dynamic and hydrodynamic motions, such as the dynamics of surfactant adsorption mono-layers, which include the Gibbs surface elasticity, and characteristic time of adsorption, mechanisms of droplet-droplet coalescence, hydrodynamic interactions and drop coalescence, interpretation of the Bancroft rule with regard to droplet symmetry, and, finally, kinetics of... 

Although flie interpretation of the amplitude of the ICG is obscured by many complicating factors, a more relevant aspect of the ICG signal may be found in the time relationships, especially when the timing of specific marker points in the ICG signal is compared with that of marker points in the ECG. Regardless of the multiple sources of the signal, the ICG reflects the mechanical/hydrodynamical aspects of the cardiac cycle, as described by... 

In summary, as a main conclusion, there is a clear and quantitative influence of the preferential solvation effect on the polymer elution behavior in SEC. In the past, the dependence of elution volumes on the sample concentration injected had been only attributed to conventional hydrodynamic aspects (solvent quality affecting the coil size), although never before the thermodynamic effects had been taken into account. 

Finally, the most noticeable result has been the understanding of the usually observed concentration effects on the elution volumes based not only on hydrodynamic aspects, but also on the important influence of thermodynamic factors such as the preferential solvation. In this sense, it has been quantitatively shown that, for a given solvent/polymer system and a given molar mass, the concentration effect is more acute in the packing that presents lower polymer-gel sorption and lower degree of cross-linking. 

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