Hydrodynamic factor

The structure of the cake formed and, consequently, its resistance to liquid flow depends on the properties of the solid particles and the liquid phase suspension, as well as on the conditions of filtration. Cake structure is first established by hydrodynamic factors (cake porosity, mean particle size, size distribution, and particle specific surface area and sphericity). It is also strongly influenced by some factors that can conditionally be denoted as physicochemical. These factors are ... 

The influence of physicochemical factors is closely related to surface phenomena at the solid-liquid boundary. It is especially manifested by the presence of small particles in the suspension. Large particle sizes result in an increase in the relative influence of hydrodynamic factors, while smaller sizes contribute to a more dramatic influence from physicochemical factors. No reliable methods exist to predict when the influence of physicochemical factors may be neglected. However, as a general rule, for rough evaluations their influence may be assumed to be most pronounced in the particle size range of 15-20 tm. 

P Singh, S Desai, D Flanagan, A Simonelli, W Higuchi. Mechanistic study of the influence of micelle solubilization and hydrodynamic factors on the dissolution rate of solid drugs. J Pharm Sci 57 959, 1968. 

The intent of this chapter is to establish a comprehensive framework in which the physicochemical properties of permeant molecules, hydrodynamic factors, and mass transport barrier properties of the transcellular and paracellular routes comprising the cell monolayer and the microporous filter support are quantitatively and mechanistically interrelated. We specifically define and quantify the biophysical properties of the paracellular route with the aid of selective hydrophilic permeants that vary in molecular size and charge (neutral, cationic, anionic, and zwitterionic). Further, the quantitative interrelationships of pH, pKa, partition... 

Scaling has many useful applications. The dynamic characteristics of different bed designs can be quickly compared. The influence of bed diameter on hydrodynamic behavior can be studied by the use of several different size models. The models allow easy experimental examination of existing operating characteristics. The beds also can be used to quickly confirm the influence of proposed modifications. Since the models usually operate at ambient conditions, it is possible to instrument them to observe detailed behavior. This allows a better understanding of the fundamental physics as well as the identification of hydrodynamic factors needed for proper correlation of performance. 

Small, properly scaled laboratory models operated at ambient conditions have been shown to accurately simulate the dynamics of large hot bubbling and circulating beds operating at atmospheric and elevated pressures. These models should shed light on the overall operating characteristics and the influence of hydrodynamics factors such as bubble distribution and trajectories. A series of different sized scale models can be used to simulate changes in bed behavior with bed size. 

At low Q the experiments measure the collective diffusion coefficient D. of concentration fluctuations. Due to the repulsive interaction the effective diffusion increases 1/S(Q). Well beyond the interaction peak at high Q, where S(Q)=1, the measured diffusion tends to become equal to the self-diffusion D. A hydrodynamics factor H(Q) describes the additional effects on D ff=DaH(Q)/S Q) due to hydrodynamics interactions (see e.g. [342]). Variations of D(Q)S(Q) with Q (Fig. 6.28) may be attributed to the modulation with H(Q) displaying a peak, where S(Q) also has its maximum. For the transport in a crowded solution inside a cell the self-diffusion coefficient is the relevant parameter. It is strongly... 

Fig. 6.28 From bottom to top effective diffusion constant from NSE experiments, S(Q) deduced from RMS A fits, and DqH(Q)=D(Q)S(Q) with H(Q) the hydrodynamic factor. The left side corresponds to a myoglobin solution of concentration c=14.7 mM and the right side c=30 mM. Note the strong reduction of the value of D upon concentration increase. (Reprinted with permission from [332]. Copyright 2003 Elsevier)...

As explained in Sect. 6, the expressions for D, Dx, Dr and r 0 contain several hydrodynamic factors related to frictional coefficients at infinite dilution. We briefly describe the method to calculate these hydrodynamic factors in this appendix. 

The hydrodynamic factors that influence the plasma polymerization process pose a complicated problem and are of importance in the application of plasma for thin film coatings. When two reaction chambers with different shapes or sizes are used and when plasma polymerization of the same monomer is operated under the same operational conditions of RF power, monomer flow rate, pressure in the reaction chamber etc., the two plasma polymers formed in the two reaction chambers are never identical because of the differences in the hydrodynamic factors. In this sense, plasma polymerization is a reactor-dependent process. Yasuda and Hirotsu [22] systematically investigated the effects of hydrodynamic factors on the plasma polymerization process. They studied the effect of the monomer flow pattern on the polymer deposition rate in a tubular reactor. The polymer deposition rate is a function of the location in the chamber. The distribution of the polymer deposition rate is mainly determined by the distance from the plasma zone and the... 

Considerable experimental evidence suggests that chemical cues are very important in substrate selection by larvae. In nature, chemical cues may interact with physical or hydrodynamic factors to induce larval settlement.5-7 Despite the evidence that chemical cues are extremely important for settling larvae, the complete chemical identity of the natural inducer molecules is known in very few cases.3-8-11 More commonly, partial chemical characterization has provided clues to the chemical identity of the natural inducers. These partially purified inducers are useful for studying the biology of larval settlement and metamorphosis.912-18... 

Perhaps the most important term in Eq. 9.12 is the time t required for the transfer or equilibration of solute molecules between high- and low-velocity states. Time teq may be controlled by diffusion or, if the separation tube is packed, by a combination of diffusion and hydrodynamic factors. If the transfer between velocity states requires the crossing of an interface, teq can depend upon interfacial kinetics. 

Grandison, A., Youravong, W., and Lewis, M.J., Hydrodynamic factors affecting flux and fouling during ultrafiltration of skimmed milk, Lait, 80, 165, 2000. 

Darcy, H., 1856. Les fontaines publiques de la ville de Dijon. Dalmont, Paris Davis, J.C., 1986. Statistics and data analysis in geology. John Wiley, New York, 646 pp. Davis, R.W., 1987. Analysis of hydrodynamic factors in petroleum migration and entrapment. The American Association of Petroleum Geologists Bulletin, Vol. 71, no. 6, pp. 643-649... 

In the case of a diffusion-limited reaction, hydrodynamic factors, such as turbulent flow, may influence the dissolution process. Humidity fluctuations also may alter the solute concentrations in the moisture film at the rock surface, and they may result in the dissolution and recrystallization, not only of the carbonates, but also of the secondary minerals, such as calcium sulfate. Wetting and drying cycles may lead to measureable changes in fluid composition at the stone surface. 

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