Viscosity design parameters

Effect of Uncertainties in Thermal Design Parameters. The parameters that are used ia the basic siting calculations of a heat exchanger iaclude heat-transfer coefficients tube dimensions, eg, tube diameter and wall thickness and physical properties, eg, thermal conductivity, density, viscosity, and specific heat. Nominal or mean values of these parameters are used ia the basic siting calculations. In reaUty, there are uncertainties ia these nominal values. For example, heat-transfer correlations from which one computes convective heat-transfer coefficients have data spreads around the mean values. Because heat-transfer tubes caimot be produced ia precise dimensions, tube wall thickness varies over a range of the mean value. In addition, the thermal conductivity of tube wall material cannot be measured exactiy, a dding to the uncertainty ia the design and performance calculations. 

Qualitative comparison of a number of design parameters for various agitators in multiphase systems uc.nuvc and are the maximum allowable agitator tip velocity and liquid viscosity. 

A quick estimate of the overall column efficiency can be obtained from the correlation given by O Connell (1946), which is shown in Figure 11.13. The overall column efficiency is correlated with the product of the relative volatility of the light key component (relative to the heavy key) and the molar average viscosity of the feed, estimated at the average column temperature. The correlation was based mainly on data obtained with hydrocarbon systems, but includes some values for chlorinated solvents and water-alcohol mixtures. It has been found to give reliable estimates of the overall column efficiency for hydrocarbon systems and can be used to make an approximate estimate of the efficiency for other systems. The method takes no account of the plate design parameters and includes only two physical property variables. 

When two liquids are immiscible, the design parameters include droplet size distribution of the disperse phase, coalescence rate, power consumption for complete dispersion, and the mass-transfer coefficient at the liquid-liquid interface. The Sauter mean diameter, dsy, of the dispersed phase depends on the Reynolds, Froudes and Weber numbers, the ratios of density and viscosity of the dispersed and continuous phases, and the volume fraction of the dispersed phase. The most important parameters are the Weber number and the volume fraction of the dispersed phase. Specifically, dsy oc We 06(l + hip ), where b is a constant that depends on the stirrer and vessel geometry and the physical properties of the system. Both dsy and the interfacial area aL remain unaltered, if the same power per unit volume (P/V) is used in the scale-up. 

The major characteristic of a polymeric reactor that is different from most other types of reactors discussed earlier is the viscous and often non-Newtonian behavior of the fluid. Shear-dependent rheological properties cause difficulties in the estimation of the design parameters, particularly when the viscosity is also time-dependent. While significant literature on the design parameters for a mechanically agitated vessel containing power-law fluid is available, similar information for viscoelastic fluid is lacking. 

Because of the strong effects of plate rotations on the rector performance for both RE and PC electrolyzers, the critical design parameters for these reactors are the Taylor number (a2w/4v)0 5 and the Reynolds number (aVf/v). Here a is the gap width between the plate, w the angular velocity of rotation (in radians per second), v the kinematic viscosity of the fluid, and V the velocity in the feed pipe. Since no asymptotic velocity profile is reached for PC, the length of the cell will be an important design parameter in a pump-cell electrolyzer. Detailed mathematical models for RE and PC electrolyzers are given by Thomas et al. (1988), Jansson (1978), Jansson et al. (1978) and Simek and Rousar (1984). 

The analyzed fluids at shear rates 30 — 2.2 x 10 s showed the properties of a Newtonian fluid. The comparison of dynamic viscosity experimental values ( /exp) obtained by us with the values calculated by the additive law showed significant negative deviation of experimental dynamic viscosity values from the design parameters, reaching 75% at 20 °C and 440% at -20 °C (see Table 2). 

In solid-liquid systems the size and shape of the baffles are important design parameters. The standard baffling is illustrated in Fig 7.1. As the solid concentration increases and the viscosity becomes high, narrower baffles (approximately 1/24T) placed a distance from the wall, should be used. This design is normally employed to avoid permanent settling of particles in the low velocity zones. In some processes such fillets (settled particles) can nevertheless be advantageous for the power consumption. 

Power consumption is an important mixing design parameter, dependent upon impeller diameter ( >), rotational speed (N), and fluid properties including viscosity (/ra) and density (p), and power consumption of impellers is usually provided as correlations of power number, Np, to Reynolds number, Nt. For fluids exhibiting time-independent power law viscosity functions, r = Kyn, the generalized Reynolds number in agitation can be expressed as ... 

This is a valid approach, being simple and easy to implement. However, it is also necessary to consider the interactions between the two processes to maximize operational performance, for example, the design MLSS concentration will have an influence on the biological design (reactor size and alpha value) and also the membrane design parameters (sludge viscosity, sludge filterability, and TMP). As MBRs... 

The sprayability of a coating is determined by its viscosity at application. The viseosity is a measure of the ability of a material to resist flow and is an important formulation design parameter. Application viscosity is affected by the ambient conditions and by the degree of... 

Monomer design/surface tension, solubility parameters, viscosity, polar-nonpolar, shrinkage during polymerization. ... 

Design parameters reactor parameters—horizontal area. A expanded bed height, Hx—and support media parameters—media density, media diameter, d total volume of media, Fixed parameters liquid phase parameters—diffusivity of substrate S in liquid, liquid density, Pl liquid viscosity, Vl—biofilm parameters—diffusivity of substrate in biofilm, Dsx maximum rate constant, < s,max Michaelis constant, —and... 

It is customary to account for the non-Newtonian fluid behavior by introducing the so called effective viscosity to define various dimensionless groups. Unlike its constant value for Newtonian liquids, the effective viscosity of non-Newtonian pseudoplastic type fluids depends upon the operating conditions (e.g., gas and liquid velocities) as well as on the geometrical details of the system. Indeed, the lack of a rationed definition of the apparent viscosity or characteristic shear rate appears to be the main impediment in extending the well established predictive correlations for Newtonian media to non-Newtonian media. When we develop correlations for design parameters in bubble columns with non-Newtonian media in an analogous manner to the case of Newtonian media, Newtonian viscosity p is simply replaced by an apparent viscosity for non-Newtonian media. 

It should be emphasized here that in the derivation of theoretical correlations for design parameters the introduction of the appeu ent viscosity concept is not necessary, and, as a result, the use of questionable definitions of characteristic shear rate such as Equation 3 is not required, as discussed in the ensuing sections. 

Eq. 12.11 shows very well the interrelationship between the screw design parameters (H, W, screw speed y = NitD), material properties (viscosity is really a function of temperature and shear rate VJH) and operating conditions of barrel temperature and screw speed. These interrelationships can be used to troubleshoot a metering section which can be understood through the impact of any particular change of materials or operating condition on the drag flow and pressure term. 

It has been shown that, despite the different damping mechanisms (viscosity of fluids, relaxation of elastomers, plasticity of metals), all these devices can significantly improve the seismic response of an existing structure, in terms of maximum displacements and floor spectra. In all cases, however, the design parameters of the added dampers must be carefully selected in order to maximize the amount of energy... 

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