Turbulent systems

Figure 7-58 show s the differences in Kg value and maximum explosion pressures for turbulent and non-turbulent systems for the same fuel-air mixtures. 

Toor, H. L. (1962). Mass transfer in dilute turbulent and non-turbulent systems with rapid irreversible reactions and equal diffusivities. AIChE Journal 8, 70-78. 

For triggering behavior, the concentration at one point in time is more important than the average concentration. Therefore, in the real world, considerable deviation from time-averaging models is observed. In addition to timeaveraging models, peak concentrations of odors in turbulent systems have to be considered. Aylor (1976) estimated peak concentrations for air currents in forests. Average concentrations, as calculated by the Sutton formula, may be as low as only a few percent of maximmn (peak) concentrations. It is often the latter, however, that would trigger an animal s response. 

Fuel system corrosion inhibitors must have a low tendency toward emulsification with water and toward foam enhancement in turbulent systems. These properties are especially critical whenever inhibitors are used in jet fuel. The sensitivity of jet fuel pumping and injection systems requires that fuel be free of emulsions and foam. 

First a derivative is given of the equations of change for a pure fluid. Then the equations of change for a multicomponent fluid mixture are given (without proof), and a discussion is given of the range of applicability of these equations. Next the basic equations for a multicomponent mixture are specialized for binary mixtures, which are then discussed in considerably more detail. Finally diffusion processes in multicomponent systems, turbulent systems, multiphase systems, and systems with convection are discussed briefly. 

Microelectrodes often display superior properties to those of larger planar electrodes. They experience hemispherical diffusion profiles which can confer stir independence on the results, which may be important if measuring turbulent systems such as in a river or in the bloodstream. They also allow measurements in high-resistance media, which may be experienced if electrolyte concentrations are very low. 

Film theory predicts that the mass transfer coefficient for a phase (or the overall mass transfer coefficient) is proportional to the diffusion coefficient and inversely proportional to the thickness of the stagnant zone. The diffusion coefficient can be calculated from either the Wilke-Chang or the FSG equations. However, 6 is difficult (if not impossible) to determine. Hence, mass transfer coefficients are often determined from empirical correlations. Also, Film theory is based on the assumption that the bulk fluid phases are perfectly mixed. While this might approach reality for well-mixed turbulent systems, this is certainly not the case for laminar systems. 

Middleton, J. Smith, J. Gas-liquid mixing in turbulent systems. In Handbook of Industrial Mixing Science and Practice Paul, E.L., Atiemo-Obeng, V.A., Kresta, S.M., Eds. John Wiley and Sons New York, 2003 585-638. 

For geometrically similar turbulent systems, which for constant power number gives... 

Critical objects exist in nature. Jean Perrin mentions salted soapy water and Brownian trajectories of particles suspended in a fluid. There are many others, and some of them have aroused the interest of physicists as, for example, the liquid vapour system at the critical point, the magnetic system at the Curie point, and turbulent systems in the inertial range. 

In this context the number of particles depositing for given hydraulic conditions (C — Ceq) must be determined. This means that the characteristics of the particulates must be correlated to local parameters describing the turbulent flow field. This leads to a critical sedimentation velocity i s.cr for a particle. It is derived on the basis of an energy balance the potential energy loss attributable to settling in a non-turbulent system must equal the turbulent kinetic energy that must be imparted on the particle in a turbulent flow system to prevent sedimentation (29). 

Thus, in a perfectly macromixed batch system, the mean concentration is constant (obviously), and the variance of the fluctuations decreases exponentially with time—the latter is obverved in turbulent systems, and is also predicted from isotropic, homogeneous turbulence theory (see Fig. 2). 

Cavities persist when the gas flow is stopped, so power depends on the history of gassing. The cavities are larger than those for the same speed and gas rate in low viscosity turbulent systems and Figure 15.18 shows the effect of this on power. Viscoelastic liquids give even larger cavities of characteristic anvil sha ... 

---