Effective Residence Time

In order to observe any temperature dependence in transient flow degradation, it would be necessary to prolong considerably the effective residence time of the polymer coil. This can be accomplished either by recirculating the solution or by using an oscillatory flow equipment as described in Sect. 4.1 (Figs. 23 and 24). 

The high temperatures and pressures created during transient cavitation are difficult both to calculate and to determine experimentally. The simplest models of collapse, which neglect heat transport and the effects of condensable vapor, predict maximum temperatures and pressures as high as 10,000 K and 10,000 atmospheres. More realistic estimates from increasingly sophisticated hydrodynamic models yield estimates of 5000 K and 1000 atmospheres with effective residence times of <100 nseconds, but the models are very sensitive to initial assumptions of the boundary conditions (30-32). 

The forms of equations 14 and 17 describing the deposition of the tracer on the ocean surface, ocean floor and into the historical layers of the sediments are all similar. However, the amplitude variations in the historical layers of sediment are attenuated considerably compared to variations in deposition on the ocean surface, i.e., at input, the attenuation being governed by the effective residence times of nuclides in sea water and in the mixed layer of the sediments. 

The probability of readsorption increases as the intrinsic readsorption reactivity of a-olefins (k,) increases and as their effective residence time within catalyst pores and bed interstices increases. The Thiele modulus [Eq. (15)] contains a parameter that contains only structural properties of the support material ( <>, pellet radius Fp, pore radius 4>, porosity) and the density of Ru or Co sites (0m) on the support surface. A similar dimensional analysis of Eqs. (l9)-(24), which describe reactant transport during FT synthesis, shows that a similar structural parameter governs intrapellet concentration gradients of CO and H2 [Eq. (25)]. In this case, the first term in the Thiele modulus (i/>co) reflects the reactive and diffusive properties of CO and H2 and the second term ( ) accounts for the effect of catalyst structure on reactant transport limitations. Not surprisingly, this second term is... 

Grasslands managed for animal production (e.g., cattle) are much more leaky with respect to loss of added Nr. The addition of fertilizer and/or grazing animals increases the amount of Nr available for loss, especially via the atmosphere (e.g., NH3 (Sommer and Hutchings, 1997) and N2O (Fowler et al., 1997)). Thus, the effective residence times for managed ecosystems are potentially less than those for unmanaged systems. 

The overall process economics examined the extraction rate as a function of power, residence time, and grind size. The full-scale design possibilities were represented in the form ofTable 18-2, which were accompanied by other charts that gave different heights of suspension in the tank for the three different particle size fractions fine, medinm, and coarse. These various combinations of power levels also gave varions blending efficiencies and had different values of the effective residence time used in a system. 

It is scientifically easier to get to grips with the thermodynamics of the metal ion complexing that actually occurs in vivo rather than with the kinetics. This arises because what may well be thermodynamically feasible may not in reality be achieved because, due to slow kinetics, the time required for complex formation is longer than the effective residence time of the complexing molecule in the region of the metal. Conversely, the manifold presence of enzymes in vivo can well speed up a reaction involving a trace element by many orders of magnitude. Thus,... 

In continuous flow mode the relaxation times are affected by the ow rate and may be expressed in terms of an effective residence time t within the flow cell. 

E/N, f(u) as well as of the fluid dynamics of the chemical discharge reactor i.e., type of flow (plug, laminar, turbulent) and related dimensionless quantities relevant to the definition of (a) velocity profiles and corresponding effective residence times,... 

In certain situations in which it is impracticable to use selective absorption or high gas flow rates as a means of securing low residence times and product concentrations, a possible alternative is to use a pulsed discharge in which the effective residence time of the gas molecules is dictated by the pulse duration and the time interval between successive pulses. By this means, very short effective residence times can be achieved and typical data, again for the ammonia—hydrazine reaction, are shown in Figure 9, in which the energy yield of hydrazine is plotted vs. the discharge duration for a constant gas flow rate. The reactor was... 

Figure 9. Effect of short residence times on hydrazine yield when the effective residence time is dictated by the pulsed discharge characteristics...

Kinetic Measurements. The results of the shale oil cracking experiments are summarized in Table I. Oil yields are reported as a percentage of the LLNL assay result on both a condensed-oil basis and a C5+ basis. To conduct the kinetic analysis, an effective residence time had to be determined. It was assumed for simplicity that the gas-and-oil evolution profile could be approximated by a square pulse. The average residence time was calculated by multiplying the void volume of the bottom reactor by the time interval over which three-fourths of the products were evolved and then dividing by the total volume of gases and vapors at the cracking temperatures (14). The void volume was... 

The time needed to separate a mixture in a discontinuous operation is the effective residence time. For continuous operation, it is the mean residence time t , of the mixture... 

The drug could be protected from the physiological environment for a longer duration of time. Thus the effective residence time of the drug could be extended. 

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