Steady-state significance

Leavens et al. (1996a, 1997) and Leavens and Bond (1996) further explored the metabolic interactions between butadiene and styrene in male B6C3Fj mice exposed to mixtures of butadiene and sty rene by inhalation. At steady state, significant inhibition of butadiene metabolism by styrene was observed with mixtures of 1000 ppm butadiene and 250 ppm styrene, but not with 100 ppm butadiene and 250 ppm styrene. Inhibition by butadiene of sty rene metabolism was evidenced by the significant increase in styrene blood concentrations (42% above that in mice exposed to styrene only) in the exposure to 1000 ppm butadiene and 250 ppm styrene. These authors concluded that while exposure to mixtures of sty rene and butadiene results in inhibition of metabolism of both sty rene and butadiene, interactive effects are seen only at high concentrations that are of little relevance to human exposure. 

The flow may be expected to settle to a new steady state significantly faster than the temperature of the... 

Atomization. A gas or Hquid may be dispersed into another Hquid by the action of shearing or turbulent impact forces that are present in the flow field. The steady-state drop si2e represents a balance between the fluid forces tending to dismpt the drop and the forces of interfacial tension tending to oppose distortion and breakup. When the flow field is laminar the abiHty to disperse is strongly affected by the ratio of viscosities of the two phases. Dispersion, in the sense of droplet formation, does not occur when the viscosity of the dispersed phase significantly exceeds that of the dispersing medium (13). 

There are many sources of errors in the plant. The principal ones are related to sampling (qv), mass flow rates, assaying, and deviations from steady state. Collecting representative samples at every stage of the flow sheet constitutes a significant task. Numerous methods and equipment are available (10,16,17). 

A steady-state rocket-type combustion spray unit has been developed, called high velocity oxy fuel (HVOF), that creates a steady state, continuous, supersonic spray stream (1.2—3 mm dia) resembling a rocket motor exhaust. The portable device injects and accelerates the particles inside a barrel (rocket nozzle). It produces coating quaHty and particle velocities equal to the D-gun at 5—10 times the spray rate with significantly reduced coating costs. 

If there is a significant resistance to transport of the reactant in the pores, a concentration gradient will exist at steady state, whereby the concentration of the reactant is a maximum at the particle periphery and a minimum at the particle center. The product concentration will be higher at the particle center than at the periphery. The concentration gradients provide the driving force for the transport. 

This procedure constitutes an application of the steady-state approximation [also called the quasi-steady-state approximation, the Bodenstein approximation, or the stationary-state hypothesis]. It is a powerful method for the simplification of complicated rate equations, but because it is an approximation, it is not always valid. Sometimes the inapplicability of the steady-state approximation is easily detected for example, Eq. (3-143) predicts simple first-order behavior, and significant deviation from this behavior is evidence that the approximation cannot be applied. In more complex systems the validity of the steady-state approximation may be difficult to assess. Because it is an approximation in wide use, much critical attention has been directed to the steady-state hypothesis. 

Either step could be rate determining. Study of many reactions has shown that most occur with a significant isotopic effect, but for some reactions the isotope effect is absent.If we apply the steady state approximation to the intermediate, this reaction scheme leads to... 

The iiitemil energy and entlialpy in Eqs. (4.5.2) uid (4.5.3), as well as in tlie other equations in tliis discussion, may be on a mass or a mole basis, or tliey may represent the total internal energy and entlialpy of tlie entire system. Most industrial facilities operate in a steady-state flow mode. If no significant mechanical or shaft work is added or withdrawn from tlie system, Eq. (4.5.3) reduces to... 

As reviewed in Chapter 2, loads are often applied abruptly, resulting in significant stress and strain increases. However, the elasticity of most TPs lets recovery usually be complete. Therefore, the steady-state stress and deflection of plastic can be considered identical to that of a product that is loaded gradually. However, when impact becomes severe, failure can result from it. 

---