Velocity effect high temperature

Theory predicts that the mobility decreases as T 3/2 because of lattice scattering (8). But because electrons have higher velocities at high temperatures, they are less effectively scattered by impurities at high temperatures. Consequently, impurity scattering becomes less important with increasing temperature. Theoretical models predict that the mobility increases as T3/2/nj, in which nx is the total impurity concentration (8). The mobility is related to the electron diffusivity, Dn, through the Einstein relation... 

What is the effect of gas velocity at high temperature Does this agree with theory ... 

Whereas corrosion-protection coatings are sup>-posed to be dense and not swell from water intake, other coatings must intentionally be porous. For example, the gas turbine engines, such as those in airplanes, can be made more efficient by increasing the temperature inside the combustion chamber. However, the turbine blades are rotating at a high velocity and high temperature, and consequently the metal surface of the blades may oxidize, and some deformation may occur because of creep. To prevent these detrimental effects, a 0.4-millimeter thin, porous layer of yttrium-stabilized zirconia (a type of... 

Units preferably should be placed in the open and at least 75-100 ft from any large building or obstruction to normal wind flow. If closer, the recirculation from downdrafts may require raising the effective inlet air temperature 2-3°F or more above the ambient selected for unobstructed locations. If wind velocities are high around congested areas, the allowance for recirculation should be raised to greater than 3°F. 

Some workers have correlated experimental data in terms of k at the arithmetic mean temperature, and some at the temperature of the bulk plasma. Experimental validation of the true effective thermal conductivity is difficult because of the high temperatures, small particle sizes and variations in velocity and temperature in plasma jets. 

When a detonation wave passes through an explosive, the first effect is compression of the explosive to a high density. This is the shock wave itself. Then reaction occurs and the explosive is changed into gaseous products at high temperature. These reaction products act as a continuously generated piston which enables the shock wave to be propagated at a constant velocity. The probable structure of the detonation zone is illustrated in Fig. 2.3. 

Some evidence appeared to support the diffusion concept, since it seemed to best explain the effect of H20 on the experimental flame velocities of CO—02. As described in the previous chapter, it is known that at high temperatures water provides the source of hydroxyl radicals to facilitate rapid reaction of CO and 02. 

ECC catalyst is subject to hydrothermal deactivation. This occurs when the A1 atom in the zeolitic cage is removed in the presence of water vapor and temperature. The result is a loss of activity and unit conversion. The effect of temperature on this process is nonlinear. The deactivation rate increases exponentially with temperature. Units that experience high afterburn have attributed high rates of catalyst deactivation on the higher dilute phase temperatures. This phenomenon is more apparent on units with high combustion air superficial velocities. The high velocity not only increases afterburn, but also increases catalyst entrainment to the cyclones and dilute area. COP is used to decrease afterburn and minimize catalyst deactivation. 

It is necessary, however, to maximize the intermediate olefin product at the expense of the aromatic/paraffin product which makes up the gasoline ( ). The olefin yield increases with increasing temperature and decreasing pressure and contact time. Judicious selection of process conditions result in high olefin selectivity and complete methanol conversion. The detailed effect of temperature, pressure, space velocity and catalyst silica/alumina ratio on conversion and selectivity has been reported earlier ( ). The distribution of products from a typical MTO experiment is compared to MTG in Figure 4. Propylene is the most abundant species produced at MTO conditions and greatly exceeds its equilibrium value as seen in the table below for 482 C. It is apparently the product of autocatalytic reaction (7) between ethylene and methanol (8). 

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