Velocity conversion

Useful velocity conversions in order to have equality of mass transport conditions between the rotating cylinder and the annulus and impinging jet are also reported by Silverman (12). 

Pilot-plant operation is conducted usually at 300-325 C., 20-atmos-pheres pressure, with recycle of 3-4 volumes end gas/volume fresh feed. The latter is 1.8 to 2.0 H2 to 1 CO, prepared by oxidationof natural gas with oxygen-steam mixtures at 300—400 p.s.i. and 1200 C. The synthesis operation is in fixed fluidized bed that is, the bed of catalyst is suspended in the flowing gas with no carry-over of powdered catalyst outside the converter. Carry-over is completely avoided by the use of Aloxite filters in the expanded section of the top of the converter. Catalyst density in the fluidized bed is 60-80 pounds/cubic foot at the start. This density decreases during the first 2-14 days of operation to 10-20 pounds/cubic foot because of spalling of the catalyst induced by carbon formation. With a hydrogen-rich total feed gas, 1600 hours of continuous operation was achieved, and with a carbon dioxide-rich feed gas, only about 400 hours. Operation is limited to 1.5-2.5 linear feet/second gas velocity at this velocity conversions of 90-95% are obtained per pass so that multistage opera-... 

Feed flow impact on membrane performance is analyzed in the range 25—110% of the design flow. It is expected that an increase of feed flow will reduce the feed conversion. In Fig. 10.11 methane conversions with and without membrane are compared versus the space velocity after 70 h of operation with ECN membrane without steam sweeping. It appears quite clearly that by increasing the space velocity conversion of methane decreases. 

Chauveteau also studied flow of biopolymers in porous rock. By using well filtered biopolymer solutions, he determined apparent viscosities as a function of Darcy velocity in Fountainbleau sandstone over permeabilities ranging from 3.3 md to 256 md. Polymer retention was low and it was possible to restore the permeability of the rock to its prepolymer value after each polymer flow experiment. Apparent viscosities were fitted with the Carreau Model A. Analysis of the experimental data yields pairs of apparent viscosity and Darcy velocity. Conversion of Darcy velocity to apparent shear rate in the porous rock was done using Equation 14. 

Find et al. [25] developed a nickel-based catalyst for methane steam reforming. As material for the microstructured plates, AluchromY steel, which is an FeCrAl alloy, was applied. This alloy forms a thin layer of alumina on its surface, which is less than 1 tm thick. This layer was used as an adhesion interface for the catalyst, a method which is also used in automotive exhaust systems based on metallic monoliths. Its formation was achieved by thermal treatment of microstructured plates for 4h at 1000 °C. The catalyst itself was based on a nickel spinel (NiAl204), which stabUizes the catalyst structure. The sol-gel technique was then used to coat the plates with the catalyst slurry. Good catalyst adhesion was proven by mechanical stress and thermal shock tests. Catalyst testing was performed in packed beds at a S/C ratio of 3 and reaction temperatures between 527 and 750 °C. The feed was composed of 12.5 vol.% methane and 37.5 vol.% steam balance argon. At a reaction temperature of 700°C and 32 h space velocity, conversion dose to the thermodynamic equilibrium could be achieved. During 96 h of operation the catalyst showed no detectable deactivation, which was not the case for a commercial nickel catalyst serving as a base for comparison. 

In summary, the stagnancy/catalyst effectiveness model predicts that liquid and/or gas velocity effects on the apparent reaction rate will be observed for catalysts vfliich are at least marginally diffusion limited and run in a trickle bed reactor under low velocity conditions. The model predicts that for scale-up of reactions which are diffusion limited or at least marginally so, the pilot plant should be designed to run at elevated velocities which do not show sensitivity to liquid velocity. Conversely, if a pilot reactor is used for providing data for scaleup showing velocity effects, there is a good likelihood that the catalyst suffers from diffusion limitations. 

At high flowrate, jet flow prevails in the centre of the monolith. The fluid velocity can be more than twice the mean velocity. Conversely, fluid velocity at the monolith boundary can be much smaller. This velocity distribution depends on the mean flowrate and on the presence of flow deflectors in the divergent section. 

As expected, a slightly earlier light-off occurs when there are channels with high gas velocity. Conversely, steady state conversions decrease when the velocity is not uniform. For non uniform velocity distributions, at steady state the maximum temperature difference between adjacent channels is about 25 K. Given that the model ignores heat conduction in the solid, the actual temperature difference is probably much smaller except at monolith boundary. 

For defect sizing by TOED, use of L waves involves a penalty in resolution of almost a factor of two at a given frequency because of difference in velocity as compared to shear waves and use of SV waves runs into difficulties because of the mode conversion problems. Further, problems due to couplant thickness variations, surface roughness affects, beam skewing and distortion problems in anisotropic welds can also be expected. On the contrary, SH waves are not affected... 

The transmission coefficient Cl (Qj,t), considering transient (broadband) sources, is time-dependent and therefore accounts for the possible pulse deformation in the refraction process. It also takes account of the quantity actually computed in the solid (displacement, velocity potential,...) and the possible mode-conversion into shear waves and is given by... 

J and Vrepresent the rotational angular momentum quantum number and tire velocity of tire CO2, respectively. The hot, excited CgFg donor can be produced via absorjDtion of a 248 nm excimer-laser pulse followed by rapid internal conversion of electronic energy to vibrational energy as described above. Note tliat tire result of this collision is to... 

I quantities x and y are different, then the correlation function js sometimes referred to ross-correlation function. When x and y are the same then the function is usually called an orrelation function. An autocorrelation function indicates the extent to which the system IS a memory of its previous values (or, conversely, how long it takes the system to its memory). A simple example is the velocity autocorrelation coefficient whose indicates how closely the velocity at a time t is correlated with the velocity at time me correlation functions can be averaged over all the particles in the system (as can elocity autocorrelation function) whereas other functions are a property of the entire m (e.g. the dipole moment of the sample). The value of the velocity autocorrelation icient can be calculated by averaging over the N atoms in the simulation ... 

Impacts and Explosives. The coUision of high velocity bullets or other projectiles with soHds causes rapid conversion of kinetic to thermal energy. Plasmas result iacidentaHy, whereas the primary effects of impact are shock and mechanical effects in the target. Impact-produced plasmas are hot enough to cause thermonuclear bum (180). 

The MTDP process, which is similar to the Tatoray process, produces an equilibrium composition of xylene isomers. A -xylene yield of 24% in the xylene product is formed at 42—48 wt % toluene conversion over the heterogeneous catalyst at 390—495°C, 4.2 MPa (600 psig), 1 2 Hquid hourly space velocity, and 4 H2/hydrocarbon molar feed ratio. A new ZSM-5 catalyst, which has higher activity and stability than the current catalyst, has been reported (93). 

Radial density gradients in FCC and other large-diameter pneumatic transfer risers reflect gas—soHd maldistributions and reduce product yields. Cold-flow units are used to measure the transverse catalyst profiles as functions of gas velocity, catalyst flux, and inlet design. Impacts of measured flow distributions have been evaluated using a simple four lump kinetic model and assuming dispersed catalyst clusters where all the reactions are assumed to occur coupled with a continuous gas phase. A 3 wt % conversion advantage is determined for injection feed around the riser circumference as compared with an axial injection design (28). 

These design fundamentals result in the requirement that space velocity, effective space—time, fraction of bubble gas exchanged with the emulsion gas, bubble residence time, bed expansion relative to settled bed height, and length-to-diameter ratio be held constant. Effective space—time, the product of bubble residence time and fraction of bubble gas exchanged, accounts for the reduction in gas residence time because of the rapid ascent of bubbles, and thereby for the lower conversions compared with a fixed bed with equal gas flow rates and catalyst weights. 

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