Cooling, trajectory

Fig. 5 Theoretical liquid-liquid demixing curves (dashed lines) and liquid-solid transition curves (solid lines) of 32-mers in a 64-sized cubic box. Three sets of energy parameters are denoted by Cl, C2, and C3, respectively. The arrow indicates the cooling trajectory of the simulations [84]...

Schematic T-T-T diagram for glass formation. If the cooling rate is too slow (cooling curve A), s. polyaystaUine solid will form. To form a glass, the cooling trajectory must miss the nose of the T-T-T curve as does the cooling curve B.

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

This analysis is limited, since it is based on a steady-state criterion. The linearisation approach, outlined above, also fails in that its analysis is restricted to variations, which are very close to the steady state. While this provides excellent information on the dynamic stability, it cannot predict the actual trajectory of the reaction, once this departs from the near steady state. A full dynamic analysis is, therefore, best considered in terms of the full dynamic model equations and this is easily effected, using digital simulation. The above case of the single CSTR, with a single exothermic reaction, is covered by the simulation examples, THERMPLOT and THERM. Other simulation examples, covering aspects of stirred-tank reactor stability are COOL, OSCIL, REFRIG and STABIL. 

The solution of the gas flow and temperature fields in the nearnozzle region (as described in the previous subsection), along with process parameters, thermophysical properties, and atomizer geometry parameters, were used as inputs for this liquid metal breakup model to calculate the liquid film and sheet characteristics, primary and secondary breakup, as well as droplet dynamics and cooling. The trajectories and temperatures of droplets were calculated until the onset of secondary breakup, the onset of solidification, or the attainment of the computational domain boundary. This procedure was repeated for all droplet size classes. Finally, the droplets were numerically sieved and the droplet size distribution was determined. 

Proximity to process equipment handling flammables or combustibles, including vents, flares, incinerators or thermal oxidizers, where either close horizontal distance or where process elevation and trajectory can result in burning material contacting the cooling tower... 

In Figure 5-1 3 are plotted the possible trajectories for the exothermic reaction. These are the limiting cases of the trajectory in a wall-cooled reactor, and any waU-cooled reactor win have a trajectory between these two straight lines. The trajectory cannot go above the equihbrium curve X,(T). For an adiabatic reactor the curve stops there, and for finite UA, the curve finishes at Xe at Tq. 

Figure 5-13 Possible region of trajectories for exothermic reversible reactions, starting at feed temperature To with cooling...

Finally we sketch the possible trajectories that might be followed in an exothermic reaction in a cooled reactor. The trajectory starts at the feed condition of Ca — Cao> X = 0, T = To, and when r goes to infinity, the trajectory will end up at Tc at the equilihrium composition X,. Sketched in Figure 5-16 are three trajectories. 

In designing a wall-cooled tubular reactor, we want to operate such that the trajectory stays near the maximum rate for all temperatures. Thus for an exothermic reversible reaction the temperature should increase initially while the conversion is low and decrease as the conversion increases to stay away from the equilibrium constraint. One can easily program a computer to compute conversion and T versus t to attain a desired conversion for rninimum T in a PFTR. These curves are shown in Figure 5-17 for the three situations. 

The reactor configurations and possible trajectories for three adiabatic reactors with interstage cooling are shown in Figure 5-20. 

Compare T (z) and T Cz) trajectories of a wall-cooled PFTR with cocurrent and countercurrent flows. Which configuration is more likely to produce more problems with a hot spot in the reactor ... 

For a same molecular ratio of aqueous NaY solutions (Y = OH, Cl), experimental data underlines specific effects of nascent OH radicals on transient UV and near-IR electronic configurations. Complex investigations of PHET reactions in the polarization CTTS well of aqueous CT and OH ions are in progress. We should wonder whether a change in the size of ionic radius (OH -1.76 A vs Cl" 2.35 A) or in the separation of the energy levels influence early branchings of ultrafast electronic trajectories. A key point of these studies is that the spectroscopic predictions of computed model-dependent analysis are compared to a direct identification of transient spectral bands, using a cooled Optical Multichannel Analyzer... 

Fig. 3.8. Reactor trajectories in adiabatic and cooled catalyst beds...

To demonstrate the main features of the flow in horizontal CVD reactors, the deposition of silicon from silane is used as an example (87). The conditions are as follows an 8-cm-wide reactor with either adiabatic side walls or side walls cooled to the top wall temperature of 300 K, a 1323 K hot susceptor (bottom wall), a total pressure of 101 kPa, and an initial partial pressure of silane in H2 of 101 Pa. The growth rate of silicon is strongly influenced by mass transfer under these conditions. Figure 8 shows fluid-particle trajectories and spatially varied growth rates for three characteristic cases. 

Figure 8. Fluid-particle trajectories (top) and growth rate variations over the susceptor (bottom) (a) adiabatic side walls, no natural convection (b) adiabatic sidewalls, inward-rolling buoyancy-driven flow and (c) cooled side-walls, outward-rolling buoyancy-driven flow (Reproduced with permission from reference 179. Copyright...

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