Short-contact-time process parameters

Effect of Process Parameters on Short Contact Time Conversions... 

By contrast, there is no doubt or any contradictions in literature concerning the importance of macro-kinetic factors (heat- and mass-transfer processes) in the reactions discussed in this section. It is generally realized that these processes proceed in spatially distributed systems and generate sharp gradients of parameters (temperature, pressure, density, concentrations, etc). It could be noted here a distinct similarity of alkane oxidation over Pt-group metals at short contact times and well studied and practically implemented ammonia oxidation and cyanic acid synthesis reactions, in which transfer processes play a dominant role (see Satterfield, 1970). 

The temperature profile is the most important aspect of operational control for pyrolysis processes. Material flow rates, both solid and gas phase, together with the reactor temperature control the key parameters of heating rate, highest process temperatures, residence time of solids and contact time between solid and gas phases. These factors affect the product distribution and the product properties. Solid residence time is another important factor in the bio-oil yields. A short residence time enhances biooil yields, while a longer residence time increases char production (Antal and Gronli, 2003). 

The effects of four processing parameters on the residual wall thickness in molded parts are illustrated by the thicknesses measured at five positions (PI, P3, P5, P7, and P9) in Figure 4. On the whole, the residual wall thickness at position P5 is smaller than those at positions PI and P3. Furthermore, the thickness obviously decreases from positions P7 to P9. Position P9, that is, the position near the end of the water channel, exhibits the minimum wall thickness. This can be explained as follows. At 68.5% short-shot size used in this work, the injected polymer melt can only reach near position P7 in the mold cavity. The cavity downstream is filled with the melt pushed by the water. The time for the pushed melt to contact the cavity is short due to high filling rate of water. Moreover, the cavity warms up because of the contact with the hot melt during the water injection delay. So the water easily pushes the melt against the mold cavity. 

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