Pre crystallization

Next, in order to study the stability of the kebabs, the flow rate was set at e = 0.001 and four, initially equilibrated (i.e. in a pre-crystallized conformation), short chains were added per t = 2000 with an initial position of 20ro length units away from the stagnation point in the x and y direction. They form a kebab around the shish which was preformed. This procedure was repeated up to 44 short chains in the kebab as shown in Fig. 31. 

The kebab is stable even though e is larger than ec for a single short chain. The kebab has a uniform thickness and does not seem to resemble the flow contour. It must be stressed that the thickness of the kebabs formed in this way is determined independent of the presence of the shish. The short chains are pre-crystallized before they are incorporated in the kebab. The kebab formed in this way is only slightly influenced by the shish, except for the fact that it was nucleated on it. The presence of already-formed kebabs clearly modifies the flow, a feature that is not present in these simulations. The flow,... 

PTT polymer pellets must be dried to a moisture level of <30 ppm, preferably in a close-loop hot air dryer, to avoid hydrolytic degradation during melt processing. Drying is carried out with 130 °C hot air with a dew point of < -40 °C for at least 4 h. Because of the faster crystallization rate, PTT pellets are already semicrystalline after pelletizing, and do not require pre-crystallization prior to drying as with PET. The dried polymer is extruded at 250-270 °C into bulk continuous filaments (BCFs), partially oriented yam (POY), spin-draw yam (SDY) and staple fiber. 

Problems arising from the crystallization of lactose in milk and whey powders may also be avoided or controlled by pre-crystallizing the lactose. Essentially, this involves adding finely divided lactose powder which acts as nuclei on which the supersaturated lactose crystallizes. Addition of 0.5 kg of finely ground lactose to the amount of concentrated product (whole milk, skim milk or whey) containing 1 tonne of lactose will induce the formation of c. 106 crystals ml-1, about 95% of which will have dimensions less than 10/an and 100% less than 15 /an, i.e. too small to cause textural defects. 

Crystallization events in chocolate manufacture include tempering (pre-crystallization), cooling (bulk crystallization), and bloom (re-crystallization). These processes influence a number of important technological (economic) and sensorial attributes of chocolate (Table 1). Much attention has been focused on bloom formation and its influence on color and gloss, and for good reason, since a consumer may never even buy, let alone eat, a moldy-looking confection. However, we are less... 

Fibers with a large excess of alumina with respect to the nominal mullite composition exhibit similar features. When fired below the mullitization temperature, they consist of a mixture of transition alumina and amorphous silica with (pre-crystallized Nextel 720 fiber) or without (Altex fiber) corundum. Conversely, after mullitization in the 1100-1200"C temperature range (Figure 2a), the crystalline phases present in the fibers are mullite and corundum [18] [33]. 

The system consists of a fluidized bed heater/pre-crystallizer and a column dryer for PET. The fluid-bed section has five main functions ... 

The influence of the solvent is also crucial in crystallization from solution, the most common crystallization technique in practice, but, as discussed in Section 13.10, there are practically no instances in the literature where this problem has appropriately been dealt with using dynamic simulation on realistic systems - not just the Lennard-Jones fluid. It is probably appropriate to say that if real progress in predicting the appearance of crystal polymorphs is desired, the current effort in improving intermolecular potentials and search algorithms for comparing static, final crystal structures should be redirected to the study of pre-crystallization states, and to the improvement of dynamic methods for the simulation of the kinetics of crystal nucleation and growth. 

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