Cooling nucleation

The steady-state simulation showed that the average reactor core channel operates in sub-cooled forced convection, with the hot core channel is in sub-cooled nucleate boiling. A minimum critical heat flux (CHF) ratio of 7.2 was calculated for the hottest location, indicating a large margin of safety during normal operation. The initial conditions obtained from the analysis of normal operation were used as the initial condition in the accident studies. 

These are miscible in the melt [5] but crystallize separately on cooling, nucleating each other as they do so [21]. They may be compatibilized by addition of ethylene-propylene block copolymers [19], or by attaching acid groups to one polymer and basic groups to the other to strengthen the interface between them and thus retain their ductility [22]. 

Cellulose Acetate. The extmsion process has also been used to produce ceUular ceUulose acetate (96) ia the deasity range of 96—112 kg/m (6—7 lbs /fT). A hot mixture of polymer, blowiag ageat, and nucleating agent is forced through an orifice iato the atmosphere. It expands, cools, and is carried away on a moving belt. 

Magnesium ferrosihcon alloys react vigorously when added to molten iron. As the magnesium vaporizes and cools, it reacts with residual surface tension modifiers such as sulfur and oxygen and greatly increases the surface tension of the molten iron. The dissolved graphite in the molten iron nucleates and grows into a spheroidal shape because of the increased surface tension of the molten iron. 

Scaling is not always related to temperature. Calcium carbonate and calcium sulfate scaling occur on unheated surfaces when their solubiUties are exceeded in the bulk water. Metallic surfaces are ideal sites for crystal nucleation because of their rough surfaces and the low velocities adjacent to the surface. Corrosion cells on the metal surface produce areas of high pH, which promote the precipitation of many cooling water salts. Once formed, scale deposits initiate additional nucleation, and crystal growth proceeds at an accelerated rate. 

Nucleation tempering of the stiU molten fat is necessary because the cocoa butter, if left to itself, can soHdify in a number of different physical forms, ie, into an unstable form if cooled rapidly, or into an equally unacceptable super stable form if cooled too slowly, as commonly happens when a chocolate turns gray or white after being left in the sun. The coarse white fat crystals that can form in the slowly cooled center of a very thick piece of chocolate are similarly in a super stable form known in the industry as fat bloom. 

Better product characteristics are obtained through control of the rate at which supersaturation (cooling, evaporation, and addition of a nonsolvent or precipitant) is generated. An objective of the operation may be to maintain the supersaturation at some constant prescribed value, usually below the metastable limit associated with primary nucleation. For example, the batch may be cooled slowly at the beginning of the cycle and more rapidly at the end. 

Because of the possibility of focusing laser beams, tlrin films can be produced at precisely defined locations. Using a microscope train of lenses to focus a laser beam makes possible tire production of microregions suitable for application in computer chip production. The photolytic process produces islands of product nuclei, which act as preferential nucleation sites for further deposition, and tlrus to some unevenness in tire product film. This is because the subsuate is relatively cool, and therefore tire surface mobility of the deposited atoms is low. In pyrolytic decomposition, the region over which deposition occurs depends on the drermal conductivity of the substrate, being wider the lower the thermal conductivity. For example, the surface area of a deposit of silicon on silicon is nanower dran the deposition of silicon on silica, or on a surface-oxidized silicon sample, using the same beam geomeU y. 

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