Thermal stress during drying

The enhancement of the surface area of ccria-based materials related to the surfactant effect that reduces the surface tension inside the pores by decreasing capillary stress during drying and calcination processes. Better thermal stability is related to the structural arrangement and the morphology of the inorganic-organic... 

ASME Code Case N-557, "In place dry annealing of a PWR nuclear reactor vessel," March, 1996. USNRC Generic Letter 92-02, Revolution of Generic Issue 79 Unanalyzed reactor vessel (PWR) thermal stress during natural convection cooling. ... 

Low temperature. Low-temperature processes (below 0°C) contain large amounts of fluids kept in the liquid state by pressure and/or low temperature. If for any reason it is not possible to keep them under pressure or keep them cold, then the liquids will begin to vaporize. If this happens, impurities in the fluids are liable to precipitate from solution as solids, especially if equipment is allowed to boil dry. Deposited solids may not only be the cause of blockage but also in some cases the cause of explosions. It is necessary, therefore, to ensure that the fluids entering a low-temperature plant are purified. A severe materials-of-construction problem in low-temperature processes is low-temperature embrittlement. Also, in low temperature as in high-temperature operations, the equipment is subject to thermal stresses, especially during start-up and shutdown. 

Careful control of hydrolysis and condensation rales by use of acid catalysis in Method 3 results in very narrow pore si/e distributions, which minimizes stress gradients during drying by thermal evaporation under ambient pressure and low temperatures. Gels dried in this manner are... 

Figure 9 shows a load-change cycle which is typical for discontinuous SCF extraction. When the pressure release phase following completion of the extraction is considered, the question arises as to the true temperature course. It is wellknown that the pressure-dependent equilibrium temperature of CO2 falls to -79 C under atmospheric conditions. This relationship leads to short-term thermal stresses within the inner surfaces of the pressure vessel, particularly in the lower part where dry ice may form. There is an additional risk to the process that the charge may freeze within the pressure vessel. When designing equipment for the extraction of natural substances, definition of the non-stationary courses of pressure and temperature during pressure release is therefore of especial importance in the choice of materials and for the geometry of the pressure vessel. 

It is interesting to note that not all defects in product crystals arise from the crystallization process itself. Thermal stresses induced in crystals are sometimes greater during the cooling and drying than during the crystallization period, and can be so large as to crack the crystalline material. These thermal stresses, which can produce defect concentrations on the order of 10 -10 /cm, ... 

Pb,Ca)TI03 Substrate deflection Stress evolution during drying, thermal-treatment ond crystallization Mendiolo (1998)... 

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