Freeze prevention techniques

In addition, freezing and corrosion due to water accumulation in pipes, dead pockets, and instruments have caused numerous pipe failures. Some of these led to gas releases and fatal accidents. A detailed discussion on preventing water accumulation in column piping is presented elsewhere (210). Extensive discussions of winterization and freeze-prevention techniques are also available (120, 266). 

Bubble-Tube Systems The commonly used bubble-tube system sharply reduces restrictions on the location of the measuring element. In order to ehminate or reduce variations in pressure drop due to the gas flow rate, a constant differential regulator is commonly employed to maintain a constant gas flow rate. Since the flow of gas through the bubble tube prevents entiy of the process liquid into the measuring system, this technique is particularly usefiil with corrosive or viscous liquids, liquids subjec t to freezing, and hquids containing entrained solids. 

The Arctic Foundations, Inc. (AFl), frozen soil barrier technology is constructed by artificially freezing the soil pore water. As the pore water freezes, the soil permeability decreases, thereby forming an impermeable barrier that surrounds and contains the contaminants. When properly installed, the frozen soil barrier prevents the migration of contaminants within groundwater and soil. Contaminants are contained in situ, with the frozen native soils serving as the containment medium. The contaminants are isolated by the wall until appropriate remediation techniques can be applied. 

According to the operational definition, it is most important that well-defined methods and clear protocols are provided describing the isolation procedure applied. After isolation, freeze-drying is often used to stabilize the final fraction and to prevent chemical and biological reactions during storage. Critical reviews on the isolation and concentration techniques for aquatic substances are given by Aiken (1985), Leenheer (1985), and Abbt-Braun and Frimmel (2002). 

One of the most practical modifications of freeze-drying synthesis is the cryoimpregnation process. This process is often considered as an independent synthesis technique. In this case, the object of freeze-drying is a porous matrix of fibers or powders soaked/wetted with a solution of microcomponents and frozen by fast cooling. The purpose of the cryoprocessing method in this case is prevention of macro- and microscopic redistribution of the microcomponents within the substrate, which is usually observed during air or thermal drying. 

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