1.4.1 Board type selection
The plate type or corrugated type should be determined according to the actual needs of the heat exchange occasion. For the case where the flow rate is large and the pressure drop is small, the plate type with low resistance should be selected, and the plate type with large resistance should be selected. Depending on the fluid pressure and temperature, it is determined whether the detachable or brazed type is selected. When determining the plate type, it is not suitable to select the plate with too small a single plate area, so as to avoid too many plates, the flow velocity between the plates is too small, and the heat transfer coefficient is too low. This problem should be paid more attention to the larger heat exchanger.
1.4.2 Process and runner selection
The process refers to a set of parallel flow channels in the same flow direction of a medium in a plate heat exchanger, and the flow path refers to a medium flow channel formed by two adjacent plates in a plate heat exchanger. In general, several flow passages are connected in parallel or in series to form different combinations of cold and heat medium passages.
The process combination should be calculated based on heat transfer and fluid resistance and determined to meet process conditions. Try to make the convective heat transfer coefficient in the cold and hot water flow channels equal or close, so as to get the best heat transfer effect. The heat transfer coefficient obtains a larger value because the convective heat transfer coefficients on both sides of the heat transfer surface are equal or close. Although the flow rates between the plates of the plate heat exchanger are not equal, the calculation is based on the average flow rate in the calculation of heat transfer and fluid resistance. Since the "U"-shaped single-flow nozzle is fixed on the pressing plate, the disassembly and assembly is convenient.
1.4.3 Pressure drop check
In the design and selection of the plate heat exchanger, there is a certain requirement for the pressure drop, so it should be checked. If the check pressure drop exceeds the allowable pressure drop, the design selection calculation must be repeated until the process requirements are met.
Hindered Phenolic Antioxidants
It is well known that Phenolic Antioxidants are favored for their non discoloration properties. But in thermal oxidation conditions or in the gas produced by the combustion of fossil fuels by-products (mainly nitrogen oxides) can also form a colored product exists, it can be used for the development of new high efficiency low antioxidant naphthol.The oxygen resistance of the hindered phenolic antioxidants is also related to the stability of the free radicals generated.
Reaction type hindered phenolic antioxidant is the use of reactive groups will be hindered phenolic antioxidant molecules to the polymer backbone, therefore, has good compatibility with polymer taking resistance and not easy to migrate, volatile and environmental advantages, can keep the antioxidant effect of unsaturated isocyanate or direct addition controllable isocyanation method can produce appropriate reaction type molecular weight antioxidants. At present, reactive hindered phenolic antioxidants have gradually become a hot topic in the field of polymer polymer.The development trend of phenolic antioxidants is to increase the molecular weight of antioxidants, reduce volatility, improve antioxidant efficiency and reduce toxicity, making them more suitable for processing and using at higher temperatures. The development and production of asymmetric hindered phenolic antioxidants represent a major trend in the field of polymer antioxidants in the world today. It has broad prospects in the application of high-performance plastic products. Reactive and polymeric hindered phenolic antioxidants are also very active. Reactive hindered phenolic antioxidants are bonded to the protected polymer chains because they contain reactive groups in polymer thermal processing or polymerization. Polymeric phenolic antioxidants are obtained by homopolymerization or copolymerization by monomers with blocked phenolic units. These two kinds of new phenolic antioxidants also represent an important research direction of antioxidant.
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