Transfer units fundamental model

HETP vs. Fundamental Mass Transfer The two-film model gives the following transfer unit relationship ... 

Artificial cation channels could give fundamental information on the mechanism of cation flow and channel conduction [6.69, 6.70]. A solid-state model of cation transfer inside a channel is provided by the crystal structure of the KBr complex of 27c (Y = Y = CH3), which contains stacks of macrocycles with cations located alternately inside and above a macrocyclic unit, like a frozen picture of cation propagation through the channel defined by the stack [6.71]. 

In order make an effort to bring the polyimide-metal adhesion problem to an even more fundamental level, we have previously proposed that model molecules, chosen as representative of selected parts of the polyimide repeat unit, may be used to predict the chemical and electronic structure of interfaces between polyimides and metals (12). Relatively small model molecules can be vapor deposited in situ under UHV conditions to form monolayer films upon atomically clean metal substrates, and detailed information about chemical bonding, charge transfer and molecular orientation can be determined, and even site-specific interactions may be recognized. The result of such studies can also be expected to be relevant in comparison with the results of studies of metal-polymer interfaces. Another very important advantage with this model molecule approach is the possibility to apply a more reliable theoretical analysis to the data, which is very difficult when studying complex polymers such as polyimide. 

The fundamental principles of the gas-to-liquid mass transfer were concisely presented. The basic mass transfer mechanisms described in the three major mass transfer models the film theory, the penetration theory, and the surface renewal theory are of help in explaining the mass transport process between the gas phase and the liquid phase. Using these theories, the controlling factors of the mass transfer process can be identified and manipulated to improve the performance of the unit operations utilizing the gas-to-liquid mass transfer process. The relevant unit operations, namely gas absorption column, three-phase fluidized bed reactor, airlift reactor, liquid-gas bubble reactor, and trickled bed reactor were reviewed in this entry. 

Modelling of CFB systems is in a period of rapid development. Practical models, based on simplified hydrodynamic schemes such as the core-annular approach, have proved effective in allowing hydrodynamics and heat transfer to be scaled from pilot units. More fundamental approaches to transfer coefficient prediction should soon reduce the dependence upon empiricism, and allow greater confidence. 

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