ABSTRACT
In an incompressible system (such as a liquid), flow rate has two significant meanings: (1) the feed-in rate of mass and (2) the ‘‘sweeping rate’’ of the molecules in the system, from which an estimate of the residence time of a molecule in the system can be calculated. However, the second meaning of flow rate requires careful examination when applied to a gas flow, depending on the conditions used. In general, the ‘‘flow’’ of gas in a vacuum should not be conceived as being similar to the flow of a liquid. In a flow of gas under a vacuum, the absolute velocity of the gas molecules and the diffusional displacement velocity (brownian motion) are large. The gas flow rate does not represent the velocity of individual gas molecules but only the total flux. It therefore does not represent the sweeping rate applicable to an individual molecule. In a polymer-forming luminous gas phase (reactive system), the flow rate of monomer should not be taken beyond the meaning of the rate of feed-in into the reactor because the flow rate is determined in the nonreactive gas state and no information about the gas under luminous gas phase is generally available. The distribution of polymer deposition is indicative of this point.
