The Ideal Continuous Flow Stirred-Tank Reactor

3 THE IDEAL CONTINUOUS FLOW STIRRED-TANK REACTOR 

The ideal continuous flow stirred-tank reactor is the easiest type of continuous flow reactor to analyze in design calculations because the temperature and composition of the reactor contents are homogeneous throughout the reactor volume. Consequently, material and energy balances can be written over the entire reactor and the outlet composition and temperature can be taken as representative of the reactor contents. In general, the temperatures of the feed and effluent streams will not be equal, and it will be necessary to use both material and energy balances and the temperature-dependent form of the reaction rate expression to determine the conditions at which the reactor operates. 

The material balance on a single CSTR operating at steady state may be represented by 

If multiple reactions are taking place and the system cannot be characterized by a single fraction conversion, an equation of the form of (10.3.1) will need to be written for each species. 

The steady-state form of the energy balance for a continuous-flow stirred-tank reactor is given by equation (10.1.4)  

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The Ideal Continuous Flow Stirred-Tank Reactor 313... 

The next case to be considered is the ideal continuous flow stirred-tank reactor. The key to the derivation of the F t) curve for this type of reactor is the realization that the assumption of perfect mixing implies that upon entry in the reactor an element of volume can instantaneously appear in any position in the reactor. Therefore, its past or future history cannot be derived from its current position. Furthermore, the probability that it will leave the system by some future time will be independent of its past history. These statements require that the probability that a fluid element will remain in the system longer than a time tj -I-12 will be the product of the two independent probabihties that it will remain in longer than times and t2, respectively. 

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