Question

Which statement about ideal flow regimes is false? a. In a PFR, the reaction term is larger compared to a CMFR because the contaminant concentration varies from Cin at the reactor influent to Cout at the reactor effluent b. In a CMFR, the time needed to reach steady-state is less than the detention time c. In a PFR, there is no axial mixing (i.e., no mixing in the direction of flow) d. In a CMFR, a change in the influent concentration will immediately impact the effluent concentration

Answer 1

This statement about ideal flow regime is false:

b. In a CMFR, the time needed to reach steady state is less than the detention time.

Explanation:

In a PFR ( Plug Flow Reactor ) , flow occurs from one end to other ( say in a pipe like structure ) without any kind of axial mixing. In a PFR , the influent concentration and effluent concentration are different. It is generally used for disinfection process in a water treatment plant. Whereas in a CMFR ( Completely Mixed Flow Reactor) , the reactants are fed continuously into a stirring tank which ensures that there is mixing of the reactants taking at all the times. In a CMFR, the concentration of the reactants/products is same as it is in the reactor vessel. Due to this continuous flow, there is no detention time of the reactants / products in the reactor vessel, and so the time taken to reach steady state is somehow greater than the detention time.