Study Questions

1. List and discuss the significance of the six assumptions commonly made during the modeling of suspended growth reactors.

2. What is meant by the terms "hydraulic residence time" and "residence time distribution?" Describe a continuous stirred tank reactor (CSTR) and a plug flow reactor (PFR) in terms of their hydraulic residence times and residence time distributions. What are the physical characteristics of each reactor that are responsible for the nature of its residence time distribution?

3. A reactor with a volume of 4.0 L receives a constant flow of water at a rate of 3.0 L/hr. At time zero an impulse of dye is added to the reactor which instantaneously places a dye concentration of 1200 mg/L into it. Effluent samples taken 1, 2, 3, 4, and 6 hr after addition of the dye have concentrations of 567, 268, 126, 60, and 13 mg/L, respectively. Is the reactor a perfect CSTR?

4. Explain how you would use the data from a tracer study to choose the appropriate model for characterizing the performance of a nonideal reactor.

5. Given in Table SQ4.1 are the response data from a reactor (t = 30 niin) to which a step input of tracer was applied. If you desired to model this reactor as a series of CSTRs, how many CSTRs would you use? If you desired to model the reactor with an axial dispersion model, what dispersion number would you use?

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