a) Briefly discuss the difference between \"plug flow\" and \"perfect mixing\" a
ID: 702062 • Letter: A
Question
a) Briefly discuss the difference between "plug flow" and "perfect mixing" and give examples of reactors which most closely fit these models. b) For a perfect mixer, the particle retention profile can be given by n/no eVtm. Clearly define all terms and sketch the resultant curve. c) Define all terms in the Ergun equation and briefly discuss the significance of the equation. In your answer, indicate the conditions under which each term predominates. = 150 d) Discuss the conditions under which the minimum fluidisation will occur, and develop the equation to calculate the minimum fluidisation velocityExplanation / Answer
Answer to question number (a)
The term " Plug flow" is associated with " Pug flow reactor" (PFR) . It is an ideal reactor. It only comprises of Tubes, where in the fluid flows. when there are catalytic reactions, catalyst are packed in tubes where in the reacting fluid passes through catalyst and the reaction occurs
The terms "perfect mixing" is associated with reactors popularly known as " Continuous stirred tank reactor" ( CSTR) . This reactors basically comprise of a tank with a stirrer. The fluid comes in gets mixed properly and than leaves the reactor. This too, just like PFR is an ideal reactor
1. There is no axial mixing in Plug flow reactor. In CSTR there is 100% mixing
2. In PFR the reactant gradually react to form product. Hence the Concentration profile of reactant gradually decreases. In CSTR as ther reactant enters the reactor, there is sudden drop is reactant concentration ( as reactant gets converted to products) . Hence the concentration profile is flat
3. Due to no mixing in PFR, Hot spots gets created in PFR which can sag the tubes and damage the reactor and flow might degrade the products. In CSTR due to mixing, the temperature is uniform throughout the reactor and hence there are no hot spots created in CSTR.
4. The conversion is high is PFR ( due to no mixing) compared to CSTR
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