Chemical engineeringLesson 2 of 5 in the course Chemical reactors

CSTR Mixing, Design Equations, Residence-Time Distributions, and Cascades

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces the continuous stirred-tank reactor (CSTR), its idealized mixing behavior, and its role in engineering. Understanding the CSTR model helps engineers compare reactor designs and identify suitable applications.

A continuous stirred-tank reactor is a vessel in which reactants flow in continuously, are mixed by agitation, and products leave continuously. It is also called a vat reactor, backmix reactor, mixed flow reactor (MFR), or continuous-flow stirred-tank reactor (CFSTR). CSTR models are used in chemical and environmental engineering to estimate operating variables needed to achieve a desired output.

All flashcards

What is a continuous stirred-tank reactor (CSTR)?
A continuous-flow, agitated vessel in which reactants enter and products leave while the contents are mixed.
What does theoretical residence time represent in a CSTR?
The characteristic average time, calculated as reactor volume divided by volumetric flow rate; individual particles do not all remain exactly this long.
How does a tanks-in-series model change as the number of equal CSTRs increases?
Its flow behavior approaches that of an ideal plug flow reactor.
How do dead space and short-circuiting differ in a reactor?
Dead space is poorly moving fluid; short-circuiting is flow that reaches the outlet unusually quickly.
Why is the outlet concentration used in the rate law for an ideal CSTR?
Perfect mixing makes the concentration uniform throughout the reactor and equal to the outlet concentration.

Quiz questions

  1. For a steady-state CSTR with constant volumetric flow, what relation gives the positive disappearance rate of reactant A?Answer: rA=(CA0−CA)/τr_A=(C_{A0}-C_A)/\tau
  2. For a first-order disappearance reaction in a single ideal CSTR, which equation gives the outlet concentration?Answer: CA=CA0/(1+kτ)C_A=C_{A0}/(1+k\tau)
  3. What is short-circuiting in a real reactor?Answer: Part of the inlet flow takes a rapid path to the outlet.
  4. What flow behavior does a sequence of many ideal CSTRs approach?Answer: The behavior of an ideal plug flow reactor.
  5. For parallel reactions from A, how can staged reactant addition favor a desired pathway with a higher reaction order in A?Answer: It can maintain a higher A concentration, favoring that pathway.

Based on the Wikipedia article Continuous stirred-tank reactor, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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