Problems - Solution

Problem 1, Solution

Problem 2, Solution

Problem 3, Solution

1) Design a model for a wetland of known dimensions through which waste water flows from left to right, assuming that the system behaves as a PFR. Assume that the degradation of chemicals -such as atrazine- follows irreversible first-order homogeneous kinetics, and that part of the waste water evaporates from the surface as it flows along the wetland. Obtain an equation that represents the molar flow of toxic substances (F_A) as a function of distance (z). Consider that evaporation occurs on the wetland's top surface area at a constant rate (Q = kmol water / hr*m²) and that none of the toxic chemicals are lost to the air by evaporation.

The final equation obtained from the model was:

	(12)
where

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2) Now that you have come up with a functional model, use Polymath to find out what the molar flow of atrazine, F_A, would be at z = 100 m and at z = 1000 m?

The final result for F_A at z = 100 m is 1.637E-04 kmol atrazine/hr. The final result for F_A at z = 1000 m is 2.682E-05 kmol atrazine/hr. During the first case, the behavior of F_A resembles a straight line; while in the second case, the values of F_A start curving inward until they finally stabilize near z = 1000 m. (As shown in the following images).

Download the original Polymath file of this problem, by clicking here:
PFR_model.pol

PFR Model

F_A at z = 100 m

F_A at z = 1000 m

x vs z, until z = 100 m

x vs z, until z = 1000 m

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3) Plot your results with three different variations: conversion (x) as a function of distance, molar flow of atrazine (F_A) as a function of distance, and reaction rate (r_A) as a function of distance. Do these runs until z = 1000 m.

Download the original Polymath file of this problem, by clicking here:
PFR_model.pol

x vs z, until z = 1000 m

F_A vs z, until z = 1000 m

r_A vs z, until z = 1000 m

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