Consider the following mixing tank problem. A well-mixed tank initially contains

Question

Consider the following mixing tank problem. A well-mixed tank initially contains 100 L of pure water. At time t=0 we start 2 flow streams into the tank. One stream has a flow rate of 2L/min and contains species A with a concentration of 5 mol/L. The other stream has a flow rate of 3L/min and contains species B with a concentration of 4 mol/L. At the same time we withdraw a stream with flow rate 5L/min from the tank. Assume that the densities of all streams are the same. Calculate the Concentration of both A and B in the tank for times of 20, 40, 60, and 100 minutes.

I know I need to set up a differential equaiton for this in terms of concentration but I'm having some major issues with this.

Explanation / Answer

All the time concentration of species A and species B in the tank will be zero.

As stream 1 flow rate is 2L/min and stream 2 has flow rate of 3L/min. So total flow rate going inside the tank is

= 2+3

5 L/min

However at the same time there is another stream which is withdrawing 5 L/min

So total stream flow rate going to the tank = total flow rate of withdrawal

All the time concentration of species A and species B in the tank will be zero.

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