Problem set up

We now wish to let the mass transfer rate vary in time.  Choosing a single frequency may not be completely realistic, but it is simple and will show the effect.  

Note that a mass transfer coefficient never is negative so we need something a little more complex than a sine wave.  Here we have a background minimum value of ka, a frequency ω and a maximum value, kb.   

Here we change the values.

This seems to work well for the mass transfer coefficient.  We can now just incorporate it into the model we have been using.

The two-phase fluctuating equations are: