Alright, I'm usually good with math, but I'm stumped on how my professor did this.

I have

Ca = -(A/D) * ln(r) + B

Boundary Conditions:
Ca1 = K*Pa1 @ r=r1
Ca2 = K*Pa2 @ r=r2

In the notes, he solves for the b/c and gets:

A = D*K*(Pa1-Pa2)/ln(r2/r1)

B = K*Pa1 + [K*(Pa1-Pa2)*ln(r1)]/ln(r2/r1)

which combine to get

Ca(r) = K*Pa1 + [K*(Pa1-Pa2)*ln(r1/r)]/ln(r2/r1)

I've apparently forgotten how to solve for boundary conditions. I remember that you could set one of the values to 0 and then solve for the other, but that will only get his B equation if you then solve for B using the value for Ca at r=r1.

In other words, I can set B to zero and get the A equation. I substitute this back in and solve for B at Ca1 = K*Pa1...which doesn't make sense to me.

I can solve for Ca(r) using the equations for A and B, but why would I solve for B using only values at r = r1?

Halp PLz!

9/22/2008 4:21:17 PM

If this is still unanswered when I get out of class I'll come back and read this

9/22/2008 5:01:00 PM

Thanks, I don't think its that complicated, its just something fundamental I'm missing.

9/22/2008 5:12:51 PM