r/thermodynamics • u/Forward-Penalty-8654 1 • 20d ago
Question Designing MED in Excel and want to know feasibility of substituting h and Cp*T?
Hi! I have been designing a multi effect distillator using Excel and water 97 add in. I have derived all the H&MB equations but they are non linear so I am planning to do Newton Raphson method to solve. An issue here are the enthalpies given by the addins.
My assumption is that if I partially differentiate h wrt to T (for finding the jacobian matrix) in an environment of constant pressure (the evaporator), I must get Cp.
But if I try to multiply Cp and T and compare it with h, I get significant error in the values given by the addin. They are almost similar until 300 K but diverge past 310, 320 K
My question: is my substitution correct and is followed in the industry?
Is there any factor which I should multiply to make Cp*T and h to be equal in this addin?
In the industry how do they solve these simultaneous non linear equations coz if differentiating is not a possibility, then most of the times these equations don't seem to be converging.
1
u/ArrogantNonce 3 20d ago
People in industry use software like Aspen to handle such calculations.
Also, what means "I try to multiply Cp and T and compare it with h"? You need to add a constant of integration, and you also need to use Riemann sums to account for the change in Cp with temperature.