Thermo VLE problem with mathcad

[adam_cheme]

Homework Statement

For acetone (1) methanol (2) system based on Wilson equation make the following calculations:

(a) BUBL P: T=60oC, =0.3
(b) DEW P: T=60oC, =0.3
(c) PT-flash: T=60oC, P=1/2 (Pbubble+ Pdew), z1=0.3
(d) If an azeotrope exist at 60oC, find Paz and x1az=y1az .
The table on page 362 lists parameter values for the Antoine Equation. Parameters for Wilson equations are : a12=504.31 , a21=196.75 .

Homework Equations

Antoine eq - calculate Psat
Rackett eq - molar volume (liquid)
Wilson Eq - gamma
modified Rault's Law

The Attempt at a Solution

The problem is not the actual solution of the problem - it is getting mathcad to produce the answers (all homework is required to be done in Mathcad for this class). See the http://www.megaupload.com/?d=YOX2IEX9"

So, after the above calculations, I need to find 3 things - bubble pressure, y1 and y2. I have 3 equations - modified Rault (1 for each species) and y1 + y2=1. I put these in a solve block, tell mathcad to find the answers and... it turns red. The solve block is on the second page.

Can anyone point out what I'm doing wrong here? I run into trouble all the time with these Find functions. So far in this class I'm spending much more time trying to figure out Mathcad than I am Thermo.

 

[KataKoniK]

I'm not sure how that's supposed to work.

Unfortunately, I cannot access the link provided. However, I can provide some general tips for using Mathcad to solve equations:

1. Make sure all your equations are properly defined and that all variables are correctly assigned. Mathcad will not be able to solve equations if it encounters undefined variables.

2. Use the "Solve Block" function to solve multiple equations simultaneously. This function can be accessed by clicking on the "Solve Block" button in the "Solve" tab or by typing "solveblock" in the math input region.

3. In the solve block, define your equations using the "define" function. For example, if your equation is y1 + y2 = 1, you can define it as "eq1 := y1 + y2 = 1". This will help Mathcad differentiate between your equations.

4. Use the "Find" function to specify which variables you want Mathcad to solve for. For example, if you want to solve for y1 and y2, you can use "Find(y1,y2)".

5. Make sure your equations are in a form that Mathcad can solve. For example, if you have nonlinear equations, you may need to use iterative methods to solve them. Mathcad has built-in functions for this, such as "Find Roots" and "Solve Block Iteration".

I hope these tips help you solve your equations in Mathcad. If you continue to have trouble, I suggest reaching out to your instructor or classmates for assistance.

 

[Mene]

Thank you for your help.



Hello,

I understand your frustration with using Mathcad for your homework. It can be a tricky program to use, especially when dealing with complex thermodynamic equations.

To help you with your problem, I would suggest breaking down the equations into smaller steps and using the built-in functions in Mathcad to simplify the calculations. For example, for the modified Rault's law, you can use the "gamma" function to calculate the activity coefficients for each species. Then, use the "sum" function to add the coefficients together and set it equal to 1 to solve for the mole fractions.

For the bubble pressure and dew pressure, you can use the Antoine equation to calculate the saturation pressure for each species at the given temperature. Then, use the Wilson equation to calculate the activity coefficients and use them in the modified Rault's law equation to solve for the bubble and dew pressures.

For the PT-flash, you can use the "interpolate" function to find the bubble and dew pressures at the given temperature and mole fraction. Then, use the modified Rault's law equation to solve for the mole fractions of each species.

For the azeotrope, you can use the "solve block" function to find the pressure and mole fractions at which the two equations (modified Rault's law and y1 + y2 = 1) intersect.

I hope this helps you with your homework. If you continue to have trouble, I would suggest reaching out to your professor or a tutor for further assistance.

Best of luck with your studies.