Difference between revisions of "ASCEND/C2/Solving-Cubic-EOS/English"

Title slide

• Create a reusable model
• Reuse the model for different components
• Import data from the Thermodynamics library
• Solve the model

System Requirement

• Ubuntu Linux OS v. 12.04
• ASCEND v. 0.9.8

Pre-requisites

• Linux
• ASCEND and
• Peng Robinson cubic Equation Of State

Pre-requisites

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Peng Robinson Cubic EOS

Peng Robinson equation of state is a cubic equation of state which contains volume terms to the third power.

It is usually expressed to give pressure in terms of temperature and molar volume.

These are the equations for Peng Robinson equation of state

Peng Robinson Cubic EOS

These are the equations which we will be using in our model to compute the value of Z.

I already have the code for Peng Robinson model in a text file.

Let me explain the code.

So, add REQUIRE “thermodynamics.a4l”.

After this, we define variables like P, T, V etc. using WILL underscore BE operator.

WILL_BE operator is used to make our model reusable.

The variables defined using WILL_BE are used as parameters in our test model

I will come back to the explanation of WILL_BE as we move ahead in our tutorial.

R IS_A molar_gas_constant;

Pc IS_A pressure;

Tc IS_A temperature;

T_degC IS_A factor;

alpha, beta, q,Tr, Pr, omega IS_A factor;

PSI, OMEGA, sigma, eps IS_A real_constant;

Note that factor denotes a dimensionless variable, Thus alpha, beta, q etc. are defined as a factor

PSI :== 0.45724;

OMEGA :== 0.07780;

sigma :== 2.414213562;

eps :== 0.414213562;

Please note that the values of these constants will be reused in our test model.

Pc = data.Pc;

Tc = data.Tc;

omega = data.omega;

Tr = T/Tc;

Pr = P/Pc;

T_degC = T/1{K} - 273.15;

And so we define

• Pc=data.Pc
• Tc=data.Tc
• and so on.

Note that labels like eq 4, eq 5 etc. are not compulsory to write but they help in debugging the problem.

• True implies fixed variables
• whereas all other variables which are not mentioned here
• are, by default, set to False, i.e. free variables

For Z, we set the upper and lower bound and also provide a nominal value to initiate the solution.

• Z.lower_bound := 0.0;

• Z.nominal := 0.1;

Let's now look at the code for test model.

We name this model as test

We define a symbol constant – c1.

And assign c1 is equal to ethylene.

Here we define cd as components_data of ethylene.

• in the parenthesis, c1 in square bracket implies fetch data for ethylene from thermodynamics library
• whereas c1 outside square bracket is set as reference component.

More on this will be explained in future tutorials.

Thus we define

• P IS_A pressure;

• T IS_A temperature and so on

Now tpeng includes all the equations and methods defined in the peng robinson model.

So we don't have to write the equations and variables again.

This is how we make our model reusable.

• Tr = T/cd.data[c1].Tc; *and similarly for Pr;

cd.date c1.Tc imports the value of Tc for ethylene from thermodynamics library.

In METHODS, we define the standard methods again.

But now

• under method specify, we run tpeng.specify
• under method values, we run tpeng.values

Now end the test model.

peng robinsing and test model

'won’t auto-initiate the model peng robinson

model requires parameters'

But the parameters defined here, will be executed in our test model.

The model opens under Simulation.

And ASCEND has successfully calculated values for z, volume, reduced Temperature and reduced Pressure

Summary

• Create a reusable model
• Reuse the model for different components
• Import data from the Thermodynamics library
• Solve the model

Assignment

Also re-use this model in a test model, to compute value of V for ethylene.

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