How to create the Gas deviation-factor chart for natural gases from Standing and Katz

Hi, I have a 1x15 sized Ppr vector, a 1x10 Tpr vector and a 15x10 matrix with the values of the compressibility factor Z corresponding to each Pr and Tr. How can I plot such values in the same plot to get a plot like this one :

 From <https://link.springer.com/article/10.1007/s13202-015-0209-3 New explicit correlation for the compressibility factor of natural gas: linearized z-factor isotherms>

Can this be done with a for loop ? I intend to use the script to generate a basic user interface for a school project, and the user should be able to change the dimensions of those vectors and by consequence the size of the matrix is dynamic.

Answer 1

[Are Mjaavatten]

plot(Ppr,Z);
xlabel('Ppr');
ylabel('Z');
legends = cell(10,1);
for i = 1:10;
    legends{i} = sprintf('Tpr = %3.2f',Tpr(i));
end
legend(legends,'location','eastoutside')
% Or maybe better:
% legend(legends,'location','southeast')

Answer 2

[erik.alcala99]

So many thanks Are Mjaavatten, the solution you provided works perfectly. Now I have to get those values correct...

Answer 3

[lili lili]

Hello, I am having a problem in my plot, I am not getting those curves in the graphs, I am just getting lines. Can you please suggest me any idea to fix it? Thank you.

[erik.alcala99]

Hi lili lili , thats maybe bacause of the range, may you are just plotting Ppr: 12 - 14 and Tpr: 1.4 - 1.6, check your values, if necessary first get a value at a time, after those are correct you can then put the code in a couple of for loops, one for Ppr values and another for Tpr values

[lili lili]

erik.alcala99 thank you so much for your answer, but i still get the same thing with one value and for different values :(

[erik.alcala99]

Then the Z values calculation is incorrect, are you using the Newton-Raphson method or the bisection method (or a different one) to calculate Z ?

[lili lili]

Actually I have to use fzero on matlab to calculate the values of Z, so normally the values are correct unless i made some mistake in the equation which I don't really think it happened

[lili lili]

I did this:

for i=1:length(tpr)

for j=1:length(ppr)

z(j)=fzero(f,0.1,[],pr(j),tr(i));

end

plot(ppr,z)

hold on

end

xlabel('ppr')

ylabel('z')

[lili lili]

I finally found it, I used spline and plot. thank you so much for your time sir, I really appreciate that ^^

[erik.alcala99]

Thats great, no problem, we are here to help, hapy plotting :)