Hello, ı have a problem with Z factor, although ı have different Pr values which plays as a variable in finding Z factor,ı still have the same value for Z factor as 1.0001 each time .Can anyone help me ı will be grateful

yH2S=0;  
yCO2 =0;
yN2=0;
 N2=input(' N2 enter:');
   CO2=input('CO2 enter:');
    H2S=input('H2S enter:');
   Gg=input('Gg enter:');
    T=60;

      P=zeros(1,100);
         for i=1:100
             P(1)=0;
             P(i+1)=P(i)+100;
          yN2 = N2 / 100;
          yCO2 = CO2 / 100;
          yH2S = H2S / 100;
          cGg = (Gg - 0.9672 * yN2 - 1.5197 * yCO2 - 1.1768 * yH2S) / (1 - yN2 - yCO2 - yH2S);
          Tpc = 168 + 325 * cGg - 12.5 * cGg ^ 2;
          CorrTpc = Tpc - 80 * yCO2 + 130 * yH2S - 250 * yN2;
          Ppc = 677 + 15 * cGg - 37.5 * cGg ^ 2;
          CorrPpc = Ppc + 440 * yCO2 + 600 * yH2S - 170 * yN2;
          Tr = (T + 460) / CorrTpc;
          Pr = P / CorrPpc;
          a = 0.064225133;
          b = 0.53530771 * Tr - 0.61232032;
          c = 0.31506237 * Tr - 1.0467099 - 0.57832729 / Tr ^ 2;
          d = Tr;
          e = 0.68157001 / Tr ^ 2;
          f = 0.68446549;
          g = 0.27 * Pr;
         rho = 0.27 * Pr / Tr ;
         rhoold = rho;
          for i = 1:100
              frho = a * rho .^ 6 + b * rho .^ 3 + c * rho .^ 2 + d * rho + e * rho .^ 3 .* (1 + f * rho .^ 2) .* exp(-f * rho .^ 2) - g;
              dfrho = 6 * a * rho .^ 5 + 3 * b * rho .^ 2 + 2 * c * rho + d + e * rho .^ 2 .* (3 + f * rho .^ 2 .* (3 - 2 * f * rho .^ 2)) .* exp(-f * rho .^ 2);
              rho = rho - frho / dfrho;
              test = abs((rho - rhoold) / rho);
             if test < 0.0001 
             rhoold = rho;
             ZFactor = 0.27 * Pr / rho / Tr;
             end
          end
        Zm=ZFactor;
        MW = 28.97 * Gg;
              a = (9.4 + 0.02 * MW) * (T + 460) ^ 1.5 / (209 + 19 * MW + (T + 460)) / 10000;
              b = 3.5 + 986 / (T + 460) + 0.01 * MW;
              c = 2.4 - 0.2 * b;
              rho = P * MW / Zm / 10.73 / (T + 460);
              Ug = a * exp(b * (rho / 62.4) .^ c);
            mP1 = 0;
          Pold = 0;
          Xold = 0;
          Pstep = P / 20;
       for j=0:20
              Pnew = Pold + Pstep;
              Pr = Pnew / Ppc;
              Xnew = 2 * Pnew / Zm / Ug;
              mP1 = mP1 + (Xold + Xnew) / 2 * Pstep;
              Pold = Pnew;
              Xold = Xnew;
       end
          end

Answer 1

[Adam]

You seem to just keep reassigning to ZFactor inside a for loop.

If you want multiple answers you need someting like:

ZFactor(i) = 0.27 * Pr / rho / Tr;

You also have nested loops that both use 'i' as the loop variable. To be honest I have no idea what the behaviour is when this happens, but I doubt it will be what you want. Even if it is don't do it as it isn't good practice!

Answer 2

[Star Strider]

If you substitute ‘rho’ into ‘ZFactor’:

rho = 0.27 * Pr / Tr ;
ZFactor = 0.27 * Pr / rho / Tr;

and do some simple algebra, you will see that:

ZFactor = 1

regardless of the values of the other variables.

[Star Strider]

Your ‘Z’ variable will be what you calculate it to be, not what you want it to be!

Answer 3

[Hakki]

yes I am also aware of this part but in reality there must be such number like Z=1.2 or 1.4 something