Undefined function or variable "C".Error in line

Hi

I've been given a function by my professor that calculates PT flash for non -ideal systems. I'm trying to use it to simulate an experiment. But continously get error.

I think it may be the way i've set my input up.

The function is below:

function[Xeq, Yeq, alphaV, Fl, Fv]=PTFLASH_VLE_Wilson(C,MW,rhoL,BIP,P,T,Z)
%this is a function that calculates PT flash for non -ideal systems where K
%cannot be explicit since it depends on X which is also a variable
c=length(Z);
for i=1:c
  
    Ps=exp((C(i,1))+(C(i,2)/T)+(C(i,3)*log(T))+(C(i,4)*T^C(i,5)));
end

% validating the possibility of having VLE

[PB,y]=PB_VLE_Wilson(Z,C,MW,rhoL,T,BIP);

[PD,x]=PD_VLE_wilson (C,MW,rhoL,BIP,T,Z);

% checking if there is VLE
if  P<=PD           %% y here represents the mole fraction of componenets
    Xeq=0;
    Yeq=y;
    alphaV=1;
    Fl=0;
    Fv=P*Z;    
elseif P>=PB           %% x here represents the mole fraction of components
    Xeq=x;
    Yeq=0;
    alphaV=0;
    [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,Xeq);
    Fl=Ps.*Xeq.*gamma;
    Fv=0;
else
    Xeq=(x+y)/2 ;      % first guess on x
    [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,Xeq);   %first guess on gamma
    K=(Ps.*gamma)/P;  % first guess on K
     Psi_0=sum(z.*(K-1));
        Psi_1=sum(z.*(K-1)./K);
        if Psi_0*Psi_1>=0    % bad initial guess
    Xeq=0;
    Yeq=0;
    alphaV=0;
    Fl=0;
    Fv=0;
    disp("bad initial guess")
        else       %supposedly good initial guess
            Fl=zeros(1,c);     % trick to enter the while cycle at the begininng
            Fv=Fl+1;
            iter=0;            % initialization of iteration count
            while max(abs((Fv-Fl)./Fv))>0.00001 && iter<10000 && Psi_0*Psi_1<0
                [ alphaV ] = RACHFORDRICE_BISECT( K,Z );
     xeq=Z./((1-alphaV)+alphaV*K);
            Yeq=K.*xeq;
           [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,Z);   %Gamma new guess
            K=(Ps.*gamma)/P;
            psi_0=sum(z.*(K-1));
            psi_1=sum(z.*(K-1)./K);
            Fv=P*Yeq;
            Fl=Ps.Xeq.*gamma;
            iter=iter+1;
            end
        end
end
end

The input:
T=320;
Z=[0.1 0.9];
P=1.5E04
MW=[60.09 100.16];
rhoL=[803 802];
T=303.15;
BIP=[196.250 386.133;196.250 386.133];
C=[88.1834 -8498.6 -9.0766 8.330e18 6;153.23 -10055 -19.488 1.6426e5 2];
C1=[88.134 153.23];
C2=[-8498.6 -10055];
C3=[-9.0766  -19.488];
C4=[8.330e18 1.6426e5];
C5=[6  2];
C = [C1' C2' C3' C4' C5'];
Tc=[301  263];

[KALYAN ACHARJYA]

Provide this PB_VLE_Wilson function file

Answer 1

[KALYAN ACHARJYA]

I didnot find the same error, in my case the error is expected that I dont have PB_VLE_Wilson function file.

P =
       15000
Undefined function or variable 'PB_VLE_Wilson'.

Why you are considering two C

C=[88.1834 -8498.6 -9.0766 8.330e18 6;153.23 -10055 -19.488 1.6426e5 2];
......
C = [C1' C2' C3' C4' C5'];

Is this both are same, if not in this case peivious C is replaced by later C, whch pass to the finction.

[Chinaemerem Valentine Nwobi]

function [PD,xDew]=PD_VLE_wilson (C,MW,rhoL,BIP,T,Z)

% this is a function that calculates the dewpoint of a mixture with the

% wilson correlation for generating activity coefficients for non ideal

%liquid phase

c=length(Z);

for i=1:c

Ps=exp((C(i,1))+(C(i,2)/T)+(C(i,3)*log(T))+(C(i,4)*T^C(i,5)));

end

% initial guess of Pdew using PD_VLE_ID(C,T,y)

[PD,xDew]=PDew_Raoult(Ps,Z,T); %initial guess of PD(1) and calculation of x1

[gamma,~]=ACTIVITY_WILSON(MW,rhoL,BIP,T,Z);% calculation of gamma at the initial guess of x1

iter=0;

while max(abs((PD*Z-Ps.*x.*gamma)./(PD*Z)))>0.001 &&iter<1000 %isofugacity conditions and control on the number of iterations

PD=1/sum(Z./Ps.*gamma);

xDew=(PD*Z)./(Ps.*gamma);

[gamma,~]=ACTIVITY_WILSON(MW,rhoL,BIP,T,x);% initial guess of gamma

iter =iter +1;

end

if iter<1000

PD=1/sum(Z./Ps.*gamma);

xDew=(PD*Z)./(Ps.*gamma);

else

PD=0;

xDew=0;

disp("bubble point not found");

end

end

[KALYAN ACHARJYA]

What about PB_VLE_Wilson?

[KALYAN ACHARJYA]

I am tired now there are more functions

Undefined function or variable 'ACTIVITY_WILSON'.

Answer 2

[Chinaemerem Valentine Nwobi]

Hi Kalyan,

sorry for the inconveniences attached to this. please find enclosed the requested script

function [gamma,a]=ACTIVITY_WILSON(MW,rhoL,BIP,T,Z)
%This program calculates the activity coefficients (gamma) and the 
%activities (a) of each component of a mixture of c components using the 
%Wilson model. 
%INPUT PARAMETERS: MW: vector (1xc) reporting the molecular weights of the 
%c components; rhoL, vector (1xc) reporting the liquid density of the c 
%pure components at temperature T; BIP is a matrix cxc reporting the energy   
%interaction parameters (BIP(i,j)=lambda_ij-lambda_ii, J/mol). The energy
%interaction parameters are temperature independent; T: temperature of the 
%system; x vector (1xc) reporting the mole fractions of the components of 
%the mixture.   
%OUTPUT PARAMETERS: gamma: vector 1xc reporting the activity 
%coefficients of the components of the mixture; a: vector 1xc reporting the 
%activities of the components of the mixture. 
%Unless otherwise stated, all input/output parameters are expressed
%according to MKS.

R=8.314;
c=length(Z);

%Molar volumes of the pure liquid components composing the mixture
Vl=1./((rhoL*1000)./MW);

%Lambda terms (dimensionless) of the Wilson formula
for i=1:c
    for j=1:c
        Lambda(i,j)=(Vl(j)/Vl(i))*exp(-BIP(i,j)/(R*T));
    end
end

for i=1:c
    for j=1:c
        A=sum(Z.*Lambda(j,:));
        C(j)=Z(j)*Lambda(j,i)/A;
    end
    lngamma(i)=1-log(sum(Z.*Lambda(i,:)))-sum(C);
    gamma(i)=exp(lngamma(i));
    a(i)=gamma(i)*Z(i);
end

end