Solving arrays in an equation to a variable

syms T p
pfun=fun_EthanolDampfdruck(T);

Unrecognized function or variable 'fun_EthanolDampfdruck'.

TSiede=vpasolve(pfun==1.01325,T,300); %Boilingtemperature of Ethanol at 1.013 bar
fprintf('The vapor pressure of Ethanol is %4.2f °C at a system pressure of 1.013bar ',TSiede-273.15)
R=8.314; %universal Gas constant J/(mol*K)
q=38720; %Heat of vaporization in J/mol at 78.27°C and 1.013bar
p=[1.013; 1.05; 1.08; 1.013; 1.05; 1.08; 1.013; 1.05; 1.08; 1.013; 1.05; 1.08; 1.013; 1.05; 1.08; 1.013; 1.05; 1.08; 1.013; 1.05; 1.08];
TS=zeros(1,length(p));
for i=1:length(p)
    TS(i)=vpasolve(pfun==p(i),T,300);
end
x=[0.1; 0.1; 0.1; 0.15; 0.15; 0.15; 0.18; 0.18; 0.18; 0.20; 0.20; 0.20; 0.21; 0.21; 0.21; 0.22; 0.22; 0.22; 0.23; 0.23; 0.23]; %Weightfraction of A in Ethanol-Solution
T=[81.62; 82.53; 83.25; 84.98; 85.92; 86.63; 87.84; 88.75; 89.45; 90.07; 90.88; 91.6; 91.24; 92.04; 92.74; 92.5; 93.33; 94.03; 93.72; 94.52; 95.23]; %Temperature in °C
T=T+273.15; %Temperature in K
for i=1:length(T)
    px(i)=fun_EthanolDampfdruck(T(i));
end
px;
dp=px-p'; %Delta Partialpressure of the solution to pure Ethanol 
dTb=TS'-T % Delta Boiltingtemperature of the Solution to pure Ethanol
syms m
for i=length(dTb)
    m(i)=solve(dTb(i)==m*(1-x(i))/x(i)*R*T(i)^2/q,m) % Equation is dTb=m*(1-x)/x*R*T^2/q 
end

With my Code m shows me the following image with only one solution at m(1,21). dTb,x,T are all 21x1. How can i get m for dTb/x/T(1:21). If there is a basic failure in my Script please let me know, im new to matlab :)

[Torsten]

Don't name the symbolic variable and the array in which you save the solution both "m".

[Kevin]

i changed

m(i)=solve(dTb(i)==m*(1-x(i))/x(i)*R*T(i)^2/q,m)
to
l(i)=solve(dTb(i)==m*(1-x(i))/x(i)*R*T(i)^2/q,m)

And the result is almost the same

[Torsten]

We need to know the array dTb.

[Dyuman Joshi]

@Kevin, could you share the function fun_EthanolDampfdruck?

Without it, we don't know the values obtained, as @Torsten points above, and it is difficult to suggest anything.

[Kevin]

function y=fun_EthanolDampfdruck(T) %Temperatur in °C
A=-8.33801;
B=0.08719;
C=-3.30578;
D=-0.25986;
Tc=513.90; %kritische Temperatur in Kelvin
F=1-T/Tc;
pc=61.48; %kritscher Druck in bar
y=exp(Tc/T*(A*F+B*F^1.5+C*F^2.5+D*F^5))*pc;
end

The function works without Problems.

dTb is shown in the following picture

Answer 1

[Dyuman Joshi]

Quite a minor mistake.

The loop index is of the last for loop is only length(dTb), that's why only the last value is obtained as you mentioned earlier in the comments.

for i=length(dTb)
    % ^ see here
    l(i)=solve(dTb(i)==m*(1-x(i))/x(i)*R*T(i)^2/q,m); % Equation is dTb=m*(1-x)/x)*R*T^2/q 
end

It should be 1:length(dTb)

for i=1:length(dTb)
    % ^ corrected
    l(i)=solve(dTb(i)==m*(1-x(i))/x(i)*R*T(i)^2/q,m); % Equation is dTb=m*(1-x)/x)*R*T^2/q 
end

Your code works after the correction.

Use double if you want to convert the symbolic values of the output variable to numeric values.

[Kevin]

Thank you very much, that was the mistake :)