- #1

- 40

- 0

Final Time= about 15 seconds

Final Temp= about 700 R

Final Mass= about 20 lbs

%%%%%%%%%%%%%%

My program is getting these answers but it is not converging at each time step so my plots are all linear when the should not be. Please any suggestions will be greatly appreciated!!

Code:

```
P1=75; % in psi
T1=(80+459.67); %in R
A1=(pi*1)/(4*144); % Area in ft^2
D1=1; % Diameter in inch
P2=(14.7); % in psi
T2=T1; %in R
V2=70; % in ft^3
Cp=0.24; % in Btu/lb-R
Cv=0.17; % in Btu/lb-R
Cd=0.6; % is unitless
R=53.33; % in ft-lb/lb/R
rho1=(P1*144)/(R*T1); % density in lb/ft^3
rho2=(P2*144)/(R*T2); % density in lb/ft^3
mass2=(rho2*V2); % mass in lb
g=32.174; % in ft/sec^2
dt=0.01; % change in time intervals
t=0;
n=1;
k=1.4;
m(1)=mass2;
P(1)=P2;
T(1)=T2;
Pcrit=(2/(k+1))^(k/(k-1));
Prat= (P2/P1);
while P2<P1-.01
t==0+dt;
error=1;
n=n+1;
while error>0.001
%Equations
mdot=A1*sqrt(((2*k)/(k-1))*P1*18*g*rho1*Prat^(2/k)*(1-(Prat))^(k-1/k));
if Prat <= Pcrit;
Prat= Pcrit;
end
mass2new=mass2+mdot*dt;
u=(mass2*Cv*T2+mdot*Cp*T1*dt)/mass2new; %energy equation
T2=u/Cv;
P2new=mass2new*R*T2/(V2*144);
error=abs(P2new-P2)/P2;
P2=P2new;
end
mass2=mass2new;
T(n)=T2;
P(n)=P2;
m(n)=mass2new;
t(n)=n*dt;
end
%% Output
fprintf('The final temperature = %7.3f R\n',T2)
fprintf('The mass of air in tank = %7.3f lb\n',mass2new)
fprintf('The time required to pressurize the tank = %7.3f s\n',t(n))
figure(1)
plot(t,T,'g','Linewidth',2)
grid
ylabel('Temperature (R)')
xlabel('Time (s)')
title('Time Vs Temperature')
figure(2)
plot(t,P,'b','Linewidth',2)
grid
xlabel('Time (s)')
ylabel('Pressure (psi)')
title('Time Vs Pressure')
figure(3)
plot(t,m,'r','Linewidth',2)
grid
xlabel('Time (s)')
ylabel('Mass (lb)')
title('Time Vs Mass')
```