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Help With Integrating a function with certain bounds

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Areg Arzoomanian
Areg Arzoomanian on 14 Mar 2020
Commented: Walter Roberson on 14 Mar 2020
So here is my code:
%% Givens
P1= 160; %kpa
P2= 500; %kpa
P3= P2; %kpa
Mg= 2; %kg
Mf= 1; %kg
Mt= 3; %kg
syms V1 V2
V3=1.2*V1; %m^3
V3=1.2*V1==V2; %m^3
%% Part A
%Table A-5 %
Pa=160;
Pl= 150; Ph= 175; P2= 500;
vfl= 0.001053; vfh= 0.001057; vf2= 0.001093;
vgl= 1.1594; vgh= 1.0037; vg2= 0.37483;
Tl= 111.35; Th= 116.04; T_500= 151.83;
%Table A-6
P2= 500;
Tl2= 600; Th2=700;
vl2= 0.80409; vh2= 0.89696;
% To test if state '2' is in vapor or staurated
Vfa= ((vfh-vfl)/(Ph-Pl))*(Pa-Pl)+vfl;
Vga= ((vgh-vgl)/(Ph-Pl))*(Pa-Pl)+vgl;
X=Mg/Mt;
v1=Vfa+X*(Vga-Vfa);
V1=v1*Mt;
V3=1.2*V1;
V2=V1;
v2=V1/Mt;
v3=V3/Mt;
if X<1;
T1= ((Th-Tl)/(Ph-Pl))*(Pa-Pl)+Tl
end
if v2>vg2
T2= ((Th2-Tl2)/(vh2-vl2))*(v3-vl2)+Tl2
else T2=T_500
end
%% Part B
if v2>vg2
Mf=0
end
%% Part C
for P=P1;
V_1=V1; V_2=V2;
fun= @(V) P.*V;
Work_12= integral(fun,V_1,V_2)
end
for P=P2;
V_2=V2; V_3=V3;
fun=@(V) P*V;
Work_23= integral(fun,V_2,V_3)
end
Work_total=Work_12+Work_23
Everything works, except the final part "Part C"
For Work_23, I need to take the integral of 'P dV' with the bounds being V2 and V3. Basically once integrated I need it to look like P2(V3-V2) and im expecting an answer of 219.xxx however its giving me 530.xxx. Can someone please help

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Answers (1)

Walter Roberson
Walter Roberson on 14 Mar 2020
fun=@(V) P*V;
The indefinite integral of a*x is 1/2*a*x^2 so the definite integrap from b to c would be 1/2*a*(c^2-b^2)
Basically once integrated I need it to look like P2(V3-V2)
That is something that would happen if you were doing not

  2 Comments

Areg Arzoomanian
Areg Arzoomanian on 14 Mar 2020
so if i wanted to make it P2dV how would I change my code?
Walter Roberson
Walter Roberson on 14 Mar 2020
fun=@(V) P*ones(size(V));
The ones() is important for integral(): integral() will pass in a vector of V values and needs something the same size as V in return.

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