Why is my loop not working? "Index exceeds array bounds"

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smith
smith on 24 Sep 2022
Commented: VBBV on 12 Nov 2022 at 22:12
Function:
function [ row, cp, k] = apd (T)
if T > 318 & T < 320
row = 1.11
cp = 1007
k = 0.02781
else if T > 316 & T< 318
row = 1.1135
cp= 1007
k = 0.027635
else if T > 314 & T < 316
row= 1.1205
cp= 1007
k= 0.02749
else if T > 312 & T <314
row= 1.1277
cp = 1006.5
k = 0.02734
else if T >310 & T < 312
row = 1.1349
cp= 1006
k= 0.02719
else if T >308 & T < 310
row = 1.142
cp = 1006
k = 0.02704
else if T > 306 & T < 308
row= 1.14975
cp= 1006
k=0.0269
else if T > 304 & T < 306
row = 1.1573
cp = 1006
k= 0.02682
else if T >302 & T < 304
row = 1.16495
cp = 1006
k = 0.02666
else if T >297 & T < 302
row = 1.17865
cp = 1006
k = 0.026345
end
end
end
end
end
end
end
end
end
end
end
This function supposedly generates 3 air properties for a range of temperatures.
now, for the upcoming code that monitors the change of temperature and the distance crossed as air enters a tube where heat transfer by convection occurs:
%%%%%% DEFINITIONS %%%%%%%
clear
Q_lpm=15;
Q(1) =(Q_lpm/1000)/60; %m3/s [INPUT]
diameter = 0.01; % m [INPUT]
t =0.01; % time step [INPUT]
viscosity = 1.95*10^-5; % N.s/m2
Pr = 0.702;
area = pi*(diameter)^2/4; %m2
xtraveled = 0
xtube = 1.5
xprev = 0
V(1) = Q(1)*t;
x(1) = V(1)/area;
T(1) = 30 + 273;
Twall = 25+273;
i = 0
%%%%% ITERATIONS %%%%%
while xtraveled < xtube
xprev =xtraveled
i= i+1
T = T(i)
[row,cp,k]=apd(T) %% generates new row, cp and k every iteration
mdot(i)= Q(i)*row; %% getting the mass flow rate at that specific row
velocity = Q(i) / area;
Re(i) = (row*velocity*diameter)/(viscosity) % if Re> 2300 - turbulent (calculated at that row)
Nu(i) = 0.023*(Re(i)^0.8)*(Pr^0.4) %% nusselts number at that row
h1(i) = Nu(i)*k /diameter %% Heat transfer coeefficient at each density
As(i) = pi*diameter*x(i) %% surface area at each distance crossed inside the tube
L(i) = (h1(i)*As(i)*(T(i)-Twall)*t)/(row*cp*V(i)) %% energy balance parameter
T(i+1) = - L(i) +T(i) %% the new temperature at the new control volume
Q(i+1) = mdot(i) /row %% the new flow with the new temperature (new density)
V (i+1) = Q(i+1) * t %% the new control volume of the new flow
x (i+1) = V(i+1) / area %% the new distance crossed inside the tube
xtraveled = xprev + x(i+1) %% total distance travelled by the flow is the previous travelled one plus the new x at each iteration
end
whenever i run the code, it stops at L(i) showing an error of "Index exceeds array bounds"
  1 Comment
Dyuman Joshi
Dyuman Joshi on 24 Sep 2022
Edited: Dyuman Joshi on 24 Sep 2022
You are overwriting the variable T in each iteration.
T = T(i) %over-writing
[row,cp,k]=apd(T)
change this to
t = T(i)
[row,cp,k]=apd(t)
%or directly
[row,cp,k]=apd(T(i))
and move "i=i+1;" line to below the apd function call line or at the bottom
Also, what would happen in the value of T is a boundary value.
For example - T = 302 / 304 / 306 ...
What will be the values of row, cp and k for these values?

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Answers (1)

VBBV
VBBV on 24 Sep 2022
Edited: VBBV on 24 Sep 2022
%%%%%% DEFINITIONS %%%%%%%
clear
Q_lpm=15;
Q(1) =(Q_lpm/1000)/60; %m3/s [INPUT]
diameter = 0.01; % m [INPUT]
t =0.01; % time step [INPUT]
viscosity = 1.95*10^-5; % N.s/m2
Pr = 0.702;
area = pi*(diameter)^2/4; %m2
xtraveled = 0
xtraveled = 0
xtube = 1.5
xtube = 1.5000
xprev = 0
xprev = 0
V(1) = Q(1)*t;
x(1) = V(1)/area;
T(1) = 30 + 273;
Twall = 25+273;
i = 0
i = 0
%%%%% ITERATIONS %%%%%
while (xtraveled < xtube)
xprev =xtraveled ;
i= i+1;
% T = T(i)
[row,cp,k]=apd(T(i)); %% generates new row, cp and k every iteration
mdot(i)= Q(i)*row; %% getting the mass flow rate at that specific row
velocity(i) = Q(i) / area;
Re(i) = (row*velocity(i)*diameter)/(viscosity); % if Re> 2300 - turbulent (calculated at that row)
Nu(i) = 0.023*(Re(i)^0.8)*(Pr^0.4) ;%% nusselts number at that row
h1(i) = Nu(i)*k /diameter; %% Heat transfer coeefficient at each density
As(i) = pi*diameter*x(i); %% surface area at each distance crossed inside the tube
L(i) = (h1(i)*As(i)*(T(i)-Twall)*t)/(row*cp*V(i)); %% energy balance parameter
T(i+1) = - L(i) +T(i); %% the new temperature at the new control volume
Q(i+1) = mdot(i) /row; %% the new flow with the new temperature (new density)
V (i+1) = Q(i+1) * t; %% the new control volume of the new flow
x (i+1) = V(i+1) / area; %% the new distance crossed inside the tube
xtraveled = xprev + x(i+1); %% total distance travelled by the flow is the previous travelled one plus the new x at each iteration
end
subplot(211); plot(T); subplot(212);plot(Re)
function [row, cp, k] = apd (T)
if T > 318 & T < 320
row = 1.11;
cp = 1007;
k = 0.02781;
else if T > 316 & T< 318
row = 1.1135;
cp= 1007;
k = 0.027635;
else if T > 314 & T < 316
row= 1.1205;
cp= 1007;
k= 0.02749;
else if T > 312 & T <314
row= 1.1277;
cp = 1006.5;
k = 0.02734;
else if T >310 & T < 312
row = 1.1349;
cp= 1006;
k= 0.02719;
else if T >308 & T < 310
row = 1.142;
cp = 1006;
k = 0.02704;
else if T > 306 & T < 308
row= 1.14975;
cp= 1006;
k=0.0269;
else if T > 304 & T < 306
row = 1.1573;
cp = 1006;
k= 0.02682;
else if T >302 & T < 304
row = 1.16495;
cp = 1006;
k = 0.02666;
else if T >297 & T < 302
row = 1.17865;
cp = 1006;
k = 0.026345;
else
return
end
end
end
end
end
end
end
end
end
end
end
  3 Comments
VBBV
VBBV on 12 Nov 2022 at 22:12
The row, cp and k values change for corresponding termperature (iteration) using the below line
[row,cp,k]=apd(T(i)); % the function here returns a different row, cp and k value

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