Why is my loop not running? (Error using / Matrix dimensions must agree)

1 view (last 30 days)
That's my code, supposedly it is about a water particle undergoing both, heat and mass transfer at the same time, and I'm monitoring the rate of change of both, diameter and temperature at the same time with a time step of 0.00001 seconds.
%%% DEFINITIONS %%%
clear;
Tb = 20; % temperature of the bulk air surrounding the particle [C]
Tp(1) = 15; % temperature of the particle's surface [C]
RHo = 0.5; % Relative Humidity air [%]
psat = 2.34; % saturation pressure at room temp [kpa]
pinf = RHo*psat; % partial pressure in bulk [kpa]
M=0.018; % molar mass of water molecule [Kg.mol-1]
Ru = 8.314; % Universal gas constant [Kg.mol.m2/s2.K]
cinf = (pinf*1000)*(M) / ((Ru)*(Tb+273)); % vapor concentration in air at 20 degrees
RHp = 1; %Relative Humidity at surface particle [%]
p = RHp*psat; % partial pressure at the surface of particle [kpa]
st = 0.0727; % surface tension at room temp [N/m]
den = 1000; % density at room temp [kg/m3]
dp(1)=200*10^-9; % initial diameter of the water particle [m]
Kr(1) = exp((4*st*M)/(Ru*den*dp(1)*(Tb+273))); % kelvin effect ratio
pd =Kr*p; % real partial pressure at the surface of the particle [kpa]
cp(1) =(pd*1000)*(M)/((Ru)*(Tp(1)+273)); % water vapor concentration at the particle's surface [Kg/m3]
t = 0.00001; % timestep [s]
D = 2.5*10^-5; % diffusivity coefficient of water at room temp [m2/s]
L = 2.44*10^6; % latent heat of vaporization for water at room temp
cp = 1007; %specific heat at room temp
kair = 0.026; % thermal conductivity for air at room temp [W/mK]
%%% INITIAL CONDITIONS %%%
Tp(1) = 15;
dp(1) = 200*10^-9;
Kr(1) = exp((4*st*M)/(Ru*den*dp(1)*(Tb+273)));
cp(1) =(pd*1000)*(M)/((Ru)*(Tp(1)+273));
mp(1) = (pi/6) *den*(dp(1))^3; %mass particle initially
mpdot(1)=(pi/6)*D*dp(1)*(cp(1)-cinf); %mass rate of the particle initially
t2(1) = 0; %time interval initially
i = 0;
%%% ITERATIONS %%%
while dp(i+1) > 0
i=i+1;
% mass transfer %
mp(i+1) = mp(i) - mpdot(i)*t; %% new mass every iteration
dp(i+1)= ((6*mp(i+1))/(pi*den))^(1/3); %% new diameter every iteration
%heat transfer %
A(i) = -((L*D*(cp(i) - cinf)) + (kair*(Tp(i) - Tb)));
B(i) = ((12*t)/(den*cp*(dp(i))^2));
Tp(i+1) = (B(i)*A(i)) + Tp(i);
Kr(i+1)= exp((4*st*M)/(Ru*den*dp(i+1)*(Tb+273)));
cp(i+1) =(p*Kr(i+1)*1000)*(M)/((Ru)*(Tp(i+1)+273));
t2(i+1) =t2(i) + t;
mpdot(i+1) = (pi/6)*D*dp(i+1)*(cp(i+1)-cinf);
% break if imaginary numbers start appearing %
if imag(dp(i+1)) ~= 0
break;
end
end
%%% PLOTTING %%%
subplot (2,1,1)
plot (t2 ,dp*10^9)
xlabel('time [s]'), ylabel('diameter [nm]')
subplot (2,1,2)
plot (t2,Tp)
xlabel('time [s]'), ylabel('Particle Temperature [C]')
When it comes to the B parameter, it shows this error; ( Error using / Matrix dimensions must agree.)
A and B are parameters to be used for the differential equation that gets me the new temperature at the new timestep.
Why is it not working for B ?

Accepted Answer

David Hill
David Hill on 26 Sep 2022
Cannot multiply by the entire array (cp).
%heat transfer %
A(i) = -((L*D*(cp(i) - cinf)) + (kair*(Tp(i) - Tb)));
B(i) = ((12*t)/(den*cp(i)*(dp(i))^2));%cp(i)
Tp(i+1) = (B(i)*A(i)) + Tp(i);

More Answers (1)

Walter Roberson
Walter Roberson on 26 Sep 2022
cp(1) =(pd*1000)*(M)/((Ru)*(Tp(1)+273));
%[...]
cp(i+1) =(p*Kr(i+1)*1000)*(M)/((Ru)*(Tp(i+1)+273));
cp is a matrix.
B(i) = ((12*t)/(den*cp*(dp(i))^2));
You are dividing by something that involves all of cp. After the first iteration, cp would be a vector. Even if the / operation worked properly, the result would surely be a vector that could not be assignd to B(i)
The MATLAB / operator is matrix division. P/Q is similar to P*inv(Q) but with some restrictions on size. P/Q is effectively a "fitting" operation. The element-by-element division operator in MATLAB is ./ like P./Q

Categories

Find more on Thermal Analysis in Help Center and File Exchange

Products


Release

R2019a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!