Temperature variation against time

Hi,

I'm trying to model how the temperature changes with time of the day however I'm having difficulties since the result is not what I expect. Below is the code. Basically I want the mass of the product to decrease by 6.5 kg after every hour and I expect the temperature to increase, peak and then decrease. What am I doing wrong ? I'm pretty bad at Matlab

m = 150;    % Mass of product to dry (Kg)
me = 78;    % Mass of water to dry from the product(Kg)
mw = 6.5;   % Mass of water loss in hr(Kg)
lw = 2260000; % Latent heat of vaporisation of water (J/Kg)
A = 1;      % Surface Area of Collector (m^2)
cp= 3746; %Specific heat capacity of product (J/Kg/C)
t = 1;    % Time step
T(1) = 24;  % Initial Temperature (°C)

Time2=(1:t:12); hours
QQ2=960*(sin(2*pi*Time2/24)).^2; % Solar irradiation in tropical regions at specific time (W/m2)

for j = (1:t:11)
  T(j+1)= ((((QQ2(j)*A*3600))-(mw*lw))/(m*cp))+T(j);
  m = m-mw ;
 end 

figure(2)
plot(T)
title('Temperature')
xlabel('time (hours)') 
ylabel('Temperature (°C)')

Answer 1

[Bruno Luong]

Your expectation is wrong

(((QQ2(j)*A*3600))-(mw*lw))

are negative (from -1.4458e+07 to -1.1234e+7)

Therefore as long as the mass m is positive

   ((((QQ2(j)*A*3600))-(mw*lw))/(m*cp))

is negative. Since every iteration you perform

T(j+1) = T(j) + something negative

T must decrease regardless how you change the mass m.

When you expect something try to explain clearly step by step. By doing so you might find by yourself the mistake.