fzero error using a root

Q_i = S*tau*e_paint*A_pt;
Q_rad = @(T_pt)(e_paint*sigma*A_pt*(T_pt^4 - T_sun^4));
Q_conv = @(T_pt, T_air)((1.68*(T_pt-T_air)^(1/2))*A_pt*(T_pt-T_air));
Q_heat_plate = @(T_pt, T_pt_LAST)((m_p*c_a+m_t*c_c)*(T_pt -T_pt_LAST));
Q_water = @(T_w,T_pt)(h_w*A_inside*(T_pt - T_w));

solver_T_pt = @(T_pt)(Q_rad(T_pt) + Q_conv(T_pt, T_air) + Q_heat_plate(T_pt, T_pt_LAST) + Q_water(T_water_average, T_pt) - Q_i);
T_pt_num = fzero(solver_T_pt, 293);                 %[K]        temperature aluminiumplate and tube
            
q_heat_air = Q_conv(T_pt_num, T_air);               %Determining the energy to the air through convection
T_air_num = (q_heat_air)/(m_air*c_air_p) + T_air;   %[K]        New Temperature of air

I am using a fzero function here to solve this problem, however in line 3 an error eccors when using ^1/2. When I use ^2 for example the function works fine so the fzero probably goes bad on the root but how do I fix this?

Answer 1

[madhan ravi]

.* .^

[Tim Pijnacker]

I have tried this but it did not help, I am working with variables and not with an array so then it shouldn't be a problem right?

[madhan ravi]

Did you say what error occurred? Did you define the variables? Did you think others could run the code without providing the datas? fzero(...) expects numeric input and not symbolic.

doc fzero

[Tim Pijnacker]

The variables are defined, I can just no supply the whole code because it would be way to huge.

The error I am getting is

Error in plate_v2 (line 44)
T_pt_num = fzero(solver_T_pt, 293);                 %[K]        temperature aluminiumplate and tube

[Steven Lord]

That doesn't look like the whole error message. Can you show us all the text displayed in red when you run your code? There should be something displayed before the "Error in plate_v2" line.

[Tim Pijnacker]

You are right! I actually missed that bit thanks. Could the problem be that T_pt and T_air are to close at the start which makes it infinitely small, or should this then also be a problem when squaring it?

(For a bit more background on the code, it is a tempertature model for a solar collector. At the start T_pt and T_air are both room temperature and after that they both rise due to radiation of the sun but T_pt rises faster then T_air)