Evaluate Nusselt Numer in thermal transient problem

Hello! I am trying to evaluate the Nusselt Numer in a thermal transient problem. I have to evaluate this numer on the line x=0, y=1 and z variable.

This is my solution but it doesn't bring to the requested result. Where is the problem?

Tintrp = interpolateTemperature(results,0,0.999,1:1);

for n=1:1:11

y = 0:0.05:0.999;

fede2 = (y - y.^3).*Tintrp;

Tb = 4*trapz(y,fede2);

[qx,qy] = evaluateTemperatureGradient(results,0,0.999,n:n);

end

Nu = (2/(Tintrp-Tb))*qy;

disp('Numero di Nusselt')

disp(Nu)