Quiet@Remove["Global`*"];
$HistoryLength=2;
SetDirectory[NotebookDirectory[]];

cm=0.01;
Dchar=10cm;
Ts=80;
Ta=20;
Tdef=((Ts+Ta)/2);
Print["Tdef= ",Tdef," °C"]
liter=0.001;
VolumeFlow=10liter;
CrossSectionArea=Pi*((Dchar^2)/4);
velocity=(VolumeFlow/CrossSectionArea);
Print["velocity= ",velocity," m.(s^(-1))"]

kinematicViscosity=5.541*(10^(-7));
Reynolds=((velocity*Dchar)/kinematicViscosity);
Print["Re= ",Reynolds," -"]

Prandtl=3.56;

Nusselt=0.023*(Reynolds^0.8)*(Prandtl^0.4);
Print["Nu= ",Nusselt," -"]

λ=640.60*(10^(-3));

α=Nusselt*(λ/Dchar);
Print["α= ",α," W.(m^(-2)).(K^(-1))"]