Quiet@Remove["Global`*"];
$HistoryLength=2;
SetDirectory[NotebookDirectory[]];
SetAttributes[exp,{HoldAll,Listable}];
exp[co_]:=Module[{a,graf},a=ToString[Unevaluated[co]];graf:=Evaluate[co];Export[Evaluate[a<>".png"],graf,ImageResolution->300]];

cm=0.01;
Dchar=10cm;
Ts=80;
To=20;
Tdef=0.5*(Ts+To);
Print["Tdef= ",Tdef," °C"]
β=(1./(Tdef+273));
Print["β= ",β," (K^(-1))"]
ΔT=Ts-To;
g=9.81;
Pr=0.7;
ν=17.88*(10^(-6));
Gr=((β*ΔT*g*(Dchar^3))/(ν^2));
Print["Gr= ",Gr," -"]
Ra=Gr*Pr;
Print["Ra= ",Ra," -"]
NuOld=0.54*(Ra^(1/4));
NuNew=(((0.6+((0.387*(Ra^(1/6)))/(((1+((((0.559/Pr)))^(9/16))))^(8/27)))))^2);
nus={NuOld,NuNew}

λ=28.08*(10^(-3));
alfas=(λ/Dchar)*nus;
vykon1metr=alfas*Pi*Dchar*ΔT*1
σ=5.67*(10^(-8));
ϵ=0.95;
vykonSalani1metr=Pi*Dchar*1*ϵ*σ*((((Ts+273))^4)-(((To+273))^4))

eta=1-((20.+273)/(100+273))
1-%