Off[General::"spell1", FindRoot::"lstol", 
        General::"spell"];

SetDirectory["FileName" /. NotebookInformation[
              EvaluationNotebook[]] /. FrontEnd`FileName[
              d_List, nam_, ___] :> ToFileName[d]];

ny[T_] = << "ny";
lambda[
          T_] = << "lambda";
Pr[
          T_] = << "Pr";
σ = 
        5.667*(10^(-8));
Qrvlastni[
          T_, ϵ_, S_] := ϵ*σ*
          S*(((T + 273))^4);
g = 
        9.81;
koefrozt[T_] := 
        (1/(T + 273));
Gr[T1_, T2_, 
          delka_] := ((koefrozt[((T1 + T2)/2)]*(delka^3)*Abs[(T2 - T1)]*g)/((ny[((T1 + T2)/2)])))^2;
Nu[T1_, T2_, delka_]:=1.18*(Gr[T1, T2, delka]*Pr[((T1 + T2)/2)])^(1/8)/;0≤Gr[T1, T2, delka]*Pr[((T1 + T2)/2)]<500;
Nu[T1_, T2_, delka_] := 
          0.54*(Gr[T1, T2, delka]*Pr[((T1 + T2)/2)])^(1/4) /; 
            500 ≤ Gr[T1, T2, delka]*Pr[((T1 + T2)/2)] < 2*10^7;

Nu[T1_, T2_, delka_] := 
          0.135*(Gr[T1, T2, delka]*Pr[((T1 + T2)/2)])^(1/3) /; 
            2*10^7 ≤ Gr[T1, T2, delka]*Pr[((T1 + T2)/2)] < 
              10^13;

alfa[T1_, T2_, 
          delka_] := ((Nu[T1, T2, delka]*lambda[((T1 + T2)/2)])/delka);

S = 1;
To = 20;
Tp = 105;
Dch = 0.5;
λiz = 0.04;
Qr = σ*
          S*ϵ*((((Ta + 273))^4) - (((To + 273))^4));
Qk[Ta_] := 
        S*alfa[Ta, To, Dch]*(Ta - To);
Qved = ((S*λiz)/diz)*(Tp - 
              Ta);
res[dizNas_, ϵNas_] := 
        FindRoot[
          Qr + Qk[Ta] == 
              Qved /. {diz -> dizNas, ϵ -> ϵNas}, {Ta, 
            100}];
teplota[diz_, ϵ_] := 
      Ta /. res[diz, ϵ]
ztraty[dizz_, ϵ_] := Qved /. res[dizz, ϵ] /. 
        diz -> dizz

Plot[{0, teplota[0.2, ϵ], 
          teplota[0.01, ϵ]}, {ϵ, 0, 1}, 
        AxesLabel -> {"ϵ", "T[°C]"}, 
        PlotStyle -> {{GrayLevel[0], Thickness[0.001]}, {Hue[0.6], 
              Thickness[0.008]}, {Hue[0.0], Thickness[0.008]}}];

Plot[{0, ztraty[0.05, ϵ], 
          ztraty[0.01, ϵ]}, {ϵ, 0, 1}, 
        AxesLabel -> {"ϵ", "Pz[W]"}, 
        PlotStyle -> {{GrayLevel[0], Thickness[0.001]}, {Hue[0.6], 
              Thickness[0.008]}, {Hue[0.0], Thickness[0.008]}}];