vysl=T[x]/.DSolve[{T''[x]==0,T[0]==T1,T[d]==T2},T[x],x][[1]]

Needs["VectorAnalysis`"]

SetCoordinates[Cartesian[x,y,z]]

Grad[vysl]

λ*((T1-T2)/d)/.{d->0.6,λ->0.8,T1->15,T2->-15}

λ*((T1-T2)/d)/.{d->0.1,λ->0.04,T1->15,T2->-15}

Rth1=(0.45/(0.8*100));
Print["Rth1= ",Rth1," \!\(\*FractionBox[\(K\), \(\(\\ \\ \)\(W\)\)]\)"]

Rth2=(0.12/(.04*100));
Print["Rth2= ",Rth2," \!\(\*FractionBox[\(K\), \(\(\\ \\ \)\(W\)\)]\)"]

Q=((15-(-15))/(Rth1+Rth2));
Print["vykon= ",Q," W"]

Solve[((15-Tx)/Rth1)==Q]

SetCoordinates[Cylindrical[r,fi,z]]

0==Numerator[Div[Grad[T[r]]]]

res=T[r]/.DSolve[{0==Numerator[Div[Grad[T[r]]]],T[rmin]==T1,T[rmax]==T2},T[r],r][[1]]

Simplify[(-λ*Grad[res][[1]]/.r->rmin)*2*Pi*rmin*delka]

Plot[{Log[ksi],0.05((((ksi))^2)-1)},{ksi,1,10},AxesLabel->{"(r2/r1)"}]

c=4186.;
ΔT=36;
msteckou=0.3;
P=msteckou*c*ΔT;
Print["P= ",(10^(-3))P," kW"]

(*dale*)

γ=Fit[{{10,(1/35)},{50,(1/10)}},{1,T[x]},T[x]]

mm=0.001;
cm=10mm;
m=15cm;
d=3mm;
Vsteckou=0.3*(10^(-3));
vx=(Vsteckou/(d*m));
ρ=1000;
cp=4186;
u=230;
rce=ρ*cp*T'[x]==γ*((((u/d)))^2);
poc=T[0]==4;
tepl=T/.NDSolve[{rce,poc},T,{x,0,1}][[1]];
Tout=40;
Plot[{Tout,tepl[x]},{x,0,1}]
xmax=delka/.FindRoot[tepl[delka]==Tout,{delka,0.1,1}];

poc=T[0]==12;
tepl=T/.NDSolve[{rce,poc},T,{x,0,1}][[1]];
tepl[xmax]

γMB=Fit[{{20,(1/72)},{75,(1/30)}},{1,T[x]},T[x]];
rce=ρ*cp*T'[x]==γMB*((((u/d)))^2);
poc=T[0]==4;
tepl=T/.NDSolve[{rce,poc},T,{x,0,1}][[1]];
tepl[xmax]

Remove["Global`*"];

Tpoc=5;
hodina=3600;
Tin[t_]:=5+15*Tanh[(t/(2*hodina))];
Tout=-2;
a=5.2*(10^(-7));
αout=20;
αin=5;
d=0.6;
λ=0.8;
rce=D[T[x,t],t]==a*D[T[x,t],{x,2}];
okrout=-λ*D[T[x,t],x]==αout*(T[x,t]-Tout)/.x->d;
okrin=-λ*D[T[x,t],x]==αin*(Tin[t]-T[x,t])/.x->0;
poc=T[x,0]==Tpoc;
dohr={rce,okrin,okrout,poc};
den=24*hodina;
tmax=2*den;
res=NDSolve[dohr,T[x,t],{x,0,d},{t,0,tmax}][[1]];
Plot3D[T[x,t]/.res,{x,0,d},{t,0,tmax}]