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]==Tanh[t]*αout*(T[x,t]-Tout)/.x->d;
okrin=-λ*D[T[x,t],x]==Tanh[t]*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}]

pom=pom;
Remove["Global`*"];

σ=5.67*(10^(-8));
t=8*60;
c0=3*(10^8);
rZS=t*c0;
qZem=1351;
QSlunce=4.*Pi*(rZS^2)*qZem;
Solve[QSlunce==σ*1*(6000^4)*4.*Pi*(rSlunce^2),rSlunce][[2]]

Ie=1;
U=10;
P=Ie*U;
α=10;
Tokoli=35;
S=2*(a^2);
ϵ=0.96;

pohltivost=ϵ;
Pslunce=1*1200*(a^2)*pohltivost;

Pk=α*S*(Tchladic-Tokoli);
Ps=σ*ϵ*S*((((Tchladic+273))^4)-(((Tokoli+273))^4));
Rth=2;
rce={P==Pk+Ps-Pslunce,P==((150-Tchladic)/Rth)};
FindRoot[rce,{Tchladic,0.5*(Tokoli+150)},{a,0.1}]

ClearAll[P,t,T]
mm=0.001;
b=5mm;
a=0.072;
ro=2700;
c=910;
objem=(a^2)*b;
mcp=objem*ro*c;
P[t_]:=If[Sin[2*(Pi/2)*t]>0,20,0];
Pk=α*S*(T[t]-Tokoli);
Ps=σ*ϵ*S*((((T[t]+273))^4)-(((Tokoli+273))^4));
rce={mcp*T'[t]==P[t]-Pk-Ps,T[0]==80};
resT=NDSolve[rce,T,{t,0,100},MaxStepSize->0.01,MaxSteps->(10^6)][[1]];
Plot[T[t]/.resT,{t,0,100},PlotPoints->300]

((1250+80)/2)

pom=pom;
Remove["Global`*"];
σ=5.67*(10^(-8));
cm=0.01;
d1=3cm;
λ1=0.5;
λ2=0.178;
a=1;
α=5;
ϵ=0.95;

Rth1=(d1/(λ1*0.5*(6*(a^2)+6*(((a+2d1))^2))));
Rth2=(d2/(λ2*0.5*(6*(((a+2d1))^2)+6*(((a+2d1+2d2))^2))));
Qk=α*6*(((a+2d1+2d2))^2)*(80-35);
Qr=ϵ*σ*(((a+2d1+2d2))^2)*((((80+273))^4)-(((35+273))^4));
rce=((1250-80)/(Rth1+Rth2))==Qk+Qr;
dosd2=Solve[rce][[-1]]
Pztraty=Qk+Qr/.dosd2

Tpoc=35;
hodina=3600;

Tout=35;
αout=5;
a=((λ1)/(100*750));
d=0.5;
λ=λ1;
rce=D[T[x,t],t]==a*D[T[x,t],{x,2}];
okrout=-λ*D[T[x,t],x]==Tanh[t]*αout*(T[x,t]-Tout)/.x->d;
okrin=-λ*D[T[x,t],x]==Tanh[t]*((2*Pztraty)/(6*(1^2)))/.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}]

Plot[{Evaluate[T[x,t]/.res/.x->0],1250},{t,0,tmax}]

Uf=1.1*230;
PjedenClanek=((2*Pztraty)/9)
U1clanek=(Uf/3)
Rjedenclanek=R1c/.Solve[PjedenClanek==((U1clanek^2)/R1c)][[1]]

Tdratmax=1300;
Tpec=1250;
ϵ=0.95;
Smin=Smidr/.Solve[PjedenClanek==0.8*σ*ϵ*Smidr*((((1300+273))^4)-(((Tpec+273))^4))][[1]]

Smincmkv=(Smin/(cm^2))

Rjedenclanek

(Smincmkv/Rjedenclanek)

"drat prumer 1.8mm a ten ma odpor 0.57 Ω/m"

R1m=0.57;

Ldrat=(Rjedenclanek/R1m)