rce={ρ*Cp*D[T[x,t],t]==λ*D[D[T[x,t],x],x]}/.{ρ->3000,Cp->1200,λ->0.4};
(*D[T[x,t],{x,2}]*)
podm={T[x,0]==0,T[0,t]==20Tanh[1000t],T[0.4,t]==0};
rceVse=Union[rce,podm];

res=NDSolve[rceVse,T[x,t],{x,0,0.4},{t,0,50*3600}]

rePrograf=T[x,t]/.res[[1]]
Plot3D[T[x,t]/.res,{x,0,0.4},{t,0,100*3600}]

Plot[20Tanh[1000x],{x,-10,10},PlotStyle->Thick]

rePrograf//TreeForm

rePrograf//FullForm

T[x,t][[1]]

res=DSolve[{1000*4200*0.15*((10^(-3))/(0.01*0.4))*D[T[x],x]==(0.017*T[x]+0.011)*((((230/0.01)))^2),T[0]==25},T[x],x];

k=T[x]/.res;
Plot[{k,40},{x,0,0.12},PlotStyle->{{Thick,Blue},{Thick,Red}}]

20*1*(400-380)

1*1*((((40+400))^4)-(((20+380))^4))*5.66*(10^(-8))