hodnotyParam[Teplota_]:=Module[{out,hustotaVzduch,kinematickaVizkozitaVzduch,tepelnavodivost,mernaTepelnaKapacitaPriStalemTlaku},{hustotaVzduch=Interpolation[{{-100,-50,-20,0,10,20,40,60,80,100,120,140,160,180,200,250,300,350,400,500,600,800,1000},{2.012,1.561,1.376,1.275,1.230,1.188,1.112,1.046,0.986,0.934,0.886,0.843,0.804,0.769,0.736,0.666,0.608,0.559,0.517,0.451,0.399,0.325,0.274}}\[Transpose], InterpolationOrder->1];
tepelnavodivost=Interpolation[{{-100,-50,-20,0,10,20,40,60,80,100,120,140,160,180,200,250,300,350,400,500,600,800,1000},0.01*{1.62,2.04,2.26,2.37,2.45,2.52,2.65,2.80,2.93,3.07,3.2,3.33,3.44,3.57,3.70,3.98,4.29,4.57,4.81,5.4,5.82,6.69,7.62}}\[Transpose]];
mernaTepelnaKapacitaPriStalemTlaku=Interpolation[{{-100,-50,-20,0,10,20,40,60,80,100,120,140,160,180,200,250,300,350,400,500,600,800,1000},{1022,1013,1009,1005,1005,1010,1013,1017,1020,1022,1024,1027,1030,1034,1037,1044,1049,1055,1059,1072,1089,1114,1139}}\[Transpose]];
kinematickaVizkozitaVzduch=Interpolation[{{-100,-50,-20,0,10,20,40,60,80,100,120,140,160,180,200,250,300,350,400,500,600,800,1000},0.000001*{5.86,9.35,11.85,13.49,14.47,15.32,17.27,19.22,21.3,23.34,25.73,27.88,29.98,32.51,35.19,42.04,48.85,56.35,63.83,80.27,98.25,136.9,180.7}}\[Transpose]];
 out={hustotaVzduch[Teplota],kinematickaVizkozitaVzduch[Teplota],tepelnavodivost[Teplota],mernaTepelnaKapacitaPriStalemTlaku[Teplota]}};
out
]

hodnotyParam[40]

Tvzduch=60+273;
Tmax=273+125;
Dchar=0.4;
S=0.5;
{ρ,viskozita,λ,Cp}=hodnotyParam[((Tvzduch+Tmax)/2)];
{ρf,viskozitaf,λf,Cpf}=hodnotyParam[Tvzduch-273];
Prf=((viskozitaf*ρf*Cpf)/(λf));
Ref=((v*Dchar)/viskozitaf);
Nu=0.0356*(Ref^0.8)*(Prf^0.4);
α=((Nu*λ)/Dchar);
proud=500;
ubytek=2.3;
res=FindRoot[proud*ubytek==α*S*(Tmax-Tvzduch),{v,1}]

ρf

α