Pr = 0.7;
g = 10;
Dchar = 0.5;
T1 = 60;
T2 = 10;
Tdef = 0.5*(T1 + T2);
β = (1/(Tdef + 273));
datany = {{20, 15.32}, {40, 17.27}};
ν = (10^(-6)) Fit[datany, {1, T}, T] /. 
          T -> Tdef;
Gr = ((β*(T1 - T2)*g*(Dchar^3))/(ν^2));
GrPr = Gr*Pr;
Nu = 0.135*(GrPr^((1/3)));
Print["Gr.Pr= ", GrPr]
Print["Nu= ", Nu]

datalambda = {{30, 2.22}, {40, 2.28}};
λ = 
        (10^(-2))*(4186/3600)*Fit[datalambda, {1, T}, T] /. 
          T -> Tdef;
\(Print["λ= ", λ, \*"" W.(m^(-1)).(K^(-1))""]\)

α = Nu*(λ/Dchar);
\(Print["α= ", α, \*"" W.(m^(-2)).(K^(-1))""]\)