@Mariusz Iwaniuk, Thanks for your response. It will be used for my work.
One more question.
I tried to solve this problem for the parameter values m = 2;
phi = 0.1;
rho[f_] := 997.1;
Cp[f_] := 4179;
k[f_] := 0.613;
rho[s_] := 5200;
Cp[s_] := 670;
k[s_] := 6;
k[nf_] := k[f]*(k[s]+(m-1)*k[f]-(m-1)*phi*(k[f]-k[s]))/(k[s]+(m-1)*k[f]+phi*(k[f]-k[s]));
alpha = (1/2)*Pi;
M = 1;
Pr = 6.2;
But I got an error
