“…Framework the procedure to calculate approximations of the n-th order of the above concentrations we replace the functions C(x,y,z,t), I(x,y,z,t), V(x,y,z,t), Φ I (x,y,z,t) and Φ V (x,y,z,t) in the Eqs. (1), (3), (5) We calculate average values of the second-order approximations of required functions by using the following standard relation [25][26][27][28][29][30] …”