This book provides four problems out of which two are for natural convective fluid flow model in porous enclosure and the other two are mixed convective flow in an enclosure filled with fluid saturated porous medium and double diffusive convective flow in an enclosure filled with fluid saturated porous medium. All the four problems are solved using the explicit finite difference technique with Marker and Cell Method (MAC). The Rosseland approximations are used to describe the radiative heat transfer. The computed numerical results are compared with the numerical results available from the literature. Excellent agreement between the results is obtained. Also, the convergence of the numerical solutions is observed as the numbers of elements is increased. The influence of various important physical parameters on velocity, temperature, concentration, local Nusselt number and local Sherwood number is studied extensively and depicted graphically.