This paper proposes a novel Diffusive Multi-Phase Particle-In-Cell (DMPPIC) solver that incorporates the random walk behavior of particles, improving the realism of the Computational Fluid Dynamics (CFD) simulations. Built upon the Multi-Phase Particle-In-Cell (MPPIC) solver from the OpenFOAM software suite for Computational Fluid Dynamics (CFD) simulation, our proposed solver, the Diffusive Multi-Phase Particle-In-Cell (DMPPIC) solver, aims to more accurately model complex scenarios in the mixed and dispersive regime, e.g., in human capillaries. A comparative analysis of our enhanced solver and the original solver demonstrates improvements in simulation accuracy.