A numerical investigation of the particle behaviors and entropy generation in mixed convection inside a vented enclosure

Abstract

The present study is to focus on the numerical investigation of the transportation, deposition and removal of solid particles in the range of 5 μm to 0.01 μm for mixed convection flow in the vented square cavity by utilizing the Eulerian–Lagrangian method with one-way coupling. The change in the deposition and removal mechanisms affected by the forces acting on the particles is addressed for mixed convection of ventilation airflow. In the analysis of entropy generation, the irreversibilities due to the presence of solid particles are studied with a new approach for both dominant natural and forced convection. The governing equations for fluid phase and the Lagrangian particle tracking are scrutinized by employing the finite volume method with SIMPLE algorithm and explicitly integrating the set of ordinary differential equations, respectively. The examination of the thermal and flow fields is carried out in the cases of various Reynolds numbers and Richardson numbers. The minimum and maximum values of the average Nusselt number are determined with related operating parameters. By using the results of thermal behaviors and flow structures obtained at steady-state condition, the particle velocity, temperature and location are presented for the combined natural and forced convection. By investigating the particles deposited on the walls and ones removed from the exit section for different Reynolds numbers and Richardson numbers, it is demonstrated that the sum rate of deposition and removal is low at 1≤Ri≤10 and high Reynolds number for 1 μm and 0.1 μm particles. For given Reynolds number, increasing the buoyancy effect results in substantial changes in the thermal field and flow pattern, therefore the particles remaining suspended show different behaviors when the effect of natural convection alters from weak to dominant. It is observed that the Brownian and thermophoretic forces play an important role in the small particle deposition and removal. As a result of entropy generation analysis, the minimum total entropy generation is determined at Ri=5 for given Reynolds number except for Re=50. Moreover, it is proposed to investigate the irreversibilities due to the heat transfer between the particles and the fluid surrounding them and the frictional total force acting on the suspended particles.