Abstract:The paper describes a comparison between four numerical models of porosity, for better understanding the influence of porosity on the hydrodynamics (macroscopic and microscopic) behaviors of fluidized beds. The study has been done through an approach based on combine discretecontinuum to achieve the simulations. This approach deals with the modeling of the interactions between the fluid-solid. In which the discrete approach is used for localizing the position and velocity of each individual particles based on Newton's 2 nd law of motion, using a numerical time stepping scheme. While the continuum approach is based on finite volume method, which is solved the fluid flow equations (Navier-Stokes equations). The geometry of fluidizing column was; column diameter (D=0.096 m) and column height (H=1 m). Glass grains were firstly deposited inside the column, and then subjected to the range of inlet water velocity (0-0.14 m.s -1 ). The results of simulations are point out those four models of porosity, achieved comparable results for simulating fluidized beds. The simulations results were compared and showed a good agreement and consistency with the experimental data in the literatures. In other hand, the simulations results revealed that the models of porosity, which based on the microscopic scale, are most reliable between the models of porosity. However the differences between these models must be analyzed and kept in mind in order to select the appropriate porosity model. The results revealed that the porosity is an important parameter which effect on the hydrodynamics behavior of fluidized beds during the fluidization processes.

The exchange of mass and heat transport in fluidized beds is a complicated and extensive topic, making it a rich field for scientific and industrial applications. This numerical research implements the CFD-DEM coupling to investigate the transport of heat energy in a fluidized bed.A numerical test compares the numerical and analytical results for a single particle in a column.Two cases of heating and cooling are compared. The numerical results present well adequacy with the analytical results. The development of fluidized bed units, within fluidized bed units is vital to improving the designs of these units. Therefore, three methods of column heating, including base heating, walls heating, and as well as walls and base heating, have been proposed in the simulations.The results reveal that the fluid inlet velocity increase during the fluidized beds' heating process is invalid. Thus, the fluid's proper inlet velocity and imposed temperature are crucial in the heating process for the fluidized beds since the particles need to provide time for the heat transport process.

Heat transfer in fluid-solid fluidized beds is investigated using a combined of computational fluid dynamics (CFD) and discrete element method (DEM) approach, incorporated with a thermal model. The approach has taken into account almost all the mechanisms in heat transfer in fluidized beds. A comparison and validation of hydrodynamic and thermal data of fluidized bed obtained using CFD-DEM thermal approach with experimental and numerical results data in the literature is carried out. The simulations results reveal a good thermal steady state during the simulation time for calculating the thermal behaviors of fluidized beds like; the mean particle temperature, bed porosity, heat transfer coefficient and mean particle Reynolds number. The simulations results are showed a good agreement and consistency with the experimental and numerical data in the literatures. Thus, the integration of combined CFD-DEM with the thermal model is a step toward for the prediction, development the heat transfer efficiency in fluid-solid system, and the decrease of energy consumption of the industrial applications.