Numerical Study of Fluid Flow and Heat Transfer In Reticulated Porous Media

Abstract

The transport of heat and mass in porous media have a significant influence on a wide range of engineering applications such as solar reactors, building thermal insulation, packed cryogenic microsphere insulation, combustors, chemical and biological reactors, etc. The reticulated porous media are heterogeneous systems consisting of several interconnected solid phases with continuous void/fluid space. It is well acknowledged that more efficient heat transfer technologies and novel materials are required to improve performance of energy and heat transfer devices while maintaining tolerable levels of power consumption, size, and cost. Reticulated porous structures are excellent candidates for enhancing the thermal efficiency of heat transfer devices while simultaneously enabling the use of smaller and lighter equipment. The present research work involved in studying the fluid flow, heat and mass transfer in open-cell reticulated porous structures with help of Direct Pore Level Simulations (DPLS). The reticulated porous structures are modelled based on the theoretical Kelvin model. The geometry of these structures are generated with the help of in-house code and visualisation tool kit (VTK) libraries. The ideal and randomized Kelvin structures are generated for different PPI & porosities. By varying the geometrical parameters, the influence of geometries on pressure drop, dispersion, and heat transfer between the flowing fluid and solid phase of open-cell foams are investigated. For this reason, the mass, momentum and energy equations in reticulated structures are solved using the standard CFD-FVM approach. The simulation results are used to acquire the pressure drop across the structures. The pressure drop variation with respect to pore density, porosity, specific surface area, and randomization are analyzed. The fluid transport properties such as permeability and drag coefficient are calculated for various porous structures and a pressure drop iii correlation with new values of viscous and inertial coefficients is proposed. Along with the fluid flow, the dispersion of a tracer is traced across the structures and analysed in terms of the effective diffusivity coefficient. Then the influence of dispersion on mass transfer is characterized by estimating the longitudinal dispersion coefficient. The effect of tortuosity on dispersion is also studied. The characteristic length dependent correlation is proposed in terms of strut diameter and flow tortuosity to relate the longitudinal Peclet number as a function of molecular Peclet number. Subsequent simulations are performed to evaluate the forced convective heat transfer coefficient for different fluids of Prandtl numbers (air, water & seawater). Based on the simulation outcomes, two new correlations are proposed to calculate the heat transfer coefficients in the reticulated porous structures. The proposed correlation is validated by comparing it with numerical and experimental data of real reticulated porous structures available in the literature.