Fluid flow, heat transfer and entropy generation analyses of turbulent forced convection through isotropic porous media using RANS models

Karimi

International Journal of Heat and Mass Transfer

et al. 2020

Self Cite

Micro energy systems have progressed significantly over the last two decades, as has the utilization of micro thermofluidic and thermochemical systems. Several studies were conducted to analyze the thermophysical and chemical characteristics of these systems. In general, the large rates of heat and mass transfer typically encountered in these microsystems make them susceptible to significant irreversibilities and as a result, poor second-law performances. Although the understanding and modelling of entropy generation rate in microsystems is an inevitable part of their performance analyses, no reviews were found on the second law analysis, and more specifically on the entropy generation rate of micro thermal and thermochemical systems.To address this shortcoming, the current review explores the mechanisms of entropy generation rate in these micro energy systems and identifies the possible future avenues of research in this field. The existing literature on entropy generation rate in micro single and multiphase thermofluidic systems, with the inclusion of various effects such as magnetic and electric fields, nanoparticles and thermochemical reactions are reviewed in detail. The unexplored and less investigated areas such as second law analysis of micro porous systems using pore-scale modeling and entropy generation rate of airflow through microchannels with inserts are identified, and recommendations are made for future research.

Section: Fundamental Formulationsmentioning

confidence: 99%

Generation of entropy in micro thermofluidic and thermochemical energy systems-A critical review

Karimi

International Journal of Heat and Mass Transfer

et al. 2020

Self Cite

“…This technique gives a macro-scale generalized Darcy-Forchheimer equation to which is associated a closure problem that can be used to evaluate the apparent permeability tensor including inertia effects [19]. Torabi et al analyzed fluid flow, heat transfer and entropy generation of turbulent forced convection through isotropic porous media using RANS models [20]. They investigated different Re numbers, porosities and cross-sections for two turbulence models.…”

Section: Nomenclaturementioning

confidence: 99%

Numerical simulation of turbulent oscillating flow in porous media

Kardgar

Jafarian

2020

Scientia Iranica

Two macroscopic turbulent models, P-dL and N-K, have been proposed in recent years for simulating turbulent unidirectional flow in porous media. In this paper a modification on N-K model has been proposed for turbulent oscillating flow in porous media. To this purpose, Turbulent oscillating flow in porous media has been simulated in microscale employing a periodic array. The k-ε model was applied to solve turbulent oscillating flow in periodic array. Control volume approach has been used to discretize Navier-Stokes and k-ε equations and the well-established SIMPLE method has been conducted to deal with pressure and velocity coupling. To modify N-K model the effect of different parameters such as frequency and Reynolds number has been investigated and the constants in source terms of turbulent kinetic energy and its dissipation rate has been modified versus Re according to microscale results. In order to validate the new modified constants, the modified N-K model was applied to turbulent oscillating flow in porous media and results were compared to original N-K macroscopic model.

“…1 The geometry of the thin porous media in the present study a staggered arrangement of circular cylinders, b random arrangement of circular cylinders, c top view of the x-z plane of the geometry in (a) array of cylinders. Pore-scale study of turbulent flow in an array of cylinders with different cross sections has been initially carried out in the literature with an aim to calculate the macroscopic (macroscale) values of flow and turbulence parameters such as pressure drop, turbulent kinetic energy and dissipation rate (Pedras and de Lemos 2001;Nakayama and Kuwahara 1999;Yang et al 2014;Torabi et al 2019). However, due to the incorporation of eddy-viscosity turbulence models in these studies, they were not able to report the values of Reynolds stresses and hydrodynamic dispersion terms from a direct calculation of these parameters within the pores.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Post-Darcy Flow in Thin Porous Media

Jouybari

Lundström

2021

Transp Porous Med

We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of cylinders bounded between walls. The simulations span a range of Reynolds numbers, 40 to 4000, where the pressure drop varies nonlinearly with the average velocity, covering nonlinear laminar flow to the fully turbulent regime. The results are compared to those obtained by replacing the bounding walls with symmetric boundaries with the aim to reveal the effect of bounding walls on microscopic characteristics and macroscopic measures, i.e., pressure drop, hydrodynamic dispersion and Reynolds stresses. We use large eddy simulation to directly calculate the Reynolds stresses and turbulent intensity. The simulations show that vortical structures emerge at the boundary between the cylinders and the bounding walls causing a difference between the microscopic flow in the confined and non-confined porous media. This affects the averaged values of pressure drop, the hydrodynamic dispersion and the Reynolds stresses. Finally, the distance between the bounding walls is altered with the particle Reynolds number kept constant. It is observed that the difference between results calculated in confined and non-confined cases increases when the bounding walls are narrower.