Characterization of heat transfer in consolidated, highly porous media using a hybrid-scale CFD approach

Author(s):  
Sebastian Meinicke ◽  
Konrad Dubil ◽  
Thomas Wetzel ◽  
Benjamin Dietrich
Author(s):  
H. L. Pan ◽  
O. Pickena¨cker ◽  
D. Trimis

In this paper, a method for the experimental characterization of the equivalent pore diameter of highly porous open structures is presented. The commonly used characterization of such structures through geometrical properties like ppi number (porous per inch) and porosity proves to be not sufficient for the characterization of length scales related to heat and mass transfer. The procedure used here utilizes the quenching limits for flame propagation as characterization criterion. The determined equivalent pore diameter corresponds to the quenching diameter for a tube-geometry filled with the same combustible mixture. The quenching limit was determined by adjusting critical conditions, which are defined by a constant critical Pe´clet number comprising the laminar flame velocity instead of the flow velocity. Variations of oxygen content and air ratio were used in order to change the laminar flame speed and find the quenching limit for a given porous medium. The equivalent pore diameter determined with this method is a characteristic length scale of the porous medium geometry and is related to the heat transfer between the gas phase and the solid porous structure. The validation of the method was performed on sphere packings with well-documented properties. Several practically relevant highly porous media like foams and fabric lamellae structures were characterized and the results are discussed. Based on the effective heat conductivity (EHC) models of Zehner, Bauer and Schlu¨nder [1–3] for packed beds, an adapted model for foam structures was developed. The adapted model utilizes the equivalent pore diameters determined in the paper and predictions are presented.


Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6308
Author(s):  
Nihad Dukhan

A new geometric modeling of isotropic highly-porous cellular media, e.g., open-cell metal, ceramic, and graphite foams, is developed. The modelling is valid strictly for macroscopically two-dimensional heat transfer due to the fluid flow in highly-porous media. Unlike the current geometrical modelling of such media, the current model employs simple geometry, and is derived from equivalency conditions that are imposed on the model’s geometry a priori, in order to ensure that the model produces the same pressure drop and heat transfer as the porous medium it represents. The model embodies the internal structure of the highly-porous media, e.g., metal foam, using equivalent parallel strands (EPS), which are rods arranged in a spatially periodic two-dimensional pattern. The dimensions of these strands and their arrangement are derived from equivalency conditions, ensuring that the porosity and the surface area density of the model and of the foam are indeed equal. In order to obtain the pressure drop and heat transfer results, the governing equations are solved on the geometrically-simple EPS model, instead of the complex structure of the foam. By virtue of the simple geometry of parallel strands, huge savings on computational time and cost are realized. The application of the modeling approach to metal foam is provided. It shows how an EPS model is obtained from an actual metal foam with known morphology. Predictions of the model are compared to experimental data on metal foam from the literature. The predicted local temperatures of the model are found to be in very good agreement with their experimental counterparts, with a maximum error of less than 11%. The pressure drop in the model follows the Forchheimer equation.


2018 ◽  
Vol 49 (1) ◽  
pp. 77-90
Author(s):  
Eren Ucar ◽  
Moghtada Mobedi ◽  
Azita Ahmadi

Sign in / Sign up

Export Citation Format

Share Document