Double-layer Porous Media Research Articles

Analytical Analysis of Heat Transfer and Entropy Generation in a Tube Filled with Double-Layer Porous Media.

The heat transfer and entropy generation in a tube filled with double-layer porous media are analytically investigated. The wall of the tube is subjected to a constant heat flux. The Darcy-Brinkman model is utilized to describe the fluid flow, and the local thermal non-equilibrium model is employed to establish the energy equations. The solutions of the temperature and velocity distributions are analytically derived and validated in limiting case. The analytical solutions of the local and total entropy generation, as well as the Nusselt number, are further derived to analyze the performance of heat transfer and irreversibility of the tube. The influences of the Darcy number, the Biot number, the dimensionless interfacial radius, and the thermal conductivity ratio, on flow and heat transfer are discussed. The results indicate, for the first time, that the Nusselt number for the tube filled with double-layer porous media can be larger than that for the tube filled with single layer porous medium, while the total entropy generation rate for the tube filled with double-layer porous media can be less than that for the tube filled with single layer porous medium. And the dimensionless interfacial radius corresponding to the maximum value of the Nusselt number is different from that corresponding to the minimum value of the total entropy generation rate.

Analysis of storage capacity and energy conversion on the performance of gradient and double-layered porous electrode in all-vanadium redox flow batteries

In the general monolayer electrode of constant porosity, the conflict between the available specific surface area and the hydraulic permeability is a momentous hinder in designing the high-performance electrodes of VRFB. In this paper, several novel electrode structures with gradient or double-layered porous media (GPM or DLPM) are installed in the stack to decouple the conflict and connection between hydraulic permeability and specific surface area. Ten kinds of electrode structures with constant, linear or stepwise decreasing/increasing porosity respectively are designed and compared. The lower concentration polarization loss, higher cell energy efficiency and capacity in the stepwise and linear increasing of porosity profiles are related to the electrolyte flow uniformity in porous electrode and alleviation of conflict between permeability and specific surface area. The higher pumping losses in these arrangements serve as deteriorative factor. In the stepwise increasing porosity mode, the effects of the thickness ratio between two porous layers with different porosities, electrode thickness and porosity variation amplitude were investigated. There is an optimum thickness ratio and electrode thickness to obtain the saturated cell capacity and more energy efficiency, and the rise amplitude of porosity will reduce the system efficiency while increasing the cell capacity.

Transient analytical solution for one-dimensional transport of organic contaminants through GM/GCL/SL composite liner

Analytical solution for transport of organic contaminants through composite liner consisting of a geomembrane (GM), a geosynthetic clay liner (GCL), and a soil liner (SL) with finite thickness is presented. The transient diffusion-advection processes in the whole composite liner and adsorption in GCL and SL can be described by the present method. The method is successfully verified against analytical solution to a coupling transient diffusion-advection problem in double-layer porous media. The rationality of the steady-state transport assumption in GM and GCL and the semi-infinite bottom boundary assumption, which are widely adopted in the existing works, is comprehensively investigated. The overestimated zone, underestimated zone and no difference zone caused by the two assumptions under various conditions are identified. With the increase of elapsed time, the overestimated zone disappears, and the underestimated zone becomes smaller and smaller and finally is overwhelmed by the no difference zone. Moreover, the equivalency between GM/GCL/SL and GM/CCL composite liners is also properly assessed by the present method. GM/GCL/SL composite liner performs better than GM/CCL composite liner under high leachate level condition.

Errata to ‘Analytical solutions for advective-dispersive solute transport in double-layered finite porous media’, International Journal of Numerical and Analytical Methods in Geomechanics, 2011; 35:438-460 , DOI: 10.1002/nag.903

Errata to ‘Analytical solutions for advective-dispersive solute transport in double-layered finite porous media’, <i>International Journal of Numerical and Analytical Methods in Geomechanics, 2011; 35:438-460</i> , <i>DOI: 10.1002/nag.903</i>

10.1007/s11823-008-1006-0

The present work focuses on numerical simulation of the sequential absorption of two droplets at an arbitrary location on the surface of single-and double-layer porous media. For description of fluid flow from a droplet into a porous medium, the Euler equations taking into account surface tension forces were used together with the unsteady filtration equations. The layers of porous media were characterized by effective permeability coefficients dependent on the porosity and pore size. The change in the droplet shape during absorption, the propagation of the absorbed fluid in a porous medium, and the fields of velocities and pressure are the output data of the problem. The effect of the porous medium structure parameters and relative location of droplets on the rate of absorption and distribution of absorbed liquids is analyzed using a numerical experiment. It is shown that the presence of the second layer can significantly affect the duration and result of the droplet absorption. The ratio of the pore size in the layers is found to be the main parameter that governs the effect of the second layer.