Porous asphalt (PA) are used to drain water from the surface of the asphalt pavements. It reduces aquaplaning and subsequently decreases splash and spray. Clogging reduces the permeability of PA over the years. The double layer PA are used to mitigate this problem. Different aggregate gradations and binder types can alter the performance of double layer PA. The objective of this research is to evaluate the effects of these parameters on the performance of double layer PA. For this purpose, different samples were fabricated using various aggregate gradations based on Malaysian asphalt mixture standards. Indirect tensile strength, permeability and air voids of the samples were determined. The proposed aggregate gradation for top and bottom layers were mixed with two different asphalt binders. Cantabro and binder drainage tests were later carried out on these samples. The results were then compared with the corresponding results from the Dutch double layer PA gradations. Laboratory test results showed that aggregate gradation significantly affect the indirect tensile strength, permeability and air voids of both top and bottom layer of PA. The design binder content for the bottom layer is also lower than that for the top layer. However, the binder type did not significantly change the design binder content.

An instability analysis in a horizontal Porous layer is made for a fluid with an inverse density gradient. The governing equations resulted when instability analysis is applied to this problem, are non-linear and therefore mathematically complex. In published literature, the problem is solved with some simplifications such as ignoring certain terms in the governing equations, or finding algebraic approximations that are valid in some specific range of physical parameters. In this study, the problem is solved in its general form for two rigid, and one rigid and one free boundary conditions using variational methods. The resulting critical Rayleigh numbers and critical wave numbers vs. l2/K curves are compared to previous works.        

The linear and nonlinear stability analysis of double diffusive reaction-convection in a sparsely packed anisotropic Porous layer subjected to chemical equilibrium on the boundaries is investigated analytically. The linear analysis is based on the usual normal mode method and the nonlinear theory on the truncated representation of Fourier series method. The Darcy-Brinkman model is employed for the momentum equation. The onset criterion for stationary, oscillatory and finite amplitude convection is derived analytically.The effect of Darcy number, Damkohler number, anisotropy parameters, Lewis number, and normalized porosity on the stationary, oscillatory, and finite amplitude convection is shown graphically. It is found that the effect of Darcy number and mechanical anisotropy parameter have destabilizing effect, while the thermal anisotropy parameter has stabilizing effect on the stationary, oscillatory and finite amplitude convection. The Damkohler number has destabilizing effect in the case of stationary mode, with stabilizing effect in the case of oscillatory and finite amplitude modes. Further, the transient behavior of the Nusselt and Sherwood numbers are investigated by solving the nonlinear system of ordinary differential equations numerically using the Runge-Kutta method.

Combustion in Porous media is an effective method to minimize dissipations and save energy. Therefore, Study on the Porous burners has been the focus of many researches in the past decade, due to the favorable features of these burners. The conditions for the formation of a steady-state submerged flame in a ceramic (Silicon Carbide) Porous medium were investigated at four firing rates. The results were obtained on a ceramic foam with a cross section area of 63.6 cm2 and pore density of either 10 or 30 ppi. The reactants were air and natural gas with various equivalence ratios. In this experimental study, eight thermocouples were mounted on the burner walls along its axis in order to track the flame position, and the results were presented as temperature profiles of the Porous wall. It was observed that the formation of submerged flame depends on firing rate and equivalence ratio. The stability limit of submerged flame (the range between surface flame and flash back limits) is reduced by increasing the firing rate. Results show that, when the mixture velocity is low, the stability limit extends. Finally, the ranges of equivalence ratio and mixture velocity for the formation of submerged flame are presented at various firing rates.

The onset of convection in a Porous medium saturated by a dielectric nanofluid with vertical AC electric field is investigated. The flux of volume fraction of a nanoparticle with the effect of thermophoresis is taken to be zero on the boundaries and the eigenvalue problem is solved using the Galerkin method. The model used for nanofluid incorporates the combined effect of Brownian diffusion, thermophoresis and electrophoresis, while for Porous medium Darcy model is employed. The results show that increase in the AC electric Rayleigh-Darcy number, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh-Darcy number are to hasten the onset of convection. The size of convection cells does not depend on nanofluid parameters, but decreases with increasing the AC electric Rayleigh-Darcy number. The non-existence of oscillatory convection is also obtained.