This work experimentally investigates the pressure-driven flow of a pure Newtonian fluid through ... more This work experimentally investigates the pressure-driven flow of a pure Newtonian fluid through three-dimensional (3D) porous media models. The porous media model consists of square arrays of rods that also could be interpreted as a periodic tandem rod arrangement. We employed a time-resolved three-dimensional particle tracking velocimetry (3D Shake-the-Box) technique for a range of Reynolds numbers [Formula: see text] to observe flow structures and vortex formation between the rods in porous media structures with different porosities of [Formula: see text] which corresponds to the spacing ratio of [Formula: see text], where L is the distance between the centers of the rods, and D is the diameter of the rods. For all the examined cases, we further analyzed the effect of the Reynolds number and the spacing ratio on the instantaneous and averaged patterns of velocity, vorticity, and the other flow parameters after obtaining the two-dimensional velocity fields using the bin-averaging ...
Laboratory experiments were conducted to study particle migration and flow properties of non-Brow... more Laboratory experiments were conducted to study particle migration and flow properties of non-Brownian, noncolloidal suspensions ranging from 10% to 40% particle volume fraction in a pressure-driven flow over and through a porous structure at a low Reynolds number. Particle concentration maps, velocity maps, and corresponding profiles were acquired using a magnetic resonance imaging technique. The model porous medium consists of square arrays of circular rods oriented across the flow in a rectangular microchannel. It was observed that the square arrays of the circular rods modify the velocity profiles and result in heterogeneous concentration fields for various suspensions. As the bulk particle volume fraction of the suspension increases, particles tend to concentrate in the free channel relative to the porous medium while the centerline velocity profile along the lateral direction becomes increasingly blunted. Within the porous structure, concentrated suspensions exhibit smaller per...
Abstract This study explores thermal convection in suspensions of neutrally buoyant, non-colloida... more Abstract This study explores thermal convection in suspensions of neutrally buoyant, non-colloidal suspensions confined between horizontal plates. A constitutive diffusion equation is used to model the dynamics of the particles suspended in a viscous fluid and it is coupled with the flow equations. We employ a simple model that was proposed by Metzger, Rahli & Yin (J. Fluid Mech., vol. 724, 2013, pp. 527–552) for the effective thermal diffusivity of suspensions. This model considers the effect of shear-induced diffusion and gives the thermal diffusivity increasing linearly with the thermal Péclet number (Pe) and the particle volume fraction (ϕ). Both linear stability analysis and numerical simulation based on the mathematical models are performed for various bulk particle volume fractions $({\phi _b})$ ranging from 0 to 0.3. The critical Rayleigh number $(R{a_c})$ grows gradually by increasing ${\phi _b}$ from the critical value $(R{a_c} = 1708)$ for a pure Newtonian fluid, while the critical wavenumber $({k_c})$ remains constant at 3.12. The transition from the conduction state of suspensions is subcritical, whereas it is supercritical for the convection in a pure Newtonian fluid $({\phi _b} = 0)$. The heat transfer in moderately dense suspensions $({\phi _b} = 0.2\text{--}0.3)$ is significantly enhanced by convection rolls for small Rayleigh number (Ra) close to $R{a_c}$. We also found a power-law increase of the Nusselt number (Nu) with Ra, namely, $Nu\sim R{a^b}$ for relatively large values of Ra where the scaling exponent b decreases with ${\phi _b}$. Finally, it turns out that the shear-induced migration of particles can modify the heat transfer.
An experiment has been designed to examine the generation of dynamic lift forces during compactio... more An experiment has been designed to examine the generation of dynamic lift forces during compaction of soft highly compressible fibrous materials in a piston/cylinder apparatus. Novel experimental techniques have been developed to simultaneously measure and separate out the dynamic forces acting on the compressing piston by the air and solid phases respectively. The measurements clearly demonstrate that the excess pore pressure builds up inside the porous material and reaches its maximum before there is any significant rise in the solid phase force. The air pressure subsequently decays due to air venting into the ambient environment at the edges of the testing apparatus as the solid phase force rapidly rises. We also examine the internal stresses and strains within the solid phase that develop as a result of friction forces along the sidewalls of the cylinder and show that these lead to important hysteresis effects when the loads on the piston are gradually removed. The experiments are performed on a polyester material with a trace of silk which has recently been proposed for a soft porous track wherein a high speed train is supported by large a planing surface or ski that rides within a confined channel in which this venting is substantially reduced or eliminated, Mirbod et al (2008).
This work experimentally investigates the pressure-driven flow of a pure Newtonian fluid through ... more This work experimentally investigates the pressure-driven flow of a pure Newtonian fluid through three-dimensional (3D) porous media models. The porous media model consists of square arrays of rods that also could be interpreted as a periodic tandem rod arrangement. We employed a time-resolved three-dimensional particle tracking velocimetry (3D Shake-the-Box) technique for a range of Reynolds numbers [Formula: see text] to observe flow structures and vortex formation between the rods in porous media structures with different porosities of [Formula: see text] which corresponds to the spacing ratio of [Formula: see text], where L is the distance between the centers of the rods, and D is the diameter of the rods. For all the examined cases, we further analyzed the effect of the Reynolds number and the spacing ratio on the instantaneous and averaged patterns of velocity, vorticity, and the other flow parameters after obtaining the two-dimensional velocity fields using the bin-averaging ...
Laboratory experiments were conducted to study particle migration and flow properties of non-Brow... more Laboratory experiments were conducted to study particle migration and flow properties of non-Brownian, noncolloidal suspensions ranging from 10% to 40% particle volume fraction in a pressure-driven flow over and through a porous structure at a low Reynolds number. Particle concentration maps, velocity maps, and corresponding profiles were acquired using a magnetic resonance imaging technique. The model porous medium consists of square arrays of circular rods oriented across the flow in a rectangular microchannel. It was observed that the square arrays of the circular rods modify the velocity profiles and result in heterogeneous concentration fields for various suspensions. As the bulk particle volume fraction of the suspension increases, particles tend to concentrate in the free channel relative to the porous medium while the centerline velocity profile along the lateral direction becomes increasingly blunted. Within the porous structure, concentrated suspensions exhibit smaller per...
Abstract This study explores thermal convection in suspensions of neutrally buoyant, non-colloida... more Abstract This study explores thermal convection in suspensions of neutrally buoyant, non-colloidal suspensions confined between horizontal plates. A constitutive diffusion equation is used to model the dynamics of the particles suspended in a viscous fluid and it is coupled with the flow equations. We employ a simple model that was proposed by Metzger, Rahli & Yin (J. Fluid Mech., vol. 724, 2013, pp. 527–552) for the effective thermal diffusivity of suspensions. This model considers the effect of shear-induced diffusion and gives the thermal diffusivity increasing linearly with the thermal Péclet number (Pe) and the particle volume fraction (ϕ). Both linear stability analysis and numerical simulation based on the mathematical models are performed for various bulk particle volume fractions $({\phi _b})$ ranging from 0 to 0.3. The critical Rayleigh number $(R{a_c})$ grows gradually by increasing ${\phi _b}$ from the critical value $(R{a_c} = 1708)$ for a pure Newtonian fluid, while the critical wavenumber $({k_c})$ remains constant at 3.12. The transition from the conduction state of suspensions is subcritical, whereas it is supercritical for the convection in a pure Newtonian fluid $({\phi _b} = 0)$. The heat transfer in moderately dense suspensions $({\phi _b} = 0.2\text{--}0.3)$ is significantly enhanced by convection rolls for small Rayleigh number (Ra) close to $R{a_c}$. We also found a power-law increase of the Nusselt number (Nu) with Ra, namely, $Nu\sim R{a^b}$ for relatively large values of Ra where the scaling exponent b decreases with ${\phi _b}$. Finally, it turns out that the shear-induced migration of particles can modify the heat transfer.
An experiment has been designed to examine the generation of dynamic lift forces during compactio... more An experiment has been designed to examine the generation of dynamic lift forces during compaction of soft highly compressible fibrous materials in a piston/cylinder apparatus. Novel experimental techniques have been developed to simultaneously measure and separate out the dynamic forces acting on the compressing piston by the air and solid phases respectively. The measurements clearly demonstrate that the excess pore pressure builds up inside the porous material and reaches its maximum before there is any significant rise in the solid phase force. The air pressure subsequently decays due to air venting into the ambient environment at the edges of the testing apparatus as the solid phase force rapidly rises. We also examine the internal stresses and strains within the solid phase that develop as a result of friction forces along the sidewalls of the cylinder and show that these lead to important hysteresis effects when the loads on the piston are gradually removed. The experiments are performed on a polyester material with a trace of silk which has recently been proposed for a soft porous track wherein a high speed train is supported by large a planing surface or ski that rides within a confined channel in which this venting is substantially reduced or eliminated, Mirbod et al (2008).
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