1,720,975 research outputs found
Smart mixers and reactors for the production of pharmaceutical nanoparticles: proof of concept
No full textSmart mixers and reactors for the production of pharmaceutical nanoparticles: proof of concept
No full textPrecipitation of nanoparticles for pharmaceutical applications: experimental and modeling study
No full textStrategies to control the particle size distribution of poly-ε-Caprolactone nanoparticles for pharmaceutical applications
No full textExtension of the Darcy–Forchheimer Law for Shear-Thinning Fluids and Validation via Pore-Scale Flow Simulations
Full text linkFlow of non-Newtonian fluids through porous media at high Reynolds numbers is often encountered in chemical, pharmaceutical and food, as well as petroleum and groundwater engineering, and inmany other industrial applications. Under the majority of operating conditions typically explored, the dependence of pressure drops on flowrate is non-linear and the development of models capable of describing accurately this dependence, in conjunction with non-trivial rheological behaviors, is of paramount importance. In this work, pore-scale single-phase flowsimulations conducted on synthetic two-dimensional porous media are performed via computational fluid dynamics for both Newtonian and non-Newtonian fluids and the results are used for the extension and validation of the Darcy–Forchheimer law, herein proposed for shear-thinning fluid models of Cross, Ellis and Carreau. The inertial parameter β is demonstrated to be independent of the viscous properties of the fluids. The results of flow simulations show the superposition of two contributions to pressure drops: one, strictly related to the non-Newtonian properties of the fluid, dominates at lowReynolds numbers,while a quadratic one, arising at higher Reynolds numbers, is dependent on the porous medium properties. The use of pore-scale flow simulations on limited portions of the porous medium is here proposed for the determination of the macroscale-averaged parameters (permeability K, inertial coefficient β and shift factor α), which are required for the estimation of pressure drops via the extended Darcy–Forchheimer law. The method can be applied for those fluids which would lead to critical conditions (high pressures for low permeability media and/or high flow rates) in laboratory tests
Micro-Scale Modelling of Flow and Particle Transport In Porous Media Via CFD
No full textPorous media are ubiquitous in chemical engineering. They are involved in many separation processes (e.g., filtration, chromatography) and they play an important role in numerous chemically reacting systems such as in catalysis and in remediation of contaminated aquifers. Very often the fluids involved are characterized by very diverse rheological properties, ranging from classical Newtonian to non-Newtonian behaviors. Although the final applications are very different from each other and are typically characterized by very different features there are some common issues that despite the huge amount of experimental data still need to be addressed. These are generally related to the need of describing the porous medium at the macro-scale as a continuum defined in terms of a set of parameters that quantify its flow properties (e.g., porosity, permeability) and its particle transport characteristics (e.g., collection efficiency). This work (co-funded by European Union project AQUAREHAB FP7 - Grant Agreement Nr. 226565) aims at tackling these issues from a fundamental perspective by the use of pore-scale (or micro-scale) simulations via computational fluid dynamics. Porous media with different characteristics have been analyzed and used to extract some representative two-dimensional geometries of a few millimeters in size. Grids were created with Gambit whereas the flow of Newtonian and non-Newtonian (i.e., Carreau and Cross models) fluids through these media was investigated with Fluent 12.0. Data were analyzed in terms of the flow field and pressure drops across the media for different superficial velocities ranging from laminar to turbulent flows. Simulation predictions were then analyzed with different classical approaches (i.e., Darcy, Ergun, Darcy-Forchheimer equations) and the corresponding parameters were eventually extracted. Results show that the considered geometry are large enough to model and represent a fraction of the porous medium and allowed to correct and extend the Darcy-Forchheimer law to non-Newtonian fluids. In the second part of the work the presence of solid particles suspended in the fluid was considered. The collection efficiency of the different porous media was then quantified with computational fluid dynamics by using an Eulerian approach. The gathered simulation predictions were then compared with classical approaches for the estimation of the collection efficiency of the porous medium (i.e., classical filtration theory). Results show that these theories generally under-predict the overall efficiency and a correction was eventually formulated. Future work includes the use and implementation of these corrections in macro-scale simulation
Extension of Darcy-Forchheimer law to shear thinning fluids by CFD pore-scale simulations
No full textFlow of non-Newtonian fluids through porous media at high Reynolds numbers is often encountered in chemical, pharmaceutical and food as well as petroleum and groundwater engineering and in many other industrial applications. In all abovementioned applications, it is of paramount importance to correctly predict the pressure drop resulting from non-Newtonian fluid flow through the porous medium. The Darcy law is used to describe steady-state flow of Newtonian fluids through porous media at low Reynolds numbers. For higher Reynolds numbers non linearities between pressure drop and flow rate arise, the and the Darcy-Forchheimer law can be applied. For non-Newtonian fluids, the usual formulation of Darcy law can be applied in the low flow regime, provided that all non-Newtonian effects are lumped together into a proper viscosity parameter. Similarly, at higher Reynolds numbers the Forchheimer law could be applied under the same hypotheses. In this work, an extended formulation of the Darcy-Forchheimer law for shear-thinning fluids is proposed and validated against results of micro-scale flow simulations. Flow simulations were performed on four different 2D porous domains for Newtonian and non-Newtonian fluids (Cross, Ellis and Carreau models). The micro-scale flow simulation results are analyzed in terms of "macroscale" pressure drop between inlet and outlet of the model domain as a function of flow rate. The validity of the extended Darcy-Forchheimer law is shown for the three shear-thinning model
Modelling the mobility in porous media of iron colloids for groundwater remediation: from micro- to macroscale
No full textColloidal suspensions of engineered nanoparticles have been studied in recent years for waste water and in-situ groundwater remediation. Zero-valent iron micro- and nano-particles represent a promising technology for groundwater remediation. Due to their large surface area, reactivity and mobility, iron micro- and nano-particles are extremely effective in contaminants degradation, allowing source treatment, as they can be injected directly in the subsurface in the form of viscous dispersions, characterized by complex rheological properties. Assessing the mobility of iron-based colloids is a key issue for field applications of these materials. In this work, co-funded by European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), micro- and macro-scale modelling approaches are proposed to determine the key factors that control the mobility of iron suspensions, and to simulate their transport at both laboratory and field scale. A micro-scale model can improve knowledge of pore-scale interaction mechanisms, that are lumped together in semi-empirical coefficients in macro-scale simulations. A macro-scale model can in turn help interpreting laboratory transport tests, and provide an estimation of the radius of influence for the injection points, for a correct dimensioning of full scale remediation and to predict short- and long-term mobility of the iron particles injected in the subsurface. In the micro-scale model, CFD was used to describe the flow of a non-Newtonian fluid carrying the particles through the pores of a two-dimension geometry representing a small portion of the porous medium. The Navier-Stokes and continuity equations were solved with Newtonian and non-Newtonian rheological models. In the range of superficial velocity (10-6-10 m/s), particle size (1-103 nm) and porosity investigated, the continuum hypothesis was always valid. In the macro-scale model, a numerical solution of the transport equations was developed coupling the advection/dispersion equation with kinetic expressions for dual-phase, non-equilibrium interactions between particles in the liquid (water) and solid (grains) phase. Rheological properties of the shear-thinning carrier fluid, hydrodynamic parameters of the porous medium (porosity, permeability), and colloid concentrations (both suspended and deposed) are strongly inter-dependent, thus resulting in a complex set of coupled partial differential equations and constitutive relationship
A comparative study for nanoparticle production with passive mixers via solvent-displacement: use of CFD models for optimization and design
No full textMicro-scale modelling of iron particles transport in saturated porous media
No full textZero-valent iron micro- and nano-particles represent a promising technology for groundwater remediation, since their exert their degradation capabilities through inexpensive injections. Macro-scale mathematical models are often used to design and optimize the injection strategy. These models generally take into account micro-scale phenomena, such as particle-particle and particle-grain interactions, that significantly affect particle mobility. However, the most popular approach, based on empirical attachment/detachment kinetics, seems to be unable to properly describe them. The aim of this work, co-funded by the European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), is to use Computational Fluid Dynamics (CFD) and Population Balance Models (PBM) at the micro-scale to derive more accurate (with respect to the empirical kinetics) "constitutive" equations to be implemented in the macro-scale mode
- …
