Experimental Investigation of Transitional Flow in Porous Media with Usage of a Pore Doublet Model

The transition from laminar to turbulent flow in porous media is studied with a new method. To mimic interconnected pores, a simplified geometry consisting of a pipe with a relatively large diameter that is split into two parallel pipes with different diameters is studied. This is a pore-doublet setup and the pressure drops over the parallel pipes are recorded by pressure transducers for different flow rates. Results show that the flow in the parallel pipes is redistributed when turbulent slugs pass through one of them. The presence of the slugs is revealed by positive skewness in the pressure signals as well as an increase of the standard deviation of the pressure drops and correlation between the pressure drops of the pipes. A frequency analysis of the pressure drops show that lower band frequency pressure variations in one pipe are communicated to the other pipe while higher band frequencies are filtered out.     

Investigation of Post-Darcy Flow in Thin Porous Media

Transport in Porous Media - We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of...     

Transitional and Turbulent Flow in a Bed of Spheres as Measured with Stereoscopic Particle Image Velocimetry

Stereoscopic particle image velocimetry has been used to investigate inertia dominated, transitional and turbulent flow in a randomly packed bed of monosized PMMA spheres. By using an index-matched fluid, the bed is optically transparent and measurements can be performed in an arbitrary position within the porous bed. The velocity field observations are carried out for particle Reynolds numbers, \({Re}_{{p}}\), between 20 and 3220, and the sampling is done at a frequency of 75 Hz. Results show that, in porous media, the dynamics of the flow can vary significantly from pore to pore. At \({Re}_{{p}}\) around 400 the spatially averaged time fluctuations of total velocity reach a maximum and the spatial variation of the time-averaged total velocity, \(u_\mathrm{tot}\) increases up to about the same \({Re}_{{p}}\) and then it decreases. Also in the studied planes, a considerable amount of the fluid moves in the perpendicular directions to the main flow direction and the time-averaged magnitude of the velocity in the main direction, \(u_{x}\), has an averaged minimum of 40% of the magnitude of \(u_\mathrm{tot}\) at \({Re}_{{p}}\) about 400. For \({Re}_{{p}} > 1600\), this ratio is nearly constant and \(u_{x}\) is on average a little bit less than 50% of \(u_\mathrm{tot}\). The importance of the results for longitudinal and transverse dispersion is discussed.     

Nanoparticle‐based capillary electroseparation of proteins in polymer capillaries under physiological conditions

Totally porous lipid‐based liquid crystalline nanoparticles were used as pseudostationary phase for capillary electroseparation with LIF detection of proteins at physiological conditions using unmodified cyclic olefin copolymer capillaries (Topas^®, 6.7 cm effective length). In the absence of nanoparticles, i.e. in CE mode, the protein samples adsorbed completely to the capillary walls and could not be recovered. In contrast, nanoparticle‐based capillary electroseparation resolved green fluorescent protein from several of its impurities within 1 min. Furthermore, a mixture of native green fluorescent protein and two of its single‐amino‐acid‐substituted variants was separated within 2.5 min with efficiencies of 400 000 plates/m. The nanoparticles prevent adsorption by introducing a large interacting surface and by obstructing the attachment of the protein to the capillary wall. A one‐step procedure based on self‐assembly of lipids was used to prepare the nanoparticles, which benefit from their biocompatibility and suspension stability at high concentrations. An aqueous tricine buffer at pH 7.5 containing lipid‐based nanoparticles (2% w/w) was used as electrolyte, enabling separation at protein friendly conditions. The developed capillary‐based method facilitates future electrochromatography of proteins on polymer‐based microchips under physiological conditions and enables the initial optimization of separation conditions in parallel to the chip development.     

Fibre suspension rheology: effect of concentration, aspect ratio and fibre size.

Viscosity data for fibre suspensions are produced using cone-and-plate geometry of enhanced dimensions for the reduced influence of fibre-wall interactions. Semi-concentrated suspensions of monodisperse polyamide fibres in silicone oil, with a variety of fibre concentrations (2, 5 and 8%), lengths and diameters, were studied. The suspension viscosity was measured in a range of shear stress in order to study the stress dependence. The study here focuses on the nature of the forces and interactions that contribute to the suspension viscosity. The results show that at sufficiently high stress levels, the suspension viscosity tends to reach a steady-state. At very low stress levels the suspension viscosity increases over time, most likely due to structures formed by adhesive forces. At higher concentrations, the viscosity depends on the absolute size of the fibres, again indicating the presence of non-hydrodynamic interactions.     

Use of nanoparticles in capillary and microchip electrochromatography

Applications of nanoparticles are of rising interest in separation science, due to their favorable surface-to-volume ratio as well as their applicability in miniaturization. A stationary phase with large surface area in combination with an electroosmotic flow-driven system has great potential in a highly efficient separation system. This review covers the use of various nanoparticles as stationary or pseudostationary phase in capillary and microchip electrochromatography. The use of nanoparticles in pseudostationary phase capillary electrochromatography and open-tubular capillary electrochromatography are thoroughly discussed. The stationary and pseudostationary phases that are described include polymer nanoparticles, gold nanoparticles, silica nanoparticles, fullerenes and carbon nanotubes.     

Synthesis of butenolides recently isolated from marine microorganisms

The syntheses and ¹³C NMR analyses of four diastereomeric butenolides, two of which were recently isolated from the marine microorganisms Streptomycete B 5632 and Streptoverticillium luteoverticillatum 11014 are described. The two isolated butenolides were found to be one of the two diastereomers (4S,10R^∗,11R^∗)-4,11-dihydroxy-10-methyl-dodec-2-en-1,4-olide (RRS-1 or SSS-1) and one of the two diastereomers (4S,10S^∗,11R^∗)-4,11-dihydroxy-10-methyl-dodec-2-en-1,4-olide (SRS-1 or RSS-1). An asymmetric 1,3-dipolar cycloaddition of a thiocarbonyl ylide with a dipolarophile attached to camphorsultam and a ring-opening of an enantiomerically pure vinyloxirane by lithiated dithiane served as key steps for the construction of the three stereogenic centres. Further elaborations including ring-closing metathesis and Mitsunobu inversion furnished the four diastereomeric butenolides.     

Extracting syringe for extraction of phthalate esters in aqueous environmental samples

The use of the extracting syringe (ESy), a fully automated membrane-based extraction technique, for analysis of phthalate esters in complex aqueous samples has been investigated. The ESy, working as an autosampler that combines the extraction process and injection into the gas chromatograph (GC) in one single step, is placed on top of the GC equipped with a flame ionisation detector. The aqueous samples are loaded in a tray and automatically extracted by employing microporous membrane liquid-liquid extraction principle. After the extraction, the extract is directly injected into the GC's programmable temperature vaporisation injector. Six different phthalate esters were used as model compounds. Four extraction solvents were tested and the addition of sample organic modifier was examined.Toluene was the optimal solvent to use for extraction. Due to the large variation in polarity of phthalate esters, 50% methanol as organic modifier had to be added to the samples so as to extract the most nonpolar phthalate esters; di-2-ethylhexylphthalate and di-n-octylphthalate, whereas the other four relatively polar phthalate esters were extracted from unmodified samples. No significant difference between extraction of river water, leachate water from a landfill and reagent water was noted, except for minor deviations. The extraction time was 20 min for extraction of a 1-mL sample, resulting in a good linearity for all aqueous media investigated, good enrichment factors (54-110 folds) and low LOD values (0.2-10 ng mL⁻¹) and relative standard deviation (%R.S.D.; 0.9-3.7%).     

Self‐consistent theory of dynamic melting of a vortex lattice

The dynamic melting of vortex lattices in type II superconductors is considered. A field‐theoretic formulation of the pinning problem allows the average over the quenched disorder to be performed exactly. A self‐consistent theory is constructed using a functional method for the effective action, allowing a determination of the pinning force and the vortex fluctuations. The phase diagram for the dynamic melting transition is determined numerically. In contrast to perturbation theory, the self‐consistent theory is in quantitative agreement with the prediction of a recent phenomenological theory and simulations and experimental data.