Numerical modeling of multiphase flows in microfluidics and micro process engineering: a review of methods and applications

This article presents a comprehensive review of numerical methods and models for interface resolving simulations of multiphase flows in microfluidics and micro process engineering. The focus of the paper is on continuum methods where it covers the three common approaches in the sharp interface limit, namely the volume-of-fluid method with interface reconstruction, the level set method and the front tracking method, as well as methods with finite interface thickness such as color-function based methods and the phase-field method. Variants of the mesoscopic lattice Boltzmann method for two-fluid flows are also discussed, as well as various hybrid approaches. The mathematical foundation of each method is given and its specific advantages and limitations are highlighted. For continuum methods, the coupling of the interface evolution equation with the single-field Navier–Stokes equations and related issues are discussed. Methods and models for surface tension forces, contact lines, heat and mass transfer and phase change are presented. In the second part of this article applications of the methods in microfluidics and micro process engineering are reviewed, including flow hydrodynamics (separated and segmented flow, bubble and drop formation, breakup and coalescence), heat and mass transfer (with and without chemical reactions), mixing and dispersion, Marangoni flows and surfactants, and boiling.     

Tantalum—processing,properties and applications

Tantalum— the Earth’s 49th most abundant element— is frequently produced as a by-product of tin smelting. The metal is also extracted from concentrates by reduction with sodium or fused-salt electrolysis; tantalum carbide is produced by carburization of Ta₂O₅ or tantalum hydride. Sintering, electric-arc melting and electron-beam melting are used to refine and purify raw tantalum. Tantalum’s unique properties make it suitable for a number of diverse applications, including capacitors, chemical equipment, hard-metal tooling and alloys. Tantalum consumption is expected to increase in the capacitor market, because of the demand for electronics equipment.     

Ionic conductivity of synthetic analcime,sodalite and offretite

The ionic conductivity of pressed pellets of dehydrated synthetic analcime, sodalite and offretite was determined by a.c. measurements within the range 10 Hz to 10 MHz. The ionic conductivity values of those zeolites exchanged with various monovalent cations were determined by the complex impedance plane method. The conduction activation energies range between 63 and 101 kJ mol^–1. Sodium analcime shows the best ionic conductivity, namely 1.8×10^–4–1 cm^–1 at 400° C. A comparison with the conductivity of other ion-conducting solids was made.     

Production of rapidly solidified Al/SiC composites

Rapidly solidified metal matrix composites have been produced on a laboratory scale either by (1) melt spinning a composite after introduction of the ceramic phase and extrusion of the flakes obtained, or (2) blending melt-spun powder (basic alloy) with the ceramic phase and subsequent extrusion. AlMg(Si) alloys were used as matrix material while SiC particles with diameters of 3 or 20 m were used as the ceramic phase. For the composites prepared by route 1 it was found that the basic alloy was reinforced by the addition of 3 m particles whereas for the 20m particles reinforcement was observed only for very ductile matrices. The bond between SiC particles and matrix was good. A diffusion and wetting bond was formed. For the composites prepared by route 2 it was found that reinforcement did not occur and that the bond between particles and matrix was weak. Debonding of the particles took place in the case of tensile fracture. The advantage of a rapidly solidified matrix for these composites is that relatively high ductilities are combined with good reinforcement effects. Prior contact of the ceramic phase and the aluminium melt is needed for a good bond between SiC and the matrix material. It is concluded that route 1 should be preferred for the production of rapidly solidified aluminium matrix composites.     

Fourier Transform Spectrometer for the 1 to 10mm region

A Fourier Transform Spectrometer using a 250 Watt Mercury lamp, a lamellar grating and a pumped He-cooled detector is applied to the millimeter wave spectral region. The pure rotation spectrum of CH₂F, the transmission of graphite particles in a cloud chamber, the interference on round copper dots and the absorption of iron whiskers have been observed.     

Floral volatiles ofTanacetum vulgare L. attractive toLobesia botrana den. et schiff. females

The European grapevine moth (EGVM),Lobesia botrana, is a major pest of grapes in Europe. Females are attracted to a nonhost plant: tansy (Tanacetum vulgare L.), which is a common weed in Slovakian vineyards. A steam distillate extract of tansy flowers was analyzed by means of a GC-EAG technique to screen constituents detected by the olfactory receptors of EGVM females. From more than 200 GC peaks, nine peaks corresponding to monoterpenoids released an EAG response in more than 70% of the females (N=15):p-cymene,d-limonene,-thujene,-thujone,-thujone, thujyl alcohol, terpinene-4-ol, (Z)-verbenol, and piperitone. The steam distillate of tansy as well as a synthetic blend of identified compounds released consistent attraction in a field cage. The use of nonhost plants and host plant odors in integrated pest management is discussed.     

Measurements of the characteristic lengths of smoke detectors

The dynamic performance of point-type smoke detectors is described by a simple model including two independent parameters, the static response threshold, and the characteristic length of the detector. An experimental system with constant rate of increase of smoke density under varying velocity conditions is used to determine the model parameters.Nomenclature k constant smoke density gradient (dB/m/s) - L characteristic length of the detector (m) - m _i smoke density inside the detector (dB/m) - m _o smoke density outside the detector (dB/m) - m _or measured smoke density at response (dB/m) - m _r response threshold of the detector (dB/m) - t time(s) - v gas flow velocity at the detector (m/s) - time constant(s)     

The effect of appraisers in estimating metabolic rate with the Edholm scale

A study was made of the appraisers' effect on the estimation of metabolic rate with the Edholm scale and a table of the ISO 7243 heat stress standard. The appraisers, five experienced and five inexperienced persons, estimated the metabolic rate of three different work tasks from videotapes. Analysis of variance indicated significant ( [Formula: see text] ) differences in the appraisers' recordings of the activities. The appraisers were grouped according to the similarity of the estimated values they gave. The groups thus contained both experienced and inexperienced appraisers, and it was not possible to classify the appraisers into experienced and inexperienced groups according to their earlier experience. The metabolic rates according to the Edholm scale were higher than according to the ISO 7243 table. The differences in metabolic rates given by the individual observers varied from 38 to 118 W/m(2). The variations in the estimation of metabolic rates were greater when the Edholm scale was used. This variation caused considerable variation also in the predicted mean vote, PMV index. It is recommended that the appraisers be selected carefully, because it is not possible to know whether a randomly selected appraiser is an 'average' or an 'extreme' appraiser without a test. Before conducting extensive field surveys where several appraisers estimate the metabolic rates, it would be useful to arrange training in order to calibrate the levels of the Edholm scale as well as ISO method among the appraisers because training clearly unified the estimation.     

Variation in light scattering and water-holding capacity along the porcine Longissimus dorsi muscle

The meat quality of M. longissimus muscle was evaluated in 851 pigs by using the Fibre Optic Probe (FOP) at three sites in the muscle and in both halves of the carcass. A systematic difference between sites was found, with the lowest light scattering (indicating the best meat quality) in the mid-part of the muscle and higher light scattering in the anterior and posterior parts. A non-systematic variation was also observed, with the opposite pattern in some animals, even though it was not frequent. A negative influence of the shackling was found, yielding higher FOP values in the shackled half.

Drip loss measurements in the Longissimus muscle, taken from another 100 pig carcasses, were evaluated using three methods. Drip loss, too, showed a considerable variation along the Longissimus muscle, with minimum losses around the last rib. Repeatability estimates, calculated from two non-consecutive pieces of the Longissimus dorsi muscle from each carcass, varied from 0·4 when keeping samples vacuum packed for 2 days, to 0·5 when the samples were either kept in plain plastic bags for 2 days or in a meat container with a squared inset for 1 or 2 days.