Secondary Drops Research Articles

Hydrodynamic Processes Involving Drops

Expressions based on wave theory are derived for calculating the size of drops that result from dropwise or jet outflow of a liquid into another liquid or a gas. Conditions for outflow mode change, the velocities of floating and sinking drops, and the size of secondary drops that result from the fragmentation of primary drops are expressed. The calculated and observed data are in satisfactory agreement.

Influence of Substrate Properties in Drop on Demand Printing

Drop on demand ink jet printing has become a very important printing technology combining excellent ease of use with good image quality. Optimal image quality, however, is only possible after proper tuning of ink, media and driver settings. In this study, final image quality is correlated with intermediate phases taking place after a droplet has been jetted from an ink jet head. As such, droplet impact upon the substrate with associated spreading, liquid imbibition into the porous receiving layer, and finally evaporation of the liquid into the surrounding air are considered.The experimental methods used are based on highspeed cinematography and proprietary phase controlled ultra short snap shots of the impact process. Different grades of papers were considered covering a wide range of porosities. A wide range of flow regimes is covered in the impact phase: spreading, retraction, oscillation and eventual splashing of secondary drops. It is shown here that the transient evolution during the impact phase is paramount in determining the initial conditions of the imbibition and could be well expressed in terms of dimensionless numbers that are defined in the paper.It is also demonstrated that in contrast to the inertial spreading, the capillary wicking process takes place on a quite different time scale and is not easily amenable to dimensional analysis because of the strong interaction between flow parameters and substrate properties. In a third phase the liquid penetrating into the pores is shown to be evaporating into the environment at another time scale. Finally, the different results that have been obtained are compared with existing data, the possible physical mechanisms are pinpointed and explained and a unified framework of the impact process considering the image quality on substrates is suggested.

Validation of a reverse transcription nested polymerase chain reaction (RT-nPCR) to detect bovine viral diarrhea virus (BVDV) associated with in vitro-derived bovine embryos and co-cultured cells

Sensitive RT-nPCR assays can be used for the rapid detection of viruses. The objective of this research was to validate an RT-nPCR assay for detection of BVDV associated with various samples collected from an IVF system. In 12 research replicates, we maintained matured COCs as negative controls or exposed them to 1 of 4 noncytopathic strains (SD-1, NY-1, CD-87, or PA-131) of BVDV for 1 h immediately before IVF. After 4 d of IVC, we harvested groups of 5 nonfertile ova or degenerated embryos (NFD) and some associated cumulus cells and transferred developing embryos and the remaining cumulus cells into secondary IVC drops. On the seventh d of IVC, cumulus cells, groups of 5 washed NFD and groups of 5 developed, washed embryos were harvested. We also collected single developed embryos after washing, washing with trypsin, washing and cryopreservation in ethylene glycol, or washing with trypsin and cryopreservation in ethylene glycol. All washes were performed according to International Embryo Transfer Society standards. Developed embryos and NFD were sonicated prior to assay. All samples were assayed for BVDV using virus isolation and RT-nPCR. The virus isolation and RT-nPCR assays determined that all negative control samples were BVDV-free. Virus was detected in association with all exposed cumulus cells and groups of developed embryos using both virus isolation and RT-nPCR. Results from viral assays of other exposed samples indicate enhanced sensitivity of the RT-nPCR assay. The RT-nPCR assay used in this research exhibited acceptable sensitivity, specificity, predictive value and repeatability for rapid detection of BVDV associated with the various samples obtained from an IVF system.

SPECIFIC FEATURES OF THE ACOUSTIC DIFFRACTION FROM A PERIODIC SYSTEM OF PLANAR SLIDING-CONTACT INTERFACES

Propagation of sagittally polarized plane acoustic waves is considered in an orthorhombic medium with a periodic system of N+1 infinite planar cuts maintaining sliding contact (ideal cracks). The reflection and transmission rates are derived by the propagator-matrix method. Two essentially different types of stop bands exist, in which the imaginary part of the Bloch vector either remains finite or reaches infinity. The latter corresponds to the transmission cut-off, which may come about specifically at the sliding-contact interface. Coupling of the Bragg phenomenon with the cutting-off effect produces quite specific resonant features of reflection and transmission. Especially sharp filtering properties of the spectra come about at a small deviation Δθ from such angles of incidence, which provide total transmission (anti-reflection) independent of frequency, namely, at nearly normal incidence of the fast mode, and at angles of incidence of the slow mode close to a certain critical value. At ∣Δθ∣⪡1, the spectrum of transmission (without mode conversion) represents a nearly periodic group of abrupt dips to zero and a modulated group of secondary drops increasing with growing (Δθ)2N2, whereas the general spectral background is close to unity. In turn, the reflection spectrum at ∣Δθ∣⪡1 contains sharp principal peaks with modulated heights, reaching nearly unit height, and the secondary peaks against almost zero background. Changes in the spectra shape on varying the angle of incidence θ become drastic near the specific threshold value of θ, which corresponds to the mutual transformation of the ordinary stop bands and cutting-off bands. After the cross-over, the transmission spectrum contains significantly wide step-wise dips, within which the rate stays very close to zero if N2⪢1.

Theory of free fall breakup of large drops

This paper presents a theoretical investigation of the bag-mode breakup of liquid drops freely falling through the gas or another liquid of less density. A shape of flattened drop is postulated, a condition of equilibrium of drop formulated, a model of blowing up of the bag proposed and the respective definition of critical Weber number introduced. There are computed: minimal Weber number when the drop begins to flatten, degree of flattening, critical Weber number and secondary drops diameter. Appendix contains a generalization of the investigation on the drop of liquid and bubble of gas travelling upwards. The paper may be utilized in the study of precipitation, as well as in designing of cooling towers and the scrubbers.

Secondary drop production in packed-bed coalescers

The separation of secondary oil in water dispersions in packed-bed coalescers has become a subject of growing interest. This interest is driven largely by environmental legislation. Permitted oil in water concentrations in effluent are being limited to the 15 to 30 ppm level in many jurisdictions. As packed gravity separators are standard separating devices for oil-water separation, the question arises as to whether such devices can meet the new effluent limits. It is apparent that such low effluent concentrations from gravity separators can only be realized, in general, if the finest drops in a dispersion, secondary drops (drops with diameters less than 100 μm), coalesce and are separated from the continuous phase. In this paper we show that while drops from all size ranges coalesce on packing surfaces, secondary drops are also produced during drop detachment from all packing surfaces and the net coalescence rate for secondary drops is low. Our principal conclusions are that the maximum size of secondary drops produced on packing surfaces is independent of the nature of the packing material, and that this drop size can be expressed as a simple function of the physical properties of the dispersion.

Dependence of rainfall interception on drop size: 1. Development of the two-layer stochastic model

The original stochastic interception model (Calder, 1986, J. Hydrol., 89: 65–71) showed, through the use of Poisson probability statistics, that the rate at which vegetation canopies are wetted is dependent on the volume of the individual raindrops; for the same depth of rain applied, a greater depth of water will be retained on the canopy when raindrop volumes are small. This paper recognizes that vegetation canopies are wetted through both the primary impact of raindrops to the top layer of the canopy and secondary impacts, from drops falling from the vegetation, to lower layers of the canopy. It shows how drop volumes of primary raindrops can be calculated from the Marshall-Palmer distribution and drop volumes of secondary drops can be calculated from the `characteristic' volume appropriate to the particular vegetation species. A two-layer stochastic model is described which calculates the rate at which canopies are wetted in relation to both primary and secondary drops. The paper also shows that, in addition to the volume-dependent stochastic wetting effect, there is also another drop-size-dependent wetting effect, related to the kinetic energy of the raindrops, which influences the maximum storage that can be achieved on the canopy. The wetting functions predicted for canopies of different density are described and the application of the model for assessing interception loss from forests, in relation to vegetation, climate and possible climatic change, is discussed.

Rainfall interception and drop size-development and calibration of the two-layer stochastic interception model.

This paper reviews the development of the stochastic interception model from the original, single-layer, drop-size-dependent model to the two-layer model that recognizes that vegetation canopies are wetted through both the primary impact of raindrops to the top layer of the canopy and secondary impacts from drops falling from the vegetation to lower layers of the canopy. It is shown that drop volumes of primary raindrops can be calculated from the Marshall-Palmer distribution and drop volumes of secondary drops can be estimated from disdrometer measurements of the characteristic volume appropriate to the particular vegetation species. It is recognized that, in addition to the volume-dependent stochastic wetting effect, there is also another drop-size-dependent wetting effect that is related to the kinetic energy of the raindrops, which reduces the maximum storage that can be achieved on the canopy. The predicted wetting functions for canopies of different density are described and compared with observations made with the use of a rainfall simulator. It is also shown that the species-dependent model parameters can be determined from measurements made with the rainfall simulator. The improved performance of the model compared with conventional interception models is demonstrated for a tropical forest in Sri Lanka. Application of the two-layer model may explain why interception losses from coniferous, fine-leaved forests in the temperate, low-intensity rainfall climate of the uplands of the U.K. are among the highest in the world, whereas interception losses from tropical broad leaved forest in high-intensity rainfall climates of the tropics are among the lowest.

Instability of liquid coatings on cylindrical surfaces

Capillary instability of long annular viscous liquid layers coating the surface of a cylindrical wire is studied. Effects of Reynolds number, Re, initial disturbance wave numbers, k, and wire radii, s on the growth rate of the instability are considered. The initial disturbance amplitude is chosen as 5% of the initial unperturbed liquid thickness. It is found that the growth rate of the disturbance amplitude is composed of a linear portion, which is well predicted by the linear theory, and a relatively flat portion, which is not predicted by the linear theory and is strongly dependent on the Re, k, and s. A unique feature of this instability is a double pinch-off process (in certain parameter range) which results in the formation of secondary satellite drops.

Thermohydrodynamic study of a drop impact against a heated surface

Heat-transfer and hydrodynamic processes occurring during the impact of a drop against a heated wall were studied by using surface temperature transducers with a high time and coordinate resolution and spark photography. Acoustic and chemical effects were also used. New phenomena (cumulative expulsion of secondary drops upon collisions and statistical variability of heat-transfer parameters under identical conditions of collision) are described. The role of heat-exchange mode parameters, properties of liquid and surface materials in heat removal by drops are elucidated.

The capillary instability of annular layers and liquid threads

The capillary instability and break-up of an annular liquid layer coating the inner surface of a cylindrical tube while surrounding another core fluid is studied. In the limiting case where the thickness of the layer is almost equal to the radius of the tube, we obtain a thread of core fluid suspended in a virtually unbounded ambient liquid. The evolution of a layer or thread with a cylindrical or unduloidal interface subject to an axisymmetric perturbation is computed using a boundary integral method. It is shown that for large and moderate layer thicknesses the instability causes the core to transform into an alternating array of primary and secondary spherical drops along the centreline of the tube. The relative volume of the drops depends primarily on the ratio of the core radius to the tube radius, a/R, and the type of initial perturbation. The evolution of thin layers with a/R > 0.82 leads to formation of an array of lobes or collars. These results are used to assess the accuracy of previous approximate analyses based on lubrication flow and minimization of interfacial area.

Spectrum of secondary drops with impulsive breakup of a large single drop

Spectrum of secondary drops with impulsive breakup of a large single drop

The breakup of organic drops falling freely through water

The breakup of drops of chlorobenzene, dichloroethane and ethyl bromide, which were falling freely through water, was studied. All observed breakages occurred during the oscillation which followed the first shedding of a class III attached wake. Secondary drops were produced from protruding columns of liquid which were formed at both the front and rear of the drops. The factors which govern the sizes of these secondary drops are discussed and empirical relationships are presented. Theoretical predictions of the liquid column diameter immediately prior to necking and of the rate of necking of the column are compared with experimentally determined values.

Analysis of the nonequilibrium two-phase flow with coagulation and crushing of condensate particles for arbitrary mass and velocity distributions of the secondary drops

The problem of the nonequilibrium flow of a two-phase gas-polydisperse condensate drop mixture is considered in a one-dimensional approximation taking account of coagulation and crushing of particles of different size during collisions. A closed system of equations in the flow characteristics is obtained in application to the general case of arbitrary size, velocity, and temperature distributions of the secondary drops formed during crushing. Regularities in the interaction of freely moving drops during collisions are investigated experimentally.

Dynamic strain aging in magnesium oxide single crystals

Dynamic strain aging characteristics have been observed in MgO single crystals when deformed above 600°C. Serrated flow has been identified, which has been shown to depend on the deformation rate and temperature. The extent of aging has been found to be directly proportional to the time of aging at a given strain and temperature; t 2 3 law which has been found to be applicable in b.c.c. iron and C-doped Ni is not observed in MgO. Secondary load drops are observed under certain conditions during strain rate change experiments. Dynamic strain aging in MgO seems to be due to Cottrell type impurity atmospheres formed around dislocation lines, but the identity of the impurity responsible for this behavior is not yet known.

The mechanism of partial coalescence of liquid drops at liquid/liquid interfaces

The mechanism of formation of a secondary drop from the coalescence of a liquid drop (Phase 1) at a liquid/liquid interface was investigated. It was shown by means of high-speed photographs that partial coalescence results from the formation of a liquid column of Phase 1 in Phase 2 which contracts at the base and detaches itself to form the secondary drop. The diameter ratio, secondary to primary, varied with the viscosity ratio p = η 1 η 2 , and passed through a maximum near p = 1. When p was less than 0.02 or greater than 11, no secondary drops formed. Secondary drop formation could be suppressed by adding a high concentration of surfactant or by applying an electrostatic field. The experimental results were analyzed with reasonable success with the aid of Rayleigh's theory of unstable liquid threads.

Liquid Drops on the Same Liquid Surface

IN two previous papers,1 I have mentioned that water at ordinary temperature is not a suitable liquid for forming “liquid drops floating on the same liquid surface”. In August 1930, however, I observed at Den Kund (Dalhousie hills), at a height of about 1000 ft. above the sea-level, that water is quite a suitable liquid for easy formation of either primary2 or secondary drops. The life of these drops is also found to be longer. The splashing gives easy formation of secondary drops of quite a long life. The temperature of the water was about 34° F. The surface tension of water at this temperature is 76.53 dynes per cm., and viscosity 0.0179 c.g.s. units.