Frontal impingement of nanojets: formation,disintegration and mixing of nano liquid sheets

We investigate nano liquid sheets formed by frontal impingement of two cylindrical nanojets using the molecular dynamics method. The results show that only with a high enough velocity can a stable liquid sheet be formed because of the strong surface tension effect in nanoscale. In relatively low jet velocity range, the relationship between the intact sheet radius and the jet velocity takes on the power function form with the power being ? 0.502. This relationship is explained by considering the thermal fluctuation effect, thus confirming the dominating role of the thermal fluctuation effect in the disintegration process. The influence of the jet velocity on the time-domain evolution of mixing of the system and the spatial mixing distribution of the liquid sheet are also investigated. Our results suggest that nanojets do not coalesce at the impingement point, the mixing occurs mainly through diffusion. And there is recoil that happens at the stagnation plane.     

Application of Bioinspired Superhydrophobic Surfaces in Two-phase Heat Transfer Experiments

This paper addresses the potential to use Lotus leaf bioinspired surfaces in applications involving heat transfer with phase change,namely pool boiling and spray impingement.Besides describing the role of bioinspired topographical features,using an innovative technique combining high-speed visualization and time-resolved infrared thermography,surface durability is also addressed.Water is used for pool boiling and for spray impingement systems (simplified as single droplet impact),while HFE7000 is used in a pool boiling cooler for electronic components.Results show that surface durability is quickly compromised for water pool boiling applications,as the chemical treatment does not withstand high temperatures (T ＞ 100 ℃) during long time intervals (3 h-4 h).For HFE7000 pool boiling (depicting lower saturation temperature-34 ℃),heat transfer enhancement is governed by the topography.The regular hierarchical pattern of the bioinspired surfaces promotes the heat transfer coefficient to increase up to 22.2％,when compared to smooth surfaces,while allowing good control of the interaction mechanisms until a distance between micro-structures of 300 μm-400 μm.Droplet impingement was studied for surface temperatures ranging between 60 ℃-100 ℃.The results do not support the use of superhydrophobic surfaces for cooling applications,but reveal great potential for other applications involving droplet impact on heated surfaces (e.g.metallurgy industry).     

Effect of spray application technology on the biological control of aphids in Brussels sprouts

A field trial was carried out to evaluate different application techniques for crop penetration and biological efficacy of aphid control in Brussels sprouts. Six different application techniques were tested at a pressure of 4.0 bar in a field trial in 3 parallels at the Provincial Vegetable Research Centre in Kruishoutem (PCG): a standard ISO 02 flat fan nozzle (at 200 l/ha), an ISO 04 twin air inclusion nozzle (at 800 l/ha), an ISO 03 drift reducing nozzle, an air injection nozzle (Airjet,) droplegs in combination with an ISO 03 drift reducing nozzle and an ISO 03 air inclusion nozzle (all at 400 l/ha). Best biological control of the aphids and spray distribution was found for the twin air inclusion nozzle, the air inclusion nozzle and the airjet-system. These are all drift reducing techniques because of their coarse droplet size spectrum or the effect of air support which makes the droplets faster. Both effects improve crop penetration. No added value was found for the droplegs for this type of spray treatments. Fine droplets, produced by a standard flat fan, did not give good results on biological control or penetration into the crop.     

Orientation measurements of microsphere doublets and metaphase chromosomes in flow

Obtaining information about the shape of particles from slit-scan profiles is facilitated if the particles are oriented. Elongated particles orient in the nozzle of flow cytometers, but orientation may be disrupted before the particles get to the point of measurement. We have used our slit-scan flow cytometer to investigate the orientation of microsphere doublets in a liquid jet in air, in flow across a glass surface, and in a 200-microns-square capillary tube as a function of distance from the flow chamber nozzle. Particles were classified as being oriented if there was a centrally located dip in the slit-scan profile. Essentially all the doublets in the jet were oriented, and no disorientation was noted over the distances measured (up to 10 mm from the nozzle). Particle orientation was maintained for 80 microns in flow across a glass surface. In the capillary-type flow chamber, essentially all of the particles were oriented at the tube entrance and for several millimeters into the tube. There then occurred a region where particle tumbling started and progressively fewer doublets met the orientation criteria. The distance to where tumbling began could be estimated by calculating the length required to establish the parabolic flow profile in the tube. Finally, the fraction of oriented particles reached a constant value that did not change with increased distance into the tube. When sample was injected off axis (i.e., halfway between the chamber center and the chamber walls), particle tumbling began closer to the tube entrance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantifying Cell Adhesion through Impingement of a Controlled Microjet

The impingement of a submerged, liquid jet onto a cell-covered surface allows assessing cell attachment on surfaces in a straightforward and quantitative manner and in real time, yielding valuable information on cell adhesion. However, this approach is insufficiently characterized for reliable and routine use. In this work, we both model and measure the shear stress exerted by the jet on the impingement surface in the micrometer-domain, and subsequently correlate this to jet-induced cell detachment. The measured and numerically calculated shear stress data are in good agreement with each other, and with previously published values. Real-time monitoring of the cell detachment reveals the creation of a circular cell-free area upon jet impingement, with two successive detachment regimes: 1), a dynamic regime, during which the cell-free area grows as a function of both the maximum shear stress exerted by the jet and the jet diameter; followed by 2), a stationary regime, with no further evolution of the cell-free area. For the latter regime, which is relevant for cell adhesion strength assessment, a relationship between the jet Reynolds number, the cell-free area, and the cell adhesion strength is proposed. To illustrate the capability of the technique, the adhesion strength of HeLa cervical cancer cells is determined ((34 ± 14) N/m²). Real-time visualization of cell detachment in the dynamic regime shows that cells detach either cell-by-cell or by collectively (for which intact parts of the monolayer detach as cell sheets). This process is dictated by the cell monolayer density, with a typical threshold of (1.8 ± 0.2) × 10⁹ cells/m², above which the collective behavior is mostly observed. The jet impingement method presents great promises for the field of tissue engineering, as the influence of both the shear stress and the surface characteristics on cell adhesion can be systematically studied.     

A spinning-disk sprayer for applying residual insecticides

The apparatus consists essentially of a spinning disk which throws off liquid, applied to its centre, in the form of small droplets. These are of the same order of size (about 0.1–0.4 mm. diameter) as those produced by knapsack sprayers, but they are more uniform and consistent.
The sprayer can be used to coat various surfaces, up to 1 ft. square, with deposits of insecticides in oil solution or in aqueous suspensions or emulsions. The deposits can be controlled and estimated with a fair degree of precision.
Some rough samples of the spray clouds produced by a knapsack sprayer are recorded.     

Nanocontraction flows of short-chain polyethylene via molecular dynamics simulations

Nanocontraction flows of liquid short-chain polyethylene ([CH₂]₅₀) that were uniformly extruded by a constant-speed piston into a surrounding vacuum from a reservoir through an abrupt contraction nozzle were performed by employing molecular dynamics simulations. The extrudate exhibits a similar die swell phenomenon around the exit of the nozzle. In addition, numerous molecular chains are strongly adsorbed on the external surface of the nozzle. At high extrusion speeds, the velocity and temperature profiles in the nozzle show convex and concave parabolic curves, respectively, whereas the profiles are relatively flat at lower speeds. Near the internal boundary of the nozzle, the wall slip is inspected. Significantly, during the flow, the molecular chains undergo structural deformation, including compressed, stretched and shrunk motions. Comparisons with related experimental observations show that the simulated probability distributions of the bending and dihedral angles, and variations of the squared radius of gyration and orientations, are in reasonable agreement.     

Simple Liquid Scrubber for Large-Volume Air Sampling

A new large-volume air sampler called the "simple liquid scrubber" is described. It can recover a high percentage of microorganisms from large volumes of air, up to 950 liters/min, and concentrate them into a small volume of liquid at a ratio of about 400,000 to 1. The principle of operation of the scrubber is based on the production of a fine mist in a rapidly moving airstream with ultimate collection of the airborne particles by impingement into the film of liquid formed upon impaction of the mist droplets on the scrubber walls. The scrubber compared favorably with the all-glass impinger (AGI-30) and the slit sampler in tests with the normal flora and with experimental aerosols of Bacillus subtilis var. niger spores.     

The penetration of a soft solid by a liquid jet, with application to the administration of a needle-free injection

Liquid jet injections have been performed on human skin in vivo and silicone rubber using Intraject needle-free injectors. The discharge characteristics of the liquid jet were measured using a custom-built test instrument. The experiments reveal that a high-speed liquid jet penetrates a soft solid by the formation and opening of a planar crack. The fluid stagnation pressure required for skin penetration decreases with increasing diameter of the liquid jet. These findings are consistent with the slow-speed penetration of a soft solid by a sharp-tipped punch. It is demonstrated that the Shergold-Fleck sharp-tipped punch penetration model [Shergold, O.A., Fleck, N.A., 2004. Mechanisms of deep penetration of soft solids. Proc. Roy. Soc. Lond. A 460, 3037-3058.] gives adequate predictions for the pressure required to penetrate a soft solid by a high-speed liquid jet.     

Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust aggregates with sizes up to ~10 cm and porosities up to 70% can be collided. One of the drop towers is primarily used for very low impact speeds down to below 0.01 m/sec and makes use of a double release mechanism. Collisions are recorded in stereo-view by two high-speed cameras, which fall along the glass vacuum tube in the center-of-mass frame of the two dust aggregates. The other free-fall tower makes use of an electromagnetic accelerator that is capable of gently accelerating dust aggregates to up to 5 m/sec. In combination with the release of another dust aggregate to free fall, collision speeds up to ~10 m/sec can be achieved. Here, two fixed high-speed cameras record the collision events. In both drop towers, the dust aggregates are in free fall during the collision so that they are weightless and match the conditions in the early Solar System.     

Programmable illumination and high-speed, multi-wavelength, confocal microscopy using a digital micromirror

Confocal microscopy is routinely used for high-resolution fluorescence imaging of biological specimens. Most standard confocal systems scan a laser across a specimen and collect emitted light passing through a single pinhole to produce an optical section of the sample. Sequential scanning on a point-by-point basis limits the speed of image acquisition and even the fastest commercial instruments struggle to resolve the temporal dynamics of rapid cellular events such as calcium signals. Various approaches have been introduced that increase the speed of confocal imaging. Nipkov disk microscopes, for example, use arrays of pinholes or slits on a spinning disk to achieve parallel scanning which significantly increases the speed of acquisition. Here we report the development of a microscope module that utilises a digital micromirror device as a spatial light modulator to provide programmable confocal optical sectioning with a single camera, at high spatial and axial resolution at speeds limited by the frame rate of the camera. The digital micromirror acts as a solid state Nipkov disk but with the added ability to change the pinholes size and separation and to control the light intensity on a mirror-by-mirror basis. The use of an arrangement of concave and convex mirrors in the emission pathway instead of lenses overcomes the astigmatism inherent with DMD devices, increases light collection efficiency and ensures image collection is achromatic so that images are perfectly aligned at different wavelengths. Combined with non-laser light sources, this allows low cost, high-speed, multi-wavelength image acquisition without the need for complex wavelength-dependent image alignment. The micromirror can also be used for programmable illumination allowing spatially defined photoactivation of fluorescent proteins. We demonstrate the use of this system for high-speed calcium imaging using both a single wavelength calcium indicator and a genetically encoded, ratiometric, calcium sensor.     

Adhesion Strength of Settled Spores of the Green Alga Enteromorpha

Strengths of attachment of spores of the green fouling alga Enteromorpha to glass have been measured using a modified water jet apparatus. Surface pressures of ～250 kPa were required to quantitatively remove attached spores after 4 h contact with a surface. The development of adhesive and cohesive strength is highly time-dependent; after 8 h in contact with a surface spores did not detach, even at pressures in excess of 250 kPa. Spores settled in groups are more resistant to detachment than single spores, which suggests that the adaptive value of gregarious settlement behaviour may lie in the greater resistance of groups to detachment forces in a naturally turbulent environment. The interfacial forces exerted as water impinges on the surface and the derivation of adhesion strength values in terms of wall shear stress are discussed and compared with those obtained by other methods. A surface pressure of 250 kPa approximates to 325 Pa wall shear stress. Calculation using the power-law formula predicts that detachment forces of this magnitude are unlikely to be realized at operating speeds for most vessels and that most Enteromorpha spores would not detach from untreated hulls.     

Repetitive torch in a coaxial waveguide: Temperature of the neutral component

The temperature of the neutral component in a repetitive microwave torch excited in an argon jet injected into atmospheric air is measured using different optical methods. The microwave energy is efficiently converted into the thermal energy of the argon jet. The gas temperature is maximum at the nozzle, where it reaches 4.5–5.0 kK, and decreases to 2.5–3.0 kK along the jet. The torch plasma, which is not in thermal equilibrium, drastically influences the working gas and the surrounding air.     

Dynamic ejection behaviour of water molecules passing through a nano-aperture nozzle

This study used molecular dynamics (MD) simulation to investigate the passage of water molecules through a composite graphene/Au nano-nozzle. Our focus was on the degree to which system temperature, extrusion speed, and nozzle diameter affect jet dynamics and the associated transient phenomena. Our findings show that high pressure and spatial confinement cause the nanojet from a small nozzle diameter (1.0?nm) to bend and twist, whereas the jets from a nozzle with a diameter of 1.5?nm present columns of greater stability. At 100?K, the H₂O nanojet froze at the outlet of the nozzle in the form of condensed icicles. At 500?K, the H₂O nanojet formed a loose spray and gaseous clusters. High extrusion speed of 55.824?m/s produced recirculating flow downstream from the nanojet with the appearance of an erupting volcano, which further prompted the jet column to thicken. Lower extrusion speeds produced jets with flow velocity insufficient to overcome the capillary force at the outlet of the nozzle, which subsequently manifests as unstable fluctuations in the flow rate.

• HIGHLIGHTS

• Water molecules through a composite graphene/Au nano-nozzle forming a nanojet is investigated.

• High pressure and spatial confinement cause the nanojet from a small nozzle diameter (≤1.0?nm) to bend and twist.

• High extrusion speed (≧55.824?m/s) produced recirculating flow downstream from the nanojet.

• Figure abstract: Schematic of the H₂O nano-jet through a nano-nozzle of graphene/Au

     

Gaulin homogenization: a mechanistic study

Free radical-based oxidation has been detected in the normal operating regime of the Gaulin homogenizer, demonstrating that cavitation occurs in this important industrial bioprocessing equipment. Free radical generation is suppressed by imposition of back pressure, proving that such cavitation occurs in the impingement section. The calculated value of the cavitation number is consistent with submerged jet cavitation, wherein a high-speed jet exiting from the valve gap accelerates fluid in the impingement region, creating the vacuum conditions for cavitation. Using polysaccharides as a model shear-sensitive compound, their breakage pattern in the homogenizer was characterized by molecular size and polydispersity and compared to those of fluid shear flows in capillary tubes and cavitating flow from a sonic horn. The results indicate that breakage occurs primarily by fluid shear, although a contribution by cavitation is also apparent when back pressure is applied. Because biological molecules can readily react with free radicals and the alterations caused thereby are subtle in nature, a thorough evaluation of the impact of free radicals in upstream homogenization is warranted.     

Investigation on Side-Spray Fluidized Bed Granulation with Swirling Airflow

Top-spray fluidized bed granulation with axial fluidization airflow from the bottom of the granulator is well-established in the pharmaceutical industry. The application of swirling airflow for fluidized bed granulation was more recently introduced. This study examined the effects of various process parameters on the granules produced by side-spray fluidized bed with swirling airflow using the central composite and Box–Behnken design of experiment. Influence of the amount of binder solution, spray rate, and distance between spray nozzle and powder bed were initially studied to establish operationally viable values for these parameters. This was followed by an in-depth investigation on the effects of inlet airflow rate, atomizing air pressure and distance between spray nozzle and powder bed on granule properties. It was found that the amount of binder solution had a positive correlation with granule size and percentage of lumps but a negative correlation with size distribution and Hausner ratio of the granules. Binder solution spray rate was also found to affect the granules size. High drug content uniformity was observed in all the batches of granules produced. Both inlet airflow rate and atomizing air pressure were found to correlate negatively with granule size and percentage of lumps but correlate positively with the size distribution of the granule produced. Percentage of fines was found to be significantly affected by inlet airflow rate. Distance between spray nozzle and powder bed generally affected the percentage of lumps.     

Effect of Design Parameters on Oxygen Mass Transfer Coefficient in a Free Jet Bioreactor

The rate of oxygen delivery is a very important factor in aerobic processes. In many cases, this determines the efficiency of processes such as biological wastewater treatment. The availability of oxygen is essential for sustaining the growth of microorganisms necessary for degrading the organic matter. In this work, a continuous, re‐circulation, constant hold‐up plunging free jet‐loop system was designed to study the effects of design parameters on the oxygen mass transfer. This was investigated using three different nozzle diameters 6, 10 and 14 mm. For a fixed value of diameter, the distance between the nozzle mouth and the free liquid surface was varied to cover the range 14–26 cm. The experimental results showed significant effects of these two parameters. The oxygen mass transfer coefficient was found to increase with either increasing the nozzle position or decreasing its diameter.     

Local overall volumetric gas-liquid mass transfer coefficients in gas-liquid-solid reversed flow jet loop bioreactor with a non-Newtonian fluid

The local overall volumetric gas-liquid mass transfer coefficients at the specified point in a gas-liquid-solid three-phase reversed flow jet loop bioreactor (JLB) with a non-Newtonian fluid was experimentally investigated by a transient gassing-in method. The effects of liquid jet flow rate, gas jet flow rate, particle density, particle diameter, solids loading, nozzle diameter and CMC concentration on the local overall volumetric gas-liquid mass transfer coefficient (K(L)a) profiles were discussed. It was observed that local overall K(L)a profiles in the three-phase reversed flow JLB with non-Newtonian fluid increased with the increase of gas jet flow rate, liquid jet flow rate, particle density and particle diameter, but decreased with the increase of the nozzle diameter and CMC concentration. The presence of solids at a low concentration increased the local overall K(L)a profiles, and the optimum of solids loading for a maximum profile of the local overall K(L)a was found to be 0.18x10(-3)m(3) corresponding to a solids volume fraction, varepsilon(S)=2.8%.     

Spinning-disk confocal microscopy -- a cutting-edge tool for imaging of membrane traffic

Confocal laser scanning microscopy is experiencing a revolution in speed from the world of seconds to that of milliseconds. The spinning Nipkow disk method with microlenses has made this remarkable innovation possible. In combination with the ultrahigh-sensitivity, high-speed and high-resolution camera system based on avalanche multiplication of photoconduction, we are now able to observe the extremely dynamic movement of small vesicles in living cells in real time.     

Solving the aerodynamics of fungal flight: how air viscosity slows spore motion

Viscous drag causes the rapid deceleration of fungal spores after high-speed launches and limits discharge distance. Stokes' law posits a linear relationship between drag force and velocity. It provides an excellent fit to experimental measurements of the terminal velocity of free-falling spores and other instances of low Reynolds number motion (Re<1). More complex, non-linear drag models have been devised for movements characterized by higher Re, but their effectiveness for modeling the launch of fast-moving fungal spores has not been tested. In this paper, we use data on spore discharge processes obtained from ultra-high-speed video recordings to evaluate the effects of air viscosity predicted by Stokes' law and a commonly used non-linear drag model. We find that discharge distances predicted from launch speeds by Stokes' model provide a much better match to measured distances than estimates from the more complex drag model. Stokes' model works better over a wide range projectile sizes, launch speeds, and discharge distances, from microscopic mushroom ballistospores discharged at <1 m s(-1) over a distance of <0.1mm (Re<1.0), to macroscopic sporangia of Pilobolus that are launched at >10 m s(-1) and travel as far as 2.5m (Re>100).