67,595 research outputs found
Concentration-adjustable micromixer using droplet injection into a microchannel
A novel micromixing technique that exploit a thrust of droplets into the
mixing interface is developed. The technique enhances the mixing by injecting
immiscible droplets in a mixing channel and the methodology enables a control
of the mixing level simply by changing the droplet injection frequency. We
experimentally characterize the mixing performance with various droplet
injection frequencies, channel geometries, and diffusion coefficients.
Consequently, it is revealed that the mixing level increases with the injection
frequency, the droplet-diameter-to-channel-width ratio, and the diffusion
coefficient. Moreover, the mixing level is found to be a linear function of the
droplet volume fraction in the mixing section. The results suggest that the
developed technique can produce a large amount of sample solution whose
concentration is arbitrary and precisely controllable with a simple and stable
operation.Comment: 12 + 3 pages, 6 + 4 figure
Full-coverage film cooling on flat, isothermal surfaces: Data and predictions
The heat transfer and fluid mechanics characteristics of full-coverage film cooling were investigated. The results for flat, isothermal plates for three injection geometries (normal, slant, and compound angle) are summarized and data concerning the spanwise distribution of the heat transfer coefficient within the blowing region are presented. Data are also presented for two different numbers of rows of holes (6 and 11). The experimental results summarized can be predicted with a two dimensional boundary layer code, STANCOOL, by providing descriptors of the injection parameters as inputs
Time-resolved fuel injector flow characterisation based on 3D laser Doppler vibrometry
In order to enable investigations of the fuel flow inside unmodified
injectors, we have developed a new experimental approach to measure
time-resolved vibration spectra of diesel nozzles using a three dimensional
laser vibrometer. The technique we propose is based on the triangulation of the
vibrometer and fuel pressure transducer signals, and enables the quantitative
characterisation of quasi-cyclic internal flows without requiring modifications
to the injector, the working fluid, or limiting the fuel injection pressure.
The vibrometer, which uses the Doppler effect to measure the velocity of a
vibrating object, was used to scan injector nozzle tips during the injection
event. The data were processed using a discrete Fourier transform to provide
time-resolved spectra for valve-closed-orifice, minisac and microsac nozzle
geometries, and injection pressures ranging from 60 to 160MPa, hence offering
unprecedented insight into cyclic cavitation and internal mechanical dynamic
processes. A peak was consistently found in the spectrograms between 6 and
7.5kHz for all nozzles and injection pressures. Further evidence of a similar
spectral peak was obtained from the fuel pressure transducer and a needle lift
sensor mounted into the injector body. Evidence of propagation of the nozzle
oscillations to the liquid sprays was obtained by recording high-speed videos
of the near-nozzle diesel jet, and computing the fast Fourier transform for a
number of pixel locations at the interface of the jets. This 6-7.5kHz frequency
peak is proposed to be the natural frequency for the injector's main internal
fuel line. Other spectral peaks were found between 35 and 45kHz for certain
nozzle geometries, suggesting that these particular frequencies may be linked
to nozzle dependent cavitation phenomena.Comment: 12 pages, 10 figure
Charge injection instability in perfect insulators
We show that in a macroscopic perfect insulator, charge injection at a
field-enhancing defect is associated with an instability of the insulating
state or with bistability of the insulating and the charged state. The effect
of a nonlinear carrier mobility is emphasized. The formation of the charged
state is governed by two different processes with clearly separated time
scales. First, due to a fast growth of a charge-injection mode, a localized
charge cloud forms near the injecting defect (or contact). Charge injection
stops when the field enhancement is screened below criticality. Secondly, the
charge slowly redistributes in the bulk. The linear instability mechanism and
the final charged steady state are discussed for a simple model and for
cylindrical and spherical geometries. The theory explains an experimentally
observed increase of the critical electric field with decreasing size of the
injecting contact. Numerical results are presented for dc and ac biased
insulators.Comment: Revtex, 7pages, 4 ps figure
2D Rutherford-Like Scattering in Ballistic Nanodevices
Ballistic injection in a nanodevice is a complex process where electrons can
either be transmitted or reflected, thereby introducing deviations from the
otherwise quantized conductance. In this context, quantum rings (QRs) appear as
model geometries: in a semiclassical view, most electrons bounce against the
central QR antidot, which strongly reduces injection efficiency. Thanks to an
analogy with Rutherford scattering, we show that a local partial depletion of
the QR close to the edge of the antidot can counter-intuitively ease ballistic
electron injection. On the contrary, local charge accumulation can focus the
semi-classical trajectories on the hard-wall potential and strongly enhance
reflection back to the lead. Scanning gate experiments on a ballistic QR, and
simulations of the conductance of the same device are consistent, and agree to
show that the effect is directly proportional to the ratio between the strength
of the perturbation and the Fermi energy. Our observation surprisingly fits the
simple Rutherford formalism in two-dimensions in the classical limit
Comptonization signatures in the rapid aperiodic variability of Galactic black-hole candidates
We investigate the effect of inverse-Compton scattering of flares of soft
radiation in different geometries of a hot, Comptonizing region and a colder
accretion disk around a solar-mass black hole. The photon-energy dependent
light curves, their Fourier transforms, power spectra and Fourier-period
dependent time lags of hard photons with respect to softer photons are
discussed. On the basis of a comparison with existing data we find arguments
against Comptonization of external soft radiation as well as Comptonization in
a homogeneous medium as dominant mechanisms for the rapid aperiodic variability
in Galactic black-hole candidates. Possible further observational tests for the
influence of Comptonization on the rapid aperiodic variability of Galactic
black-hole candidates are suggested.Comment: 32 pages, including 10 figures and 2 tables; uses epsf.sty,
rotate.sty; submitted to Ap
Creating movable interfaces by micro-powder injection moulding
This paper presents a novel in situ technique to produce articulated components with high-precision, micro-scale movable interfaces by micro-powder injection moulding (μPIM). The presented process route is based on the use of micro-scale sacrificial layer between the movable subcomponents which is eliminated during the debinding step, creating a dimensionally-controlled, micro-scale mobile interface. The fabrication technique combines the advantages of micro-powder overmoulding, catalytic debinding and sintering. The demonstrated example was a finger bone prosthesis joint consisting of two sub-components with an interface between components of 200 μm in size. The geometries of the sub-components were designed such that they are inseparable throughout the process whilst allowing them to move relative to each other after the debinding stage. The components produced showed the feasibility of the process route to produce readily-assembled meso-, and potentially micro-, scale articulated system
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