Function Of Jet Velocity Research Articles

Optimization of Portable Electronically Controlled Needle-Free Jet Injection Systems

Jet injection is a process by which a fluid drug is delivered through the skin in the form of a high-velocity jet. Powering jet injection using a controllable actuator, such as a moving-coil permanent magnet motor, offers many advantages, but to date has required large and heavy injection systems to provide the required power and control bandwidth. In order to minimize the size of the injection system, we developed a scaling model for jet injection systems powered by permanent magnet motors, giving the optimal actuator mass as a function of jet velocity, injection volume, motor efficiency, and energy storage density. We combined this model with an existing electromagnetic model to confirm the predicted scaling relationships and find optimal actuator designs. On this basis, we designed an injection system for 50 $\mathrm{\mu {}L}$ volumes, including a compact power amplifier and control system, and verified its performance by performing injections into pig skin. The total mass of the injector system was 578 g, with a 178 g handpiece. This model illustrates fundamental relationships that govern the design of any jet-production device powered by linear electric motors for jet injection or other applications.

Modelling of turbulent lifted jet flames using flamelets: a priori assessment and a posteriori validation

This study focuses on the modelling of turbulent lifted jet flames using flamelets and a presumed Probability Density Function (PDF) approach with interest in both flame lift-off height and flame brush structure. First, flamelet models used to capture contributions from premixed and non-premixed modes of the partially premixed combustion in the lifted jet flame are assessed using a Direct Numerical Simulation (DNS) data for a turbulent lifted hydrogen jet flame. The joint PDFs of mixture fraction Z and progress variable c, including their statistical correlation, are obtained using a copula method, which is also validated using the DNS data. The statistically independent PDFs are found to be generally inadequate to represent the joint PDFs from the DNS data. The effects of Z–c correlation and the contribution from the non-premixed combustion mode on the flame lift-off height are studied systematically by including one effect at a time in the simulations used for a posteriori validation. A simple model including the effects of chemical kinetics and scalar dissipation rate is suggested and used for non-premixed combustion contributions. The results clearly show that both Z–c correlation and non-premixed combustion effects are required in the premixed flamelets approach to get good agreement with the measured flame lift-off heights as a function of jet velocity. The flame brush structure reported in earlier experimental studies is also captured reasonably well for various axial positions. It seems that flame stabilisation is influenced by both premixed and non-premixed combustion modes, and their mutual influences.

A Weak-Scattering Model for Turbine-Tone Haystacking outside the Cone of Silence

We consider the scattering of sound by turbulence in a jet shear layer. The turbulent, time-varying inhomogeneities in the flow scatter tonal sound fields in such a way as to give spectral broadening, which decreases the level of the incident tone, but increases the broadband level around the frequency of the tone. The scattering process is modelled for observers outside the cone of silence of the jet, using high-frequency asymptotic methods and a weak-scattering assumption. An analytical model for the far-field power spectral density of the scattered field is derived, and the result is compared to experimental data. The model correctly predicts the behaviour of the scattered field as a function of jet velocity and tone frequency.

Rebounding of a shaped-charge jet

The phenomenon of rebounding of a shaped-charge jet from the armour surface with small angles between the jet axis and the target surface is considered. Rebounding angles as a function of jet velocity are obtained in experiments for a copper shaped-charge jet. An engineering calculation technique is developed. The results calculated with the use of this technique are in reasonable agreement with experimental data.

산소부화공기가 동축 비예혼합 제트의 연소특성에 미치는 영향 (I) - 화염의 부상과 안정성

Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improving the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with increase of coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. In particular, lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Great flame stability was obtained since lift-off and blowout limit significantly increased with increase of OEC.

A MODELLING OF THE NOISE FROM SIMPLE COAXIAL JETS, PART II: WITH HEATED PRIMARY FLOW

This paper reports the second part of a continuing study of the noise of coaxial jets, and describes modifications to the model developed previously to allow for the effects of a heated flow from the primary nozzle. The essential feature of the model described previously for the prediction of the noise from isothermal coaxial jets was the identification of three flow regions, within the coaxial jet flow, the noise production of which could be estimated from single-jet prediction methods. In particular, it was shown that noise from the principal interaction zone could be calculated by using single-jet prediction methods as long as account was taken of the fact that measured turbulence levels in this region were lower than those observed in a single isolated jet at the same centerline velocity. For isothermal flows, for which only quadrupole sources exist, allowance for this reduced turbulence level was entirely straightforward. However, for heated flow both dipole and quadrupole sources exist, and these have different dependencies on the turbulence level. Hence to predict the noise one needs to know the relative contributions of the dipole and quadrupole sources. In the present work, use has been made of previously published results for these relative contributions, as a function of jet velocity and temperature, for single jets. This then permits prediction of the noise from the interaction zone, which is subsequently combined with that from the secondary jet shear layer and fully mixed flow region, as before. Comparison between data and prediction over a range of jet velocity, temperature and angle of observation again show very acceptable agreement.

IMAGING OF IMPINGING JET BREAKUP AND ATOMIZATION PROCESSES USING COPPER-VAPOR-LASER-SHEET-ILLUMINATED PHOTOGRAPHY

Observation of a like-on-like injector element in the near-injector region has been accomplished with laser-sheet- illuminated photography to investigate spray characteristics as a function of jet velocity and injector geometry. Short duration exposures from single laser pulses produced instantaneous pictures of the injection and subsequent breakup processes, while multiple-exposure photographs revealed a time-averaged representation of the spray. In addition to the four previously documented spray regimes, the data suggested inclusion of a higher Reynolds number regime in which the pre-impingement jets are fully turbulent and undergoing surface breakup. The equation of a conic section was used to map multiple-exposure photographs revealing the overall spray shape. Further examination of the higher Reynolds number regime using transparent injector pieces revealed the presence of a cavitating region within the orifice. Discharge coefficients were calculated and found to be relatively constant for each injector tested, regardless of the presence of cavitation. The orientation of the injector orifice created a stable cavitating region in which the phenomenon of hydraulic flip was not observed, but the enhanced turbulence level led to an onset of jet atomization prior to impingement.

IMAGING OF IMPINGING JET BREAKUP AND ATOMIZATION PROCESSES USING COPPER-VAPOR-LASER-SHEET-ILLUMINATED PHOTOGRAPHY

Observation of a like-on-like injector element in the near-injector region has been accomplished with laser-sheet- illuminated photography to investigate spray characteristics as a function of jet velocity and injector geometry. Short duration exposures from single laser pulses produced instantaneous pictures of the injection and subsequent breakup processes, while multiple-exposure photographs revealed a time-averaged representation of the spray. In addition to the four previously documented spray regimes, the data suggested inclusion of a higher Reynolds number regime in which the pre-impingement jets are fully turbulent and undergoing surface breakup. The equation of a conic section was used to map multiple-exposure photographs revealing the overall spray shape. Further examination of the higher Reynolds number regime using transparent injector pieces revealed the presence of a cavitating region within the orifice. Discharge coefficients were calculated and found to be relatively constant for each injector tested, regardless of the presence of cavitation. The orientation of the injector orifice created a stable cavitating region in which the phenomenon of hydraulic flip was not observed, but the enhanced turbulence level led to an onset of jet atomization prior to impingement.

An x-ray-.gamma.-ray method of measurement of binary solids concentrations and voids in fluidized beds

A new experimental technique has been developed to measure time-averaged volume fractions of particles and of the gas in fluidized beds involving particles of two sizes, such as glass beads and leaded glass beads, using two radiation densitometers. In such fluidized beds, the coarse and the fine particles segregate. The boundary line of segregation was found as a function of jet velocity and grid flow rate. This experimental technique was then applied to the removal of pyrites from a coal-pyrite mixture in a fluidized bed with a jet.

Fluid mechanics of the edgetone

A model is proposed to explain the means by which an edgetone transforms the energy of a fully developed plane jet into energy which is radiated as sound. The edgetone configuration considered consists of a flat plate located in the medial plane of a fully developed two-dimensional jet. The flow is modeled as follows. A periodic disturbance at the jet origin leads to the formation of an asymmetric vortex street which propagates downstream with a fixed convection velocity and wavelength. The vortex strength, convection velocity, and wavelength are determined as functions of the Strouhal number by applying conservation laws and kinematic relationships. A potential flow analysis of the interaction of the vortices with the edge is used to estimate the nearfield oscillating flow at the jet exit which, in turn, is used to calculate the phase of the feedback mechanism. The phase then determines the operating frequency as a function of jet velocity and edge stand-off distance. It is shown that the proposed model is capable of predicting the major observed features of edgetone operation. The frequency predictions of the theory are compared with experiments for a wide range of jet parameters in both air and water. The comparison indicates that the frequency predictions are as good or better than previous empirical or semiempirical formulas.