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51.
In the present study, gas jet emerging from an annular nozzle and impinging onto a cylindrical cavity is considered. The geometric configuration of the nozzle is varied in the simulations. Air is used as impinging gas while stainless steel is considered as workpiece material. Reynolds turbulence model is accommodated to account for the turbulence. A numerical scheme employing a control volume approach is used to simulate the flow field. Heat transfer characteristic and shear stress distribution around the cavity are computed. It is found that outer cone angle of the annular nozzle influences the heat transfer rates from the cavity wall. The flow structure around the cavity changes significantly with increasing cavity diameter. Moreover, increasing cavity depth results in stagnation zone moving into the cavity. 相似文献
52.
Turbulent free jets issuing from five different nozzle geometries; smooth pipe, contracted circular, rectangular, triangular,
and square, are experimentally investigated by using TSI 2-D laser Doppler velocimetry (LDV) to assess the effect of nozzle
geometry and quarl (i.e. a cylindrical sudden expansion) on jet entrainment and spreading. The centerline mean velocity decay
and the jet half-velocity width, which are indicators of jet entrainment and spreading rates, are determined for each nozzle’s
flow configuration, i.e. with and without sudden expansion. Furthermore, turbulence quantities, such as the flow mean velocities
and their mean fluctuating components, as well as Reynolds shear stresses, are all measured along the centerline plane of
the jet to facilitate understanding the extent of the effect of nozzle’s geometry (i.e. nozzle’s orifice shape and sudden
expansion) on jet’s entrainment and spreading. The main results show that the jet flow with the presence of sudden expansion
exhibits higher rates of entrainment and spreading than without. In addition, these results reveal that sudden expansion exercises
a greater effect on the asymmetric jet characteristics, especially for the triangular and rectangular nozzles compared to
their axisymmetric counterparts (i.e. circular contracted nozzle). 相似文献
53.
Yu Lin Song Chih Hsiao Cheng Luh-Maan Chang Chia-Fone Lee Yuan Fang Chou 《Applied Acoustics》2011,(12):949-952
Mono-disperse polycarbonate (PC) nanoparticles 20 nm in diameter was spray coated on silicon substrate using a novel high-frequency ultrasonic nozzle. Specifically, Bisphenol-A polycarbonate with a molecular weight (Mw) of approximately 6.4 × 104 g/mol was first dissolved in pyridine. The resulting solution was sprayed into surfactant-containing de-ionized (DI) water using a 300 kHz silicon-based multiple-Fourier horn nozzle (MFHN). As pyridine was extracted into the water, PC nanoparticles formed but remained dispersed. This suspension of PC nanoparticles was then sprayed onto a silicon substrate using a 500 kHz 3-Fourier horn nozzle. Scanning electron microscopy (SEM) of the dried substrate revealed that PC nanoparticles were spread uniformly with no aggregation. 相似文献
54.
The problem of determining the optimal contour of a two-dimensional jet engine outlet system was solved in [1] using the direct method of the calculus of variations. In this study the method is developed for designing the optimal contour of a three-dimensional outlet system providing maximum thrust in a given direction. 相似文献
55.
Properties and applications of cold supersonic gas jet 总被引:1,自引:1,他引:0
By analyzing the formation mechanism of a supersonic gas jet, a set of equations which describe the atomic beam properties
were established. The influence of initial temperature, initial pressure, background gas pressure and pumping speed was discussed
in detail. A simulation program was developed based on the equations, and the results under different initial conditions were
obtained. The results are in good agreement with the experimental data, and suggest that, in order to get much smaller transverse
momentum in collision experiments, it is necessary to lower the initial temperature and the initial pressure of the supersonic
gas jet, together with increasing the pumping speed. These results are very instructive for construction of a new generation
of cold supersonic gas jets. 相似文献
56.
A new design for a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization has been developed: There were two requirements: supersonic free jet nozzle and the high work function surface of Re-oxide. This detector, which is highly sensitive in response to all organic compounds, can be operated as an universal detector with an additional selectivity towards some species that have low ionization energy, but with selectivity to a much lesser degree than a conventional surface ionization detector. The minimum detectable amount of toluene is ca. 10−12 g/s with a linearity greater than 104. Some applications are demonstrated using three examples for the analysis of different formulations: (1), terpene mixture, (2), polycyclic aromatic hydrocarbon mixture and (3), alkyl alcohol mixture. 相似文献
57.
Investigations of gas and particle dynamics in first generation needle-free drug delivery devices 总被引:1,自引:0,他引:1
Abstract. Transdermal powdered drug delivery involves the propulsion of solid drug particles into the skin by means of high-speed gas-particle
flow. The fluid dynamics of this technology have been investigated in devices consisting of a convergent-divergent nozzle
located downstream of a bursting membrane, which serves both to initiate gas flow (functioning as the diaphragm of a shock
tube) and to retain the drug particles before actuation. Pressure surveys of flow in devices with contoured nozzles of relatively
low exit-to-throat area ratio and a conical nozzle of higher area ratio have indicated a starting process of approximately
200 s typical duration, followed by a quasi-steady supersonic flow. The velocity of drug particles exiting the contoured nozzles
was measured at up to 1050 m/s, indicating that particle acceleration took place primarily in the quasi-steady flow. In the
conical nozzle, which had larger exit area ratio, the quasi-steady nozzle flow was found to be overexpanded, resulting in
a shock system within the nozzle. Particles were typically delivered by these nozzles at 400 m/s, suggesting that the starting
process and the quasi-steady shock processed flow are both responsible for acceleration of the particle payload. The larger
exit area of the conical nozzle tested enables drug delivery over a larger target disc, which may be advantageous.
Received 12 March 2000 / Accepted 8 June 2000 相似文献
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