Clustering in expanding nozzle flows

The paper describes the results obtained by an approach to simulating the time evolution of cluster fusion. Further calculations and measurements suggested by these results are also discussed.     

Silver clusters from nozzle expansions

This note reports on the first successfull experiments to generate silver clusters (N≦100) in supersonic nozzle flows. A mixture of argon/silver-vapor was used expanding from a conical nozzle (0.35 mm, 10° full cone angle, 17 mm long conical section). Source temperature and total pressure ranged up to 2200 K/300 kPa, and silver partial pressure up to 25 kPa. The data confirm the scaling laws developed to compare clustering of metals with that of rare gases.     

Methanol nucleation in a supersonic nozzle

We determined the partial pressures p(Jmax), temperatures T(Jmax), monomer supersaturations S(Jmax), and characteristic times Δt(Jmax?) corresponding to the maximum nucleation rates of methanol in a supersonic nozzle. We found that T(Jmax) increased from 202.2 K to 223.7 K as p(Jmax) increased from 67.1 to 413.2 Pa, while the maximum nucleation rate J(max) changed by less than a factor of 4 over the measurement range. Our nucleation rates appear reasonably consistent with measurements in other devices and are within one order of magnitude of the nucleation rates predicted by classical nucleation theory.     

Formation of silver clusters in nozzle expansions

The first successful experiments to generate continuum silver cluster beams from nozzle expansions are described. A mixture Ar/Ag expands out of a conical nozzle (0.35 mm dia., 10° cone angle, length 17 mm). At 2150 K, total pressure 300 kPa, silver partial pressure 8 kPa the silver intensity measured with a rate meter 479mm away from the source is 1.8 nm/s, or 0.02 g m^?2s^?1. The data for the onset of clustering confirm the predictions of the scaling laws developed to compare condensation in nozzle expansions of metal vapors with that of rare gases.     

Nitrogen nucleation in a cryogenic supersonic nozzle

We follow the vapor-liquid phase transition of N(2) in a cryogenic supersonic nozzle apparatus using static pressure measurements. Under our operating conditions, condensation always occurs well below the triple point. Mean field kinetic nucleation theory (MKNT) does a better job of predicting the conditions corresponding to the estimated maximum nucleation rates, J(max) = 10(17±1) cm(-3) s(-1), than two variants of classical nucleation theory. Combining the current results with the nucleation pulse chamber measurements of Iland et al. [J. Chem. Phys. 130, 114508-1 (2009)], we use nucleation theorems to estimate the critical cluster properties. Both the theories overestimate the size of the critical cluster, but MKNT does a good job of estimating the excess internal energy of the clusters.     

Non-activated metal cluster growth during nozzle jet expansion

Based on the classical liquid-drop nucleation theory for small clusters, we show quantitatively the existence of a boundary which separates the nucleation and growth and non-activated (physical spinodal) cluster growth regions for supersaturated vapors. We found that for the expansion geometry such as the one used by Yamada and Takagi in their nozzle jet experiments for producing metal clusters, the non-activated growth process may play an important, if not predominant, role in the growth of clusters.     

Gas distribution in the layer of irregular ring nozzle

Results of experiments on evaluation of velocity fields in the apparatus of diameter 98 mm loaded with irregular ring nozzle of different type so that the ratio of the diameter of the apparatus to the diameter of the packing D/d = 10 are analyzed in the article. The significant influence of the walls limiting the layer of packing on the uniformity of distribution of the velocity field in the cross-section of the apparatus with packing is shown. Raschig rings, rings of MS type and rings of N1 type of dimensions 10 × 10 × 0.9 mm made of metal were used as packing. The data obtained on Raschig rings were compared with published data.     

Breakup of double emulsion droplets in a tapered nozzle

When double emulsion droplets flow through a tapered nozzle, the droplets may break up and cause the core to be released. We model the system on the basis of the capillary instability and show that a droplet will not break up when the tilt angle of the nozzle is larger than 9°. For smaller tilt angles, whether the droplet breaks up also depends on the diameter ratio of the core of the droplet to the orifice of the nozzle. We verified this mechanism by experiments. The ideas are useful for the design of nozzles not only to break droplets for controlled release but also to prevent the droplet from rupturing in applications requiring the reinjection of an emulsion.     

Optimizing nozzle convergent angle using central composite design on the particle velocity and acoustic power level for single-hose dry ice blasting nozzle

Journal of Thermal Analysis and Calorimetry - One of the important parameters in developing dry ice blasting nozzle is the high-speed dry ice pellets. However, many studies focus primarily only on...     

A new nozzle design for dc plasma spray guns

A new design is proposed for dc plasma spray gas shroud attachments. It has been found experimentally that the performance of a conventional conical gas shroud is not satisfactory due to the entrainment of the cold air inside the gas shroud. Numerical simulations confirmed this finding. Parameters such as the cone angle and the main gas flow rate can significantly influence the flow pattern inside the nozzle, resulting in air entrainnient and formation of a circulation zone at the exit region. A new design is proposed which can considerably improve the performance of shrouded nozzles. The superior performance of the proposed design has been demonstrated by numerical simulation. The new design is based on a modification of the conical shape by optimizing the profile of the nozzle from a conical shape with a constant angle to a streamlined configuration. The optimized shape was obtained from an analysis of the streamlines of a fixed angle nozzle.     

Analytical investigation of simultaneous effects of convergent section heating of Laval nozzle,steam inlet condition,and nozzle geometry on condensation shock

Rapid expansion and supercooling of dry vapor in low-pressure steam turbines trigger nucleation phenomenon. Subsequently, following the occurrence of vapor condensation, a vapor–liquid two-phase flow is established. Entropy generation mainly by condensation shock, blade erosion, and ultimately, destruction of equipment and efficiency reduction are among adverse effects of vapor condensation, which should be either attenuated or controlled. In the present research, which is a continuation to the research performed by original authors, a one-dimensional analytical Eulerian–Lagrangian model is used to apply convergent section heating to different supersonic nozzles under various inlet conditions. The results indicate that the flow response to the heating is well dependent on the intensity of condensation shock or inlet conditions. In order to compensate for the mass flow rate resulted from the convergent section heating, effects of simultaneous reduction of inlet stagnation temperature and convergent section heating were investigated. Finally, it was found that, maintaining constant mass flow rate, simultaneous reduction of inlet stagnation temperature and convergent section heating cannot attenuate the condensation shock significantly. Therefore, the best approach to compensate for the reduction in the mass flow rate due to convergent section heating is to simultaneously increase inlet stagnation pressure.     

Influence of nozzle geometry on polystyrene degradation in convergent flow

Polymer degradation is readily observed in flows where the extensional component surpasses the rotational component of the velocity gradient. This type of flow is conveniently obtained by pushing a liquid into a convergent channel across an orifice. Kinetics of chain scission is sensitive to subtle modification of the coil conformation, which in turn depends on the details of the pervading flow field. By changing the orifice diameter and the conical angle of the inlet, it is possible to modify the spatial distribution of the velocity gradient, and hence, the residence time of a fluid element in the high strain-rate region. Degradation yields, measured under -conditions in decalin by Gel Permeation Chromatography, showed a strong dependence on the fluid velocity at the orifice, but not on the magnitude of the strain-rate. This result is contrary to the common belief that assumes viscous friction, proportional to the strain-rate, is the determining factor for the scission rate of a bond under stress. Rather, experimental findings tend to indicate that the driving force for chain scission was provided by the energy accumulated in the coil during the flow-induced deformation process. The sharp propensity for mid-chain scission was maintained regardless of the nozzle geometry.Dedicated to Prof. W. R. Pechhold on the occasion of his 60th birthday     

Spin-orbit cooling and population inversion in nozzle expansions of NH

Cooling of molecular spin-orbit fine structure in a nozzle expansion is demonstrated with a non-case (a) diatomic molecule, the A ³Π, state of NH. Not only is cooling rapid, comparable to the rate of rotational cooling, but several population inversions are observed.     

Micro-fabricated metal nozzle plates used for water-in-oil and oil-in-water emulsification

In this paper the fabrication and use of micro-structured metal nozzle plates as emulsification devices is investigated and discussed. These structured metal nozzle plates were fabricated via two distinct routes. Laser ablation, performed with a femtosecond laser, was used to drill micrometer-sized holes into stainless steel and aluminum foils. Also a conventional steel mesh with an average pore size of 2.4 μm fabricated by weaving and roll compaction of micrometer-sized steel wires was investigated. The perforated metal nozzle plates were used for oil-in-water and after hydrophobization with alkylchlorosilanes for water-in-oil emulsification as well. In both cases, two types of drop formation processes were observed. The first one is the shear-induced drop formation well known for cross-flow membrane emulsification. The second is the spontaneous drop formation known from microchannel emulsification.     

A comparative study of nozzle/diffuser micropumps with novel valves

This study conducts an experimental study concerning the improvement of nozzle/diffuser micropump design using some novel no-moving-part valves. A total of three micropumps, including two enhancement structures having two-fin or obstacle structure and one conventional micro nozzle/diffuser design, are made and tested in this study. It is found that dramatic increase of the pressure drops across the designed micro nozzles/diffusers are seen when the obstacle or fin structure is added. The resultant maximum flow rates are 47.07 mm3/s and 53.39 mm3/s, respectively, for the conventional micro nozzle/diffuser and the added two-fin structure in micro nozzle/diffuser operated at a frequency of 400 Hz. Yet the mass flow rate for two-fin design surpasses that of conventional one when the frequency is below 425 Hz but the trend is reversed with a further increase of frequency. This is because the maximum efficiency ratio improvement for added two-fin is appreciably higher than the other design at a lower operating frequency. In the meantime, despite the efficiency ratio of the obstacle structure also reveals a similar trend as that of two-fin design, its significant pressure drop (flow resistance) had offset its superiority at low operating frequency, thereby leading to a lesser flow rate throughout the test range.     

Non-maxwellian velocity distributions and molecular beam intensities in sonic nozzle expansions

The thermal conduction model is used to calculate the second moment of the kinetic energy distributions in both the parallel and perpendicular degrees of freedom of sonic nozzle expansions. Comparisons with the first moment affords a measure of the departure from maxwellian distributions in these coordinates. Agreement between the computed parallel velocity distribution and measurements described in the literature is good. A Monte Carlo simulation is then used to get further information on the perpendicular velocity distribution at large distances and, in particular, on the intensity of molecular beams which can be skimmed from these expansions.The sonic nozzle expansion constitutes a potentially useful medium for the study of molecular relaxation phenomena. Our understanding of the evolution of the parallel temperature is now virtually complete. The present study has also shown how Monte Carlo calculations can supplement the thermal conduction model to get information on the less tractable problem of the perpendicular velocity distribution. The methodology can be readily extended to polyatomic media [5].We have focused on the central portion of the perpendicular velocity distribution, as this is the regime of greatest interest. It is disappointing to f     

Inlet section of hydrodynamic stabilization of flow in a regular nozzle

Russian Journal of Applied Chemistry -     

A new on-chip ESI nozzle for coupling of MS with microfluidic devices

This paper presents a new on-chip electrospray ionisation (ESI) nozzle, which can be used as an interface for coupling microfluidic devices with mass spectrometric (MS) detection. The nozzle was micromilled in a polymer foil (polymethylmethacrylate (PMMA) 750 microm thick), normally used as a cover for microfluidic chips. The performance of this device was examined in the ESI-MS analysis of the tetrapeptide MRFA (methionine-argenine-phenylalanine-alanine). The spray quality is basically dependent on the inner diameter of the nozzle, beside the part of the organic modifier in the solution to be sprayed. Three different inner nozzle diameters (30, 50, 100 microm) and two different apex angles were investigated. Stable electrospray conditions can be generated with a relative standard deviation less than 10% of the total ion current, and down to a concentration of 0.01 micromol L(-1). The production of this ESI interface is relatively simple for the purpose of a low-cost batch fabrication of miniaturized analytical instruments.     

Relaxation in a Na/Na2 nozzle expansion

Atom—molecule collisions in a Na/Na₂ nozzle expansion are investigated. The atoms are marked near the nozzle exit by preparing them alternatively into the 3²S and 3²P state. The effect of collisions between these atoms and the molecules is studied far downstream the beam. We find that the internal energy distribution of the molecules depends on the internal energy of the atoms. The specific change of the internal energy distribution gives information on the energy relaxation in the nozzle expansion.