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In this paper, a substream coaxial powder feeding nozzle was investigated for use in cold spraying. The relationship between nozzle structure and gas flow, the acceleration behavior of copper particles were examined by computational simulation method. Also, one of the nozzle was used to spray copper coating on steel substrate. The simulation results indicate that: the velocity of gas at the center of the nozzle is lower than that of the conventional nozzle. Powders are well restrained near the central line of the nozzle, no collision occurred between the nozzle wall and the powders. This type of nozzle with expansion 3.25 can successfully deposit copper coating on steel substrate, the copper coating has low porosity about 3.1 % – 3.8 % and high bonding strength about 23.5 MPa – 26.8 MPa. DOI: http://dx.doi.org/10.5755/j01.ms.20.3.4244

Proper estimation of droplet growth rate plays a crucial role on appropriate prediction of supersonic separators performance for separation of fine droplets from a gas stream. Up to now, all available researches employ empirical or semi-empirical correlations to define the relationship between droplet growth rate (dr/dt) and other operating variables such as temperatures (T and TL), Pressure (P) and condensation rate (mL). These empirical or semi-empirical equations are developed for pure component systems and should not be extended to binary or multi-components systems. A novel theoretical approach is presented in this article which provides a fundamental equation to find the droplet growth rate by resorting to mass transfer equations. The new model uses a combination of mass transfer equations and mass and energy balances to estimate the droplet growth rate, droplet temperature and condensation rate simultaneously. Although the simulation results indicate that the proposed method provides impressive results when validated with several real experimental data, however, the main advantage of the present approach is that it can be easily extended to binary or multi-components systems. To the best of our knowledge, the proposed approach has not been addressed previously.

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The aim of the present paper is to investigate the propulsive performance of the hollow rotating detonation engine (RDE) with a Laval nozzle. Three-dimensional simulations are carried out with a one-step Arrhenius chemistry model. The Laval nozzle is found to improve the propulsive performance of hollow RDE in all respects. The thrust and fuel-based specific impulse are increased up to 12.60 kN and 7484.40 s, respectively, from 6.46 kN and 6720.48 s. Meanwhile, the total mass flow rate increases from 3.63 kg/s to 6.68 kg/s. Overall, the Laval nozzle significantly improves the propulsive performance of the hollow RDE and makes it a promising model among detonation engines. [ABSTRACT FROM AUTHOR]

We propose an approach for the design of the subsonic part of plane and axisymmetric Laval nozzles for real gases. The proposed approach is based on the hodograph method and allows one to solve the inverse design problem directly. Real gas effects are taken into consideration using the chemical equilibrium model. We present nozzle contours computed with the proposed method for a stoichiometric methane-air mixture. Results confirm that real gas effects have a strong influence on the nozzle shape. The described method can be used in the design of nozzles for rocket engines and for high-enthalpy wind tunnels.

Aiming at the load surface location problem of the nozzle which was in the satellite attitude adjustment capsule, the fluid calculation software Fluent was used to simulate the Laval nozzle and its extensional flow field by adopting finite volume method, according to the baffle position and inlet total pressure. Furthermore, the effect of the baffle on the nozzle and its extensional flow field were analyzed. Three kinds of Laval nozzles of which outlet diameters were respectively 5. 1, 3. 6 and 2. 3 were employed to make numerical calculation, and the size of their thrust were all within 10 N. The results indicate when the baffle is fixed, the baffle makes an influence on the outlet pressure of nozzles if nozzle Ⅰ, Ⅱ, Ⅲ of inlet and outlet pressure ratios respectively exceed 10, 12 and 15. When the inlet total pressure is constant, each type of nozzle has its corresponding location area of suitable placing the baffle, which is not the same with each other. [ABSTRACT FROM AUTHOR]

Injector-type sandblasters are commonly sold with cylindrical of convergent-divergent Laval nozzles. While Laval nozzles are advertised to be more efficient, very little research on this topic has been published yet. Therefore, the advantages of Laval blasting nozzles in combination with injector-type abrasive blasting units were evaluated within this paper. Numerical simulations on basis of different solvers have been utilized to calculate the compressible multiphase-flow and also to identify the ideal numerical model in terms of stability and computational effort. By comparing flow and particle velocity distributions of cylindrical nozzles against the results of Laval-type nozzles, it has been found that using the latter type offers an increased productivity and a more uniform particle velocity distribution at the same air and particle flow rates. Further, it was concluded that the air flow rate and therefore the pressure and compressor energy demand can be reduced significantly without losing productivity in abrasive blasting. • An injector-type sand blaster was investigated via numerical methods. • Conventional cylindrical and Laval-type nozzles were evaluated. • Several disadvantages of cylindrical nozzles were identified. • Laval nozzles offer a potential reduction of compressor power by 40 %. • Pressure-based coupled and density-based solver algorithms were evaluated. [ABSTRACT FROM AUTHOR]

We propose and discuss an experiment for the study of neutral gas phase nucleation on a molecular level using propane as the condensable gas. The experiment combines a uniform Laval expansion with soft mass spectrometric detection. The uniform Laval expansion allows nucleation experiments under well-defined conditions while the mass spectrometric detection provides molecular-level information on the molecular aggregates formed. It is discussed how one could observe the onset of nucleation and retrieve the size of the critical nucleus from the mass spectra. [ABSTRACT FROM AUTHOR]

Surface roughness has substantial effects on micronozzle velocity performance of micro-propulsion system and supersonic velocity spraying process. Nozzle internal surface roughness is mainly influenced by the axial depth of cut when the nozzle is fabricated with micromilling technology. This study aims to develop the model of internal flow with friction to predict nozzle velocity performance and to reveal the relationship between the axial depth of cut and nozzle velocity performance by means of the machined surface roughness. Firstly, 3D model of surface roughness for machined nozzle with micro-end milling process is proposed. Then, a theoretical calculation process for nozzle velocity performance is presented on the basis of flow with friction. CFD (Computational Fluid Dynamics) numerical simulation is used to validate the calculated results of nozzle velocity performance. Three NC programming strategies for microcutting of micro-Laval nozzle are recommended. One of these three strategies to realize high-efficiency machining is selected to satisfy the requirement of nozzle velocity performance. The research results show that fluid mechanics combined with mechanical micro-machining is an effective method for optimizing functional performance of microcomponents. [ABSTRACT FROM AUTHOR]

Experimental investigations of non-equilibrium spontaneous condensation in transonic steam flow were carried out in nozzles and linear blade cascade. For the tests the geometry of the half arc nozzles were used. The linear cascade consists of the stator blades of the last stage low pressure steam turbine. The applied experimental test section is a part of small scale steam power station located at the Silesian University of Technology. The steam parameters at the test section inlet correspond to the real conditions in low pressure part of steam turbine. The static pressure measurements as well as the Schlieren pictures were used to assess the flow field in nozzles and linear stator blades cascade. The capabilities of used measurement techniques were estimated for gaining insight into condensation process in steam flow. The experimental results were compared with numerical calculations carried out by means of an in-house CFD code. [ABSTRACT FROM AUTHOR]

The development of steam power units aims to increase the working steam parameters as they are the main factors that determine the efficiency of energy conversion. Most state of the art units are designed for supercritical steam parameters. However, the temperature level of steam feeding the turbine is limited by thermal strength of the material used to make the machine components. In this situation, using nickel alloys or cooling the elements exposed to the impact of high temperatures could be the appropriate solution. The former is rather expensive and the latter - technically difficult. The cooling option would require that the cooled element should be fed by a steam with a very high pressure and with a lower temperature than the temperature in the machine flow system. This paper presents the concept of using working steam as the cooling medium after it is expanded in a convergent-divergent nozzle. In such a case, the cooling system is very simple and the performed simulations indicate, for example, that the turbine blades may be cooled in this way. [ABSTRACT FROM AUTHOR]

Hydrogen production from ethanol by non-thermal arc discharge was investigated in a novel miniaturized plasma reactor. It is observed that ethanol–water mixture was converted into hydrogen, carbon monoxide and other products. The V – I characteristic was recorded by an oscilloscope to study the effect of discharge on the ethanol reforming. In the experiments, ethanol–water mixture entered the reaction chamber through a special gas–liquid spray nozzle for a quick evaporation and a rapid mixing with air at room temperature. Assisted by a Laval nozzle electrode, non-thermal arc plasma can improve the performance of ethanol reforming. It is found that the maximum conversion rate of ethanol was 90.9% at O/C = 1.4, S/C = 1.2 and ethanol flow rate = 0.05 g/s, and the maximum hydrogen yield was 40.9% at O/C = 1.4, S/C = 1.2 and ethanol flow rate = 0.10 g/s. The ethanol reforming process produced little coke and nitrogen oxide which was less than 10 ppm in the supersonic/subsonic plasma working condition. [ABSTRACT FROM AUTHOR]

This study focuses on numerical modeling of condensation of water vapor in a Laval nozzle, using the liquid drop nucleation theory. Influence of nozzle geometry, pressure, and temperature on the average drop size is reported. A computer program written in MATLAB was used used to calculate the nucleation and condensation of water vapor in the nozzle. The simulation results are validated with the available experimental data in the literature for steam condensation. The model reveals that the average drop size is reduced by increasing the divergent angle of the nozzle. The results also confirm that increasing the inlet pressure has a direct effect on the average drop size while temperature rise has an inverse effect on the drop size. [ABSTRACT FROM AUTHOR]

Instead of injected by high pressure powder feeder, powders can be drawn into the nozzle by syphonage effect generated by supersonic gas flow in low pressure cold spray. This characteristic makes low pressure cold spray conveniently for on-site operation. However, no data have ever been reported on the relationship between the nozzle structures and the gas flow in the powder feeder pipe. In this paper, a CFD software (STAR CCM+) was used to calculate the gas flow in nozzle of the DYMET 413 commercial low pressure cold spray system. Variation of structures and process parameters based on the commercial system were also investigated. The syphonage effect is strongly influenced by the powder feeding location, the temperature and pressure in prechamber has little effect on syphonage effect in powder feeder pipe. The syphonaged gas will decelerate the gas velocity and low down the gas temperature in nozzle, so it is best to control the mass flow rate of powder feeding gas by selecting the location. One of the disadvantages is that the particles will collide with the nozzle wall which makes the nozzle a short service life. [ABSTRACT FROM AUTHOR]

Under the influence of intense expansion and supersonic acceleration of the steam flow in a divergent channel, the instability of the flow intensifies. In the lack of external surfaces, this non-equilibrium state causes nucleation and consequent growth of formed nuclei. Due to the release of latent heat from condensation to the supersonic flow at the location of nucleation, an increase in pressure is developed in this small region, which is known as condensation shock. In this research, the effects of this shock on boundary layer parameters are investigated. First, the water vapor flow that has the capability of nucleation is modeled analytically, as adiabatic, inviscid and one dimensional, and then, using the mathematical equations of laminar and turbulent boundary layer parameters and the inviscid-viscous Interaction method. The results of this analytical modeling show that although the influence of the boundary layer on the expansion flow is limited, it still causes approximately 3% increase in the diameter of the water droplets. However, the effects of two-phase flow on the boundary layer parameters at the location of the condensation shock are considerable. The major novelty of this research is determining the quantification and qualification of these effects. [ABSTRACT FROM AUTHOR]

In supersonic water vapor flow of low pressure turbines, nucleation phenomena and consequent condensation are commonly observed. Internal heat transfer, which is caused by phase change, is strongly irreversible and has unwanted effects on turbine efficiency. Also, the strike of formed droplets on the surfaces results in large amounts of mechanical damage. Condensation heat release to supersonic flow, named condensation shock, leads to considerable pressure rise, which, in turn, reduces outlet velocity and occasionally causes severe oscillations, making the flow supercritical. The authors have presented a novel analytical approach for the reduction of these unwanted results in Laval nozzles by volumetric heating of the convergent section. In this paper, and in continuation of the series of papers by the same authors, one dimensional, supersonic and two-phase flow is modeled analytically, and the simultaneous effects of volumetric heat transfer and friction in the convergent nozzle are investigated. It is concluded that the simultaneous use of friction and volumetric heating can be an appropriate and useful technique for the control of two-phase flow conditions, keeping them within the desired range. [ABSTRACT FROM AUTHOR]

Results of experimental investigations of flows around wedge-shaped obstacles of different height installed in a supersonic conical nozzle at M = 2.7 by the methods of color surface visualization and "laser knife" are presented. The influence of the interaction of weak disturbances of these flows by the passive side of the obstacles with the boundary layer on their structure and behavior was determined. The side force of the nozzle was measured. [ABSTRACT FROM AUTHOR]

Melt spinning of the fibers by supersonic air jet in the Laval nozzle is a novel, efficient and energy saving method of formation of super-thin fibers. In the process, polymer melt is extruded from a row of orifices and fast drawn by the pneumatic forces. In the modelling, air velocity, temperature and pressure distributions are computed from the k-! aerodynamic model. Computations of the polymer air-drawing dynamics are based on the mathematical model of melt spinning in a single-, thin-filament approximation and Phan-Thien/Tanner non-linear viscoelasticity of the polymer melt. Axial profiles of the polymer velocity, temperature, tensile stress and rheological extra-pressure are computed. Influence of the Laval nozzle geometry, initial air compression, an initial melt temperature, a polymer mass output and the diameter of the melt extrusion die is discussed. The role of the polymer molecular weight, melt viscosity and relaxation time is considered. Example computations show the influence of important processing and material parameters. In the supersonic process, a high negative internal extra-pressure is predicted in the polymer melt under high elongation rates which may lead to cavitation and longitudinal burst splitting of the filament into a high number of sub-filaments. A hypothetical number of sub-filaments at the splitting is estimated from an energetic criterion. The diameter of the sub-filaments may reach the range of nano-fibers. A substantial influence of the Laval nozzle geometry is also predicted. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of pipeline transportation and chemical industrial utilization, natural gas must be dehydrated. Supersonic separation is a new technology for natural gas dehydration, which has obvious advantages compared with the traditional techniques. This paper introduces the working principle of supersonic separation and the structure design of Laval nozzle, analyses the internal application statue of 3S in natural gas dehydration. Through the comparison, it is considered that 3S in parallel with J-T valve and then in tandem with molecular sieves is a best way for natural gas dehydration, which could meet the requirements of dehydration process of internal natural gas. [ABSTRACT FROM AUTHOR]

Cold spray additive manufacturing (CSAM) shows great potential in titanium-alloy production as it is a solid-state process. However, data published so far have demonstrated the difficulty of producing dense and high-strength Ti alloy parts. Our previous studies have shown that nozzle design together with high-cost helium propulsive gas plays a crucial role in particle acceleration. In this work, special nozzles for Ti alloy were designed and validated experimentally with commercially available Ti6Al4V powder. Simulation results show that particle impact temperature increases remarkably for a long convergent length, while particle kinetic energy slightly increases, which is validated by experiments. The relationship between the particle impact temperature and practice diameter shows the first increase and then decrease. The experimental results show that as the nozzle convergent section becomes longer, the edges of the single-pass deposits become smoother, and the width, density, deposition efficiency, and microhardness of the single-pass deposits increase. [ABSTRACT FROM AUTHOR]

Full-scale and computational experiments were used to investigate the flows in the jet thrust unit with annular nozzle and deflector in the form of a spherical segment. The used working gas was the combustion products of air mixtures with acetylene, gas-phase aviation kerosene, and natural gas. Experimental studies were carried out in a hot-shot wind tunnel in the range of stagnation pressure from 0.48 to 2.05 MPa. The calculations for the cases of combustion products outflow in terrestrial and high altitude conditions were performed with the original computer program that used the Euler and Navier-Stokes systems supplemented by equations of chemical kinetics. It was found that the thrust of the jet module with an annular nozzle at high altitude almost twice exceeds the sound nozzle thrust, but is lesser (about 25 %) than the thrust of the ideal calculated Laval nozzle; the difference therewith decreases markedly with the decrease of flight altitude and stagnation pressure. [ABSTRACT FROM AUTHOR]

A new dual-fluid model considering phase transition and velocity slip was proposed in this paper and the Cunningham correction was used in the droplet resistance calculation. This dual-fluid model was applied to the numerical simulations of wet steam flow in a 2D LAVAL nozzle and in the White cascade respectively. The results of two simulations demonstrate that the model is reliable. Meanwhile, the spontaneous condensing flow in White cascade was analyzed and it infers that the irreversible loss caused by condensation accounts for the largest share (about 8.78% of inlet total pressure) in total pressure loss while the loss caused by velocity slip takes the smallest share (nearly 0.42%), and another part of total pressure loss caused by pneumatic factors contributes a less share than condensation, i.e. almost 3.95% of inlet total pressure. [ABSTRACT FROM AUTHOR]