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Unstable airflow driven by natural wind forces inside a grass aerial seeding tower is a technical problem that needs to be improved. The authors used FLUENT 2020 R2 to simulate a basic nozzle unit, which is the fundamental component of a grass aerial seeding tower. The interior flow characteristics of the tower were first analyzed. Then, an optimization was undertaken to enhance the internal airflow's uniform stability, taking the cross-sectional inclination angle as the design parameter. The coefficient of variation, uniformity index, and velocity direction index were considered as constraints. The simulation results indicate that, subsequent to traversing the Laval nozzle unit, the grass seeds undergo a considerable acceleration. At an inclination angle of 15°, while ensuring the attainment of desired exit velocities, a commendable balance of uniformity and directional consistency was achieved. [ABSTRACT FROM AUTHOR]

The cutting thickness of the flame cutting nozzle mainly depends on the characteristics of the cutting oxygen jet, and in the process of designing and manufacturing a flame cutting nozzle with an ultralarge thickness, it is impossible to carry out multiple experiments to optimize the design due to the difficulty in testing, safety, manufacturing cost, environmental pollution, and other problems. In this paper, the Laval-type cutting oxygen orifice channel was first designed by theoretical calculation, the pressure, velocity, Mach number, and density distribution characteristics of the cutting oxygen jet were investigated by numerical simulation, and the reliability and adaptability of the numerical simulation results were verified by experiments. Then, the numerical simulation comparison and estimation method of jet characteristics with the general-purpose G301-7# nozzle was used to study the cutting oxygen orifice channel of the ultralarge thickness flame cutting nozzle. The results show that under the condition of a 19 mm throat diameter and 10 atm inlet pressure, it was estimated that the length of cutting oxygen flow from the design nozzle can reach 1800 mm and the cutting thickness can reach 2500 mm based on the density value; the length of cutting oxygen flow can reach 2000 mm and the cutting thickness can reach 3800 mm based on the velocity value; the length of cutting oxygen flow can reach 1600 mm according to the value of the oxygen quality fraction; and the cutting thickness can reach 2800 mm based on the oxygen mass fraction content. Finally, trial production of the nozzle design, verification of the cutting test, the nozzle with a cutting thickness of 2500 mm at an oxygen pressure of 7 atm, and the cutting quality were all good.

The use of a supersonic separator presents a novel approach for separating ammonia (NH3) from hydrogen (H2). Even trace amounts of water (H2O) can significantly influence the condensation characteristics of NH3. This study presents mathematical models for homogeneous NH3 and H2O condensation and heterogeneous NH3–H2O condensation. Through computational analysis, we revealed that the droplet radius and liquid mass fraction of a single condensable gas condensation increased accordingly with increasing inlet condensable gas content. Interactions between the condensation processes of NH3 and H2O were also captured in the simulation. Notably, at 100 ppm H2O content, H2O spontaneously condensed before NH3, serving as a condensation nucleus for NH3, and the heterogeneous condensation of NH3 decreased the rate of its spontaneous condensation. At an inlet H2O content of 50 ppm, the onset of spontaneous NH3 condensation coincided with that of H2O, with H2O having a negligible effect on NH3 condensation. The impact of H2O on NH3 condensation transitioned from minimal to inhibitory and then to facilitative as the content of H2O increased from 25 ppm to 250 ppm. At the nozzle outlet, the liquid mass fraction of NH3 initially decreased from 0.0414 to 0.0352 and then increased to 0.0446.

Unstable airflow driven by natural wind forces inside a grass aerial seeding tower is a technical problem that needs to be improved. The authors used FLUENT 2020 R2 to simulate a basic nozzle unit, which is the fundamental component of a grass aerial seeding tower. The interior flow characteristics of the tower were first analyzed. Then, an optimization was undertaken to enhance the internal airflow’s uniform stability, taking the cross-sectional inclination angle as the design parameter. The coefficient of variation, uniformity index, and velocity direction index were considered as constraints. The simulation results indicate that, subsequent to traversing the Laval nozzle unit, the grass seeds undergo a considerable acceleration. At an inclination angle of 15°, while ensuring the attainment of desired exit velocities, a commendable balance of uniformity and directional consistency was achieved.

Measurement while drilling (MWD) plays an important role in controlling well trajectory, improving drilling efficiency and saving drilling cost. In recent years, a large number of high-temperature wells have appeared, which makes the traditional MWD instruments no longer applicable. So far, no active cooling method has been successfully applied to MWD instruments for high-temperature oil and gas wells. This paper presents a new active cooling method for air drilling by utilizing the throttling and cooling of drilling gas, and the cooling system is designed. An axisymmetric numerical model of internal fluid is established, and different drilling gas flow channel design methods are discussed. The research results indicate that the wall temperature of the cooling section is much higher than the center fluid temperature, but lower than the ambient temperature, and can be used for active cooling of downhole drilling instruments. Compared with other design methods, the supersonic nozzle designed using the Bezier method has better parallelism of the gas in cooling section. The diffusion capability of straight wall diffuser is better than that of curved wall diffuser, and it can withstand greater back pressure. For straight wall diffuser, increasing the throat length and reducing the contraction and expansion angle can improve the diffusion capacity, but they also lead to a longer diffuser.

Transonic planar flows around a circular cylinder are investigated numerically for laminar and turbulent flow conditions with Reynolds numbers of 50 ≤ R e D ≤ 300 and 8890 ≤ R e D ≤ 80,000 and free stream Mach numbers in the range of 0.2 ≤ M a ∞ ≤ 2 . A commercially available CFD tool is used and validated for this purpose. The results show that the flow phenomena occurring can be grouped into eight regimes. Compared to the incompressible flow regimes, several new phenomena can be found. In contrast, at higher M a ∞ of 0.6 ≤ M a ∞ ≤ 0.8 vortices in the wake of the cylinder are suppressed for R e D = 50 . In some cases, M a ∞ = 0.8 and R e D ≥ 300 , λ -shocks are formed in the near cylinder wake. For supersonic M a ∞ , two different phenomena are observed. Beside the well-known oblique and detached shocks, for 50 ≤ R e D ≤ 300 a wake with instabilities is formed downstream of the cylinder. Furthermore, the temporal mean drag coefficient C ¯ D , the Strouhal number S t r , as well as the critical Mach number M a crit are calculated from the simulation results and are interpreted. [ABSTRACT FROM AUTHOR]

The back pressure at the outlet of supersonic cyclone separator usually causes aerodynamic shock wave in Laval nozzle, and the interaction of supersonic flow, shock wave and phase transition is very complicated. In order to explore the supersonic flow properties of wet gas under the action of shock wave, study was performed on the methane-water vapor mixtures. Then, a mathematical model for the supersonic condensation and flow of wet natural gas was established. Meanwhile, the effect of the outlet back pressure and inlet pressure on the supersonic condensation property of wet natural gas was analyzed to evaluate the performance of the supersonic cyclone separator under the action of shock waves. The simulation results show that the shock waves can cause the rapid increase in pressure and temperature of water vapor in a short time, leading to the condensed droplets re-evaporate and the liquid mass fraction at outlet reduces sharply. Besides, as the inlet pressure increases, the location of nucleation approaches the throat of Laval nozzle gradually, and the limit nucleation rate and the droplet number decrease accordingly. However, the liquid mass fraction increases due to the increasing of growth rate and sizes of droplets. Moreover, the nozzle loses its function of liquefaction when the back pressure is higher than 25 kPa (i.e., the pressure ratio is higher than 0.58), and then the nozzle cannot operate normally. Therefore, it is necessary to control the reasonable pressure ratio to ensure the dehydration efficiency of the supersonic separator with back pressure.

High velocity oxygen fuel (HVOF) coatings have high bonding strengths and compactness, which can improve the wear, corrosion, and fatigue resistance of an underlying matrix. These coatings are widely used in chemical industries, metallurgy, aerospace, and other fields. Here, we studied hypersonic flame spraying through simulating flame flow fields and particle flight processes using the computational fluid dynamics software Fluent. The HVOF system uses oxygen as a combustion-supporting gas and kerosene as fuel. The temperature, velocity, and pressure distributions of the flame flow in a spray gun before adding particles were studied. The dynamic flight behavior of spray particles was calculated using a discrete phase model, and the effects of particle size, injection velocity, and sphericity on particle trajectory, velocity, and temperature were investigated. The optimal particle size range was 30–50 μm. Particles that were too large collided with the inner walls of the spray gun, hindering the combination of the particles and matrix. Particles that were too small were liquid during flight, and readily reacted with oxygen, leading to a reduction in the amorphous content of the prepared coatings. In the optimal size range, particles were uniformly distributed in the center of the flame flow, and the particles were in a molten state, ideal for forming coatings with higher bonding strengths. A systematic study of injection velocities on spray particle dynamics, determined the optimal injection velocity for small, medium, and large particles as 10–15, 5–10, and 1–5 m·s−1, respectively. Compared with spherical particles, nonspherical particles had higher drag coefficients, greater acceleration in the flow field of the flame, and gained more kinetic energy and less heat during flight.

The cutting thickness of the flame cutting nozzle mainly depends on the characteristics of the cutting oxygen jet, and in the process of designing and manufacturing a flame cutting nozzle with an ultralarge thickness, it is impossible to carry out multiple experiments to optimize the design due to the difficulty in testing, safety, manufacturing cost, environmental pollution, and other problems. In this paper, the Laval-type cutting oxygen orifice channel was first designed by theoretical calculation, the pressure, velocity, Mach number, and density distribution characteristics of the cutting oxygen jet were investigated by numerical simulation, and the reliability and adaptability of the numerical simulation results were verified by experiments. Then, the numerical simulation comparison and estimation method of jet characteristics with the general-purpose G301-7# nozzle was used to study the cutting oxygen orifice channel of the ultralarge thickness flame cutting nozzle. The results show that under the condition of a 19 mm throat diameter and 10 atm inlet pressure, it was estimated that the length of cutting oxygen flow from the design nozzle can reach 1800 mm and the cutting thickness can reach 2500 mm based on the density value; the length of cutting oxygen flow can reach 2000 mm and the cutting thickness can reach 3800 mm based on the velocity value; the length of cutting oxygen flow can reach 1600 mm according to the value of the oxygen quality fraction; and the cutting thickness can reach 2800 mm based on the oxygen mass fraction content. Finally, trial production of the nozzle design, verification of the cutting test, the nozzle with a cutting thickness of 2500 mm at an oxygen pressure of 7 atm, and the cutting quality were all good. [ABSTRACT FROM AUTHOR]

The possibility of using a convergent-divergent nozzle with a Busemann diffuser in ramjet engines for aerospace engineering applications is studied. Kerosene vapors are considered as a fuel, the combustion of which is carried out in the detonation mode at a hypersonic speed of the oncoming air flow. It is shown that at the altitude of about 40 km with the flight Mach number of 9, the Busemann diffuser can provide stable detonation combustion of kerosene with the efficiency of over 50%. Modeling was carried out on the basis of two-dimensional unsteady Euler equations of motion for axisymmetric flows of a multicomponent reacting gas using the modification of the Godunov numerical scheme, which provides the second order of the solution approximation in terms of spatial variables. The previously published kinetic scheme of ignition and combustion of kerosene vapors is supplemented by the processes of low-temperature combustion of the initial fuel. • The possibility of initiation of kerosene vapor detonation in the Busemann diffuser is shown. • The Busemann diffuser for a scramjet based on detonation combustion of kerosene vapor is proposed. • In conditions of high-altitude atmosphere, the efficiency of such a scramjet may be higher than 50%. • The kinetic scheme is supplemented with low-temperature decomposition of kerosene. [ABSTRACT FROM AUTHOR]

The energy efficiency of a supersonic ramjet engine with detonation combustion of a hydrogen-air mixture in an axisymmetric Laval nozzle is considered. First of all, within the framework of the one-dimensional (1D) theory, it is shown that extreme combustion corresponding to the Chapman-Jouguet (C.-J.) deflagration, like constant pressure combustion, surpasses detonation in energy efficiency. However, this advantage becomes insignificant with an increasing the free-flow Mach number. Based on the results of the 1D theory, an axisymmetric Laval nozzle is constructed, which provides steady-state detonation combustion of a stoichiometric hydrogen-air mixture at an altitude of about 40 km and with freestream Mach numbers 9 and 12. The efficiency of detonation combustion in this case is about 35% instead of the maximum 65% according to the 1D theory. • In terms of efficiency, detonation reaches deflagration at a high flight Mach number. • In 1D-theory a stationary combustion in Laval nozzle has a maximum flight Mach number. • 1D theory gives overestimated values of the efficiency and expansion of the diffuser. • The detonation slope expands the limits of its applicability in terms of speed and height. • The steady-state detonation in the Laval nozzle can provide an efficiency of about 35%. [ABSTRACT FROM AUTHOR]

The blowing of oxygen at supersonic velocity through nozzles is a fundamental method and key technology for basic oxygen furnace process used in the steelmaking process. During the process, the high-speed oxygen jets penetrate the liquid slag leading to the formation of the impaction cavity on the surface of the molten bath. Further, the dynamic energy and mass transfer would occur at the three-phase (oxygen–liquid slag–molten steel) region. As a result, the impurity elements are removed, the temperature of molten bath is controlled, and the solid slag is melted faster. Moreover, many complex wave structures are formed in the traditional Laval nozzle depending on its gas flow field, resulting in suppression of the initial stirring ability of the oxygen jet. However, the new Laval nozzle designed by the characteristic-line method can solve this problem. Additionally, Mach number, dynamic pressure, and entrainment phenomenon of both traditional and new Laval nozzle structures were tested using various oxygen flow rates at the high-temperature ambition environment. The results prove that the new Laval nozzle structure prolongs the velocity core length of oxygen jet, increases the molten bath stirring effect, and improves the mass transfer process.

The existence of back pressure at outlet has a direct impact on the separation performance of the separation separator. However, the influence of back pressure is not understood well due to the complicated interaction of the supersonic flow, condensation and shock waves. In this study, the condensation flow models of water vapor were established, the influence of back pressure on supersonic condensation properties of water vapor was investigated. The results show that when the back pressure exists, the position of the shock wave is more forward than that without condensation, and the strength of shock wave is weaker. The nucleation rate is generated around the position of x = 115 mm and increases sharply from 0 to 1025 m−3 s−1. The shock wave is generated at x = 145 mm and x = 122 mm when the outlet back pressure is 20 kPa and 30 kPa, respectively. The condensed droplets evaporate again with the effect of shock wave, and then the secondary condensation of droplets occurs owing to the cooling effect of nozzle. When the back pressure is higher than a certain value, the refrigeration environment in the nozzle is completely destroyed with the effect of shock wave, and the condensed droplets evaporate again.

Abstract To simulate the transonic atomization jet process in Laval nozzles, to test the law of droplet atomization and distribution, to find a method of supersonic atomization for dust-removing nozzles, and to improve nozzle efficiency, the finite element method has been used in this study based on the COMSOL computational fluid dynamics module. The study results showed that the process cannot be realized alone under the two-dimensional axisymmetric, three-dimensional and three-dimensional symmetric models, but it can be calculated with the transformation dimension method, which uses the parameter equations generated from the two-dimensional axisymmetric flow field data of the three-dimensional model. The visualization of this complex process, which is difficult to measure and analyze experimentally, was realized in this study. The physical process, macro phenomena and particle distribution of supersonic atomization are analyzed in combination with this simulation. The rationality of the simulation was verified by experiments. A new method for the study of the atomization process and the exploration of its mechanism in a compressible transonic speed flow field based on the Laval nozzle has been provided, and a numerical platform for the study of supersonic atomization dust removal has been established.

For practical applications, the description of processes occurring during the flow of two-phase gas-liquid mixtures requires a simple physical and mathematical model that describes the behavior of a two-phase medium in the entire range of phase concentrations changes and in a wide range of pressure changes. Problems of this kind arise in various branches of industry and technology. In the space industry, one often has to deal with the movement of various gases in rocket nozzles, consider the combustion, condensation of various vapors on the nozzle walls and their further impact on the velocity sublayer at the nozzle wall. The large acoustic effect arising from the engines affects the gas-liquid mixture in the nozzles of rocket engines. In the metal industry, metal cooling occurs with the help of nozzles in which the emulsion mixture is supplied under high overpressure. But this is only a short list of applied issues in which one has to deal with a problem of this type. The paper presents the results and directions of study of the problems of two-phase dispersed gas-droplet flows in the nozzles. The main methods of investigation of two- phase heterogeneous flows are described. The main characteristics of heterogeneous two-phase flows in the nozzles, which were confirmed by experimental results, are presented. The calculation of the air-droplet flow in the Laval nozzle is given. The technique, which is based on integral energy equations for two-phase dispersed flows, is described. The main problems and questions concerning the further description and studying of two-component flows are stated.

The cold spray technology mainly accelerates the powder in the Laval nozzle by gas, ensuring that the powder has a greater velocity at the exit of the Laval nozzle, and achieving high-efficiency deposition on the substrate, thereby obtaining a better performance of the deposition coating. The article uses numerical simulation to study the influence of the length of the expansion section of the Dimet Laval nozzle on the acceleration effect of Al powder. The results show that the length of the expansion section of the nozzle is an essential factor affecting the velocity of the Al powder at the nozzle outlet. Through analysis, it can be known that the pressure inlet range of the Dimet Laval nozzle is 1.0 MPa, and the length of the expansion section is about 210 mm, which can ensure that the Al powder has a better acceleration effect in the nozzle and has a better velocity at the nozzle outlet. It is recommended that the joints between the small sections of the nozzle expansion section should be kept as smooth as possible so that the accelerating effect of the accelerating gas on the Al powder is more uniform and stable.

The relevance of the study is caused by the need to improve the efficiency of the allocation of valuable components from natural gas in field conditions.The existing gas treatment technologies of gas condensate fields are characterized by a low degree of extraction of propane-butane and ethane fractions. It is known that natural gases of the Valanginian and Achimov deposits contain a large number of components necessary for petrochemical products. Field preparation of natural gas of gas condensate fields is usually based on low-temperature separation technology, where the extraction of liquid hydrocarbons from gas stream occurs by reducing the temperature by throttling, followed by separation of gas and liquid phases in independent separators. The technology has low efficiency and is limited by dependence on high pressures. The article deals with the issue of retrofitting gas treatment plants with small-sized high-performance equipment that provides deep cooling of the medium and simultaneous separation into components. The aim of the work is theoretical study of high-speed processes of natural gas preparation, numerical experiment for establishing the influence of the main parameters of the equipment on efficiency of separation of high-molecular components from methane. Objects: complex gas treatment plants of gas condensate fields, mean values of gas composition, critical parameters and derivative values of which correspond to the conditions of the Northern fields. Methods: construction of a mathematical model that takes into account gas component composition, determination of distribution of temperature, pressure, velocity, density and the Mach number of gas in a high-speed separator with separation into components. Results. The authors have proposed the technology of obtaining lower temperatures required for complex gas treatment of gas condensate fields. It is implemented on the basis of gas-dynamic high-speed technology with the use of the Ranque–Hilsh tube and Laval nozzle. The calculated dependences of extraction of propane-butane and ethane fractions on the achieved low temperatures are established.

Two-phase nozzles, in which the phase transition process takes place, can work in jet superchargers for various purposes, including jet thermal pumps (steam-water injectors) and thermal compressors. In such schemes of thermal transformers, the ejector performs the function of a preliminary compression stage in order to reduce the load on the compression of the working substance in the main compressor. The use of fluxes of boiling liquid as energy-efficient working fluids is inhibited due to the lack of a reliable description of the mechanism of their flow. Finding the dependence of the steam content on the pressure and temperature at the nozzle exit will make it possible to determine the variant of the initial parameters at which the overproduction of steam will be greatest. It is also worth determining the change in the velocity factor, as well as the change in the thrust of the nozzle in the studied range of parameters, in order to find out whether the pressure at the nozzle outlet is a determining factor when choosing the design parameters of the nozzles. The article proposes to investigate the boiling streams in such nozzles by the method of mathematical modeling using a model that takes into account the relaxation nature of vaporization. The study used a compressible two-phase medium model, a kinetic model of evaporation / condensation. The model also takes into account the dynamic and mechanical equilibrium of the process of evaporation-condensation. The calculations were performed using an Ansys CFX commercial CFD product. The value of the mean square relative error of pressure measurement does not exceed 0,119%. The average discrepancy between the obtained data between the mathematical model and the field experiment does not exceed 3%.

Laval nozzle is the critical part of supersonic separator to provide refrigeration environment. Due to the back pressure at the outlet of supersonic separator in dehydration process, the condensation characteristics of water vapor and the refrigeration performances of the nozzles are affected by the shock wave. Herein, mathematical models for the supersonic condensation and flow of the methane-water two-phase flow model were established, which were verified by the experimental data. The effects of different divergent angles on the refrigeration and condensation behavior in the Laval nozzle were studied considering shock wave. The results show that the refrigeration performance of the nozzle will be worsen under the presence of shock waves. With the divergent angle of the nozzle increased from 2° to 8°, the lowest temperature was decreased from 304.4 K to 291.8 K, the liquid mass fraction at the nozzle outlet was decreased from 0.84% to 0.133%, the maximum droplet radius that can be obtained was reduced from 2.54 × 10−7 m to 1.69 × 10−7 m due to the forward movements of the shock waves. The divergent angle of the nozzle is recommended to be designed to 4°–6° in consideration of the refrigeration performance.

To simulate the transonic atomization jet process in Laval nozzles, to test the law of droplet atomization and distribution, to find a method of supersonic atomization for dust-removing nozzles, and to improve nozzle efficiency, the finite element method has been used in this study based on the COMSOL computational fluid dynamics module. The study results showed that the process cannot be realized alone under the two-dimensional axisymmetric, three-dimensional and three-dimensional symmetric models, but it can be calculated with the transformation dimension method, which uses the parameter equations generated from the two-dimensional axisymmetric flow field data of the three-dimensional model. The visualization of this complex process, which is difficult to measure and analyze experimentally, was realized in this study. The physical process, macro phenomena and particle distribution of supersonic atomization are analyzed in combination with this simulation. The rationality of the simulation was verified by experiments. A new method for the study of the atomization process and the exploration of its mechanism in a compressible transonic speed flow field based on the Laval nozzle has been provided, and a numerical platform for the study of supersonic atomization dust removal has been established. [ABSTRACT FROM AUTHOR]

In the duplex steelmaking process, the oxygen flow rate is suppressed to reduce the increasing rate of the temperature in the molten bath, resulting in severe dynamic conditions. To improve the mixing effect of the molten bath, a Laval nozzle structure designed for combination gas has been proposed. In this research, five types of Laval nozzle structure have been built based on the combination gas content, and both numerical simulations and experiments are performed to analyze the flow field of the supersonic jet. The axial velocity and oxygen concentration were measured in the experiment, which agreed well with the numerically simulated data. The results show that both initial axial velocity and potential core length increase with the flow rate of combination gas. Further, applying a higher N2 flow rate could improve the oxygen utilization rate at different ambient temperatures, but this issue increases the oxygen utilization rate; however, the latter can be reduced at higher ambient temperatures.

In this paper, we describe the possibility of using the energy of a compressed air flow, where cryogenic temperatures are achieved within the flow behind the nozzle, when reaching a critical flow in order to maximize the energy gained. Compared to the energy of compressed air, the energy obtained thermoelectrically is negligible, but not zero. We are therefore primarily aiming to maximize the use of available energy sources. Behind the aperture separating regions with a pressure difference of several atmospheres, a supersonic flow with a large temperature drop develops. Based on the Seebeck effect, a thermocouple is placed in these low temperatures to create a thermoelectric voltage. This paper contains a mathematical-physical analysis for proper nozzle design, controlled gas expansion and ideal placement of a thermocouple within the flow for best utilization of the low temperature before a shockwave formation. If the gas flow passes through a perpendicular shockwave, the velocity drops sharply and the gas pressure rises, thereby increasing the temperature. In contrast, with a conical shockwave, such dramatic changes do not occur and the cooling effect is not impaired. This article also contains analyses for proper forming of the head shape of the thermocouple to avoid the formation of a detached shockwave, which causes temperature stagnation resulting in lower thermocouple cooling efficiency.

When water vapor in moist air reaches supersaturation in a transonic flow system, non-equilibrium condensation forms a large number of droplets which may adversely affect the operation of some thermal-hydraulic equipment. For a better understanding of this non-equilibrium condensing phenomenon, a numerical model is applied to analyze moist air condensation in a transonic flow system by using the theory of nucleation and droplet growth. The Benson model is adopted to correct the liquid-plane surface tension equation for realistic results. The results show that the distributions of pressure, temperature and Mach number in moist air are significantly different from those in dry air. The dry air model exaggerates the Mach number by 19% and reduces both the pressure and the temperature by 34% at the nozzle exit as compared with the moist air model. At a Laval nozzle, for example, the nucleation rate, droplet number and condensation rate increase significantly with increasing relative humidity. The results also reveal the fact that the number of condensate droplets increases rapidly when moist air reaches 60% relative humidity. These findings provide a fundamental approach to account for the effect of condensate droplet formation on moist gas in a transonic flow system.

The article deals with the cavitation phenomenon affected by full and partial wetting of the wall. For the numerical computation of flow in the Laval nozzle the Schnerr-Sauer cavitation model was tested and was used for cavitation research of flow within the nozzle considering partial surface wetting. The coefficient of wetting for various materials was determined using experimental, theoretical and numerical methods of fluid flow due to partial surface wetting.

Two-phase nozzles, in which the phase transition process takes place, can work in jet superchargers for various purposes, including jet thermal pumps (steam-water injectors) and thermal compressors. In such schemes of thermal transformers, the ejector performs the function of a preliminary compression stage in order to reduce the load on the compression of the working substance in the main compressor. The use of fluxes of boiling liquid as energy-efficient working fluids is inhibited due to the lack of a reliable description of the mechanism of their flow. Finding the dependence of the steam content on the pressure and temperature at the nozzle exit will make it possible to determine the variant of the initial parameters at which the overproduction of steam will be greatest. It is also worth determining the change in the velocity factor, as well as the change in the thrust of the nozzle in the studied range of parameters, in order to find out whether the pressure at the nozzle outlet is a determining factor when choosing the design parameters of the nozzles. The article proposes to investigate the boiling streams in such nozzles by the method of mathematical modeling using a model that takes into account the relaxation nature of vaporization. The study used a compressible two-phase medium model, a kinetic model of evaporation / condensation. The model also takes into account the dynamic and mechanical equilibrium of the process of evaporation-condensation. The calculations were performed using an Ansys CFX commercial CFD product. The value of the mean square relative error of pressure measurement does not exceed 0,119%. The average discrepancy between the obtained data between the mathematical model and the field experiment does not exceed 3%. [ABSTRACT FROM AUTHOR]

Graphical abstract The numerical simulations of CH 4 -CO 2 mixture gas in the nozzle were carried out applying User Define Function, which convergent section is designed by different curves respectively. Due to the intense performance of spontaneous condensation and the stable variation of temperature and pressure, Translation of Witoszynski curve is recommended to design the convergent section in supersonic separator. Highlights • Two-dimensional models of Laval nozzle were set up with different convergent section. • The numerical simulations of CH 4 -CO 2 mixture gas in the nozzle were carried out. • Condensation and flow parameters were obtained using User Define Function. • Translation of Witoszynski curve is recommended to design the convergent section. Abstract The Laval nozzle is an important part of the supersonic separator, which structure determines the separation efficiency of supersonic separator. In order to study the flow and condensation process in Laval nozzle with different convergent section, convergent section is designed by Bicubic parametric curve, Quintic polynomial curve, Witoszynski curve and Translation of Witoszynski curve, respectively. The numerical model for the supersonic condensing flow process of CH 4 -CO 2 mixture gas is established and the User Define Function is invoked for numerical simulation. The effects of different linetypes of convergent section on the flow and condensation parameters in nozzle were investigated. The results confirm the Laval nozzle designed by Translation of Witoszynski curve has strengths such as the most stable pressure change, the best refrigeration effect, the most intense spontaneous condensation, and the nucleation rate is 1.610×1022m−3s−1, the number of droplets is as high as 2.023×1015m−3 at the nozzle outlet far better than the other nozzles. Therefore, Translation of Witoszynski curve is recommended to design the convergent section of Laval nozzle in supersonic separator. [ABSTRACT FROM AUTHOR]

Abstract The ethylene-air Continuous Rotating Detonation (CRD) has been experimentally achieved with large operating domain, little velocity deficit and notable pressure rise in the hollow chamber with Laval nozzle. The results show that the lean limit increases while operating domain decreases with contraction ratio increasing. Deflagration flame in recirculation zone and larger width combustor enable the ethylene-air CRD to be readily achieved. Three different propagation modes are presented. Most of the achieved CRD experiments are single-wave mode. The highest frequency and velocity are 6.10 kHz and 1915.40 m/s respectively. Two-waves mode can be obtained when contraction ratio is 12. Sawtooth wave mode appears around lean limit when contraction ratio is 1,2 and 4. Sawtooth wave, as a critical condition, can be transformed into typical CRD wave or extinguish. For contraction ratios of 1,2,4 and 6, the propagation stability increases with equivalence ratio (ER) increasing. For contraction ratios of 8,10 and 12, the stability decreases with a concomitant increase of ER. The contraction ratios of 2 and 4 are beneficial for CRD wave to propagate with high frequency and stability. The study will deepen the understanding of ethylene-air CRD and enrich the combustor design theory of CRD Engine fueled by hydrocarbon fuels. Highlights • The ethylene-air Continuous Rotating Detonation is experimentally achieved. • The hollow chamber contributes to Continuous Rotating Detonation realization. • The highest frequency and velocity are 6.10 kHz and 1915.40 m/s, respectively. • The Laval nozzles (ε =2, 4) are beneficial for detonation wave propagating. [ABSTRACT FROM AUTHOR]

Ground-based methods for accurately representing high-altitude, high-speed flight conditions have been an important research topic in the aerospace field. Based on an analysis of the requirements for high-altitude supersonic flight tests, a ground-based test bed was designed combining Laval nozzle, which is often found in wind tunnels, with a rocket sled system. Sled tests were used to verify the performance of the test bed. The test results indicated that the test bed produced a uniform-flow field with a static pressure and density equivalent to atmospheric conditions at an altitude of 13–15km and at a flow velocity of approximately M 2.4. This test method has the advantages of accuracy, fewer experimental limitations, and reusability. [ABSTRACT FROM AUTHOR]

Micro Abrasive jet machining (MAJM) is one of the most convenient micromachining technologies for hard and brittle materials. Now a day’s mostly ceramics and semiconductor materials are used for manufacturing electronic devices and micro fluidic channels. This process is having various distinct advantages, as compare to other micro-fabrication techniques this method is represented a very high erosion rate. In this paper attempt has been made to develop MAJM for difficult to machine materials such as stainless steel ANSI 304 plate. In order to raise the machining productivity of micromachining, the new design and fabrication of Laval nozzle has been first reported. Circular cross sectional nozzle is developed for high velocity, precise etching and patterning on difficult to machine material such as stainless steel ANSI 304 Plate. The present study focus the effect of different parameters like air pressure, abrasive material, abrasive mesh size, nozzle diameter, guiding pressure and Standoff distance on machining performance is investigated using Taguchi’s Design of Experiment methodology. Analysis of variance (ANOVA) is implementing to find out the significant influence of each factor. [ABSTRACT FROM AUTHOR]

We show that, as the pressure of a metal-air jet increases from 0.6 to 1.2 МРа, its velocity increases from 300 to 600 m/sec. It is established that with increase in the velocity of the flow of particles, the time of transportation of drops from the arc to the substrate increases and they strike against a prepared surface at higher temperatures. It is shown that as the air pressure increases, the size of drops and oxides between the lamellae decreases, and the mechanical characteristics improve. [ABSTRACT FROM AUTHOR]

In the separation process of the conventional supersonic separator, the shock wave easily appears in diverging section of the nozzle and the swirling flow occurs in subsonic conditions with poor efficiency, which make the low temperature section short and the cooling effect dissatisfied. In this paper, a novel supersonic separator with reflow channel that has axial outlet or tangential outlet has been designed. The fluid can be drawn into the nozzle by the differential pressure between the discharge clearance on the wall and the throat zone near the centerline. Axial and radial distribution of the main parameters and the effect of pressure ratio are investigated with Reynolds Stress Mode (RSM) turbulence model. The results show that compared with the device without reflow channel, the pressure recovery in the diffuser with reflow channel is faster, the centrifugal acceleration is higher and the temperature is lower, which manifest the new device has a better refrigeration and separation performance. The supersonic separator with axial reflow outlet can obtain the better performance with pressure ratio of 1.5 that has a low temperature (221 K) and high centrifugal acceleration (2.2 × 10 7  m/s 2 ), while the high centrifugal acceleration (9.89 × 10 9  m/s 2 ) and low temperature (223 K) can be achieved in the device with tangential reflow outlet when pressure ratio is 2.0. Moreover, the structure with axial reflow outlet enlarges the supersonic region in the novel device and has a better ability to resist flow fluctuation and backmixing under the same condition when pressure ratio is 1.5. As the pressure ratio increases, the position of shock wave shifts downstream and the centrifugal acceleration and the reflow impetus increase, while the minimum temperature decreases, which prove that the increasing pressure ratio can improve the fluid expansion characteristics. [ABSTRACT FROM AUTHOR]

In view of the low efficiency of coal breakage by high-pressure gas jet, this paper put forward a new method of efficient coal breakage method by abrasive gas jet (AGJ). According to the theory o f aerodynamics theory, the nozzle structure was established. On this basis, the influence rule of jet parameters on the velocity and erosion rate of abrasive was studied by numerical simulation. Moreover, the experiment explored the relationship of the pressure of high-pressure abrasive jet and the target distance with the erosion depth, the erosion volume as well as the diameter of the erosion pit. According to the experimental results, based on the engineering application parameter range, when the jet pressure was 15MPa, the erosion rate was the largest and the erosion effect was the optimum on the premise of definite target distance. The erosion depth and erosion volume increased with the jet pressure. When the pressure was greater than 15MPa, the erosion depth and erosion volume did not increase obviously. The diameter of erosion pit was basically constant as the change of pressure. In the case of the definite jet flow pressure, the erosion depth first increased and then decreased with the increase of the target distance. The erosion volume and erosion pit diameter were in direct proportion to the target distance. Based on the comparative analysis of erosion depth, erosion volume, and erosion pit diameter, it has been determined that the optimal jet pressure of the abrasive gas is 15MPa, and the optimum target distance of jet flow is about 10cm. [ABSTRACT FROM AUTHOR]

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.

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.

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]

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]

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]