Nozzle Divergence Angle Research Articles

Optimization of hydrogen recirculation ejector for proton-exchange membrane fuel cells (PEMFC) systems considering non-equilibrium condensation

In proton exchange membrane fuel cell (PEMFC) systems, unconsumed hydrogen recirculation is enabled by utilizing an ejector, and the PEMFC system's efficiency is thereby enhanced. Apart from the structural parameters, an ejector's performance is also significantly affected by the non-equilibrium condensation phenomenon. Therefore, the ejector structural parameters' impact upon non-equilibrium condensation intensity and ejector efficiency is investigated under design conditions. Structural optimization of the ejector is performed within its operating range to uphold optimal efficiency in the presence of fluctuations in secondary flow pressure. The result shows that non-equilibrium condensation negatively affects the ejector's efficiency, but its impact diminishes with larger mixing chamber diameters and nozzle divergence angles. The optimized ejector performs best with a 2.40 mm diameter mixing chamber and an 11.0o nozzle divergence angle. On average, the optimized ejector's performance improves by 16.8%, reaching a maximum improvement of 22.8% within the effective operating range.

Operational performance parameter range in ICF propulsion theory

This paper explores the operational performance parameter range for inertial confinement fusion propulsion systems under the assumption of best case and worst case mission scenarios. This includes the spacecraft thrust, jet power and specific power. We show the derivation of the key driving equations and then simplify these with approximations for ease of domain space analysis. This includes a consideration of minimum and maximum values for jet efficiency, momentum weighting factor, nozzle divergence angle, fuel burn-up fraction, capsule mass and detonation pulse frequency. It is estimated that the range of parameter values may be of order 0.001 N–100 MN thrust, 1000 W–1,000 TW jet power, 0.01 W/kg–10 GW/kg specific power. Although this range includes values that are likely outside the realistic design space of applicability and to show this data from published designs is also examined. The analysis is considered for reaction isotopes of low mass hydrogen and helium nuclei only and does not take into account the possibility of propellant expellant augmentation, vehicle staging, design optimality or enhanced fuel reactions.

The Submerged Nozzle Damping Characteristics in Solid Rocket Motor

In this paper, the effects of the geometry of a submerged nozzle on the nozzle damping characteristics are studied numerically. Firstly, the numerical method is verified by the previous experimental data. Then, the mesh sensitivity analysis and the monitor position independence analysis are carried out. Thirdly, the effects of nozzle geometry on nozzle damping are systematically studied, and focuses are placed on the cavity size, convergent angle and divergent angle. The pulse decay method is utilized to evaluate the nozzle decay coefficient. Several important results are obtained: the submerged cavity with large volume leads to low frequency acoustic oscillations in the combustion chamber and corresponds to a small nozzle decay coefficient; then, as the nozzle convergent angle is decreased, the nozzle decay coefficient is increased. In addition, the nozzle divergent angle has a trivial effect on the nozzle decay coefficient; and lastly, the effects of the temperature on the nozzle damping capability are conducted. The results show that an increase of the working temperature leads to an increase of the nozzle decay coefficient; therefore, the damping force is increased.

Flow-visualization and numerical investigation on the optimum design of cavitating jet nozzle

Cavitating jet is widely used in drilling, rock cutting and ocean resource exploitation because of its strong erosion ability. The analysis of the relationship between the flow characteristics and the structure of cavitating jet nozzle is critical. Here, we utilized 3D printed technology and high-speed photography to design visualization experiments to analyse the impact of the variation of resonator and throat size of the organ-pipe self-resonating cavitating nozzles on the cavitation characteristics through image processing. The velocity field, pressure field and vapor volume fraction injected by the nozzle were taken as the objective functions to study the influence of different structural parameters on the cavitation effect based on FLUENT 19.0 software, and the results were compared with the experimental results. The results show that increasing the length and diameter of the resonator contributes to the occurrence of cavitation and the structure stability of the flow field. However, excessive size affects self-resonant of the nozzle and makes it difficult to form resonance effect. In this study, the optimal values of nozzle throat length and divergent angle are twice the throat diameter and 40°, respectively. This research provides an integrated research method to study the optimization of self-resonating nozzle and cavitating jet characteristics.

Effect of Structural Parameters and Operational Characteristic Analysis on Ejector Used in Proton Exchange Membrane Fuel Cell

A hydrogen ejector for PEMFC system is designed based on thermodynamic theory with considering the influence of water vapor. A CFD model is built in order to optimize the geometric parameters, comprehensively considering performance of different operating conditions. Moreover, effect of structural parameters and operating conditions on PEMFC ejector performance was studied using single-factor and multi-factor analysis methods. The single-factors analysis results show that the nozzle throat diameter, nozzle divergent angle (A), nozzle throat length (B), nozzle exit position (C), mixing tube diameter (D), mixing tube length (E) and are crucial structural parameters that affect the performance of the ejector significantly. Multi-factors analysis is carried to gain the sensitivity of the crucial parameters and further optimize performance of the ejector on PEMFC. For low current (110 A), middle current (275 A), and high current (412.5 A), the order of influence of performance were (D > A > B > C > E), (D > A > B> E > C), and (D > C > E > B > A), respectively. The optimized ejector by multi-factor analysis method has a better performance than one optimized by single-factor. This study may provide a new way of thinking for optimization of structural parameters of any PEMFC ejector with various operating condition.

Numerical analysis of the activated combustion high-velocity air-fuel (AC-HVAF) thermal spray process: A survey on the parameters of operation and nozzle geometry

WC-12Co coatings deposited by an activated combustion-high velocity air-fuel (AC-HVAF) spray process can improve surface quality and prolong the service life of parts. It is of considerable significance to quantitatively reveal the impact of process parameters on spraying behavior to improve high-quality coatings. In this study, a combustion model and a discrete phase model (DPM) are established based on the computational fluid dynamics (CFD) method. The flame flow characteristics (including pressure, temperature, velocity, and Mach number), mass fraction of the gas components, and particle flight characteristics (including temperature and velocity) are calculated. The results show that the Air/Fuel (A/F) ratio directly determines the maximum temperature of thermal spraying. When the A/F ratio remains constant, the temperature and velocity of the particles increase as the mass flow of the reactants increases. However, a higher A/F ratio and flow rate of the reactant increase the risk of particle oxidation. It is further found that a reduction in the Laval nozzle throat diameter increases the particle velocity; however, these changes do not obviously affect the particle temperature. The reduced Laval nozzle divergent angle causes an increase in the particle temperature and velocity. The longer the length of the Laval nozzle divergent part, the higher the temperature of particles. When its length is 190 mm, the particle velocity reaches the highest value.

Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet

High-pressure submerged cavitation jet is widely used in the fields of material peening, petroleum drilling, and ocean engineering. The impact performance of the jet with intensive cavitation is related to the factors such as working condition and the nozzle geometry. To reveal the relationship between the nozzle divergent angle and the jet pressure on the unsteady characteristics of the jet, high-speed photography with frame rate of 20000 fps is used to record the image of the cavitation clouds. Grayscale analysis algorithm developed in MATLAB is used to study the effects of injecting condition on the special structure, unsteady characteristics, and shedding frequency of the cavitation bubbles. The impact load characteristics of the cavitation jet with different cavitation numbers and stand-off distances are recorded using a high-response pressure transducer. It is found that the cavitation number is the main factor affecting the cavitation morphology of the submerged jet. The lower the cavitation number is, the more intense the cavitation occurs. The outlet divergent angle of the convergent-divergent nozzle also has a significant influence on the development of the cavitation clouds. In the three nozzles with the outlet divergent angles of 40°, 80°, and 120°, the highest bubble concentration is formed usinga nozzle with a divergent angle of 40°, but the high-concentration cavitating bubbles are only distributed in a very small range of the nozzle outlet. The cavities generated by using the nozzle with a divergent angle of 80° can achieve good results in terms of concentration and distribution range, while the nozzle with divergent angle of 120° has lower cavitation performance due to the lack of the constraint at the outlet which intensifies the shear stress of the jet. According to the result of frame difference method (FDM) analysis, the jet cavitation is mainly formed in the vortex structure generated by the shearing layer at the nozzle exit, and the most severe region in the collapse stage is the rear end of the downstream segment after the bubble cloud sheds off. The impact load of the cavitation jet is mainly affected by the stand-off distance of the nozzle from the impinged target, while the nozzle outlet geometry also has an effect on the impact performance. Optimizing the stand-off distance and the outlet geometry of the nozzles is found to be a good way to improve the performance of the cavitation jet.

Influence of Nozzle Type, Divergence Angle and Area Ratio on Impulse of Pulse Detonation Engine

The influence of nozzle geometry on the impulse produced by the single cycle Pulse detonation engine (PDE) was experimentally investigated. For each experiment the nozzles were attached at the end of the engine. The impulse produced by the pulse detonation engine was calculated from the measured thrust. The thrust measurement was done by sliding the engine on the central bar of the thrust stand. The main structure of the basic PDE has a detonation tube with one terminal closed, a Schelkin spiral used as deflagration to detonation device, and a thrust stand to support the structure. Stoichiometric acetylene and oxygen mixture were used as detonation mixture. Various nozzles with a range of divergent angle and area ratios were tested. The calculations of the impulse were made from the thrust pulse for the duration it lasted. The effect of the type of nozzle, divergent angle and area ratio were observed. The bell shaped nozzle with large angle of divergence produced maximum specific impulse of 80 Sec with 20° divergence angle and area ratio of 6.942; maximum impulse was produced by the bell shaped nozzle with a small area ratio of 2.969 and 10° divergence angle. The maximum total impulse obtained was 1200 N-sec.

Effect of heat transfer and geometry on micro-thruster performance

Coupled Navier-Stokes and Direct Simulation Monte Carlo (NS-DSMC) simulations of gas flow in micro-nozzles for various wall thermal conditions and geometrical aspects are presented. Micro-thrusters employed in miniature spacecraft and microsatellites experience substantial changes in wall thermal conditions. This can influence the internal boundary layer development and the exit plume structure of a micro-nozzle. These changes in flow physics differ with the nozzle divergence angle and the proximity of a similar nozzle in the cluster. Continuum solvers often fail to analyze the micro-nozzles operating in vacuum conditions as the flow in micro-nozzles experiences continuum, transitional, and rarefied regimes. Coupled NS-DSMC solver is an effective alternative that can simulate the non-equilibrium effects in a micro-nozzle flow field. A steady solution of the entire flow field has been obtained using a non-linear Harten-Lax-van Leer-Contact (HLLC) scheme based finite volume solver with a higher order slip boundary condition. Continuum breakdown regions are identified based on the gradient-length local (GLL) Knudsen number condition. This initial steady solution on the flow transition boundary is implemented in the DSMC solver as a Dirichlet boundary condition. The present computations are useful in calibrating micro-propulsion controllers to adapt to the substantial momentum changes associated with various nozzle wall thermal conditions and the proximity of similar nozzles in the cluster.

Effects of Variation of Operating Parameterson the Performance of Ejector: A Review

The purpose of this review is to analyze the representation of the ejector based on geometrical parameters like primary nozzle, mixing section and diffuser section. In the current era the ejector system is used to entrain low grade energy (secondary flow) with the help of primary supersonic flow. Different types of fluids are used for different application of ejector. The main role of supersonic nozzle is to entrain the secondary fluid at inlet in the mixing chamber. Researchers have done huge work in the field of ejector. The major parameters of mixing chamber are area, length, nozzle exit position (NXP) and nozzle divergence angle to improve the performance of the ejector without shock waves in mixing section. Diffuser is used as booster to increase the pressure. The broad scope of improvement has been seen in the nozzle and mixing section. Experimental as well as numerical based investigations have been studied to identify the performance.

Effects of orifice divergence on hollow cone spray at low injection pressures

In this work, the effects of orifice divergence on spray characteristics have been reported. Parameters such as spray cone angle, liquid sheet thickness, coefficient of discharge, break-up length, and Sauter mean diameter are greatly affected by the half divergence angle [Formula: see text] at orifice exit. An experimental investigation is carried out in which water sprays from five atomizers having half divergence angle values of 0°, 5°, 10°, 15°, and 20° are studied at different injection pressures. Image processing techniques are used to measure spray cone angle and break-up length from spray images, whereas the sheet thickness outside the orifice exit is obtained using the scattered light from a thin Nd-YAG Laser beam. Phase Doppler interferometry is also used to obtain the Sauter mean diameter at different axial locations. A few numerical simulations based on the volume of fluid method are included to obtain physical insight of the liquid film development and air core flow inside the atomizer. It is observed that the liquid sheet thickness as well as tangential and radial components of velocity at orifice exit are modified drastically with a change in half divergence angle. As a consequence, the droplet size distribution is also altered by variation in the nozzle divergence angle. The mechanism responsible for such variations in the spray behavior is identified as the formation of an air core or air cone inside the liquid injector as a result of the swirl imparted to the liquid flow.

Effect of Channel Geometry and Properties of a Vapor–Gas Mixture on Volume Condensation in a Flow through a Nozzle

A method of direct numerical solution of the kinetic equation for the droplet size distribution function was used for the numerical investigation of volume condensation in a supersonic vapor–gas flow. Distributions of temperature for the gas phase and droplets, degree of supersaturation, pressure, fraction of droplets by weight, the number of droplets per unit mass, and of the nucleation rate along the channel were determined. The influence of nozzle geometry, mixture composition, and temperature dependence of the mixture properties on the investigated process was evaluated. It has been found that the nozzle divergence angle determines the vapor–gas mixture expansion rate: an increase in the divergence angle enhances the temperature decrease rate and the supersaturation degree raise rate. With an increase or decrease in the partial pressure of incondensable gas, the droplet temperature approaches the gas phase temperature or the saturation temperature at the partial gas pressure, respectively. A considerable effect of the temperature dependence of the liquid surface tension and properties on gas phase parameters and the integral characteristics of condensation aerosol was revealed. However, the difference in results obtained with or without considering the temperature dependence of evaporation heat is negligible. The predictions are compared with experimental data of other investigations for two mixtures: a mixture of heavy water vapor with nitrogen (incondensable gas) or n-nonane vapor with nitrogen. The predictions agree quite well qualitatively and quantitatively with the experiment. The comparison of the predictions with numerical results from other publications obtained using the method of moments demonstrates the usefulness of the direct numerical solution method and the method of moments in a wide range of input data.

Supersonic flow gradients at an overexpanded nozzle lip

The flowfield of a planar, overexpanded jet flow and an axisymmetric one are analyzed theoretically for a wide range of governing flow parameters (such as the nozzle divergence angle, the initial flow Mach number, the jet expansion ratio, and the ratio of specific heats). Significant differences are discovered between these parameters of the incident shock and the downstream flow for a planar jet and for an axisymmetric overexpanded jet flow. Incident shock curvature, shock strength variation, the geometrical curvature of the jet boundary, gradients of total and static pressure and Mach number, and flow vorticity parameters in post-shock flow are studied theoretically for non-separated nozzle flows. Flow parameters indicating zero and extrema values of these gradients are reported. Some theoretical results (such as concavities of incident shock and jet boundary, local decreases in the incident shock strength, increases and decreases in the static pressure, and the Mach number downstream of the incident shock) seem rather specific and non-evident at first sight. The theoretical results, achieved while using an inviscid flow model, are compared and confirmed with experimental data obtained by other authors.

Drag reduction of supersonic blunt bodies using opposing jet and nozzle geometric variations

Passive and active flow control methods are used to manipulate flow fields to reduce acoustic signature, aerodynamic drag and heating experienced by blunt bodies flying at supersonic and hypersonic speeds. This paper investigate the use of active opposing jet concept in combination with geometric variations of the opposing jet nozzle to alleviate high wave drag formation. A numerical study is conducted to observe the effects of simple jet as well as jet emanating from a divergent nozzle located at the nose of a blunt hemispherical body. An initial discussion is presented of the complex shock wave pattern flow physics occurring when opposing jet ejected from a nozzle under various operating conditions interacts with the free stream flow. The complex flow physics that include long penetration and short penetration mode is studied in conjunction with effect on drag. The numerical setup consists of supersonic free stream flow interacting with an opposing sonic jet under varying pressure ratios. Initial computational results are validated by identifying prominent flow features as well as comparing available experimental data of surface pressure distributions. Preliminary validation is followed by the introduction of a divergent nozzle in the blunt body nose region. A series of numerical iterations are performed by varying nozzle geometric parameters that include nozzle divergent angle and nozzle length for a certain jet pressure ratio. Long penetration mode, short penetration mode as well as flow separations are captured accurately during the analysis. The results show a considerable reduction in drag by the use of a divergent nozzle. Specifically, 46% and 56% reduction in drag coefficient is achieved at pressure ratio of 0.6 and 0.8 respectively in the divergent nozzle cases as compared to the simple blunt body without any nozzle.

Experimental Study on Performance of Double-throttling Device Transcritical CO2 Ejector Refrigeration System

The double-throttling devices are adopted in the transcritical CO2 refrigeration system, and the devices are introduced in this paper. The first expansion valve is used to control the high-side pressure, and the second expansion valve is replaced by a two-phase flow ejector to recover the system expansion work. The performance of the double-throttling ejector refrigeration system is conducted experimentally, and the influence of the geometries and working conditions on the performance of the ejector and the COP is analyzed. The experimental results indicate that under a fixed working condition, with the increase in the first nozzle divergence angle, the entrainment ratio firstly increases and then decreases, but the COP has an opposite trend. As the equivalent diameter of the first throat is 2.00mm, the entrainment ratio and the COP reach the maximum value. With the increase in the outlet pressure and temperature of the gas cooler, the COP is a downward trend, and the entrainment ratio is on the rise. With the increase in the evaporation temperature, the entrainment ratio firstly increases and then decreases and the COP gradually increases, as the evaporation temperature is -1°C and -3°C, the COP and the entrainment ratio reach the maximum value respectively. And there is a certain relationship between the entrainment ratio of the ejector and the ability of the main ejection fluid entraining the suction fluid. Compared with the traditional system, the COP of the ejector refrigeration system with the double-throttling devices is higher and the maximum increase is up to 32.4%.

Aerodynamics Numerical Study on Vapor Flowing of the Oil Booster Pump

The pumping power of oil booster pump is the vapor jet stream that determined pump performance. The key importance is the study of vapor flowing characteristics, and also is the method of improvement pump structure and saving energy. The aerodynamics is adopted to study the oil vapor flowing characteristics. The study shows that it should adopted the higher oil boiler pressure in order to increase the density of the oil vapor, and so it can be benefit to pumping gas in 1Pa—10Pa. The nozzle divergence angle and divergence rate also should be increased in order to increase the oil vapor velocity and kinetic energy, and so increased the pumping rate on 0.1Pa. Increasing divergence angle and divergence rate of the first nozzle at constant compression ratio, the upper bottom of jet stream can be moved up, and the eject stream thickness was increased. In other word, increasing the compression ratio at constant eject stream thickness, the oulett pressure was increased. When the pump was operated at higher pressure, it should be decreased compression ratio of first stage. The main pump body was also designed to prominence chamber in order to increase the pumping rate.

Simulation of interference effects in particle streams following impact with a flat surface: Part II. Parametric study and implications for erosion testing and blast cleaning

In a companion paper [Simulation of interference effects in particle streams following impact with a flat surface. Part I. Theory and analysis, submitted for publication], a computer simulation capable of describing the interference between an incident stream of spheres and those rebounding from a flat surface was presented. In the present paper, the model is used to study the effect of the following parameters on the severity of inter-particle collisions: stream angle of incidence, nozzle divergence angle, incident particle velocity, particle size, particle flux, particle–particle and particle–surface impact parameters, and standoff distance. Useful dimensionless parameters are identified and their significance is characterised using a sensitivity analysis. A detailed parametric study of the most important input parameters revealed that interference effects strongly depend not only on flux, but also on angle of attack, standoff distance, coefficient of restitution between particle and surface, and nozzle to particle radius ratio. It is thus important that a full description of experimental conditions in erosion tests be given. Finally, a series of non-dimensional results was presented that can be used to assess the reduction, due to interference effects, in stream power from that available at the nozzle exit. This can be used to estimate how coverage in shot peening, and erosive power in erosion testing, will be affected by interference effects.

Simulation of interference effects in particle streams following impact with a flat surface: Part I. Theory and analysis

The interference between an incident stream of spheres and those rebounding from a flat surface is described using a computer model. The model was capable of examining the effect of the following parameters on the severity and frequency of inter-particle collisions: stream angle of incidence, nozzle divergence angle, incident particle velocity and flux, particle size, particle–particle and particle–surface impact parameters, and stand-off distance. The collision dynamics for systems consisting in excess of 10 4 particles were obtained. Frictionless inter-particle collisions were assumed, but friction for particles impacting the surface was considered. For all collisions, a coefficient of restitution model of impact behaviour was assumed. Dimensionless parameters used to aid in the presentation of the results were identified, and a companion paper [Simulation of interference effects in particle streams following impact with a flat surface. Part II. Parametric study and implications for erosion testing and blast cleaning, submitted for publication] presents a parametric study of their role in erosion testing and blast cleaning processes.

Nozzle Performance Modeling

A polytropic analytical equation system for the internal e ow of nozzles and ducts has been developed by a solution to the combined friction/area change compressible e ow equations. Validation of the system is sought through comparison with experimental data and numerical simulations using FLUENT in the prediction of the performances of two conventional axisymmetric nozzles. Analytical performance coefe cient equations have been developed from the polytropic equation system for this purpose. The predictions with consideration of nozzle divergence angle and roughness are presented for the e rst time. It is demonstrated that the analytical model well matches the experimental data after the throat is fully choked. The numerical and analytical results are compared and discussed. Such an analytical model is extremely useful in bridging the gap between accepted empirical parameters, such as the friction factor and performance factors, and analytical performance modeling. In aircraft nozzle simulations, where empirical data may not be available, this model provides more precise simulation capability especially applicable to modern thrust-vectoring nozzles.

Performance Analysis of Secondary Gas Injection into a Conical Rocket Nozzle

The effects of injection location of secondary jet and nozzle divergent cone angle on the performance of secondary gas injection for thrust vector control (SITVC) were numerically investigated. Three-dimensional Reynolds-averaged Navier-Stokes equations with an algebraic turbulence model solved the complex three-dimensional nozzle flows perturbed by the secondary gas jet. The numerical code was properly validated by experiment. The results showed that downstream secondary jet injection and smaller nozzle divergent cone angles lead to higher efficiencies over a wide range of pressure ratios. The occurrence of reflected shock waves severely lowers SITVC propulsion performance. Upstream jet injection is more effective in a narrow range of deflection.