Slot Nozzle Research Articles

Flow and Heat Transfer Characteristics of Swirling Impinging Micro-Slot Jets by Adopting Circular Ribs in the Wall Jet Region

The flow and heat transfer behaviors of swirling impinging micro-slot jets using circular ribs in the wall jet region have been numerically studied. In this study, the total spiraling length was defined as 290 mm due to the two complete revolutions of the helix generated at a slot nozzle thickness of 1.0 mm. The range of circular rib radius ratios varied from 1 to 4 under the jet-to-target spacing ratio at 2 and 4. Predictions were made using the turbulent kinetic energy-epsilon model at Reynolds numbers ranging from 5000 to 20000. The results showed that the heat transfer enhancement on the target wall depended on the circular rib radius ratios. The jet flow at a low circular rib radius ratio generated recirculating ambient fluid behind the rib zone and a minuscule vortex within a circular rib region. At a high ratio, the jet’s potential flow directly affected the top rib surface and generated secondary flows in the circular rib. The heat transfer rate tended to increase as the Reynolds number increased. The average heat transfer value at a circular rib radius ratio of 3 became the best, up to 18.1% for jet-to-target spacing of 2. Whereas above 14.8% average value at a circular rib radius ratio of 1 in the case of jet-to-target spacing of 4 gained the highest.

Effect of Jet-to-Target Spacing on Flow and Heat Transfer Characteristics for Swirling Impinging Micro-Slot Jets

The influence of jet-to-target spacing on flow and heat transfer behaviors for swirling impinging micro-slot jets has been extensively studied. In this study, two complete revolutions of the generated helix under the slot nozzle thickness of 1.0 mm constrained the total spiraling length to 290 mm. The range of jet-to-target spacing varied from 1 to 6. The turbulent kinetic energy-epsilon model was employed to make predictions at Reynolds numbers from 5000 to 20000. The results showed that the heat transfer enhancement on the target wall depended on the pacing between the jet and the target. This is the jet flow structure exhibited a notable intensity of high-velocity vortices at the low jet-to-target spacing, whereas the jet flow impingement was abruptly reduced at the high jet-to-target spacing. The heat transfer rate also tended to increase as the Reynolds number increased. In addition, when the jet-to-target spacing was at 1, the average heat transfer value was between 32.9% and 54.2% higher than in other conditions due to high fluid acceleration.

Effect of flow on heat transfer between a translating plate and gas discharged from multiple inclined slot nozzles

The presented study aims to reveal flow and heat transfer characteristics as a translating aluminum plate is impinged by high-temperature gas discharged from inclined slot nozzles. The computational fluid dynamics (CFD) and the fluid-solid interaction (FSI) techniques were used to simulate the impingement process. A comprehensive comparison of flow, heat transfer, and structural parameters was implemented. The results indicate that twin vortices are produced between the two inclined nozzles. When the velocity ratio increases from 0.1 to 1.0, the vortex at the left expands, while the right one is compressed. Meanwhile, average Nusselt number and the pressure coefficient exhibit opposite variation tendencies. The highest average pressure coefficient of 0.45 arises at a velocity ratio of 0.5. As the plate-nozzle distance increases, characteristic flow structures are developed, and the distributions of temperature and the pressure coefficient are uniformized. The maximum Nusselt number decreases from 473 to 266 when the nondimensional plate-nozzle distance increases from 4 to 8. Large deformation occurs at the middle part of the plate. High equivalent stress is concentrated at the front and rear ends of the plate, which is insensitive to the velocity ratio and the plate-nozzle distance.

Numerical research on kerosene/hydrogen/air rotating detonation engines with discrete injection strategies

The two-dimensional simulation of two-phase rotating detonation engines commonly adopts the nozzle–wall configuration, which is inconsistent with the real configurations in experiments. In the annular slot–nozzle structure, the oxidant is completely injected into the annular gap, whereas the fuel is partially injected into the nozzle hole, which is closer to the real operation condition. In this study, a gas–liquid two-dimensional numerical investigation was conducted to explore a more accurate operating condition with a discrete injection configuration. The effects of the kerosene/hydrogen injection area ratio and hydrogen equivalence ratio on the propagation mode and operating performance were investigated. The simulation results show that the kerosene droplet/hydrogen/air gas–liquid two-phase rotating detonation wave exhibits different propagation modes depending on the hydrogen equivalence ratio. When the hydrogen equivalence ratio (φH2) is 0, the detonation wave cannot be successfully initiated. When φH2 is increased to 0.2 and 0.5, a single-wave propagation mode is generated. When φH2 is 1, a double-wave propagation mode is produced initially in the combustion chamber and is subsequently converted into the deflagration mode. The flow field structure, velocity performance, and propulsive performance in the detonation combustion chamber are analyzed. It was found that an appropriate amount of hydrogen addition to the liquid kerosene detonation can aid in stabilizing the propagation of the detonation wave and improving the performance of the detonation engine.

Controlling Thin Film Morphology Formation during Gas Quenching of Slot-Die Coated Perovskite Solar Modules.

Transferring record power conversion efficiency (PCE) >25% of spin coated perovskite solar cells (PSCs) from the laboratory scale to large-area photovoltaic modules requires significant advances in scalable fabrication techniques. In this work, we demonstrate the fundamental interrelation between drying dynamics of slot-die coated precursor solution thin films and the quality of resulting slot-die coated gas-quenched polycrystalline perovskite thin films. Well-defined drying conditions are established using a temperature-stabilized, movable table and a flow-controlled, oblique impinging slot nozzle purged with nitrogen. The accurately deposited solution thin film on the substrate is recorded by a tilted CCD camera, allowing for in situ monitoring of the perovskite thin film formation. With the tracking of crystallization dynamics during the drying process, we identify the critical process parameters needed for the design of optimal drying and gas quenching systems. In addition, defining different drying regimes, we derive practical slot jet adjustments preventing gas backflow and demonstrate large-area, homogeneous, and pinhole-free slot-die coated perovskite thin films that result in solar cells with PCEs of up to 18.6%. Our study reveals key interrelations of process parameters, e.g., the gas flow and drying velocity, and the exact crystallization position with the morphology formation of fabricated thin films, resulting in a homogeneous performance of corresponding 50 × 50 mm2 solar minimodules (17.2%) with only minimal upscaling loss. In addition, we validate a previously developed model on the drying dynamics of perovskite thin films on small-area slot-die coated areas of ≥100 cm2. The study provides methodical guidelines for the design of future slot-die coating setups and establishes a step forward to a successful transfer of solution processes towards industrial-scale deposition systems beyond brute force optimization.

The mixing field and flame structure near the reaction zone of turbulent planar flames at different levels of mixture inhomogeneity

Turbulent flames with compositionally inhomogeneous mixtures are commonly used in many combustion systems. In this work, turbulent planar jet flames issued from a concentric flow slot burner, CFSB, were used to study the impact of mixture inhomogeneity near the flame sheet. The CFSB burner can control the mixing inhomogeneity by changing the mixing length “L” between the concentric fuel and air slot nozzles. At various levels of mixture inhomogeneity, the mixing field, presented by mixture fraction, Z, distribution, and the flame structure was investigated via simultaneous Rayleigh and OH-PLIF imaging technique. Our previous study investigated the mixing field immediately downstream of the burner exit in non-reacting conditions. The PDFs of Z showed that the mixing field covered a wide range of mixture fractions, where the high flame stabilization occurred when a large portion of the PDF(Z) was located within the fuel flammability limits. This work showed that further downstream, the highly stabilized flames were also obtained when the range of fluctuations in the mixture fraction was close to the stoichiometric mixture fraction. Moreover, plotting the mixing field using the scatter plot within the mixing regime diagram for various flame conditions showed that the mixing field downstream of the burner exit consistently follows the mixing diagram classification. Moreover, a close inspection of the flame structure showed that the flame sheet varies from thick, and corrugated at a low and high levels of mixing to thin flame sheet but less corrugated and that at a particular mixing normalized length L/D = 7. The flame corrugation data showed that the flame stability occurs at a minimum corrugation factor.

Converging Jet Impingement for Enhanced Liquid Cooling

Abstract Jet impingement cooling is an advanced thermal management technique for high heat flux applications. Standard configurations include single, axisymmetric jets with orifice, slot, or pipe nozzles. This choice in nozzle shape, number of jets, and jet inclination greatly influences the turbulence generated by fluid entrainment due to differences in initial velocity profiles and location of secondary stagnation points. Regarding high power electronics with integrated jet impingement schemes, turbulence, and heat transfer rates must be optimized to meet the extreme cooling requirements. In this study, the heat transfer rates of dual inclined converging jets are investigated experimentally. Emphasis is placed on the comparison of different jet schemes with respect to geometrical parameters including nozzle pitch, incline angle, and nozzle-to-target plate spacing. A parametric experimental investigation is performed as a point of comparison using a modular, additively manufactured jet setup. Computational simulations are used to evaluate the effect of jet configuration on stagnation pressure associated with maximum heat transfer rates, and an empirical Nusselt number model is provided. The results show the effects of convergence height on jet behavior and the associated impacts on heat transfer.

Investigation of the Thermal Characteristics of a Novel Laser Sintering Machine for Additive Manufacturing of Continuous Carbon Fibre-Reinforced Polymer Parts.

This paper presents the thermal analysis of a novel laser sintering machine for additive manufacturing of continuous carbon fibre-reinforced polymer parts. The core element of this machine is a fibre integration unit with a heated fibre nozzle. With the help of an additional heat source, which is mounted on the bottom side of the fibre integration unit, the temperature of the powder bed surface is kept within the sintering window of the PA12 material used in the investigations. Different heat source variants differing in shape and material were analysed experimentally concerning the heat distribution achieved within the powder bed surface using an infrared camera. Based on the best-rated variant showing the most homogeneous heat distribution, operating points for successful continuous fibre integration were experimentally identified. An aluminium plate with a closed fibre nozzle slot and symmetrical surface heating power has proven to keep the powder bed surface reliably warm. Compared to the initial state, the resulting increased uniformity of heat-affected zones created by the heated fibre nozzle HAZ was evaluated by fabricating a horseshoe part made of PA12. Furthermore, a CCFRP flat pedal for mountain bikes demonstrated roving integration's process reliability and reproducibility.

Experimental and numerical investigation on design parameters of slot nozzles

Slot nozzles are altitude compensation nozzles. In the overexpansion mode, slots in the expansion section can affect the flow separation and improve the thrust. In this study, cold-flow experiments and numerical simulation are performed to study the design parameters of slot nozzles. The effects of slot location, number, and vented area on the flow field, thrust, and average specific impulse of the first-stage rocket are investigated. The results show that the thrust increases due to two reasons: the advance of the separation position and the rise of wall pressure in the recirculation zone. Moreover, the slot location is more important than other parameters in the design of slot nozzles. Only when a slot is close to the flow separation point, the influence of the slot on the flow field is apparent, thus, the thrust significantly and efficiently increases. The performance of the first-stage rocket can be significantly improved by replacing the traditional bell nozzles with slot nozzles. The average specific impulse increase of the space shuttle solid rocket booster and first-stage rocket of the nano launch vehicle (NLV) is 5.1 s and 7.9 s, respectively; further analysis of NLV shows that its payload can be increased by 16.1%.

Hydrodynamic characteristics of a new thrust vectoring ducted propeller with slotted nozzle

A thrust vectoring ducted propeller with slotted nozzle is a new approach for vector propulsion that can produce lateral forces and torques, leading to the ability of manipulating the autonomous underwater vehicle (AUV) for various movements. In this work, the geometric model of the thrust vectoring ducted propeller is designed based on slotted nozzle. The nozzle of the ducted propeller is slotted and then divided into several pieces. Divided auxiliary nozzles are deflected to redirect the outflow, achieving thrust vectoring. The key feature parameters of the slotted nozzle are extracted. The performance of the thrust vectoring ducted propeller is evaluated using Computational Fluid Dynamic (CFD) method. Different parameters of the slotted nozzle are set to evaluate the influence on the thrust vectoring capability of the ducted propeller. Through comparison, a thrust vectoring ducted propeller model is determined. Hydrodynamic characteristics including thrust vectoring performance, scale effect and vertical-horizontal interactions of the thrust vectoring ducted propeller are analyzed. It is shown that the ducted propeller with slotted nozzle at full capacity has a higher vector ratio and lower thrust loss than ideal tilted thruster with a maximum tilt angle of 40°. For high Reynolds (Re) number working conditions, all forces and torques including vector thrust can be nondimensionalized into hydrodynamic coefficients related to advance ratio J. At lower Re number working conditions, thrust vectoring capability improves in a certain extent. Interactions between perpendicular directions are caused by the counterclockwise rotation of the propeller. The pattern is quite clear and can be quantified. The performance of the thrust vectoring ducted propeller is verified through towing tank experiment. All the results show that the ducted propeller with slotted nozzle can be considered controllable with good thrust vectoring capability.

Numerical simulation of propulsive aerodynamic profiles

The problem of creating high-lift propulsive aerodynamic is considered. A method was developed for constructing an aerodynamic profile by solving the inverse problem of aerodynamics. The dependence of the lifting force of this profile on the volume of air sucked from its upper surface and from the angle of attack is studied. The profile under study was developed on the basis of the well-known Griffin/Goldschmid profile with air suction at the upper critical point. Three aerodynamic profiles have been developed. The first profile has a flat lower surface to obtain the ground effect. The second profile is similar to the first but has a slit nozzle near the trailing edge. The third profile is similar to the second but has a non-flat bottom surface and increased thickness. The solution of the inverse problem of aerodynamics was used to construct aerodynamic profiles within the model of an ideal gas. The pressure distribution on the upper part of the profile, its construction height and the range of angles of attack are from 0° to 16°, as well as the degree of rarefaction up to 0.5 atm in the gap through which the air was taken were set. For the second and third profiles, the ratio of the amount of air ejected through the nozzle to the amount of air taken from the upper surface of the profile was set. This ratio ranged from 50 % to 200 %. Numerical calculations were performed for each variant using the Spalart-Allmaras turbulence models and the Transition Shear Stress Transport (SST) and Langtry model. The parameters of the turbulence models were adjusted according to known reference data. The Reynolds number was in the range of 1.5·105–1.5·106. The profiles have a high lift coefficient Cy = 3–3.4 which is achieved when creating a vacuum in the air intake of 0.5 atm. Cy depends on the angle of attack almost linearly up to the maximum values. The greater the air flow through the slot nozzle, the greater is the Cy at a vacuum in the air intake of 0.5 atm. Significance for practical application. The developed profiles have a large thickness and create traction. These profiles are convenient to use in aircraft with large internal volumes, for example, those running on hydrogen fuel.

Study of 3D Printed Agricultural Slotted Spray Nozzles

Study of 3D Printed Agricultural Slotted Spray Nozzles

Numerical simulation of the nozzle configuration in strip casting process

This work examines the design of nozzles in continuous strip casting process. Three-dimensional (3D) simulations of steady turbulent (k-ε) flow are done at the upper part of the mould using a finite-volume (CFX) model. This is performed for different inlet systems, including the inlet nozzle jets with a free stream, the submerged nozzle jets, the slot inlet system, and the slot-submerged inlet system. The resulting heat flux to the solidifying shell has also been studied. Numerous operating parameters are examined, including the shape, size, position, and thickness of the ports and the bottom geometry. It is found that different inlet nozzle configurations change the molten flow and heat patterns, mainly in the upper region of the mould. By applying the slot nozzle inlet system, turbulence and values of the averaged velocity field in that area decrease significantly.

Assessing Phytosanitary Application Efficiency of a Boom Sprayer Machine Using RGB Sensor in Grassy Fields

The systematic use of plant protection products is now being called into question with the growing awareness of the risks they can represent for the environment and human health. The application of precision agriculture technologies helps to improve agricultural production but also to rationalize input costs and improve ecological footprints. Here we present a study on fungicide application efficiency and its impact on the grass quality of a golf course green using the free open-source image analysis software FIJI (Image J) to analyze ground RGB (high-resolution digital cameras) and multispectral aerial imagery in combination with experimental data of spray pressure and hydraulic slot nozzle size of a boom sprayer machine. The multivariate regression model best explained variance in the normalized green-red difference index (NGRDI) as a relevant indicator of healthy turfgrass fields from the aerial, ground, and machine data set.

An overview of planar flow casting of thin metallic glasses and its relation to slot coating of liquid films

Planar flow casting (PFC) is a method that can be used to make thin, long, and wide metallic alloy foils by extruding molten liquid through a nozzle slot and immediately quenching on a moving roller. The quenching rates are high enough that amorphous metallic glasses may be formed that have many desirable properties for a wide variety of applications. This paper reviews how PFC processes were developed, examines the typical operability range of PFC, and reviews the defects that commonly form. The geometrical similarities between PFC and slot coating process are apparent, and this paper highlights differences between the operability ranges of both processes.

Параметрическое исследование влияния режимных и геометрических факторов на коэффициент камеры ЖРД со щелевой форсуночной головкой

The creation of advanced spacecraft requires developing new and improving existing now liquid-propellant rocket engines. In this case, one of the decisive factors determining their perfection is the design of the nozzle head of the combustion chamber, as well as the adopted scheme of mixing and burning rocket fuel. Thus, the optimization of the geometric and operating parameters of the combustion chamber is an urgent problem, which can be solved using both experimental and computational methods. The use of the latter can significantly reduce the volume of expensive bench tests. The article describes the study of a liquid-propellant engine chamber with a slotted nozzle head, in particular, the effect of the reduced length on the efficiency of the working process, assessed by the chamber coefficient. A mathematical model of the working process behaviour in the combustion chamber of a liquid-propellant rocket engine on oxygen-kerosene fuel components has been compiled. An algorithm for solving the equations of the mathematical model for the studied mixture formation scheme has been developed. Parametric calculations were performed and the main factors influencing the characteristics of the working process in the combustion chamber of a liquid-propellant engine with a slotted nozzle head were determined. Comparison of the calculation results according to the proposed method and the available results of bench tests showed their good convergence.

CFD analysis of jet flows ejected from different nozzles

AbstractNozzles are widely used to control the rate of flow, speed, direction, mass, shape and pressure of the stream in connection with many different engineering applications. This paper presents the performance predicted by a computational fluid dynamic (CFD) model, which are 3D models that utilize parametric analysis, realizable k-epsilon turbulence models and experimental measurement for a jet. Jet flows are ejected from three different slot nozzles: round-shaped nozzle, rectangular-shaped nozzle and 2D-contoured nozzle. In this numerical study, velocities of free jets have been predicted for different axial distances from the nozzle exit in the range of $0.2\le z/B\le 12$ when center velocity at the nozzle exit. CFD simulation results are compared to experimental results from literature. These results are consistent with the existing experiments.

Experimental study of external lateral flow effects on turbulent isothermal upward/downward slot jets impinging inside an open cavity

In this work, the flow within an open cubical cavity with an inlet vertical planar jet exposed to an external lateral flow is studied experimentally using stereoscopic time-resolved particle image velocimetry (TR-PIV). The turbulent structure in the near field of the planar jet issuing perpendicularly from a rectangular slot nozzle is evaluated for both vertically upward and downward directions of the discharged jet. For both flow configurations, the jet discharge rectangular nozzle spans 30% of the cavity span leaving a clearance between the jet edge and sidewalls. The working fluid is water, and the complex dynamics of the three-dimensional (3D) flow field is investigated for fixed lateral flow Reynolds number of Re=3000 and three nozzle exit Reynolds numbers based on the mean streamwise exit jet velocity and nozzle hydraulic diameter of Rej=1500, 3000 and 5000. The spatial development and structure dynamics of the shear interface instability are analyzed in planes normal to the cavity roof. Flow visualization images of the mean and fluctuating velocity, vorticity and shear strain rate distributions are obtained for upward and downward directions of the slot jet, and spectral analysis of the oscillating instability is performed to describe and quantify the strong shear layer interactions that take place between the discharged eddies of the splitting jet and the external lateral flow.

RESEARCH OF JET PRIMARY CONVERTERS OF JOINT POSITION WHEN WELDING THIN-WALLED PRODUCTS

The main types of primary jet pneumatic converters used in argon-arc welding of thin-walled products with a thickness of no more than 0.6 mm are considered. Were investigated the static characteristics of pneumatic converters with cylindrical and slotted nozzles. During the analysis of the results, the most suitable pneumatic transducer was selected, which has the highest sensitivity.

Heat transfer and fluid flow characteristics of a turbulent wall jet with a wavy wall

The fluid flow and heat transfer characteristics of a turbulent wavy wall jet have been studied numerically using the low Reynolds number model. The three low Reynolds number models, Realizable, RNG and SST are used for code validation with the experimental results present in the literature for the plane wall jet. The best suited model is used further to study the wavy wall jet. The sinusoidal profile (y=amplitude*sin(2ΠNlx) has been used for the wavy wall, where N is total number of cycles and l is total length of wavy wall. In order to study the influence of amplitude on heat transfer and flow behavior, the wavy wall amplitude has been changed from 0 (plane wall) to 0.8 at an interval of 0.1 and number of cycles kept 10 for all the cases. The Reynolds number of heated jet is kept 15000 by using a slot nozzle of height 20 mm and exit velocity 10.95 m/s. The flow separation and re-circulation zone are studied with the help of pressure gradient (dP/dX) and streamwise velocity gradient (dU/dY) for each case. The results show that the flow remains attached till 0.3 amplitude after that flow gets separated. It is found that for amplitude 0.4, 0.5, 0.6, 0.7 and 0.8, separation starts for the first time at X=56.4,X=41,X=26.3,X=25.9 and X=25.5. The area of re-circulation zone is found to increase as the amplitude of wavy surface increases from 0.4 to 0.8. Also, the maximum streamwise velocity is found to increase with the increase in the amplitude of the wavy wall. These characteristics influenced the average Nusselt number drastically. The average Nusselt number is on the higher side as compared to the case of a plane wall. However, the trend is not monotonic; it increases till amplitude 0.7 and then it decreases. A maximum increase of 19.08% is observed for the wavy wall with amplitude 0.7. The thermal hydraulic performance (THP) is increased by 5.3% for amplitude 0.8 with respect to plane wall jet.