Slot Nozzle Research Articles

Сравнение вариантов литиевого дивертора для токамака ДЕМО-ТИН

For the DEMO-FNS tokamak being developed in Russia, the choice of the divertor concept with evaporating liquid lithium is discussed, which meets the requirements for removing the heat load from the peripheral plasma and provides an acceptable level of change in the ionic composition of the core plasma. The paper presents the results of numerical modeling and optimization of divertor parameters with several chambers partitioned by slotted nozzles. The parameters of lithium fluxes flowing into the peripheral layer are estimated for the temperature range of the divertor chambers from 500 to 1000 K under gas-kinetic and molecular flow regimes of lithium vapor from the divertor. The fulfilled analysis of processes that reduce the outflow of lithium from the chambers and its penetration into the core plasma volume inside the separatrix showed that sectioning effectively reduces the Li fluxes to acceptable levels of ~ 1020 atoms per second.

Design of a synthetic jet actuator for flow separation control

This paper describes the development of a piezo-electric synthetic jet actuator (SJA) of the AFLoNext project. Active flow—loads and noise control on next generation wing (AFLoNext) is a project within European Union’s 7th Framework Program. One of the main project goals is the application of active flow control (AFC) techniques, such as SJAs and pulsed jet actuators (PJAs) in two different application scenarios to evaluate the potential benefit for retrofit of current aircraft and also for future aircraft designs. This paper is focusing on the SJAs. For large-scale wind tunnel testing, an actuator panel with 84 SJAs including the drive electronics system was designed and pre-tested in a laboratory environment. The performance exceeds 100 m/s with outlet nozzles of 2.5 mm diameter and a span wise clearance of 10 mm. A second actuator design was prepared for the application on the outer wing region and was investigated in a harsh environmental test campaign. Two span wise rows of five actuators were integrated in a panel with 10 × 0.5 mm2 slotted outlet nozzles. With this design also velocities exceeding 100 m/s were measured. The actuators withstand different harsh environmental conditions including extreme temperature, rain, mechanical vibration and shock. With the results of the project, a technology readiness level (TRL) evaluation will conclude the maturity of the technology. Depending on the final test and evaluation results, achievement of TRL4 is expected.

Horizontal Single Belt Casting of Thin Strips of an Advanced High Strength Steel (Fe–21%Mn–2.5%Al–2.8%Si–0.08%C wt%)

This research presents numerical modeling and experimental results on thin strips of Fe–21%Mn–2.5%Al–2.8%Si–0.08%C wt% steel, obtained using the horizontal single belt casting (HSBC) process. The free stream of the molten metal, exiting from a nozzle slot, was observed to be highly unstable and nonuniform, after interacting with a 30° inclined refractory plane of a delivery system. However, increasing the inclination of the refractory plane to 45°–60° allows the falling molten metal free stream to become much more stable and less fluctuating. In addition, the molten metal can undergo a hydraulic jump when impacting and flowing down these inclined refractory planes. These hydraulic jumps result in the generation of free surface waves, which travel further downstream. Fortunately, these instabilities are not usually detrimental to the surface quality of the casting, as they are rapidly damped, to disappear within a short distance, prior to solidification. The types and numbers of solid phases then forming for this steel, under the relevant Scheil cooling conditions, are determined using FactSage software. The surface roughness of the cast strip was evaluated using a Nanovea 3D surface profilometer. Microstructures of the cast and heat‐treated strips were determined using Optical and Electron microscopes.

Experimental Study on Local Heat Transfer during Quenching Process by Slot Nozzles

Quenching is widely used in industrial applications. The heat is transferred from the ingots by spray or jet cooling at the secondary cooling zone. In this research work, the effort is focused on the influence of jet inclination on heat transfer in the boiling process, as well as the influence of heat transfer rate by changing the jet velocity through experimental work using Nicrofer sample under 850 ˚C. Different angles of the jet (25°, 45°, 65°, 90°) and flow velocities (3.5 m/s, 4.8 m/s, 7.8 m/s, 12.0 m/s) were arranged in these experiments respectively. The results indicated that due to the strong cooling effect of jet quenching the Leidenfrost point was not captured. Both the jet angle and jet velocity played important roles in promoting the cooling process. The smaller the jet angle, the faster the quenching rate. The angle of 25° presented the most optimum cooling effect. The higher the jet velocity, the shorter the cooling time. For the maximum jet velocity in this experiment v=12.0m/s, DNB-temperature even was not identified.

Three-dimensional deflecting oscillation of turbulent planar opposed jets confined in an open cavity under crossflow

In this work, the flow dynamics of two isothermal turbulent opposed water jets issuing from rectangular slot nozzles and confined inside an open cubical cavity with vertical crossflow in a rectangular duct are studied experimentally using time-resolved stereo particle image velocimetry. The turbulent structure and the deflecting oscillation of the colliding jets have been investigated for fixed nozzle separation and a crossflow Reynolds number of 3000 for three jets’ Reynolds numbers of Rej = 1500, 3000, and 5000. The probability density function of the fluctuations for the three nondimensional velocity components measured at the mean impingement height of the jets has been calculated for three different positions along the cavity span. The experimental results confirm that as Rej increases, departure from Gaussian behavior has been noted, with stronger skewness and larger scatters observed for Rej = 5000. The oscillation dynamics of the flapping jets has been characterized and examined with high spatial and temporal resolution by identifying phase-averaged velocity and vorticity fields and Reynolds stresses at several specific phases. Analysis shows that the value of Rej plays a significant role in the motion and behavior of the switching jets. A proper orthogonal decomposition (POD) analysis of the coherent structure organization of the turbulent flow has been performed to construct a reduced-order model of the turbulent flow. The results show that the first four POD modes contain about 17% of the total kinetic energy (the first 120 modes up to 79%) and that the complexity of the most energetic flow structures increases with an increase in the Rej number.

Open manifold microchannel heat sink for high heat flux electronic cooling with a reduced pressure drop

To meet the intensifying demands of electronics cooling the current study proposes an open manifold microchannel heat sink, which substantially reduces the pressure drop of a conventional manifold microchannel heat sink while retaining a low thermal resistance, thin profile (< 2 mm) and planar geometry suited to microfabrication. The open heat sink achieves this by eliminating ineffective nozzle constrictions, specifically by removing channel walls beneath the slot nozzle. Two three-dimensional conjugate heat transfer models are used, including a single microchannel or a single manifold channel pair with hundreds of interconnecting microchannels. The performance of the open geometry is compared to an unmodified baseline geometry. In the microchannel model, the open case showed ideal pressure drop reductions of 45 % to 75 % with a negligible change to thermal resistance, at flow rates between 0.2 L/min and 1.0 L/min. Chamfering the tips of the microchannel walls show similar trends, although to a lesser degree. In the manifold model, the open case showed pressure drop reductions of 25 %, with thermal resistance slightly decreasing at flow rates below 0.58 L/min (-4 % to 1 %) and increasing at flow rates above 0.70 L/min (11 % to 21 %). These changes in thermal resistance were attributed to flow maldistribution, which may be alleviated through optimisation of the manifold convergence profile. At a flow rate of 1.32 L/min, the open geometry achieved a thermal resistance of 0.120 cm2K/W with a pressure drop of 10.3 kPa.

An experimental study on two-phase characteristics of vertical injection of gas through a slot nozzle into a liquid bath

Two-phase flow characteristics of gas injection through a slot nozzle into a liquid bath were studied experimentally. A dual-sensor electrical probe measurement system was used to obtain the distributions of multiple two-phase flow parameters. Measurements were conducted under various gas flow rates, nozzle widths and at different planes vertical to the slot nozzle. It is found that the void fraction, interfacial area density and bubble frequency show peak value in the nozzle center and decrease rapidly away from the nozzle exit. Both the void fraction and interfacial area density increase drastically with increasing gas injection rates, while the bubble frequency remains almost unchanged. However, the effects of two different nozzle widths (0.1 mm and 0.5 mm) on the above three parameters are not significant. As the measurement plane deviates from the center plane vertical to the slot nozzle, all the above three parameters show slight decreasing trends indicating the bubble plume is contracting to the nozzle center downstream. For the measurement zone 15 mm above the nozzle exit, the apparent bubble diameter and velocity remain almost constant in the whole flow field for each flow configurations. Moreover, good self-similarities were demonstrated for void fraction, interfacial area density and bubble frequency, with their profiles being able to collapse into a Gaussian function.

Flow structure and heat transfer analysis of the floatation nozzle with a moving wall

PurposeThis study aims to investigate the effects of different surface-to-jet velocity ratios (Rsj) on the flow structure and the heat transfer of the floatation nozzle under different ratios (h/w) of the separation distance (h) to the slot width (w) and the differences of the flow structure and the heat transfer between the floatation nozzle and the slot nozzle.Design/methodology/approachThe Nusselt number (Nu) and the pressure distribution of the floatation nozzle with a stationary wall are measured. Then the experimental results are used to validate the numerical model. Finally, a series of numerical simulations is carried out to achieve the purpose of this study.FindingsThe flow structure and heat transfer differences between the floatation nozzle and the slot nozzle are clarified. The floatation nozzle has more than 18 times the floatation ability of the unconfined slot nozzle. The Nu and pressure distributions of the floatation nozzle are experimentally measured. The effects of wall motion on the Nu and pressure distributions are identified.Originality/valueThe effects of the wall motion on the flow structure and the heat transfer of the floatation nozzle, and the differences between the floatation nozzle and the slot nozzle are first obtained. Therefore, it is valuable for engineers in engineering design of the floatation nozzle.

Numerical Modeling of Transport Phenomena in the Horizontal Single Belt Casting (HSBC) Process for the Production of AA6111 Aluminum Alloy Strip

In this research study, numerical modelling and experimental casting of AA6111 strips, 250 mm wide, 6 mm thick, was conducted. The velocity of the molten AA6111 alloy at the nozzle slot outlet was raised to 2 m/s, whilst the belt speed was kept at 0.3 m/s. The numerical model demonstrates considerable turbulence/fluctuations in the flow of the molten AA6111 alloy in the HSBC process, rendering its free surface highly non-uniform and uneven. These discontinuites in the flow resulted from the sudden impact of molten metal onto the inclined refractory plane, and then onto the slowly moving belt. However, it has been determined that these surface variations are rapidly damped, and as such are not detrimental to final strip surface quality. Any surface perturbations remaining can be eliminated via hot plastic deformation. The experimental findings are in accordance with the model predictions. Furthermore, at high metal heads inside the delivery launder, the molten metal was observed to be flowing inwards towards the center of the strip, thereby filling the centre depression region, formed otherwise. The model predictions were validated against experimental findings. A surface roughness and microstructural analysis was also conducted to determine the surface and bulk quality of the as-cast strip.

Numerical modelling and experimental casting of 17%Mn–4%Al–3%Si–0.45%C wt-% TWIP steel via the horizontal single belt casting (HSBC) process

ABSTRACT This paper presents optimum operating parameters for the production of thin strips of 40 mm in width and ∼4 mm in thickness of Fe–17%Mn–4%Al–3%Si–0.45%C wt-% TWIP (TWinning Induced Plasticity) steel using the present version of the Horizontal Single Belt Casting (HSBC) process. A two-dimensional model was developed to examine the flow of molten metal in the HSBC process, primarily focusing on investigating the instabilities/turbulence that arises when molten metal encounters the moving belt. For computational fluid dynamics modelling, three belt speeds were tested, i.e. 0.4, 0.8 and 1.2 (m s−1), against a constant molten metal velocity of 0.8 m s−1 at the nozzle slot outlet. It was observed that the molten metal/air interface fluctuations were appreciably suppressed/reduced when the belt and molten metal velocities approached each other. The fluctuations formed are damped further downstream, and any remaining surface perturbations can be eliminated via hot plastic deformation. An appropriate heat treatment was also designed for the TWIP steel strips, in order to achieve the desired microstructure and mechanical properties.

Impingement heat transfer to the synthetic jet issuing from a nozzle with an oscillating cross section

This experimental study is focused on a rectangular synthetic (zero-net-mass-flux) jet impinging on a wall. The working fluid is air. A novel variant of a synthetic jet actuator (SJA) is proposed. Following biomimetic principles, the actuator incorporates a nozzle in which the cross-sectional area periodically oscillates during the driven cycle. Two independent actuating systems are used to drive the main SJA diaphragm (as seen in common SJAs with rigid nozzles) and the oscillating nozzle walls (unique to this study). Namely, the diaphragm is driven electrodynamically, and the nozzle walls are driven using a pair of piezoelectric transducers. The operating frequency of 62 Hz is selected by tuning both systems at their resonances. The nozzle slot width oscillates around an average value of approximately 6 mm. Four experimental methods were used: phase-locked visualization of the oscillating nozzle lips, direct measurement of the jet momentum flux using a precision scale, hot-wire anemometry, and an evaluation of the heat transfer coefficients on the exposed wall using heat flux sensors. The local distribution of the heat transfer coefficient on the wall (Nusselt number in a dimensionless form) indicated the three-dimensional character of the flow field with an axis-switching effect. It was concluded that the momentum flux and the heat transfer rate could be enhanced by the phase delay between the diaphragm and nozzle cycles. The reason is the fact that the nozzle cross-sectional area during the extrusion stroke is smaller than the area during the suction, thus the SJ velocity and momentum flux are promoted during extrusion while the losses are reduced during suction. The maximal effect was found at the phase shift of 270° for the ratio of the cross-section areas during the extrusion and suction of 0.74.

Gas-powder laser cladding with slot nozzles

The topic of this research is the investigation of technological processes of gas-powder laser cladding with the help of high-power diode lasers with rectangular cross-section of laser beam, the mutual influence of technological parameters of gas-powder streams and focused laser beam on the properties of clad layer (dimensions, shape, etc.) in particular. The research stages included the following: It was established that the use of multi-channel gas-powder delivery nozzles significantly influences the productivity and quality of laser processing.

The Acoustic Performance of 3D Printed Multiple Jet Nozzles with Different Configurations

This work investigated multiple jet nozzles with various geometrical shape, number of exits, and material on reducing noise radiated from jet flows. Nozzles are categorized in two groups with few and many exit numbers, each with various exit shapes, slot and circular, and geometry. Firstly, nozzles are designed and then fabricated by a 3D printer, Form Labs, Form2USA, with polymeric resin. Also, the nozzle with the most noise reduction made of stainless steel. Noise and air thrust were measured at three air pressure gauges, 3, 5, 7 BAR and directions from nozzle apex, 30°, 90°, 135°. Nozzles with slot exit shape made of both plastic and stainless steel revealed the most noise reduction among all nozzles with few exit numbers, nearly 11–14 dB(A) and 11.5–15 dB(A), respectively. On average, slotted nozzle noise reduction was nearly 5–6 dB(A) more than finned nozzle. However, nozzles with more exit numbers, finned and finned-central exit, illustrated much more noise reduction than nozzles with few exit numbers, by almost 16–18 dB(A), they represented similar sound. All tested nozzles and open pipe demonstrated equal air thrust at each pressure gauges. The nozzles with slotted exit shape, either plastic or stainless steel, can provide reasonable noise reduction in comparison to other configuration with few exit numbers. In contrast, nozzles with more exit numbers demonstrated the most noise reduction.

ПОРІВНЯЛЬНЕ ДОСЛІДЖЕННЯ НА ФІЗИЧНІЙ МОДЕЛІ ОСОБЛИВОСТЕЙ ВЕРХНЬОЇ ПРОДУВКИ ЧЕРЕЗ НАКОНЕЧНИК ЗІ СКЛАДЕНИМ СОПЛОМ ПРИ ПРОДУВАННІ ОДНОФАЗНОЇ РІДИНИ

The aim of the work was to study the nature and peculiarities of the interaction of the lance of the converter lance flowing from the folded nozzles with a liquid bath of single-phase liquid. The study was conducted on the basis of a physical model of the converter with top purge. The design of a folded nozzle consisting of a central cylindrical nozzle and a slit annular nozzle located around it is investigated. A visual and video recording comparative study in comparable operating conditions of the folded nozzle with different design features, in particular, with an additionally deepened central nozzle in the folded nozzle and a protruding central nozzle; with operation of one cylindrical nozzle, four nozzles of identical section and an annular slot nozzle. It is established that the jet flowing from the folded nozzle differs in the possibility of more active interaction with the liquid bath than one cylindrical nozzle and four nozzles of equivalent plane. The depth of penetration of the jet into the bath liquid, the parameters of the formed hole of the jet penetration, the oscillations of the bath were studied. It is established that the peculiarities of crater formation in the liquid, characteristic when using a folded nozzle, are due to the use of a slotted annular part of the nozzle. The wider crater is due to the use of a slotted annular part of the nozzle. It is shown that the structural variants of the folded nozzle with a recessed or protruding central nozzle do not increase either the depth or the width of the formed crater. It is also established that the peculiarities of crater formation in the liquid when using a folded nozzle are due to the use of a slotted annular part of the nozzle. To form the best purge conditions, the slice of the slotted annular part should be flush with the slice of the central nozzle. With this design, the jet pulse is maintained for a longer period compared to the use of only one central nozzle, probably due to the protection of the central jet, and due to its deep penetration properties.

Aerodynamic focusing of an abrasive air jet and its effect on machining resolution

To decrease the size of the eroded footprint resulting from abrasive air jet machining, the aerodynamic focusing of an abrasive particle jet was investigated. Using a slot nozzle abrasive jet, the best focusing employed a pair of bounding air jets tilted 60° to the abrasive jet, at an impingement height of approximately 10% of the standoff distance from the workpiece. An optimum bounding jet pressure existed to achieve the maximum focusing, resulting in a machined channel width reduction of up to 16% with a corresponding depth increase of 84% compared to no bounding jets. A novel apparatus was constructed to generate an annular bounding jet impinging a central abrasive jet formed from a round nozzle. However, aerodynamic focusing, in this case, could not be achieved due to the large stagnation zone that formed near the annular jet impingement. Computational fluid dynamics simulations were used to understand the mechanics of particle focusing.

Study on Pressure Coefficient in Process of Double Slot Nozzle Jet Impingement on Sinusoidal Colliding Strip

Air cushion furnace is widely used in the heat treatment process of aluminum strip, copper strip and silicon steel, and the double slot nozzle is the core part of the air cushion furnace device. Studying the distribution characteristics of the surface pressure coefficient of the strip during the suspension process could provide important theoretical references for the high-efficiency and high-value production of the air-cushion furnace. In this paper, the distribution of pressure coefficients is studied under the conditions of Re=48 194~12 048, high H/D=1~3, spacing L/D=17.2 and sinusoidal amplitude A=0~30 mm. The results show that with the decrease of L/D, the position of the main stop point moves to the center line of the nozzle, and the value of the second stop point increases gradually, and with the increase of the sinusoidal amplitude A, the position of the main stop point moves gradually to x/D=0. The pressure coefficient Cp decreases with the increase of sinusoidal amplitude A, the pressure coefficient Cp decreases with the increase of H/D, and the difference between the pressure coefficient at the stationary point of the double-slot nozzle and the pressure coefficient at the non-stationary point increases with the increase of H/D. This study provides an important theoretical basis for the design of double slot nozzles in air cushion furnace.

Investigation of the Spectral Composition of the Gas Pressure and Thrust Pulsations in Nozzles Equipped with a Deflector

The results of a numerical and experimental investigation of the thrust and gas pressure pulsations on the thrust wall surface in annular and linear dual slotted nozzles are presented under the laminar flow conditions. The experiments are carried out in a pulsed aerodynamic setup using the products of combustion of acetylene-air mixture as the working body. The calculations are performed on the basis of Navier—Stokes equations for a multicomponent reacting gas medium using a chemically-nonequilibrium thermochemical model. The calculated and measured spectral compositions of the pulsating gas pressure at the center of the thrust wall of the annular nozzle are compared. The dependences of the pressure pulsation frequency and amplitude at the thrust wall center and the thrust on the gas pressures at the nozzle entry and exit, the dimensions of its critical section, and the deflector shape are established.

Vortex dynamics in a normally impinging planar jet

The flow development of a jet issued from a high-aspect ratio slot nozzle impinging on a flat plate is investigated experimentally. Time-resolved, two-component particle image velocimetry is used to characterize the flow for Reynolds numbers based on slot width and streamwise jet centerline velocity of 3000 and 6000, and impingement height ratios of 2 and 4. A quantitative description of the vortex dynamics is provided and the effects of Reynolds number and impingement height on the vortex evolution are characterized for the experimental conditions investigated. Primary vortices are shed in a highly periodic manner with strengths that scale with Reynolds number. Primary vortex merging is observed in the wall-jet region for all test conditions while increasing the impingement height ratio from 2 to 4 causes vortex merging to also occur in the free-jet region. Passage of single and merged primary vortices induces the formation of secondary vortices along the impingement surface, though the shedding frequencies of these secondary structures exhibit higher variability than that of the primary vortices. The secondary vortices are similar in strength to the primary vortices for a Reynolds number of 3000, but their relative circulation is decreased at a Reynolds number of 6000. Secondary vortex shedding at the lower Reynolds number leads to a higher growth rate of the wall-jet half-width due to pairing with primary vortices and subsequent ejection away from the surface, which is not found at the higher Reynolds number investigated.

Self-Oscillation Regimes of Penetration of Free or Plunging Jets through Liquid Surface

A brief review is given for the most significant results obtained in studies carried out in the Institute of Mechanics, Moscow State University, and focused on a new class of transient flows of an incompressible liquid that form when vertical plunging or free flat or axially symmetrical water jets penetrate through the surface of water placed in relatively narrow channels or when free thin-wall water jet, flowing from a conical slotted nozzle with a vertical axis penetrates through water surface in a rectangular vessel. Wide ranges of the values of key parameters were found to exist at which self-oscillation flow regimes unknown before form in the liquid. Different formation mechanisms of such regimes and the characteristic features of the experimentally and numerically determined dependencies of self-oscillation periods on the key parameters are discribed. Possible applications of the obtained results are given.

ОСОБЕННОСТИ РЕАЛИЗАЦИИ ДОПОЛНИТЕЛЬНОГО СТРУЙНОГО ВОЗДЕЙСТВИЯ ВОДЫ НА ЛОПАСТИ ГРЕБНОГО ВИНТА ФИКСИРОВАННОГО ШАГА

Oughening the requirements of the international Convention for the prevention of the sea from vessels of 1973, with amendments, demands to reduce the environmental pollution, which can be achieved by maintaining the operational coefficient of energy efficiency of the vessel constant during the voyage. The behavior of the main engine with the fixed pitch propeller in the ship power plant is determined by the operating conditions of the vessel. The dependence of thermal load of the main engine on the operating conditions leads to increased pollution of the environment by fuel combustion products and increased operative ratio of energy efficiency. The control of the thermal and mechanical intensity of the main engine when it is working on a non-nominal screw characteristic, under its “weighting” or “relief", ensures the preservation of the required energy efficiency indicators when operating conditions change. There have been analyzed the methods of implementing the system of additional water jet impact supplied through the slot nozzle of the blade on the propeller to control the thermal and mechanical intensity of the main engine, regardless of the influence of external operating conditions. The design factors dependent on the type of the helical-steering complex of the vessel and affecting the method of liquid supply to the slotted nozzle of the blade have been analyzed. The analysis of the design features of modern fixed pitch propellers, methods of making screw propellers has been given. The main criteria for the system have been determined in order to minimize the negative impact on the propeller system and to lower the useful effect of controlled response on heat load of the main engine. The proposed design of the system of liquid supply to the slotted nozzles of propeller blades is characterized by minimal impact on the propeller unit.