Jet Length Research Articles

Investigation of the behavior of plasma jet in the presence of water under different grounded conditions

AbstractPrevious researches have demonstrated that the ground electrode would influence the performance of the plasma jet. In this study, the characteristics of plasma jets underwater for different grounded conditions are investigated. The influence of airflow rate, and electrode length underwater are experimental studies. When the water is grounded, it would provide another charge channel for the discharge, much more ions would be transferred to the water. The length and discharge intensity would be enhanced. Besides, the length of electrode underwater would also influence the performance of the plasma jet. It is found that the shorter the electrode length, the larger the ratio of plasma jet length to electrode length. Furthermore, an electric diagram is promoted to explain the corresponding mechanism, by analyzing the resistance and capacitance under different working conditions, the theoretical explanation under different experimental working conditions is given, and further analysis demonstrated that the accumulation of charges in water during the discharge process would be the main reason to influence the propagation of plasma jet under water.

Effect of tab shape, length, and placement on the over-expanded free jet at Mach 2.0

Abstract Experiments have been carried out to investigate the over expanded free jet at Mach number 2.0 without and with tabs of different cross-sectional shapes, tab length penetration into the jet core defined as blockage ratio, and symmetrical and asymmetrical placement of tabs at the jet exit. The cross-sectional shapes such as triangular, square, and circular have been studied with the penetration depth of 3 %, 7 %, and 11 % blockage. The Pitot tube and Schlieren flow visualization were carried out in experiments. The basic features of the jet with Mach disk, shock cell, and its distortion with the adoption of tabs at various nozzle pressure ratios indicate a definite influence that helps in the reduction of the core jet length. This characteristic is also influenced by changes in tab cross-section and length of penetration. Since the basic jet has three-dimensional structures, the asymmetric placement of tabs is beneficial compared to the symmetric orientation of tabs. The jet width increases with adoption of these tabs and different shapes. Whereas, a maximum core jet length reduction of the order of 60 % could be achieved using the present techniques.

Effect of tab shape, length, and placement on the over-expanded free jet at Mach 2.0

Abstract Experiments have been carried out to investigate the over expanded free jet at Mach number 2.0 without and with tabs of different cross-sectional shapes, tab length penetration into the jet core defined as blockage ratio, and symmetrical and asymmetrical placement of tabs at the jet exit. The cross-sectional shapes such as triangular, square, and circular have been studied with the penetration depth of 3 %, 7 %, and 11 % blockage. The Pitot tube and Schlieren flow visualization were carried out in experiments. The basic features of the jet with Mach disk, shock cell, and its distortion with the adoption of tabs at various nozzle pressure ratios indicate a definite influence that helps in the reduction of the core jet length. This characteristic is also influenced by changes in tab cross-section and length of penetration. Since the basic jet has three-dimensional structures, the asymmetric placement of tabs is beneficial compared to the symmetric orientation of tabs. The jet width increases with adoption of these tabs and different shapes. Whereas, a maximum core jet length reduction of the order of 60 % could be achieved using the present techniques.

A numerical study of gas focused non-Newtonian micro-jets

The present numerical study assesses the jet length, diameter and velocity of various non-Newtonian power-law fluids of a gas dynamic virtual nozzle. A related two-phase flow problem is formulated within the mixture framework and solved with the finite volume method and volume of fluid interface treatment in axisymmetry. The process parametric range allows the incompressible laminar flow assumption. A comprehensive jet characteristics analysis is carried out in a typical micro-nozzle configuration for a range of shear-thinning to shear-thickening fluids with power law indices 0.5 ≤ n < 1.5, gas mass flow rate of 10 mg/min and liquid volumetric flow rate of 43 µl/min, resulting in a gas Reynolds number of 130 with Reynolds and Weber numbers for a reference water jet being 90 and 10, respectively. It is observed that jets from shear-thinning fluids (0.5 ≤ n < 1.0) tend to be thicker, longer, and slower when compared with the shear-thickening fluids (1.0 < n ≤ 1.5). A dripping-jetting phase diagram of the nozzle is constructed by varying the power law index, gas and liquid flow rates in the range 0.9–1.1, 5–15 mg/min and 5–50 µl/min, respectively. It is observed that the area of stable jetting decreases with the increase of the power law index. The obtained novel information on the behaviour of non-Newtonian gas-focused micro-jets provides a possible new dimension for tailoring the serial crystallography sample delivery systems where the micro-jets carry dispersed crystals into an X-ray beam.

Geometric-parameter influence and orthogonal evaluation on the thermal environment for an impinging jet ventilation system inlet

Numerical simulations are conducted to illustrate the geometric-parameter influences and orthogonal evaluation of heat removal effectiveness and dimensionless buoyant jet length scale for impinging jet ventilation system, after the full-scale measurements conduced. Two geometric parameters taken into consideration are the airflow inlet length, width and height from floor. Firstly, each geometric-parameter influence is investigated individually among its varying range while maintaining the other geometric parameters. Secondly, an orthogonal analysis is performed for evaluating the importance of each geometric-parameter on the thermal environment and thermal comfort performances.

Effects of piezoelectric synthetic jet actuator parameters on synthetic jet formation process and actuator performance

Aiming at the problem that the non-linearity between the piezoelectric vibrator deflection and the excitation amplitude of the piezoelectric synthetic jet actuator (SJA) causes it difficult to obtain the variation laws of the synthetic jet (SJ) velocity accurately, a theoretical model of the whole flow field of the piezoelectric SJA is established and four important parameters (half period jet mean velocity, Reynolds number, effective jet length and energy) for evaluating the performance of the SJ are proposed. Then a two-dimensional axisymmetric numerical simulation is carried out with k-ω turbulence model to study the SJ formation process and the velocity characteristics of the SJ at the orifice. The results show that the fluid pressure in the cavity is the main reason causing the non-linearity between the piezoelectric vibrator deflection and the excitation amplitude, the influence of which decreases with the increase of the orifice diameter. The SJ velocity increases first and then decreases slowly with the increase of excitation frequency. The extreme point occurs at the first resonant frequency of the piezoelectric vibrator and the position of the maximum velocity occurs at 0.5 mm outside the orifice. Other conditions being constant, both the piezoelectric vibrator deflection and jet velocity have a maximum value when the radius ratio of the piezoelectric layer to the elastic layer is 0.75. Smaller piezoelectric layer thickness leads to larger lateral displacement of the piezoelectric vibrator, and the optimum thickness ratio is 0.25. The results of this study have important guiding significance for accurately obtaining the variation laws of the SJ velocity as well as rationally designing the piezoelectric SJA.

Droplet impact on a microhole through a partially wetting surface

In this study, we thoroughly investigate the impact dynamics of water droplets on a partially wetting substrate with a single hole. By conducting experiments using de-ionized water droplets and high-speed imaging, we observe various outcomes, including downward jetting without pinch-off, jetting with single and multiple pinch-offs, and the intriguing emergence of an upward jet during droplet recoil. A regime map is constructed to establish the relationship between the dynamics of the jet and the Weber number. We find the small amount of liquid leakage through the hole has a negligible effect on the maximum spreading of the droplet. We analyze the behavior of the downward jet resulting from droplet impact in terms of its length, speed, and breakup characteristics. The scaling relation between the maximum jet length before its breakup and the Weber number is derived and compared with experimental data. We find that the growth of the downward jet length follows a consistent power-law relationship with time regardless of impact velocity, while the maximum jet velocity scales linearly with the impact velocity, confirming the hydrodynamic focusing theory. The size of the head satellite droplet formed during the jet pinch-off process remains nearly constant across different Weber numbers. Additionally, we investigate the volume of ejected liquid through the microhole, observing an initial increase with the Weber number followed by a saturation point. The occurrence of the upward jet during droplet recoil is a significant finding, and we analyze its diameter, height, and velocity in relation to the Weber number.

A high-efficiency circle diffuser with low resistance and high jet length

A high-efficiency circle diffuser with low resistance and high jet length

A computational study of a two-fluid atomizing coaxial jet: Validation against experimental back-lit imaging and radiography and the influence of gas velocity and contact line model

Numerical simulations of liquid atomization in a two-fluid coaxial geometry have been performed using a geometric Volume-of-Fluid method. Experimental measurements have been obtained using visible light back-lit imaging and X-ray radiography. Simulations are validated against experiments, using the same geometry and fluid injection rates of air and water, by showing excellent agreement in quantities such as liquid mass distribution in the spray formation region and the liquid jet length statistics and temporal dynamics. At the nozzle exit, the coflowing liquid and gas streams are separated by a cylindrical splitter plate. The liquid is laminar and modeled using a Poiseuille flow while the gas inflow model and the contact line model are varied. For the gas velocity models, the vorticity thickness is shown to have a strong influence on the downstream liquid distribution; the difficulty of its modeling and routes to overcome them are discussed. For the contact line model, pinning the interface to the inner wall of the splitter plate leads to an initial increase in the diameter of the liquid jet just downstream of the nozzle exit. In contrast, pinning to the outer wall of the splitter plate or allowing for a free moving contact line results in a monotonic decrease in the diameter of the liquid jet as the downstream distance is increased, in agreement with the experimental observations and measurements. A sub-grid scale contact line model based on a static contact angle is introduced. The static contact angle is varied in the model, showing that the liquid remains intact longer as the static contact angle is increased.

Influence of discharge voltage on the length of atmospheric argon plasma jet

In order to widely apply the high concentration of active substances in plasma jets in sterilization, material modification, environmental protection, etc It is necessary to continuously increase the length of the jet in the external environment of atmospheric pressure under certain conditions, to increase the contact area between the jet and the action object, and to better utilize the effect of plasma. In this demonstration, a needle-ring electrode argon plasma jet device was utilized. By measuring the discharge voltage during the discharge process and capturing images of the discharge, the effect of discharge voltage on plasma jet length was studied. At an argon volume flow rate of 30 l min−1, an electrode spacing of 80 mm, and a discharge voltage of 20.5 kV, a jet length of 81.96 mm in the surrounding air was produced. The results indicate that as the discharge voltage increases, the morphology of the plasma jet changes proportionately; as the discharge voltage increases, the jet morphology changes from a small, neutral discharge to a jet with a needle-like shape, and then to a violent ‘jump’ at the end of the plasma jet; correspondingly, the plasma jet length increases with the discharge voltage, exhibiting an overall trend of first increasing and then stabilizing, but the rate of increase changes from rapid to flat; the plasma jet length increases in the process of two peaks, and after reaching the second peak, it stabilizes and no longer grows significantly; the magnitude of the excitation voltage is proportional to the distance between the two electrodes under the initial test conditions, and the plasma excitation voltage grows with increasing distance between the electrodes while the argon gas flow rate remains constant; the excitation voltage produced by the plasma jet exceeds the minimum voltage necessary to sustain the plasma discharge.

Experimental study of interface behavior and sound pressure oscillation of direct contact condensation of a steam jet in flowing water

Direct contact condensation of a vapor jet in liquid is frequently encountered in lots of industrial applications because of its high heat and mass transfer rates. However, severe interface and sound pressure oscillation associated with condensation might cause vibration and even failure of pipeline systems. In this paper, the interface behavior and the sound pressure oscillation of a steam jet in flowing water are captured respectively by a high-speed camera and a high-frequency hydrophone. According to the gray profile of the image, an identification method is proposed to determine the interface characteristics, including the plume shape, width, and penetration length of the jet. The statistical intensity and power spectrum density of the interface position and sound pressure oscillation of the steam jet are calculated. Two typical condensation regimes of Chugging and Oscillation-I under low steam mass flux (Gs < 346 kg/m2s) are observed. The intensities of the interface oscillation and sound pressure oscillation decline with increasing steam mass flux and a significant correlation coefficient of about 0.94 between them is revealed. With the incorporation of sound pressure parameters, two correlations of the dimensionless jet length and its oscillation intensity are established, with relative deviations of 20% between the experimental and predicted values. For Oscillation-I, the dominant frequencies of the interface oscillation and sound pressure oscillation are quantitatively consistent. From the time and frequency domain perspectives, it is quantitatively confirmed that the sound pressure oscillation of the steam jet under low steam mass flux is caused by its interface oscillation.

Study on the Equation of State and Jet Forming of 3D-Printed PLA and PLA-Cu Materials.

In order to improve the research and development efficiency and quality of low-density liners in production and scientific research development, PLA and PLA-Cu composite liners were prepared based on 3D-printing technology. In this paper, the relationship between the shock wave velocity D and the particle velocity u of PLA and PLA-Cu materials was tested by a one-stage light gas gun experiment device, and then the Grüneisen equation of state parameters of the two materials was obtained by fitting. The forming process of the two jets was numerically simulated by using the equation of state. When combined with the pulsed X-ray shooting results of the jets, it was found that the jets of the two materials showed obvious characteristics of "expansion particle flow", and the head of the PLA jet had a gasification phenomenon. The length of the PLA jet at 20 μs in the numerical simulation was 127.2 mm, and the average length of the PLA jet at 20 μs in the pulsed X-ray shooting experiment was 100.45 mm. The length of the PLA jet gasification part accounted for about 21% of the total length of the jet. The average velocity of the head of the PLA jet is 7798.35 m/s, and the average velocity of the head of the PLA-Cu jet is 8104.25 m/s. In this paper, 3D-printing technology is used to prepare the liner for the first time, aiming to open up a new preparation technology and provide a new material selection for low-density material liners.

Multiphase jet penetration in gas-solid systems

Thermochemical conversion of biomass in fixed/fluidized bed reactors requires efficient feedstock penetration and dispersion through reliable feed injection systems. Pneumatic biomass injection produces a gas-solid jet in the reactor that requires proper momentum to disperse the feedstock. Assessing multiphase jet penetration in fluidized beds is challenging because of system's complexity, opaqueness and lack of a universal measurement technique adapted for tracking the associated phenomena. In this work, three measurement techniques (fluorescent particle tracking, pitot tubes and Electric Capacitance Tomography (ECVT)) were employed and compared to assess the penetration of air-biomass jets into fixed/fluidized beds. Results from all techniques indicated that the jet penetration increased with solids mass flux, and jets with similar momentum provide greater penetration in fluidized beds compared to fixed beds. Tridimensional jet propagation and biomass concentration across the jet length were obtained for different operating conditions providing a useful database for CFD and other mechanistic models validation.

Experimental study on the characteristics of V‐type arc plasma torch with four electrodes

AbstractThe arc plasma is widely used in various fields due to its excellent advantages, such as elevated temperature, high enthalpy, and increased energy density. Under this direction, a four‐electrode V‐shaped arc plasma torch was developed to increase both the arc power and plasma volume. The arc dynamic characteristics, the volt‐ampere characteristics, and the thermal efficiency of the arc plasma torch were systematically studied. From the acquired results, a large‐scale, and low‐frequency re‐strike process between the arc channels was demonstrated. Compared with the common twin‐electrode structure, the stability of the four‐electrode structure during the discharging process was improved, exhibiting a wider frequency distribution of the re‐strike events. The electrode layout may also affect the dynamic evolution process of the arc. However, from a statistical point of view, no significant differences in electrical characteristics were recorded. The four‐electrode V‐shaped arc plasma torch presented a typical descending volt‐ampere characteristic, and the re‐strike frequency increased with an increase in the current. A high thermal efficiency (above 83%) was obtained in the range of arc current of 80–200 A. At a current value of 200 A, the jet enthalpy and the average gas temperature can reach 17.41 MJ/kg and 6590 K, and the corresponding jet length was close to 80 cm because of both the high thermal efficiency and enthalpy. The stable discharge process, high thermal efficiency, high jet enthalpy value, and large volume rendered the proposed four‐electrode V‐shaped arc plasma torch to be suitable for various applications including nanomaterial preparation, metal powder spheroidization, etc.

Development of Low-Temperature Atmospheric Plasma Jet Sources for Biological Applications

The research aims to develop and build a plasma jet system operating under atmospheric pressure.for biological purposes. The advanced plasma system consists of a power supply and a plasma torch. The source of the development of the system is a previous laboratory system that was developed by changing the voltage and frequency of the power supply, as the power provider equips the system with a voltage in the form of a sine wave whose value is fixed at about (7.5kV) peak to peak and its frequency is about (28 kHz). The plasma torch consists of a teflon tube with of width of (10 m ) located at (10mm) from the end of the tube. The current waveform and voltage wave were measured using a current and voltage sensor and an oscilloscope. The plasma jet was characterized. Electron temperature and electron density vary with the gas flow rate; the length of the plasma jet depends on the flow rate of argon gas, and the best length of jetting plasma was (1.5 cm) at a flow rate of (2.5 l/min). The gas temperature was measured by an infrared thermometer at a constant flow rate of (2.5 l/min) which is (18°C) after 15 minutes of irradiation. From these results, it was concluded that the developed plasma is suitable for biological applications.

Surface modification of polyethylene using argon and argon/methane DBD atmospheric pressure plasma jet

This article investigates the surface modification of polyethylene (PE) using an atmospheric pressure plasma jet of the DBD type (APPJ) maintained with pure argon (Ar) and with a premixed gas containing 90% argon and 10% of CH4. First and for both plasma jets, the jet length and the optical emissions coming from the plasma species were studied in terms of flow rate and applied voltage. Comparing to Ar, it has been shown that when the premixed gas is used, the jet length gets smaller, the transition point from laminar to turbulent regime was shifted to a low flow rate, and the emission of CH, H2 and C2 appeared, while O and N2 emission coming from ambient air was quenching. The PE surface treatment in both laminar and turbulent regime has been evaluated using water contact angle (WCA) measurement and attenuated total reflection (ATR). The obtained results showed that the hydrophilicity of PE has been improved in both plasma jets due to oxygen group (C=O) incorporation, but Ar plasma jet was observed to induce surface degradation compared to Ar/CH4 plasma due to the higher excited species.

Normalized evaluation index of jet length and resistance for square diffuser shape optimization

In public buildings, the energy consumption of HVAC system fans due to the resistance of the HVAC ducts accounts for approximately 20–40% of the total energy consumption of the building. This study focuses on the structural design of square diffusers in HVAC systems. By introducing the concept of a conversion coefficient for the diffuser jet length, a comprehensive evaluation index that is suitable for describing the performance of square diffusers is developed and improved upon. This study employs a combination of kriging surrogate modeling and multi-island genetic algorithm (MIGA) optimization to obtain the optimal structural parameters of the square diffuser. This study also analyzes the effects of different velocities on the square diffuser's resistance and jet length characteristics and conducts full-scale experimental verification of the square diffuser manufactured using 3D printing technology. The results show that the traditional square diffusers in ventilation and air-conditioning systems are optimized by using the Kriging model and multi-island genetic algorithm, resulting in a new type of square diffuser with the best parameters and a final reduction of 2.98 in the Square Diffuser Effective Index (SDEI). Through a comparative analysis of experimental data and numerical simulation results, the effectiveness and practicality of the proposed optimization method are demonstrated.

Effect of Jet Nozzle Position on Mixing Time in Large Tanks

The present investigation focuses on the impact of jet nozzle orientation on mixing time in a cylindrical tank. The aim is to identify nozzle positions that improve mixing performance and to elucidate the governing parameters that influence it. A water tank was employed for the experiment. The vertical inclination angle (α) and the horizontal inclination angle (β) of the jet nozzle determined the nozzle positions. Mixing time was determined using an inert tracer and spectrophotometry measurements. The findings show that the mixing time is significantly influenced by the position of the jet nozzle position. The accuracy of existing jet turbulence and the circulation models for the prediction of mixing time was evaluated for the different nozzle positions. Our results indicate that both models provide accurate predictions for the conventional centrally aligned (β = 0°), upward-pointing jet nozzle positions only (α &gt; 0). For the other nozzle positions where β &gt; 0° and at varying α, the data follow the same trends as the jet turbulence and circulation models; however, the proportionality constants vary. Shorter mixing times can be attributed principally to longer jet path lengths and therefore higher fluid entrainment and circulation as well as higher dissipation rates per jet length squared. However, it is suspected that the three-dimensional nature of the flow pattern generated in the tank also plays a non-negligible role since mixing is hindered when the nozzle points more towards the tank wall.

Effect of an additional floating electrode on radio frequency cross-field atmospheric pressure plasma jet

Atmospheric pressure plasma jets with cross-field electrode configuration are a potential jet design for gases with high breakdown fields. This study focuses on the effect of an additional floating electrode on the cross-field plasma jet properties. Detailed experiments are done with the additional floating electrodes of different widths introduced below the ground electrode in a plasma jet with a cross-field electrode configuration. It is observed that in the presence of an additional floating electrode in the jet propagation path, less applied power is needed for the plasma jet to cross the nozzle and jet length increases. This threshold power, as well as the maximum jet length, depends on the electrode widths. A detailed analysis of charge dynamics in the presence of an additional floating electrode shows decrement in the net charge transferred radially to the external circuit through the ground electrode, and an increment in the net charge transferred axially. Increment in the optical emission intensity of reactive oxygen and nitrogen species, as well as the relative yield of ions like N^{+}, O^{+}, OH^{+}, NO^{+}, O^{-}, and OH^{-} in the plasma plume, that are crucial for biomedical applications suggest an improvement in the reactivity of plasma plume in the presence of additional floating electrode.

Cold Plasma Jet Coupled Nanosecond Laser Ablation Scheme For Plasmonic Nanostructured Surfaces

AbstractThis paper describes a study where an argon cold plasma jet, generated by a dielectric‐barrier discharge (DBD), is combined with nanosecond laser ablation (248 nm, 25 ns, 10 Hz) to deposit silver particle aerosols onto the substrate at atmospheric pressure. The deposition of the particle is examined using various microscopy techniques and absorption spectroscopy for the plasma jet produced by operating DBD in the normal and reversed mode. Plasma facilitated the deposition process by delivering the particle to the substrate and significantly influenced its morphology depending on the jet interaction, length, and substrate position. In both cases, the particles are clustered; however, there is less deposit for the plasma ignited in the reverse mode. The theoretical analysis of the deposition process is performed using ANSYS software and evaluated in terms of plasma‐induced flow velocity. This study infers that the hybrid plasma‐laser deposition scheme considered is attractive for material processing and deposition, especially overextended substrate distances, and for altering the properties of the deposited particles for practical utilization in surface‐enhanced Raman spectroscopy, solar cells, and catalysis.