Increasing Gas Flow Rate Research Articles

Effects of Tube Diameter and Gas Flow Rate on the Discharge Dynamics Characteristics and Reactive Species of Nanosecond Pulsed Discharge Plasma in Contact With Water

ABSTRACTThe use of millimeter quartz tubes to generate non‐thermal plasma in contact with liquid is widely applied in medicine, such as the effective disinfection of catheter tubes and tooth cavities. Here, the effects of tube diameter and gas flow rate on discharge dynamics and reactive species characteristics of nanosecond pulse needle‐water discharge are studied using an ICCD camera and optical emission spectra. The discharge diffusion is increased significantly by an appropriate combination of tube diameter and gas flow rate. Besides, the discharge intensity, emission spectra intensities of reactive species, gas temperature, and electron density increase with the increase of quartz tube diameter and gas flow rate, which contributes to enhance the production of OH and H2O2 species in aqueous samples.

A study of nano-micro-bubble process for CO2 absorption in water for biogas upgrading application

The work proposed a novel micro-bubble system using swirling jet flow method for improving the physical absorption of CO2 in water. The effects of operating conditions; e.g. gas flow rate (from 500 to 2000 mL/min), inlet pressure (2 and 3.5 bar) and inlet CO2 concentration (from 5 to 60% v/v in CO2/N2 gas mixture) on the physical absorption of CO2 were studied. It was found that the CO2 absorption system reached to steady state after 30 minutes with the outlet CO2 concentrations of 2.9% and 8.8% at 40% and 60% of inlet CO2 concentrations, respectively. These outlet CO2 concentrations demonstrated the standard of bio-methane for replacing natural gas in vehicle use, from which less than 10% CO2 is required. Moreover, the increase of gas flow rate resulted in increase of outlet CO2 concentration. The rising of inlet pressure from 2 to 3.5 bars let to reduction of the outlet CO2 concentration together with enhancing the dissolved CO2 concentration in water from 49.1 to 51.7 mg/L at gas flow rate of 2000 mL/min and 60% of inlet CO2 concentration. The highest efficiency of CO2 removal was 98.41% under gas flow rate at 500 mL/min with 60% of inlet CO2 concentration. Under the optimized conditions, this system was tested with real biogas as raw material containing mainly 57.7% of CH4 and 40.3% of CO2 which achieved to remove the 95.1% of CO2 removal and no significant loss of CH4. This highlight demonstrated the potential application of this technology for biogas upgrading or purification further.

A numerical study of double flow focusing micro-jets

Purpose Double flow-focusing nozzles (DFFNs) form a coaxial flow of primary liquid with micro-crystalline samples, surrounded by secondary liquid and focusing gas. This paper aims to develop an experimentally validated numerical model and assess the performance of micro-jets from a DFFN as a function of various operating parameters for the water–ethanol–helium system, revealing the jet's stability, diameter, length and velocity. Design/methodology/approach The physical model is formulated in the mixture-continuum formulation, which includes coupled mass, momentum and species transport equations. The model is numerically formulated within the finite volume method–volume of fluid approach and implemented in OpenFOAM to allow for a non-linear variation of the fluid's material properties as a function of the mixture concentration. The numerical results are compared with the experimental data. Findings A sensitivity study of jets with Reynolds numbers between 12 and 60, Weber numbers between 4 and 120 and capillary numbers between 0.2 and 2.0 was performed. It was observed that jet diameters and lengths get larger with increased primary and secondary fluid flow rates. Increasing gas flow rates produces thinner, shorter and faster jets. Previously considered pre-mixed and linear mixing models substantially differ from the accurate representation of the water–ethanol mixing dynamics in DFFNs. The authors demonstrated that Jouyban–Acree mixing model fits the experimental data much better. Originality/value The mixing of primary and secondary liquids in the jet produced by DFFN is numerically modelled for the first time. This study provides novel insights into mixing dynamics in such micro-jets, which can be used to improve the design of DFFNs.

Experimental study on the effect of CO2 desublimation on heat transfer

Revealing the influence mechanism of CO2 desublimation on heat transfer is crucial for developing new liquefied natural gas heat exchangers. In this paper, an experimental platform for CO2 desublimation was built to investigate and analyze the intrinsic connection between CO2 desublimation and heat transfer, and systematically elaborated the mechanism of the influence of CO2 desublimation on heat transfer under different operating conditions based on the values of the heat transfer coefficient and CO2 thermal resistance. The results of the study show that CO2 can rapidly start condensation on the cooling surface when the gas flow rate is too fast (60 kg/h), which leads to a weakening and then strengthening of the effect of CO2 condensation on the heat transfer as the gas flow rate increases. In addition, as the cooling temperature drops, the amount of heat exchange between CO2 and the refrigerant decreases, and the magnitude of the changes in the values of the heat exchange coefficient and CO2 thermal resistance increases, with the value of the heat exchange coefficient decreasing by up to 39.9 %. Compared with the gas flow rate, the cooling temperature was the main factor affecting CO2 desublimation, and it has a more significant effect on heat transfer. This experimental study provides a theoretical basis for the design of a new type of liquefied natural gas heat exchanger and provides valuable insights into the mechanism of CO2 desublimation.

SEMI-BATCH EXPERIMENTAL STUDY ON MULTIPLE CARBON DIOXIDE BUBBLES ABSORPTION IN SWEETENER SOLUTION UNDER VARYING PRESSURES

Increasing the absorbed carbon dioxide amount in sweetener solution is a new trend to modify soft drinks. This research investigated the optimum increase in absorbed carbon dioxide within the limits of permissible food specifications in the bubble column. Response surface methodology (RSM) utilizing the Box Behnken design (BBD) was used to conduct experiments operating conditions for achieving desired responses within specified ranges of pressure (2-4 bar), temperature (5-25°C), gas flow rate (0.2–0.4 L/min), and absorbent concentration (0–150 g/L). The experimentally obtained results were fitted to a second-order polynomial model—the increase in pressure and gas flow rate results in an increase in absorption yield (YCO2). Also, increasing the gas flow rate and temperature will increase the volumetric mass transfer coefficient (KLa), while, at high pressure and pore size KLa will be reduced. According to the obtained results at optimum conditions, 4 bar, 5°C, gas flow rate 0.4 L/min, sucrose concentration of 0 g/L, and pore diffuser 0.5 μm; The CO2 content (YCO2) was 8.34 g/L. The optimum conditions for combining the effect of high CO2 content (6.125 g/L) and best KLa value (0.1043 L/min) were: 2.83 bar, 5 °C, a gas flow rate of 0.4 L/min, a sucrose concentration of 65.15 g/L, and pore diffuser of 0.5 μm.

Gas–liquid mass-transfer characteristics during dissolution and evolution in quasi-static and dynamic processes

This study aims to understand the comprehensive behavior of the gas–liquid flow and dissolution–evolution mass transfer. A quasi-static closed-tank experiment was designed to measure the static mass-transfer coefficients of the dissolution and evolution processes using the diffusion equation. After a detailed uncertainty analysis, a dynamic ventilated-pipe experiment with different-sized orifice plates was designed to illustrate the relationship between the hydrodynamic parameters, physical structure, and gas–liquid mass-transfer characteristics. The results showed that, as the static pressure and liquid-level height increase, both the dissolution and evolution coefficients exhibit increasing trends. However, when the physical condition reaches the initial state after pressurization and depressurization, the gas absorbed by the solution cannot completely evolve from the solution; that is, the dissolution rate is always greater than or equal to the evolution rate. For the equal-diameter pipe, as the gas flow rate increases, the concentration increment decreases slightly after reaching the peak, owing to the reduction in mass-transfer time caused by the increase in liquid flow rate. In particular, the maximal dissolved concentration, an increment of 210.9 %, occurred in the double large-orifice plate with the ventilated condition, far exceeding the maximum value in the quasi-static process. Moreover, the concentration under the layout of two small-orifice plates decreases slightly, and the larger gas content enables the solution to have more gas nuclei, making it easier to induce the gas evolution. The current study provides guidance for the gas–liquid-mixture transportation and improvement of the dissolved efficiency.

Spatial characteristics study of hydrodynamics and bubble dynamics in baffled stirred tank based on CLSVOF method

The limited understanding of intricate mesoscale bubble structures in stirred tank reactors under forced convection poses significant challenges to the design and optimization of related agitation systems. In this study, the coupled level set with volume of fluid (CLSVOF) method is employed to investigate bubble dynamics and macroscopic hydrodynamics in a gas–liquid stirred tank after model validation. The results demonstrate that: i) based on the dynamics of bubble clusters within the system, the stirred tank can be categorized into four distinct regions: the dispersal region, accumulation region, rising wall-region, and reflex region; ii) in the dispersal region, the rear of impeller blade generates large-scale vortex. Two merging modes are identified during the bubble rupture process: the merging of bubbles at adjacent orifices and the merging of discrete bubbles with the back of impeller blade due to negative pressure. Two bubble breakup modes are observed: bubble breakup at the back of the impeller blade due to stretching and the breakup of bubbles growing at orifices due to disturbance caused by the impeller blade; iii) the inertial forces predominantly control most bubbles in the system. A predictive correlation for bubble velocity is proposed; iv) elevating the stirring speed increases bubble number in the accumulation region. Moreover, enlarging gas flow rate and fluid viscosity leads to a discernible augmentation of overall bubble size; v) at the macroscopic scale, the radial, axial, and tangential velocities of the system exhibit an increase with enlarging stirring speed, while showing no significant change with the increase in gas flow rate. Additionally, as fluid viscosity and density increase, the flow undergoes a transition from turbulent flow to laminar flow.

Hydrogen reduction of iron ore pellets: A surface study using ambient pressure X-ray photoelectron spectroscopy

Using Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS), this study investigates the reduction behavior of iron oxides in direct reduction (DRI) and blast furnace (BF) pellets. H2, CO, and a H2–CO mixture are used as reducing agents at 650 °C. The investigation aimed to elucidate variations in the rate of reduction over time and under different conditions. Additionally, contour plots are generated to visualize the X-ray photoelectron peak intensity variations as a function of time. Furthermore, phase stability diagrams based on Fe–O–C and Fe–O–H systems are employed to enhance the understanding of reduction behavior. Results revealed that an increased gas flow rate significantly accelerated the reduction rate due to enhanced gas diffusion, while elevated pressure facilitated the reduction of wüstite to metallic iron. Notably, the DRI pellet achieves around 90% metallization degree reduction with hydrogen, but the introduction of carbon monoxide into the reducing gas prevented the reduction of the DRI pellet. In the case of BF pellet reduction, approximately 20% metallization degree is observed using H2–CO (50:50), yet subsequent reoxidation of the reduced iron to wüstite and magnetite occurred. Further investigation identified a significant increase in the partial pressure of H2O and CO2, particularly within the surface porosities, as the underlying cause of this reoxidation phenomenon.

Study of inclusions-removal and slag-metal dispersion phenomenon in gas-stirred ladle

Abstract The slag-metal interface serves as a crucial locus for both chemical reactions and the adsorption of inclusions during secondary refining. This study first comprehensively reviews the methods of inclusions removal and then establishes a cold-state experiment using a water-oil system to reappear the phenomenon of slag-metal dispersion and inclusion adsorption. The distribution of slag droplets under varying slag volumes is analyzed in terms of the effect of bottom blow rates. Simultaneously, the volumetric fraction of oxygen on the slag-eye surface is analyzed. The result proved that the increase in oil layer thickness or the gas flow rate increase the volume of entrained oil. The dimensionless depth of entrained droplets was positively associated with gas flow rate or oil thickness. The dimensionless depth of “large droplets” and “small droplets” was in the range of 0–25 % and 0–60 %, respectively. Moreover, analysis of the gas composition above the slag-eye in a water-oil system is used to determine the degree of secondary oxidation. The oxygen volume fraction over the surface of the slag-eye decreases with the increase of gas flow rate. The oxygen volume fraction over the surface of the slag-eye is 1.51 % when the gas flow rate is 9 L/min.

Smelting Reduction of HIsarna Slag with Methane

To study the smelting reduction behavior of methane in the HIsarna process, the isothermal reduction experiments of HIsarna slag with 6 wt% of FeO were conducted at the temperatures of 1450, 1475, and 1550 °C, using 5 vol% CH4‐Ar. The effect of the gas injection flow rate on the overall reduction rate was investigated in the range of 0.5–1.5 L min−1. The results confirm that the decomposed carbon black acts as the dominant reductant in the reduction process compared to hydrogen. Increased gas flow rate increases the reaction rate, while temperature shows no significant effect. The reduction process could be described by the JMAEK model: by fixing the gas flow rate at 1.0 L min−1 with different temperatures, the exponent n value is around 1.5, indicating FeO mass transfer is the limiting step since there are sufficient carbon blacks as nucleation sites. The reduction process follows the first‐order model controlled by the reactant concentration with the gas flow rate being at 0.5 L min−1 and in the second reaction stage of the gas flow rate at 1.5 L min−1. The determined activation energy for the methane reduction is 59.8 kJ mol−1.

Gas and powder flow characteristics of packed bed: A two-way coupled CFD-DEM study

A two-way coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) calculation was performed to numerically investigate the gas and powder flow characteristics within a packed bed. The analysis and discussion focused on the effects of gas phase velocity, particle shape, and size on the flow behavior of the powders. The results revealed that the average absolute velocity of the powder increased with an increase in the inlet gas flow rate. Conversely, the average dimensionless velocity exhibited the opposite trend. Particle shape significantly impacted the flowability of the powders. A critical value of sphericity equal to 0.96 was observed. For powders with sphericity less than 0.96, the average velocity fluctuated around a progressively decreasing value over time, and the powders tended to accumulate in the inlet region. In contrast, powders with a sphericity greater than 0.96 exhibited average velocities fluctuating around a constant value throughout the simulation. Additionally, a smaller number of these particles remained within the fluid domain, indicating a higher flow rate through the packed bed and ultimately exiting the fluid domain. Regarding the influence of particle size, the flowability reached a minimum value at a radius of 0.14 mm, with the average powder velocity mirroring this trend. Powders with a radius exceeding 0.14 mm demonstrated increasing flowability and average velocity. The observed impact on flowability was likely due to a combination of mechanisms. The findings presented in this paper offer valuable insights into the dynamics of powders within a packed bed. This knowledge can be instrumental in the design and analysis of packed bed reactors.

Optimization of microstructure and properties of thick Al alloy welded joints for one-step formation by keyhole welding

To solve the problem of insufficient strength of thick aluminum alloy welded joints, this study introduces a pioneering technique known as variable-polarity plasma arc keyhole-tungsten inert gas cover hybrid welding (VPPA keyhole-TIG covering welding), which is designed for welding large-thickness aluminum alloys without any weld groove. Using 13-mm-thick 2319 aluminum alloy plates as experimental materials, plasma arc butt welding experiments were conducted by varying the plasma gas flow rate and application of cover welding. The research findings underscored that the use of cover welding, coupled with an increase in the plasma gas flow rate, markedly improved the overall performance of the weld. An average tensile strength of 299.0±4.0 MPa and an elongation rate of 4.5±0.3 % were achieved for the welded joint. A microscopic analysis revealed that the heightened plasma gas flow rate did not precipitate the θ' phase but instead resulted in undesired grain size enlargement, leading to reduced joint hardness. The secondary thermal cycle effect of covering welding played a pivotal role in facilitating the nucleation of needle-like θ' strengthening phases within the matrix, ranging in size from 50 to 150 nm. This phenomenon has emerged as a principal factor contributing to the substantial enhancement of the mechanical properties of welded joints.

Influence of boundary conditions on initiation of gas blowout in permeable rock

Free gas in permafrost may originate from dissociating methane hydrates that are widespread in the Arctic region. Methane can migrate through sand–clay permafrost and accumulate there, particularly in sand beds. Gas migration is often accompanied by the formation of pressurised zones. As the pressure reaches some critical value, the overburden breaks down, and methane is released explosively with formation of craters on the seabed. In this paper, gas migration is simulated in two dimensions, with implications for the conditions under which an increased gas flow rate can lead to failure of granular rocks, as well as for the place of blowout initiation depending on boundary conditions. The paper shows that the location of sediment blowouts in the presence of an impermeable lid or obstacle differs from the location of blowouts without them. The paper also shows that the type of pressure source (homogeneous or heterogeneous) also affects the location of the blowout initiation. The numerical results are in good agreement with laboratory experiments carried out in a sandy medium at a Hele-Shaw cell and with field data. The presented results should be taken into account when estimating the after-effects of methane hydrate dissociation due to global warming or due to surface condition changes.

Analysis of the influence of uneveneity of the sintering process of the barch on the operation of the sintering machine

Literature data on the unevenness of temperature and composition of the gas leaving the sintering bed across the width and length of it and their influence on the productivity of sinter machines are considered. An analysis of the technologies reasons for the unevenness of the sintering process was carried out. It is shown that the reasons for the width of the pallets include the distribution of the mix bed in the loading bin, air leaks into the ignition hearth, the wall effect at the side plates of the pallets, the shape and angle of inclination of the sides relative to the grates. Along the length of the sinter machine, the unevenness of gas flow and composition is due to a decrease in the gas-dynamic re-sistance of the bed during the sintering process, segregation of the mix and fuel along the height of the bed, completion of bed drying and gaps between pallets. Using an adapted mathematical model of the sintering process, a comparison was made of the parameters of the basic (non-uniform) and calculated uniform operating modes of the AKM-312 sinter machine of the Steel Plant NLMK. I It has been established that with the vertical installation of the pallet sides accepted in the calculations that an increased gas flow rate at the periphery of the bed is accompanied by an increase in gas temperature with a corresponding decrease in the suction before exhausters. It was found that during the transition from the base to the uniform mode of operation of the sinter machine, the gas temperature in front of the exhausters decreased from 99.6 to 85.1 °C, the suction increased from 13.54 to 14.26 kPa, and in the collecting collector – by 1.15 kPa. The productivity of the sinter machine increased by 4.1%. When installing pallet sides vertically, the effectiveness of increasing the height of the layer on its periphery instead of compacting it and constructive solutions has been justified. Its increase provided an additional productivity of the sinter machine by 1.8%, a total of 5.9%. It has been shown that due to the simultaneous increase in gas temperature over the entire width of the bed in the final period of the sintering process, with a uniform operating mode of the sinter machine, the maximum gas temperature at the end of the process increases with a lower one – in front of the exhausters. From the point of view of the capabilities of exhausters in terms of the created suction, the accepted representation of their gas-dynamic characteristics at a temperature of 150 °C, which is possible only with a high level of unevenness of the sintering process, is not reasoned

Effect of TCS gas flow and pre-etching on homopitaxial growth of 4H-SiC.

In this study, the epitaxial growth of 6-inch n-type 4° off-axis Si-face substrates using a horizontal hot-wall LPCVD system was investigated. The study explored the epitaxial growth under different source gas flow rates, growth pressures, and pre-etching times, with particular emphasis on their effects on epitaxial growth rate, epitaxial layer thickness uniformity, doping concentration and uniformity, and epitaxial layer surface roughness. The observation was made that the increase in source gas flow rate led to variations in dopant concentration due to different transport models between nitrogen gas and source gas. Additionally, with the increase in etching time, overetching phenomena occurred, resulting in changes in both dopant concentration and uniformity. Furthermore, the relationships between these three factors and their corresponding indicators were explained by combining the CVD growth process with the laminar flow model. These observed patterns are beneficial for further optimizing growth conditions in industrial settings, ultimately enhancing the quality of the growth process.

Experimental study on the spray characteristics of an internal-mixing gas-liquid injector

To determine the spray characteristics of internal-mixing gas-liquid injector under various operating conditions, the experimental facilities for spraying are established. By means of high-speed camera, laser particle size analyzer and PIVlab, the effects of gas and liquid flow conditions on the spray characteristics, such as position of jet impingement, spray angle, breakup length, velocity distribution and droplet size, have been investigated in detail. Experimental results demonstrated that there are two types of atomization for this injector, namely impact atomization and aerodynamic atomization. The impingement position of the liquid jets is outside of the injector exit. Alternatively, no impingement occurs between the jets. The spray angle increases with the increase of liquid flow rate, and decreases with the increase of gas flow rate. The breakup length decreases with the increase of the liquid or gas flow rate. The higher the liquid flow rate, the greater the velocity distributed along the axial and radial direction. However, the effect of gas flow rate on the velocity along the axial and radial directions acts differently at different spatial position. An increase in the liquid flow rate causes the droplet diameter to increase first and then decrease. The droplet size will decrease when the gas-liquid momentum ratio increases.

Characterization of cascaded arc He plasma in a compact linear plasma device using voltammetry and optical emission spectroscopy

Cascaded arc plasma has been widely applied in linear plasma devices (LPDs) to produce high flux plasma for the study of plasma-material interaction. In this work, cascaded arc He plasma produced in an LPD with a compact arrangement is investigated by voltammetry and optical emission spectroscopy (OES). The results show that the cathode potential increases with the discharge current while it firstly decreases and then increases as increasing the gas flow rate. A local reverse electric field is observed at low gas flow rates between two cascaded plates (i.e. floating electrodes) near the cathode. The OES’ results reveal that as the gas flow rate increases, the intensity of He I lines increases and the electron excitation temperature (T exc ) decreases. As increasing the discharge current, the intensity of He lines exhibits various trends at different gas flow rates, showing a monotonic decline at 1.94 slm and a first increase followed by a reduction at 3.52 slm. The T exc increases with the discharge current. These findings could preliminarily shed light on the properties of cascaded arc of He plasma in the compact LPD and aid in the optimization of the device to generate the high-flux divertor-relevant plasma.

Effect of gas flow rate and nozzle diameter on bubble size and shape distributions in bubble column

The influence of gas flow rates and nozzle diameters on bubble size and aspect ratio distributions was studied using high-speed photography with an image processing algorithm. Results reveal bimodal probability density distributions (PDD) of bubble diameter under all nozzle diameters, with one peak near 1.5–2 mm and the another in the larger bubble range. Increasing gas flow rates from 0.1 to 0.2 L/min leads to a higher probability density of large bubbles, indicating prevalent bubble coalescence. As the gas flow rate rises to 1.2 L/min, the peak shifts to smaller bubble diameters, and the bubble breakage becomes dominant. For 1–2 mm bubbles, shape is less influenced by gas flow rates, while 3–9 mm bubbles exhibit aspect ratio PDD peaks at an aspect ratio (E) of 0.5 across all gas flow rates. The Iguchi and Chihara model can better predict the variation of bubble departure diameter with increasing gas flow rates.

Double-Cycle Alternating-Flow Diode Pumped Potassium Vapor Laser

A novel double-cycle alternating-flow diode-pumped potassium vapor laser is proposed, theoretically modeled and simulated. The results show that the optical-to-optical efficiency of the laser increases with increasing gas flow rates, although at high flow rates the rate of increase in efficiency decreases. The optical-to-optical efficiency reaches 74.8% at a pump power density of 30 kW/cm2 and a gas flow rate of 50 m/s. The optical-to-optical efficiency of the laser is greater with a narrow linewidth pump and high buffer gas pressure. The optical-to-optical efficiency of a flow gas cell is higher than that of a static gas cell. There is an optimal gas cell length that provides the highest optical-to-optical efficiency. At higher pump power densities, higher flow rates are required to obtain higher optical-to-optical efficiencies.

Precise surface machining of fused silica using high stability atmospheric pressure microwave plasma jet with a new internal electrode

Plasma is a promising approach for machining of fused glass substrates. Developing high-performance microwave torch is the core element to ensure the processing accuracy of this technology. In this study, a spline curve-based microwave torch internal electrode structure was proposed, which increased the internal electric field strength by 54 %. The discharge dynamics simulation based on this electrode shows that the plasma is excited at the inner electrode tip and the bottom of the resonant cavity, then it expands to form a linear discharge region and eventually fill the discharge tube. It was revealed by CCD images that with the increase of carrier gas flow rate, turbulent flow state appears in the tail of the jet. OES data shows that microwave Ar plasma can effectively dissociate CF4, and due to the oxidation effect of oxygen, CFx and C2 content decrease significantly with the addition of oxygen. The machining experiment on fused silica shows that the material removal stability of this torch reaches 3.69 %, and the removal rate increases nYarly with dwell time due to thermal effect. Finally, the machining performance of the atmospheric pressure microwave plasma jet was verified by figuring of a planar fused silica surface reducing the form error from 108.1 nm RMS to 16.5 nm RMS.