Low Gas Flow Rates Research Articles

Toward a Better Air-Assisted Flare Design for Safe and Efficient Operation during Purge Flow Conditions: Designing and Performance Testing.

In this study, a new air-assisted flare tip was designed, built, and tested under different operating conditions. Lacking sufficient energy to mix with air, low waste gas flow rates will lead to incomplete combustion of these gases. This increases pollutant emissions and soot formation which leads to a decline in flare performance. This flare tip design enhances the waste gas mixing energy through implementation of an air jet in a crossflow orientation. This is done by adjusting the exit area of the waste gas exit by injecting a radial jet of air from an inclined slot jet located around the flare tip. This flare tip design also provides protection for the flare tip from high flame temperatures that can damage through convective cooling. Several tests were conducted to assess the new flare tip design with varying waste gas flow rates of 5, 10, 25, and 120 standard liters per minute (SLPM). These tests also considered varying assistant air flow rates. In addition, test results showed high combustion efficiency of the flaring process and significant soot formation suppression. The new flare tip design yielded better flame behavior with respect to the flare tip, caused by the flame stability that prevented the flame from attaching to the flare tip.

Modelling of removal of surfactants from liquid solutions in a bubble column

This paper proposes a theoretical model for the separation of a surfactant from water in a bubble column. The proposed model includes both mass balance and adsorption thermodynamics of surfactants on bubble surfaces in the liquid solution (e.i. surface equations of state and adsorption isotherms). This is very important because models, found in the literature, did not consider adsorption thermodynamics. The proposed model successfully predicted the experimental results. It was found that the separation efficacy was higher at a lower surfactant concentration in the liquid than that at a higher surfactant concentration; the reason is probably that available bubble surface areas for adsorption of the surfactant were higher at a lower surfactant concentration. A higher cross-sectional area of the column led to a better separation performance due to a larger amount of generated bubble surfaces. A low gas flow rate and low liquid fraction resulted in the best separation performance.

Study on the Extrusion Molding Process of Polylactic Acid Micro Tubes for Biodegradable Vascular Stents.

Polylactic acid (PLA) has been widely used in the field of medical devices. However, few studies have been conducted on the extrusion molding of PLA micro tubes for the preparation of biodegradable vascular stents. In this paper, the extrusion die for PLA single-cavity micro tubes was designed and manufactured by micro-extrusion theory. Taking the outer diameter, wall thickness, wall thickness uniformity and ovality of micro tubes as the evaluation index, the influence of the main extrusion process parameters on the evaluation index was studied. The experimental results show that the outer diameter and wall thickness are significantly affected by screw speed, pulling speed and gas flow rate; extrusion process parameters have little influence on wall thickness uniformity and ovality within a certain range, which mainly depends on the processing accuracy and assembly accuracy of the extrusion die. However, excessively high screw speed and low gas flow rate have significant effects on ovality. Finally, according to the influence of extrusion process parameters on the evaluation index, a series of micro tubes that meet the design requirements are extruded and carved into vascular stent structures.

Gliding arc/glow discharge for CO2 conversion: Comparing the performance of different discharge configurations

We studied the use of low current (hundreds of milliamperes) gliding arc/glow discharges for CO2 dissociation, at atmospheric pressure, in three different configurations. All of these are based on the gliding arc design with flat diverging electrodes. The discharge is mainly in the normal glow regime with contracted positive column. The CO2 gas is injected from a nozzle, at the closest separation between the electrodes. A pair of quartz glasses is placed on both sides of the electrodes, so that the gas flow is restricted to the active plasma area, between the electrodes. For two of the tested configurations, an external magnetic field was applied, to create a magnetic force, both in the direction of the gas flow, and opposite to the gas flow. In the first case, the arc is accelerated, shortening the period between ignition and extinction, while in the second case, it is stabilized (magnetically-stabilized). We studied two quantities, namely the CO2 conversion and the energy efficiency of the conversion. Generally, the CO2 conversion decreases with increasing flow rate and increases with power. The energy efficiency increases with the flow rate, for all configurations. The magnetically-stabilized configuration is more stable and efficient at low gas flow rates, but has poor performance at high flow rates, while the non-stabilized configurations exhibit good conversion for a larger range of flow rates, but they are generally more unstable and less efficient.

Simple CPAP (SIMPAP) for Neonatal Transport—Device Development and Proof of Concept Study

Objective: To develop a low-cost, easy to use CPAP device with a simple patient interface—SIMPAP. Design: This was an in vitro experimental study. SIMPAP was designed and developed over three iterations to be able to use in clinical studies. SIMPAP consists of intersecting cylinders with each opening performing a designated function. One of the openings serves as an extremely short expiratory limb that is fitted with a calibrated occlusion. This results in a nonrebreathing system that generates predetermined pressure against which the baby has to exhale. Main Outcome Measure: To analyze the pressures generated by the initial prototypes of the SIMPAP device. Results: Four SIMPAP bodies and four pressure relief valves were tested with different combinations as four exercises. Mean (–2Sd to +2SD) pressure generated at a flow rate of 1 liter was 3.4 (2.2-4.7) cm of H2O and at 2 liters per min flow was 5.7 (4.8-6.6) cm of H2O. The 95% limit of agreement between exercises 1 and 2 was –0.4 to +1 cm of H2O, and between exercises 1 and 3 and 1 and 4 was –1 to +1 cm of H2O across the pressure range. Conclusion: SIMPAP can deliver therapeutic CPAP at low gas flow rates. Further clinical studies are warranted to establish the efficacy and safety of this new device on neonates.

Bactericidal effects of low-temperature atmospheric-pressure air plasma jets with no damage to plant nutrient solutions

The bactericidal effects of air plasma jets produced with a twisted wire-cylindrical electrode configuration were clarified in terms of plasma-induced damage to plant nutrient solutions. The bacterial suspensions were directly irradiated with air plasma jets using a low gas flow rate, which was shown to significantly inactivate the bacteria suspended in the solutions without reducing the nutrient concentrations. However, the plasma irradiation time required for inactivation depended on the type of bacteria; Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) were inactivated in 20–30 s, while Staphylococcus aureus (S. aureus) required 7 min. The inactivation of E. coli and B. subtilis decreased with increasing air gas flow rate, whereas the inactivation of S. aureus was independent of the rate. The inactivation could be attributed to a greater number of reactive oxygen and nitrogen species (RONS) from the air plasma jet, including O2 molecules in the feeding gas attaching to the bacterial suspension surface, which do not harm the nutrient components. This can be derived from the results; the air-plasma-jet-activated nutrient solutions (RONS introduced in the solutions) and the N2 plasma jets had only a limited inactivation effect on the bacteria suspended in the solutions.

Overall particles flow pattern in a two-zone gas-solid fluidized bed with a secondary-gas stream

Fluidized bed reactors with multiple input streams have been developed over the last decades to satisfy industries in the scope of multiphase catalytic reactions, and two-zone fluidized beds have been developed to perform reaction and catalyst regeneration simultaneously. However, the presence of the secondary gas nozzle in the bed significantly impacts the hydrodynamics and efficiency. Particle image velocimetry (PIV) and digital image analysis (DIA) techniques have been used to study different particle flow patterns in a two-zone pseudo-2D fluidized bed with lateral gas injection. The secondary flow nozzles' location has been changed, and different particle flow patterns have been observed in the fluidized bed. It was found that at low excess gas flow rates, when the lateral nozzle is located at the middle part of the bed, particles move downwardly at the bed center and upwardly near the walls; while when the lateral nozzle is located at the top part of the bed, particles have a reverse movement trend. At higher gas velocities for both mentioned nozzle locations, particles move upwardly at the bed center and downwardly near the walls. The formation of large bubbles was less probable when the nozzle was located at the middle of the bed.

Verneuil growth of TiO2 (rutile) crystals of large size and low dislocation density at low gas flow rate

Large (30 mm in diameter) TiO2 (rutile) single crystals with low dislocation density were grown by the Verneuil method using a single crystal furnace designed and improved by the authors. The structure of the burner was optimized by numerical simulation analysis so that the crystal could be grown at a low gas flow rate. The investigation of the growth process parameters (i.e., growth rate, outer flow rate of O2, inner flow rate of O2, and the increment of H2 flow rate) shows that the inner flow rate of O2 and the increment of H2 flow rate have the strongest influence on the crystal growth process. On this basis, other growth parameters (growth rate, outer flow rate of O2) were also optimized. Compared with the conventional Verneuil method, the crystal can be grown at a considerably low gas flow rate (40–50% lower) with the method in this work, which reduces the melt turbulence impacted by gas flow, enabling a steady and clear solid-liquid interface and improving the crystal quality. The optimum growth conditions are for the growth rate of 6 mm/h, O2 outer flow rate of 3.5 L/min, O2 inner flow rate of 5.5 L/min, and increment of H2 flow rate of 0.1 L/4 min. The etch pit density of the rutile crystals is 3.29 × 104 cm−2, an order of magnitude lower than that of the crystals grown by the conventional Verneuil method. The optical properties of the crystal are comparable to those grown by the floating zone method. Especially, it is easier to obtain a larger crystal size with lower production costs. Our results provide a possible route for industrializing the Verneuil production of large, high-quality and low-cost rutile single crystals.

Preferential removal of aromatics-dominated electronic industrial emissions using the integration of spray tower and photocatalysis technologies

Industrial emissions from the manufacturing of printed circuit boards (PCBs) are characterized by low concentration and high gas flow rates, and are one of the important sources of toxic and odorous volatile organic compounds (VOCs). They are deleterious to human health and considered as important precursors for the formation of ozone. Herein, we conducted a case study in which an integrated decontamination technique consisting of a spray tower (ST) and photocatalysis (PC) was applied to purify the waste gas emitted from a PCB manufacturing facility. Total of 66 VOCs including halogenated hydrocarbons (HHs), aromatic hydrocarbons (AHs), oxygen-containing hydrocarbons (OVOCs), and aliphatic hydrocarbons (AIHs) were quantified using GC-MS during four sampling events. The results showed that AHs were the largest group (contributing >85.0% of the total VOCs). The average removal efficiency (RE) of VOCs during the nine months’ continuous treatment was 72.39%. High RE was attributed to the following three aspects: the capture efficiencies of HHs with slight water solubility (50.16% of RE) and AIHs with low saturation pressure (54.75% of RE) were improved by the process consisting of ST upstream of PC, whereas AHs was preferentially degraded by PC (61.34% of RE). In addition, the ozone formation potential and the health risk (cancer and non-cancer risks) greatly decreased after the ST-PC treatment. This study suggests that ST-PC technique is a promising approach for removing continuously emitted organic waste gas with low concentration and high gas flow rates, as well as reducing the ozone formation and risk of health hazards.

Dynamic two-phase flow behaviors in permeable network integrated with microchannel

The performance of a direct methanol fuel cell greatly depends on the two-phase flow behaviors in the anode gas diffusion layer and flow channel. However, complex and opaque nature of gas diffusion layer poses a grand challenge for deep insight into the two-phase flow behaviors. Therefore, a homogeneous permeable network integrated with a microchannel was put forward to simulate the anode gas diffusion layer and microchannel in the present study, by which the dynamic two-phase flow behaviors were visually studied with the help of adaptive image enhancement method. The influence of the position and number of the gas inlet, and the gas and liquid flow rates on the two-phase flow behavior were analyzed. The results showed that the liquid saturation decreased and the number of the position for bubble generation increased with increasing the gas flow rate in case the gas was suppled from only one gas supply orifice. When two gas supply orifices simultaneously supplied the gas, the liquid saturation was between the cases using a single one gas supply orifice. For given liquid and gas flow rates of 0.1 mL/min and 0.5 mL/min, the liquid saturation was about 84%, which was between 83% and 92% for the single-one cases. Besides, the two-phase flow exhibited strong periodicity at low gas flow rates. The obtained results provide a deep understanding of the two-phase flow behaviors in such a simulated structure, helping better design and operation of direct methanol fuel cells.

Computational investigation of hydrodynamics, flow regimes and bubble size distribution in an airlift reactor

Airlift reactors (ALRs) are widely used in the chemical, petrochemical biological industry. A fundamental understanding of the flow field in these airlift reactors are necessary for efficient design and scaling up. In this work, the behavior of the flow field is investigated using the Euler–Eulerian approach. The liquid phase is modeled as continuous and the gas phase is dispersed in the form of bubbles. Three dimensional (3 D) transient computational fluid dynamics (CFD) simulations are performed to characterize flow behavior in ALR. The spatio-temporal variations in the flow field are quantified and an optimum liquid level in the ALR is determined. Various gas source locations are chosen and their effects on bubble plume motion are analyzed to find an optimum gas injection point that supports plume oscillation. Further, CFD simulations are performed to identify the prevailing flow regime in ALR for various gas source locations, and it is compared with experimental observations. The homogeneous and heterogeneous flow regimes are observed at lower and higher flow rates, respectively. The bubble size distribution is predicted using population balance equations through bubble coalescence and breakage models with interphase force formulations. This is computed through the discrete method of moments. The bubble size distribution is found to be narrow at lower gas flow rates and wider at higher gas flow rates. These predictions provide a unified description to characterize flow regimes in ALR.

Gas–liquid flows through porous media in microgravity: Packed Bed Reactor Experiment‐2

AbstractModifications were made to the Packed Bed Reactor Experiment (PBRE) and flown on the International Space Station as PBRE‐2 to eliminate external pressure oscillations at higher liquid flow rates and the packing diameter was reduced to increase the pressure gradient for lower flows. It is found that gas hold‐up is a function of bed history at low liquid and gas flow rates whereas higher gas hold‐up and pressure gradients are observed for the test conditions following a liquid only pre‐flow compared to the test conditions following a gas only pre‐flow period. Over the range of flow rates tested, the capillary force is the dominant contributor to the pressure gradient, which is found to be linear with the superficial liquid velocity but is a much weaker function of the superficial gas velocity and varies inversely with the particle diameter.

Investigating the Topside Choking and Riser Base Gas lifting Methods of Attenuating Severe Slug Formation in Deepwater Production Risers

Severe slugging involves large magnitude fluctuations in pressure and flow rate in a riser due to low gas flow rates and low Gas-liquid ratio (GLR). This work evaluates two mitigation concepts: topside choking and riser base gas lift to determine which technique is more desirable.
 A base case model was created to understand the nature of slugging with an input mass flowrate of 15kg/s, separator operating at 22.5Bar and 370C. After 8hours of simulation, the presence of a severe slug was observed at the production riser. Two models were created from the base case to mitigate the severe slugging. An introduction of topside choke to eliminate or reduce the riser slugging, likewise deployment of Riser base gas lift (RBGL) to achieve the same purpose.
 The result indicated that with the introduction of the topside choke and reducing the opening percentages of the choke from 80% to 5% stepwise, the slugging amplitudes were greatly reduced from 3.3bar to 0.3bar. Though this led to back pressure and a reduction in production. A 50% choke opening was suggested as the optimal choke opening for the simulated case. Results from the introduction of dehydrated gas with a mass flow rate of 1.2kg/s at the riser base indicated slug elimination from the riser and flowline. The results of this simulation were observed at the end of the riser (inlet to the separator) after about 8hours 20mins
 This report identifies that of the two simulated techniques (topside choking and RBGL), RBGL is more efficient in addressing slug issues without impacting field production.

Investigation of plasma swirl dynamics and effects of secondary gas injection in a vortex gas stabilized DC arc plasma

A numerical analysis of plasma gas swirl is performed to gain an understanding of fluid motion and the contact pattern of the plasma with a secondary gas. The secondary gas is injected into the plasma torch to either quench the hot plasma or alternatively to facilitate the heating of this secondary gas. A three-dimensional, transient fluid model is implemented in the OpenFOAM solver to examine the arc and plasma dynamics. The gases (plasma gas as well as secondary quench gases) are injected via 2 sets of 4 tangential ports spaced apart at a specified distance. The tangential injection create a plasma gas vortex that facilitates the swirling of the arc inside the torch. The plasma swirl propagates in the downstream direction where it mixes with the quench gas. The simulation results reveal that the operating arc current has a significant impact on the decay of plasma gas swirl in the downstream direction. At high arc currents, the rise in the joule heating enhances the cathode jet which suppresses the velocity gradients of the incoming swirl. A high inlet gas flow rates (e.g. Q = 18 slpm) have been observed to retain the inlet swirl intensity after passing through the arc column compared to the case with low gas flow rate (e.g. Q = 4.5 slpm). We have also examined the impact of secondary gas swirl on the quenching behaviour plasma torch plume by feeding the secondary gas in a co-current and counter-current with respect to the plasma gas rotational direction. The present simulation results help in understanding the effect of key process parameters controlling the flow and mixing behaviours in vortex stabilized plasma torch.

Effect of activated fluxes during welding of dissimilar stainless steels using semi-automatic setup

ABSTRACT In the present work, two dissimilar metals austenitic AISI 304 and 316 stainless steels were welded with duplex 2205 using semi-automatic bi-directional GMAW setup to appraise the microstructural and mechanical behavior of the welded joints. Three different activated fluxes i.e. SiO2, TiO2 and CrO3 were used to enhance the depth of penetration during joining of different stainless steels grades. Various process parameters such as welding current, voltage, filler wire, gas flow rate and activated flux were varied to observe their influences on joint tensile, bending strength, microhardness and microstructural properties. The experiments were designed using mixed level L18 orthogonal array of Taguchi method. Tensile strength was observed to be considerably dependent on the low gas flow rate, whereas welding current and activated flux influenced the toughness. The most significant effect on the bending strength and toughness was experienced with the use of SiO2 activated flux.

High performance supercapacitors assembled with hierarchical porous carbonized wood electrode prepared through self-activation

Carbonized wood (CW) electrodes with low-tortuosity and high conductivity have received extensive attention in the fields of energy storage and electrocatalysis. Directly carbonized wood electrodes have low specific surface area and high electrochemical impedance, and require secondary physical or chemical activation to achieve acceptable performance. Herein, we reported a facile method to prepare the CW electrode with superior surface area through self-activation using CO2 and water vapor generated during the pyrolysis which was conducted with a low inert gas flow rate. The specific surface area and electrical conductivity of the self-activated carbonized wood (SCW, ~ 0.46 g cm−3) were as high as 1145 m2 g−1 and 20.3 S cm−1, respectively. The SCW applied as a freestanding electrode demonstrated an impressive specific capacitance of 6.63 F cm−2 (143.6 F g−1) at 1 mA cm−2. After 10,000 cycles, the capacitance of the SCW electrode was retained as high as 101.7%. The symmetrical supercapacitor (SSC) assembled with two SCW electrodes showed an energy density of 0.27 mWh cm−2 (8.60 Wh L−1) at a power density of 0.5 mW cm−2 (11.8 W L−1). This work provides a simple, low-cost and green procedure for fabricating high-performance CW electrodes, which has great promotional significance and practical value on valorization of biomass.

Oil production from waste polyethylene and polystyrene co-pyrolysis: Interactions of temperature and carrier gas flow rate

This study investigated the co-pyrolysis of waste polyethylene (WPE) and polystyrene (WPS) for oil production under different operating conditions (temperature and carrier gas flow rate). The ratio of the real-life WPE and WPS is different in different regions. Therefore, the interactions of operating conditions were investigated under different WPE/WPS mixture compositions. A hybrid model of artificial neural network-genetic algorithm (ANN-GA) was adopted to predict and optimize the co-pyrolysis oil yield due to the complex interactions of the WPE/WPS mixture composition and operating conditions. Consequently, the highest oil yield was 82.33 wt% under 525°C, 10 wt% PS, and a non-sweeping atmosphere (0 mL/min). The results indicated that high temperature, low PS mass fraction, and low carrier gas flow rate led to a higher oil yield. The WPE/WPS co-pyrolysis oils were composed of alkanes, alkenes, and aromatics. Meanwhile, styrene accounted for the highest proportion of aromatics in oils. ANN-GA was also adopted to predict and optimize the oil components and fractions. The results revealed that low temperature, high PS mass fraction, and low carrier gas flow rate were conducive to a light WPE/WPS co-pyrolysis oil production. The findings could guide the industrial process of waste plastic pyrolysis in different regions. Moreover, ANN-GA coupled with central-composite design can be used to regulate different target products under more complex conditions due to its good robustness.

Evaluating the Effect of New Gas Solubility and Bubble Point Pressure Models on PVT Parameters and Optimizing Injected Gas Rate in Gas-Lift Dual Gradient Drilling

Gas-lift dual gradient drilling (DGD) is a solution for the complex problems caused by narrow drilling windows in deepwater drilling. Investigations are lacking on using oil-based drilling fluid in DGD, which is the principal novel idea of the present study. This research compares the results obtained from two new models with those of Standing’s correlations for solubility and bubble point pressure. Nitrogen was selected as the injection gas, then the PVT behavior of drilling fluid (oil/water/Nitrogen) in gas-lift DGD was evaluated and compared by coding in MATLAB. Then, these results were used to calculate the bottom hole pressure and finally investigate the optimization of injected gas flow rate. According to the achieved results, the Standing model has some errors in evaluating the PVT behavior of “Nitrogen and oil-based drilling fluids” and is not recommended for the mixtures in the gas-lift DGD. Regarding optimizing gas flow rate, a discrepancy was observed between pressure values obtained from the new models and the Standing model for the case of high liquid flow rates at low gas flow rates because of the difference in PVT parameters. The developed codes are deposited on an online data repository for future users. This study lays the foundation for better planning of drilling in deepwater drilling projects.

Effect of Electrolyte and Electrode Configuration on Cu‐Catalyzed Nitric Oxide Reduction to Ammonia

AbstractReduction of nitric oxide was investigated using Cu electrodes in acid and neutral pH conditions. Analysis of Cu discs in stagnant electrolyte by Electrochemical Mass Spectrometry (EC‐MS), revealed the favorable formation of ammonia (and hydrogen) in acidic electrolyte, while N2O and N2 are formed in significant quantities at neutral conditions. Additional performance evaluation of Cu electrodes in hollow fiber geometry, was performed using 10 vol % NO in Ar supplied through the porous electrode structure and off‐line determination of ammonia by 1H NMR spectroscopy. The pH dependent performance of the Cu hollow fiber is in agreement with EC‐MS data at low gas flow rates, showing the highest ammonia selectivity in acidic conditions. However, at relatively high gas flow rates, almost 90 % faradaic efficiency and a NH3 production rate of 400 μmol h−2 cm−2 were obtained in neutral electrolyte at −0.6 V vs RHE, likely due to enhanced availability of NO at the electrode surface, suppressing the hydrogen evolution reaction. This approach shows conversion of waste NO gas to valuable green fertilizer components is possible.

Amorphous molybdenum trioxide thin films for gas sensing applications

Uniform and smooth substoichiometric Molybdenum trioxide (MoO3−x) films have been achieved via thermal evaporation technique. MoO3 thin films were deposited onto glass and fluorine doped tin oxide (FTO) coated glass slides. The field-emission scanning electron microscopy micrographs reveal the amorphous behavior for films deposited either on glass or FTO substrates. The two thicknesses 500 and 650 nm of MoO3−x films which are deposited on glass and FTO coated glass slides were electrically examined as sensors towards NO,CO2 and HCl gases. The sensing process have been explained based on the electrical dipole layer formation consisting of the two unlike charged ion- layers and causing an energy band bending at the surface region of the film as a result of the gas adsorption. MoO3−x films on glass substrate is a perfect sensor towards oxidizing CO2 and NO gasses. The sensors are very sensitive towards low gas flow rate (20 standard cubic centimeters per minute (sccm)) and manifest the highest sensitivity values at relatively low temperatures compared with the other MOS with short response and recovery times (4 min for CO2 and 2 min for NO). The recorded sensitivity of MoO3−x sensor towards CO2 and NO gases at temperature 200 0 C shows that these samples are more sensitive towards CO2 gas, so this sensor is selective to CO2 gas more than NO. These results confirm that MoO3−x film deposited on glass of 500 nm thick can solve a large section of detecting CO2 gas problems such as selectivity, sensitivity to low gas concentrations, short response, recovery time, reversibility and low working temperature. Finally, the MoO3−x films (with thickness of 500 nm) deposited on FTO substrate was examined as gaseous HCl sensor at room temperature. It manifests a very high sensitivity towards gaseous HCl but cannot be applied for detecting it due to irreversibility and no stability of their properties after HCl vapor adsorption.