Gas Flow Rate Conditions Research Articles

Study on the Physical and Chemical Characteristics of DBD: The Effect of N2/O2 Mixture Ratio on the Product Regulation

The chemical product behaviors of dielectric barrier discharge (DBD) in N2/O2 gas mixtures are investigated. Besides ozone mode and nitrogen oxides mode, a transitional mode in which O3 and NO2 coexist is observed. Under higher oxygen content condition, higher applied voltage and lower gas flow rate contribute to the appearance of the transitional mode. To further investigate the physical and chemical characteristics of DBD under different oxygen contents, the energy per area is introduced. It presents a positive relationship with applied voltage and a negative relationship with gas flow rate. And the energy per area of transitional mode is higher than that of ozone mode, but lower than that of nitrogen oxides mode. As the oxygen content rises, the critical energy per area of mode transition increases. Through the analysis of chemical products, it is found that higher oxygen content is beneficial to the generation of O3. The NO concentration is positively correlated with applied voltage. And the optimum applied voltage for obtaining the maximum NO2 concentration increases with the rise of gas flow rate. With respect to N2O, they are easier to be obtained at higher applied voltage and lower oxygen content under higher gas flow rate condition. And in the case of lower gas flow rate, lower applied voltage and higher oxygen content are beneficial to its generation. Besides, the maximum N2O5 concentration tends to be obtained at 50% oxygen content in the case of lower applied voltage and higher gas flow rate.

Experiment on adaptability of feed gas flow rate and sea conditions on FLNG spiral wound heat exchanger

As one of the core equipment of floating liquid natural gas (FLNG), the spiral wound heat exchanger (SWHE) will be affected by feed gas flow and sea conditions, which will lead to more complex flow and heat transfer process inside the heat exchanger. In this paper, the experimental device of SWHE based on dual mixed refrigeration (DMR) liquefaction process is built to test the adaptability of feed gas flow and sea conditions on SWHE. Meanwhile, a multi-phase four-stream code for liquid natural gas (LNG) SWHE is developed. The following conclusions are obtained: (1) the parallel heat transfer calculation program can predict the change of the heat transfer coefficient and the temperature inside the heat exchanger well. (2) The temperature decreasing rate of feed gas inside SWHE decreases gradually. When the feed gas is liquefied completely, the temperature decreasing rate increases gradually. (3) The heat transfer performance of SWHE is greatly affected under sea conditions.

Removal of Residual Pharmaceuticals in a Secondary Effluent from a Sewage Treatment Plant by Ozonation

This study evaluated the effect of ozonation on the removal of pharmaceuticals in a secondary effluent collected from a sewage treatment plant in Korea. 26 pharmaceuticals were detected in the range of 2.3~144.7 μg/L from a secondary effluent used as a tested water. Clarithromycin etc (macrolide antibiotics), Atenolol etc (antiarrythmics), N,N-diethyl-m-toluamide (repellents), Sulpiride (antipsychotics), Bezafibrate (antilipemics) etc showed a relatively high resistance to ozone compared to other pharmaceuticals at a low ozone feed rate of 0.036 mg/L/min. A high ozone feed rate of 0.36 mg/L/min removed by more than 90% of initial concentration for most of pharmaceuticals, indicating that ozonation is a promising treatment process for residual pharmaceuticals in sewage. The ratio of the number of pharmaceuticals with a removal efficiency of more than 70% to ozone consumption during ozonation showed that the supply of ozone gas by a low concentration could improve the performance of ozonation in removing pharmaceuticals at a same ozone gas flow rate condition. Key words: Pharmaceuticals, Micropollutants, Ozone, Antibiotics

Bubble formation on submerged micrometer-sized nozzles in polymer solutions: An experimental investigation

This research presents detailed formation of air bubbles on different submerged micrometer-sized nozzles in Newtonian and non-Newtonian fluids. An experimental study is performed using the high-speed camera on three nozzles with diameters of 150, 450, and 600 μm under relatively low gas flow rate conditions (0.1∼1 ml/min). Distilled water and various concentrations of Carboxymethyl cellulose (CMC) aqueous solutions are utilized as the continuous phase for each type of fluid. Different characteristics of the bubble formation such as volume change, frequency, height, maximum width, and instantaneous contact angle are obtained using an image processing technique and the Young-Laplace equation. Effect of different parameters including gas flow rate, nozzle diameter, concentration, and rheological properties of the continuous phases are investigated. Also, a detailed dynamic force analysis is performed to survey the role of fluid properties on the effective forces. The force balance reveals that the surface tension force is dominant in the smallest orifice, while its influence decreases as the orifice diameter increases. Moreover, it was observed that the drag and hydrostatic forces have relatively noticeable contributions in this low gas flow rates. Furthermore, results show that under the conditions of this research, the characteristics of the bubble are weakly dependent on the gas flow rate. On the other hand, the concentration of the CMC and the rheological behavior of the non-Newtonian fluids so-obtained have a significant influence on bubble formation process. Also, observations made and predictions done as to the bubble’s curvature (say, based on Young-Laplace equation) suggest that the necking phenomenon does not exhibit itself at the top of the nozzle in non-Newtonian liquids flowing through micron-sized nozzles.

Analysis of Pseudo-Turbulence Flow Induced by Bubble Periodic Formation in Non-Newtonian Fluids

Laser Doppler Velocimetry (LDV) has been employed to determine pseudo-turbulence characteristics of the flow field around bubble train forming in non-Newtonian caboxymethylcellulose (CMC) aqueous solution at low gas flow rate condition. The Reynolds stress and turbulent intensity of the liquid were investigated by means of Reynolds time-averaged method. The experimental results show that axial Reynolds stress rises greatly and then fluctuates slightly with the vertical height, whereas displays symmetrical Gaussian distribution in the horizontal direction; Radial Reynolds stress changes nonobviously in the vertical direction, but increases followed by a decrease in the horizontal direction. The axial turbulent intensity begins to wave to some degree with the height for near vertical axis passing through orifice center, but maintains constant within bubble channel in the horizontal direction; Radial turbulent intensity gets down with the vertical height, compared with the opposite trend of its variation with the horizontal distance.

Numerical simulation of gas-bubble formation through two submerged orifices

In this work, two-dimensional numerical simulations are carried out to analyse the dynamics of gas-bubble formation at two adjacent orifices submerged in an immiscible Newtonian liquid under the condition of constant gas flow rate using finite-volume-based commercial CFD solver Ansys Fluent. Two conditions for the ambient liquid are considered: firstly the liquid is in quiet condition and secondly, it is also co-flowing with the gas stream. The full cycle from the bubble formation to its detachment and the corresponding dynamics are simulated using the volume of fluid (VOF) method, which is one of the efficient front capturing techniques of Eulerian family. The study includes: (i) time sequence profile of bubble formation to clearly represent the bubble growth, neck formation and bubble break-up at a given Weber number (We), Reynolds number (Re), Bond number (Bo) and liquid to gas mean velocity ratio (Vr); (ii) bubble growth history for different Vr and at constant Re, We and Bo; (iii) effect of orifice spacing on bubbling synchronicity and frequency at given Vr, We, Re and Bo and (iv) synchronous bubbling regime, bubble size and formation time determination, bubble coalescence phenomenon and technique for its inhibition.

Development of a Novel Micro Photoionization Detector for Rapid Volatile Organic Compounds Measurement.

The simulation of the gas flow field and electrostatic field in the photoionization detector by COMSOL was conducted based on principle investigation in the present study. Under the guidance of simulation results, structural optimization was carried out to significantly reduce the dead volume of the ionization chamber, and finally, the relationship between offset voltage and collection efficiency was obtained which led to a remarkable increase in the collection efficiency of charged ions in the photoionization detector. Then an ionization chamber with low interference and fast response was developed. Then experiment was performed with toluene as a VOCs gas under the condition of optimal gas flow rate of 50 ml, UV lamp ionization energy of 10.86 eV. The results showed that the ion collection efficiency reached 91% at a bias voltage of 150 V. Moreover, a preferred linearity of 99.99% was obtained, and a ppb level of LOD can be achieved. The determination results well-fitted the relationship between offset voltage and the response value obtained in the simulation.

Energy harvesting performance of hexagonal shaped thermoelectric generator for passenger vehicle applications: An experimental approach

In this study, the waste heat recovery performance of a hexagonal thermoelectric generator (TEG) was investigated experimentally. Based on the system configuration and dimensions, a total of 18 thermoelectric modules (TEMs) were used for thermal energy harvesting. The internal finned structures of the hexagonal TEG were placed on the inner surface of the exhaust gas channel, in consideration of the thermal resistance and friction factor, in order to augment the heat transfer from the exhaust gas to the thermoelectric modules (TEMs), under various operating conditions. The surface of the TEMs was positioned on the hexagonal-shaped exhaust gas channel surface, whereas the other surface of the TEMs was maintained cool by a set of coolers through which the engine coolant flowed. The coolant line was modified in order to induce a total coolant flow of 10 LPM at 353 K from a coolant controller to the hexagonal TEG. In this study, the assembled hexagonal TEG was installed in the middle of the exhaust gas pipe of the internal combustion engine manufactured for hybrid electric vehicles, and was used as the heat source. The waste heat recovery performance of the hexagonal TEG was evaluated by considering eight engine-operating conditions under which the automotive vehicles were most frequently driven. The output power of the hexagonal TEG tended to increase with the increase in engine speed and load, and ranged between 21.2 and 98.8 W, which corresponded to a conversion efficiency of ∼1.3–2.6%. An acceptable maximum pressure drop across the hexagonal TEG of ∼2.1 kPa was observed for the maximum exhaust gas flow rate condition.

Online Monitoring of Functional Electrical Properties in Aerosol Jet Printing Additive Manufacturing Process Using Shape-From-Shading Image Analysis

The goal of this research is online monitoring of functional electrical properties, e.g., resistance, of electronic devices made using aerosol jet printing (AJP) additive manufacturing (AM) process. In pursuit of this goal, the objective is to recover the cross-sectional profile of AJP-deposited electronic traces (called lines) through shape-from-shading (SfS) analysis of their online images. The aim is to use the SfS-derived cross-sectional profiles to predict the electrical resistance of the lines. An accurate characterization of the cross section is essential for monitoring the device resistance and other functional properties. For instance, as per Ohm’s law, the electrical resistance of a conductor is inversely proportional to its cross-sectional area (CSA). The central hypothesis is that the electrical resistance of an AJP-deposited line estimated online and in situ from its SfS-derived cross-sectional area is within 20% of its offline measurement. To test this hypothesis, silver nanoparticle lines were deposited using an Optomec AJ-300 printer at varying sheath gas flow rate (ShGFR) conditions. The four-point probes method, known as Kelvin sensing, was used to measure the resistance of the printed structures offline. Images of the lines were acquired online using a charge-coupled device (CCD) camera mounted coaxial to the deposition nozzle of the printer. To recover the cross-sectional profiles from the online images, three different SfS techniques were tested: Horn’s method, Pentland’s method, and Shah’s method. Optical profilometry was used to validate the SfS cross section estimates. Shah’s method was found to have the highest fidelity among the three SfS approaches tested. Line resistance was predicted as a function of ShGFR based on the SfS-estimates of line cross section using Shah’s method. The online SfS-derived line resistance was found to be within 20% of offline resistance measurements done using the Kelvin sensing technique.

Bubble Motion and Gas-Liquid Mixing in Metallurgical Reactor with a Top Submerged Lance

Abstract The multiphase fluid mixing and bubble motion in a scale-down Isa smelting furnace with a top submerged lance were investigated through cold water model experiments. The mixing time in the liquid bath was determined by a novel criterion, and the bubble formation frequency and gas-liquid contact area were also measured by high-speed photographing. The empirical equations of mixing time (Tm) relating to mixing energy (ε) were ${T_{{\rm{m}},s}} = 913{\varepsilon ^{ - 0.5}}$ for solid tracer and ${T_{{\rm{m}},l}} = 624{\varepsilon ^{ - 0.48}}$ for liquid tracer, respectively. The mixing time trended down with the increasing of bubble formation frequency, affected slightly by the bubbles with small size and decreased obviously when increasing the gas-liquid contact area. The optimal conditions of gas flow rate, bath height, lance submerged height and lance diameter to guarantee high-efficiency mixing and low-level surface fluctuation/splashing were obtained.

Decarburization and Inclusion Removal Process in Single Snorkel Vacuum Degasser

Abstract In the current work, the coupled mathematical models for decarburization, fluid flow model and inclusion collision-aggregation model were solved to investigate the spatial distribution of carbon, inclusion’s collision-aggregation and removal in a single snorkel vacuum refining furnace (SSF). The numerical results show that the turbulence kinetic energy of ladle in SSF is much greater than that in RH, which can shrink the dead zone and prompt the mixing in the ladle. The overall decarburization reaction rate can be described as a first-order reaction. On the condition of the same gas flow rate, the volumetric mass transfer coefficient for decarburization in SSF is almost twenty times bigger than that in RH, which leads to a much greater decarburization rate in SSF. The spatial distribution of carbon mass fraction in SSF is quite different from that in RH. There is the greater mass fraction of carbon at the recirculation zone under up-snorkel in RH, but this phenomenon disappears in SSF. The inclusion removal can be simplified as the mass transfer between liquid steel to slag, refractory wall and bubble surface. And the overall inclusion removal rate can be regarded as a first-order reaction. The volumetric mass transfer coefficient for inclusion removal in SSF is about three times as that in RH, the inclusion removal rate in SSF is greater than that in RH. The inclusions with different size have different removal rates in SSF. For inclusion flotation after deoxidization, the treatment time in SSF is less than that in RH.

Experimental study and numerical simulation of periodic bubble formation at submerged micron-sized nozzles with constant gas flow rate

Visualization experiments and numerical simulations were carried out to investigate the bubble dynamic behavior at the submerged micron orifice. The diameters of the orifices varied from 0.136mm to 0.204mm. The bubble formation process was recorded by a high-speed video camera. The detailed bubble characteristics were obtained through image processing and a following Matlab analysis. The outcomes indicate that under a low gas flow rate, the bubble grows and detaches individually, and the bubble formation progress can be differentiated into three stages: nucleation, stable growth, and necking. The differences between micron and millimeter level orifices are obvious at the initial level of bubble formation. At the micron level, the bubble is strongly influenced by capillary pressure and it causes a longer waiting time. It is also found that the bubble shape only depends on the instantaneous bubble volume and has no relation with the gas flow under a high flow rate. We observed that the coalescence bubbling regimes are different from the multi-period formation mechanism at the millimeter level. The final bubble volume demonstrates an index increasing law with the gas flow rate. Additionally, the volume-of-fluid method was used for numerical simulation of the bubble formation process. It indicates that numerical simulations can finely predict the dynamic features of bubbles against the experiments, under low gas flow rate conditions (0.95–4.83ml/min).

Recovery of waste tyres by pyrolysis in a fixed bed reactor for liquid fuel production: effects of pyrolysis conditions on oil yield

One of the major enviromental problems around the world is disposal of waste tyres without any purpose. Disposal of waste tyres is an increasing enviromental problem. Also because of high content of valuable chemicals and other compounds hidden in the waste tyres, disposal of them is an economical problem as well. Pyrolysis is a thermochemical process that can be used for recovery of the valuable chemicals in the waste tyre. Pyrolysis is a recycling process in which, liquid product can be used as a fuel directly or can be mixed with petroleum refined oils. Derived gaseous product can also be used as a fuel and solid product can be considered as a fuel and low grade carbon black. In this work, granulated waste tyres have been pyrolyzed in a fixed bed reactor under different conditions of temperature, heating rate and inert purging gas (N2) flow rate. The purpose of the study was to optimize the pyrolysis parameters in order to produce the highest amount of oil. 400°C, 450°C and 500°C were selected and the maximum yield of liquid product was observed at 450°C. Among the heating rates of 10°C/min, 15°C/ min and 20°C/min; 10°C/min was the parameter that gave maximum oil yield. And while working at 450°C and 10°C/min; N2(g) flow rate was examined by using 0.5 L/min, 1 L/min and 1.5 L/min. The maximum oil yield was observed at 1 L N2(g) /min. According to the results of the study; at 450°C, with a heating rate of 10°C/min and 1 L N2(g)/min gave the maximum yield of oil, which is 53.33 wt.%. The pyrolytic oil from waste tyre had the Gross Calorific Value of 42.6 MJ/kg which is very close to that of commercial diesel no 2 (around 42-46 MJ/kg). The pyrolytic oil produced is a promising fuel and can be used as a source of energy after some future work for make it suitable for use in vehicles or in other areas like factories or houses etc.

Disintegration process and performance of a coaxial porous injector

In order to understand the breakup performance of coaxial porous injectors, the sprays of coaxial porous injectors with two different porous material cylinder lengths were compared with those of conventional shear coaxial injectors. To allow comparison, the wall injection lengths were designed to be equivalent to the value of the recess depth. Cold flow sprays were visualized using back-lit photography methods and analyzed quantitatively with a laser diffraction apparatus, in order to study the effects of the momentum flux ratio and Weber number on the breakup for each type of injector. In case of the shear coaxial injector, the large liquid core was observed in low air mass flow rate condition. However, the destabilization of the liquid jet from the coaxial porous injector is almost complete within the inner region, near the injector face plate. Additionally, better breakup performance in low gas flow rate condition was obtained when the porous cylinder length decreased, while the shear coaxial injectors showed better breakup efficiency when the recess length increased. In conclusion, the different breakup process caused by the radial momentum in the inner region of the porous injector disintegrated the liquid core.

水平円柱下流の気液界面積濃度分布の遷移

Measurements of the interfacial area concentration and the void fraction in a vertical upward air-water two-phase flow downward of single horizontal tube and horizontal tube bundle were carried out by a double sensor electrical conductivity probe. The test section comprised a 50mm × 50mm square channel partially obstructed by the single horizontal tube and the horizontal tube bundle inside. Five types of the test sections which the horizontal tube arrangement is different were used to provide various distributions of air-water two-phase flow downstream of the test section. The superficial gas velocity and superficial liquid velocity ranged from 0.02 to 0.20 m/s and from 0.13 to 0.53 m/s, respectively. Local flow measurements were performed at the three axial locations of z (z') = 110 (70), 340 (300), and 640 (600) mm and the transverse locations from r = 3 to 25 mm. The single horizontal tube and the horizontal tube bundle effect the distributions of the interfacial area concentration and the void fraction at z (z') = 110 (70). This effect was decreased along the flow direction due to the diffusion of bubble toward horizontal direction. At high gas flow rate conditions, void fraction increase, while interfacial area concentration decrease with increasing gas flow rate because of the bubble coalescence.

THE EFFECT OF SOLIDS ON THE BEHAVIOUR OF THE DOWNCOMER OF A JAMESON CELL

The effect of solids on the behaviour of the downcomer of a Jameson cell was studied in terms of the hydrophobic/hydrophilic character of the solids. Hydrophobic (carbon), and hydrophilic (silica sand) solids were used, separately. The experiments were carried out under controlled conditions of gas flow rate, pulp flow rate, and pulp consistency. The observed operating variables were the extension of the downcomer operating regions (pulp jet, mixing, and collection) and gas hold-up. It was observed that gas bubbles are smaller and more uniform in size when the pulp is comprised of silica (hydrophilic particles), as compared with pulps consisted of carbon (hydrophobic particles). When measuring a profile of gas holdup in the separation cell, experimental results show that a more homogeneous radial holdup distribution is achieved in the case of a slurry with silica sand rather than the pulp made of carbon.

Performance of iodide vapour absorption in the venturi scrubber working in self-priming mode

The self-priming venturi scrubber is the key component of filtered containment venting systems for the removal of radioactive products during severe accidents in nuclear power plants. This paper is focused on the absorption performance of iodide vapour in the venturi scrubber, based on experiment and mathematical calculation. The results indicate that the absorption efficiency is closely related to solution flow rate, gas flow rate and temperature, but is not sensitive to iodide inlet concentration. When solution flow rate is low, the absorption efficiency increases rapidly with increasing the solution flow rate, and when the solution is excessive, the absorption efficiency remains around 99% stably; the influence of gas flow rate on absorption efficiency is mainly reflected in the variation of gas and liquid contacting time; when the solution flow rate is low, the increase of gas flow rate will led to an obvious decrease in absorption efficiency; temperature is not important when gas flow rate in constant but becomes effective for improving the absorption efficiency when gas velocity is constant. The proposed mathematical model can predict the iodide absorption process well in the range of experimental conditions. Especially, in the condition of lower gas flow rate and higher solution flow rate, the prediction accuracy is more satisfactory; however the accuracy of prediction will decrease at higher gas flow rates and lower solution flow rates because of neglecting the transverse exchange between gas and liquid phase.

Simultaneous Determination of Thorium and Uranium in Mineral Fertilizers by Inductively Coupled Plasma Optical Emission Spectrometry

The simultaneous determination of thorium and uranium in mineral fertilizers by inductively coupled plasma optical emission spectrometry (ICP OES) was optimized. The three-level factorial design was applied to optimize the operating conditions of radiofrequency power and nebulizer gas flow rate. The analytical method was specific and selective for both elements.

Computational modelling of the condensation of fast pyrolysis vapours in a quenching column. Part A: Hydrodynamics, heat transfer and design optimisation

Direct contact heat exchangers (quenching columns) are considered to be the optimum types of heat exchangers for the fast pyrolysis process. In this study, the hydrodynamics and heat transfer characteristics of a bench scale quenching column are presented. These have been compared with the experimental observations on flooding phenomena which are reported when the quenching column is operated at the design gas flow rates of the fast pyrolysis reactor. The quenching column was found to operate without flooding at 10% of the design flow rate, while flooding was still present even at 50% of the design gas flow rate. Four different design configurations, which are different in terms of weirs and hole placement on the disc and donut plates, are modelled and tested under full gas flow rate conditions. All four cases show normal quenching column operation without any flooding phenomena present and a gas flow time of less than 1s. The pressure drop across the system was considerably reduced to 15Pa in the modified configuration compared to 90Pa in the baseline model. The hydrodynamic and heat transfer characteristics are thoroughly analysed and proposed optimal design configuration for the effective quenching operation.

Influence of plasma characteristics on nitrogen mixing into shielding gas in helium gas tungsten arc welding

The influence of welding condition on the mixing of atmospheric nitrogen into the arc plasma in helium gas tungsten arc welding was analysed by numerical simulations. In order to evaluate the effects of the convection flow and the diffusion on the nitrogen mixing phenomenon, the distributions of the Peclet number were used. Elongation of the electrode length has low impact on the decrease of shielding gas concentration because the convection flow becomes dominant in this area, which indicates higher Peclet numbers. Meanwhile, nitrogen diffusion increases in the plasma area with a temperature of about 10,000 K, so that elongation of the arc length leads to a remarkable decrease of shielding gas concentration. Additionally, the impact of convection flow increases in the arc centre area where high-velocity plasma jet exists, and the shielding gas concentration tends to rise owing to higher welding current in the condition of sufficient shielding gas flow rate.