Carrier Gas Effects Research Articles

Biomass gasification tar removal using dielectric barrier discharge reactor: Effect of reactor geometry and carrier gases

This study investigates the impact of reactor geometry (varying external electrode length) of Dielectric Barrier Discharge (DBD) reactors on the decomposition of toluene, a model compound for biomass gasification tar, using different carrier gases and various power levels. Results reveal that toluene decomposition is higher at longer electrode lengths (30 mm) at all power levels tested. Specifically, the toluene decomposition in H2 carrier gas at 30 mm electrode length increased from 67.2 % to 97.5 % with rising power from 5 to 40 W, while it ranged from 52 % to 97.4 % at 15 mm electrode length. The decomposition of toluene was found to be higher in N2 carrier gas than in H2 carrier gas at both discharge lengths. At 30 mm external electrode and with rising power from 5 to 40 W, toluene decomposition ranged from 90.5 % to 98.7 %. Similarly, when the electrode length was reduced from 30 to 15 mm for N2 carrier gas, the decomposition of toluene ranged from 74 % to 97.9 %. Thus, the results indicate that the decomposition of toluene is affected by both the electrode length and the nature of the carrier gas. The effect of electrode length was significant at lower power levels, and the difference between the conversion at both electrode lengths nearly disappeared at higher power levels.

Homogeneous water nucleation in argon, nitrogen, and nitrous oxide as carrier gases.

Experimental results for homogeneous nucleation of water droplets in the presence of argon, nitrogen, and, for the first time, nitrous oxide as carrier gases are reported. The main objective of the study was to investigate the effects of different carrier gases on the nucleation rate. These gases differ in the number of atoms comprising the molecule, which affects the expansion ratio required to reach the target nucleation temperature. The experiments cover nucleation temperatures from 220 to 260K, nucleation pressures from 40 to 73kPa, supersaturations of 6.5-20, and nucleation rates ranging from about 4 × 105 to 4 × 109cm-3s-1. The new data obtained with a modernized expansion chamber utilizing the nucleation pulse method show good agreement with the available literature data. Another important point of our work is the application of real gas corrections to calculate the nucleation temperature and supersaturation. The results show that the influence of carrier gases on nucleation rate in the investigated pressure range is modest (less than a factor of 7), while without the real gas correction, the apparent effect of carrier gas is significant, with differences as high as a factor of 90.

Pyrolysis analysis of polyethylene terephthalate: effects of carrier gases (N2, He, and Ar) and zeolite catalyst (A4) on yield

AbstractPolyethylene terephthalate, the main material used for beverage bottle packaging, accounts for an average of 7.6% of all plastic waste in Europe. This material is not biodegradable and takes several centuries to decompose. The pyrolysis process in the presence of a catalyst and carrier gases can convert PET waste into solid, liquid, and gaseous materials that can be utilized as fuel. This study evaluated the effects of different carrier gases on the pyrolysis of PET waste in the presence and absence of a zeolite catalyst (A4). The results showed that the catalyst affected the pyrolysis yield; it increased the liquid and gaseous products, as well as the benzoic acid content. However, the effect declined when replacing the carrier gas with a larger molecular weight carrier gas. The alcohol content of the char was larger than that of the wax. The maximum alcohol content was detected under He, implying the direct impact of the carrier on the pyrolysis products. The hydrocarbons identified in the char were affected by changing the carrier gas, and a different distribution of hydrocarbon groups was found by converting the aromatic group into aliphatic compounds. Broadly speaking, in the presence of helium gas and the catalyst, the lowest amount of coke and the lightest compounds were observed. The amount of coke in the presence of nitrogen gas was the same as that of helium gas, but it had heavier compounds. Meanwhile in the presence of argon gas, which has a high molecular mass, more coke and heavier compounds were obtained. © 2022 Society of Chemical Industry (SCI).

Pyrolysis of bottle‐grade polyethylene terephthalate: Effect of carrier gases on carriage of pyrolysis products

AbstractThe production of widely‐used bottle‐grade polyethylene terephthalate (PET) is now considered an environmental problem on a global scale. The urgent need for renewable energy reveals the necessity of employing thermochemical recycling methods. The use of a carrier gas is among the parameters affecting the pyrolysis process, for it is responsible for carrying pyrolysis products to separate condensable products. In this study, PET granules were pyrolyzed at 500°C with three carrier gases: N2, He, and Ar. According to the results, using a gas with lower molecular weights increased the production of gaseous products (30.94%). However, using a gas with higher molecular weights led to the production of further char (20.2%) associated with the increased reforming reaction rate and hydrogen production in the gaseous phase. The presence of different carrier gases changed tar composition and aromatics; therefore, the highest acid benzoic level was detected in the nitrogen atmosphere. Evaluating the thermal stability of wax and char indicated that the weight loss of char was larger in nitrogen (44.8 wt%) than in the other two carrier gases. However, there were further heavy oxygenated components in wax under the helium and nitrogen atmospheres. Those components degraded more difficultly.

Decomposition of benzene vapour using non-thermal plasmas: The effect of moisture content on eliminating solid residue

This study investigated the effect of power, carrier gases and moisture content on the removal of benzene in dry air and humidified air in a DBD plasma reactor. The influence of plasma power, carrier gases and humidity on benzene conversion and product selectivity were explored. The main decomposition products were CO, CO2, lower hydrocarbons (C1-C5) and solid residue in the reactor. This study reveals that benzene removal efficiency and the selectivity to CO2 increased with power in both dry and humidified air. In contrast, the selectivity to lower hydrocarbons decreased. The most important finding of this study was that the formation of solid residue in the plasma reactor can be removed in humidified air. As the amount of water vapour increased from 0% to 35% at 20 ℃, the benzene removal efficiency and CO2 selectivity increased; O3 decreased from 7.3 ppm to 0.5 ppm; NOx and solid residue were eliminated. These effects are probably due to OH radicals, and the mechanism for the various effects are proposed. The maximum benzene removal efficiency observed was 93.7%, and the maximum selectivity to CO2 was 82.4% (both at a relative humidity of 35% at 20 ℃ and 10 W). This study demonstrated that plasma-assisted benzene remediation operating in a humid condition can overcome the major drawback of plasma-assisted VOC conversion in the air by eliminating the solid residues in the reactor.

Effect of carrier gases on the entrainment defects within AZ91 alloy castings

An entrainment defect (also known as a double oxide film defect or bifilm) acts a void containing an entrapped gas when submerged into a light-alloy melt, thus reducing the quality and reproducibility of the final castings. Previous publications, carried out with Al-alloy castings, reported that this trapped gas could be subsequently consumed by the reaction with the surrounding melt, thus reducing the void volume and negative effect of entrainment defects. Compared with Al-alloys, the entrapped gas within Mg-alloy might be more efficiently consumed due to the relatively high reactivity of magnesium. However, research into the entrainment defects within Mg alloys has been significantly limited. In the present work, AZ91 alloy castings were produced under different carrier gas atmospheres (i.e., SF6/CO2, SF6/air). The evolution processes of the entrainment defects contained in AZ91 alloy were suggested according to the microstructure inspections and thermodynamic calculations. The defects formed in the different atmospheres have a similar sandwich-like structure, but their oxide films contained different combinations of compounds. The use of carrier gases, which were associated with different entrained-gas consumption rates, affected the reproducibility of AZ91 castings.

Homogeneous water nucleation in carbon dioxide–nitrogen mixtures: Experimental study on pressure and carrier gas effects

New homogeneous nucleation experiments are presented at 240 K for water in carrier gas mixtures of nitrogen with carbon dioxide molar fractions of 5%, 15%, and 25%. The pulse expansion wave tube is used to test three different pressure conditions, namely, 0.1, 1, and 2 MPa. In addition, a restricted series of nucleation experiments is presented for 25% carbon dioxide mixtures at temperatures of 234 and 236 K at 0.1 MPa. As pressure and carbon dioxide content are increased, the nucleation rate increases accordingly. This behavior is attributed to the reduction in the water surface tension by the adsorption of carrier gas molecules. The new data are compared with theoretical predictions based on the classical nucleation theory and on extrapolations of empirical surface tension data to the supercooled conditions at 240 K. The extrapolation is carried out on the basis of a theoretical adsorption/surface tension model, extended to multi-component mixtures. The theoretical model appears to strongly overestimate the pressure and composition dependence. At relatively low pressures of 0.1 MPa, a reduction in the nucleation rates is found due to an incomplete thermalization of colliding clusters and carrier gas molecules. The observed decrease in the nucleation rate is supported by the theoretical model of Barrett, generalized here for water in multi-component carrier gas mixtures. The temperature dependence of the nucleation rate at 0.1 MPa follows the scaling model proposed by Hale [J. Chem. Phys. 122, 204509 (2005)].

Natural 222Rn as a tracer of mixing and volatilization in a shallow aquifer during a CO2 injection experiment

AbstractThis study aims to evaluate the application of 222Rn in groundwater as a tracer for monitoring CO2 plume migration in a shallow groundwater system, which is important to detect potential CO2 leakage in the carbon capture and storage (CCS) project. For this research, an artificial CO2‐infused water injection experiment was performed in a shallow aquifer by monitoring hydrogeochemical parameters, including 222Rn. Radon in groundwater can be a useful tracer because of its sensitivity to sudden changes in subsurface environment. To monitor the CO2 plume migration, the data were analysed based on (a) the influence of mixing processes on the distribution of 222Rn induced by the artificial injection experiment and (b) the influence of a carrier gas role by CO2 on the variation of 222Rn. The spatio‐temporal distributions of radon concentrations were successfully explained in association with horizontal and vertical mixing processes by the CO2‐infused water injection. Additionally, the mixing ratios of each monitoring well were calculated, quantitatively confirming the influence of these mixing processes on the distribution of radon concentrations. Moreover, one monitoring well showed a high positive relationship between 222Rn and Total dissolved inorganic carbon (TIC) by the carrier gas effect of CO2 through volatilization from the CO2 plume. It indicated the applicability of 222Rn as a sensitive tracer to directly monitor CO2 leakage. When with a little effect of carrier gas, natural 222Rn in groundwater can be used to compute mixing ratio of CO2‐infused water indicative of CO2 migration pathways. CO2 carrier gas effect can possibly increase 222Rn concentration in groundwater and, if fully verified with more field tests, will pose a great potential to be used as a natural tracer for CO2.

Homogeneous water nucleation: Experimental study on pressure and carrier gas effects.

Homogeneous nucleation of water is investigated in argon and in nitrogen at about 240 K and 0.1 MPa, 1 MPa, and 2 MPa by means of a pulse expansion wave tube. The surface tension reduction at high pressure qualitatively explains the observed enhancement of the nucleation rate of water in argon as well as in nitrogen. The differences in nucleation rates for the two mixtures at high pressure are consistent with the differences in adsorption behavior of the different carrier gas molecules. At low pressure, there is not enough carrier gas available to ensure the growing clusters are adequately thermalized by collisions with carrier gas molecules so that the nucleation rate is lower than under isothermal conditions. This reduction depends on the carrier gas, pressure, and temperature. A qualitative agreement between experiments and theory is found for argon and nitrogen as carrier gases. As expected, the reduction in the nucleation rates is more pronounced at higher temperatures. For helium as the carrier gas, non-isothermal effects appear to be substantially stronger than predicted by theory. The critical cluster sizes are determined experimentally and theoretically according to the Gibbs-Thomson equation, showing a reasonable agreement as documented in the literature. Finally, we propose an empirical correction of the classical nucleation theory for the nucleation rate calculation. The empirical expression is in agreement with the experimental data for the analyzed mixtures (water-helium, water-argon, and water-nitrogen) and thermodynamic conditions (0.06 MPa-2 MPa and 220 K-260 K).

Effects of temperature, pressure, and carrier gases on the performance of an aerosol particle mass analyser

Abstract. Effective density is a crucial parameter used to predict the transport behaviour and fate of particles in the atmosphere, and to measure instruments used ultimately in the human respiratory tract (Ristimäki et al., 2002). The aerosol particle mass analyser (APM) was first proposed by Ehara et al. (1996) and is used to determine the effective density of aerosol particles. A compact design (Kanomax APM-3601) was subsequently developed by Tajima et al. (2013). Recently, a growing number of field studies have reported application of the APM, and experimental schemes using the differential mobility analyser alongside the APM have been adopted extensively. However, environmental conditions such as ambient pressure and temperature vary with the experimental location, and this could affect the performance of the APM. Gas viscosity and Cunningham slip factors are parameters associated with temperature and pressure and are included in the APM's classification performance parameter: λ. In this study, the effects of temperature and pressure were analysed through theoretical calculation, and the influence of varying carrier gas was experimentally evaluated. The transfer function and APM operational region were further calculated and discussed to examine their applicability. Based on the theoretical analysis of the APM's operational region, the mass detection limits are changed with the properties of carrier gases under a chosen λ value. Moreover, the detection limit can be lowered when the pressure is reduced, which implies that performance may be affected during field study. In experimental evaluation, air, oxygen, and carbon dioxide were selected to atomize aerosols in the laboratory with the aim of evaluating the effect of gas viscosity on the APM's performance. Using monodisperse polystyrene latex (PSL) spheres with nominal diameters of 50 and 100 nm, the classification performance of the APM was slightly varied with carrier gases, while the classification accuracy was consistently within 10 %.

Numerical simulation of carrier gas effects on flow field, species concentration and deposition rate in the chemical vapor deposition of carbon

A 2D numerical model was established for simulating the chemical vapor deposition (CVD) of carbon in a vertical reactor. A full multi-component diffusion model was proposed to describe the diffusion of the gas species. The effects of Ar, N2or H2 carrier gases on the flow field, species concentration and deposition rate of pyrocarbon were investigated using C3H6 as the carbon source. Results show that H2 improves the stability of the gas flow. The concentration distributions of CH4, C2H2, C2H4 and C6H6 are uniform in H2. The pyrocarbon deposition rate is lowered, but the uniformity of deposition is improved when H2 is used as the carrier gas compared with N2 or Ar. The simulation results agree well with the experimental ones.

Oxygen vacancy levels on gadolinia-doped ceria interlayer deposited by atmospheric pressure plasma jet for solid oxide fuel cells

The oxygen vacancy levels as a factor on different gadolinia-doped ceria interlayer (GDCi) films deposited on yttria stabilized zirconia (YSZ) electrolyte substrates by an atmospheric pressure plasma jet (APPJ) via precursor solution of nitrate salts are investigated. Focusing on the effect of carrier gases, scanning electron microscopy (SEM), Raman, and X-ray diffraction (XRD) are implemented for the materials characterization of the as-deposited GDCi films and sintered-GDCi films at various temperatures. The higher level of oxygen vacancies in GDCi films adhered on 8YSZ electrolyte are evidently analyzed using Ar as the carrier gas during the deposition, of which the interdiffusion resulted in the formation of (GDC + YSZ) solid solution for sintering over 1300 °C degraded the total conductivity. The deposition of GDCi films on 8YSZ by APPJ method using O2 carrier gas significantly improved the total conductivities of the whole electrolyte layers. Moreover, this study provides the useful insight into the oxygen vacancy levels on GDC films as interlayer (GDCi) to improve the values of open circuit voltage in LSM/GDCi/YSZ/Pt full-cell, as well as offering the efficiency of APPJ as one step deposition process.

Study on Effects of Different Carrier Gases on Characteristics of the Supersaturated Environment in the One-/Multi-section Growth Tube

The supersaturation profiles in one/multi-section growth tube were predicted under the conditions of different carrier gases for two kinds of typical supersaturation achieving methods. The results show that Lewis number (Le) of the carrier gas is an important factor affecting the supersaturation profiles. For the one-section growth tube, the carrier gas with smaller Le is beneficial to higher level and flatter trend of supersaturation profiles for method 1, where supersaturated environment is achieved by a cool saturated flow into a warm-walled growth tube. However, for the carrier gas of larger Le, the higher level but less stable supersaturation profiles are presented from method 2, where a warm saturated flow into a cold-walled growth tube. With the carrier gas of large Le (>1) from method 1 and the carrier gas of small Le (<0.5) from method 2, efficient supersaturated environment cannot be achieved under the ordinary condition. In the multi-section growth tube, the more minimum number of the sections ...

Effect of different carrier gases on productivity enhancement of a novel multi-effect vertical concentric tubular solar brackish water desalination device

A novel multi-effect vertical concentric tubular solar brackish water desalination device is introduced in present study. The device consists of four closely spaced concentric pipes, in which the feed water gets preheated by hot brine water to guarantee the evaporation efficiency. An experimental investigation and analytical analysis were carried out to signify the effect of carrier gas-water vapor mixture on productivity enhancement of the device. Different carrier gases were used in the performance evaluation: carbon dioxide, helium, nitrogen, oxygen, air and argon. The water yield and the top/bottom temperature values of condensation surface of the device with different carrier gases were tested. In addition, the present investigation is presented an approach to predict the theory yield based on the internal heat and mass transfer mechanism. The experimental results indicate that, when the heating temperature is 80 °C and the carrier gas is helium, the water productivity rate can reach to 1.19 kg/h. It is increased by 30.76% than the carrier gas of air. The numerical results had been calculated and a consistent agreement with the experimental results had been obtained of different operation temperatures. The Dv under different heating temperature were obtained according to the experimental results.

Influence of External Gaseous Environments on the Electrical Properties of ZnO Nanostructures Obtained by a Hydrothermal Method.

This paper deals with experimental investigations of ZnO nanostructures, consisting of a mixture of nanoparticles and nanowires, obtained by the chemical (hydrothermal) method. The influences of both oxidizing (NO2) and reducing gases (H2, NH3), as well as relative humidity (RH) on the physical and chemical properties of ZnO nanostructures were tested. Carrier gas effect on the structure interaction with gases was also tested; experiments were conducted in air and nitrogen (N2) atmospheres. The effect of investigated gases on the resistance of the ZnO nanostructures was tested over a wide range of concentrations at room temperature (RT) and at 200 °C. The impact of near- ultraviolet (UV) excitation (λ = 390 nm) at RT was also studied. These investigations indicated a high response of ZnO nanostructures to small concentrations of NO2. The structure responses to 1 ppm of NO2 amounted to about: 600% in N2/230% in air at 200 °C (in dark conditions) and 430% in N2/340% in air at RT (with UV excitation). The response of the structure to the effect of NO2 at 200 °C is more than 105 times greater than the response to NH3, and more than 106 times greater than that to H2 in the relation of 1 ppm. Thus the selectivity of the structure for NO2 is very good. What is more, the selectivity to NO2 at RT with UV excitation increases in comparison at elevated temperature. This paper presents a great potential for practical applications of ZnO nanostructures (including nanoparticles) in resistive NO2 sensors.

Carrier gas effects on aluminum-catalyzed nanowire growth

Aluminum-catalyzed silicon nanowire growth under low-pressure chemical vapor deposition conditions requires higher reactor pressures than gold-catalyzed growth, but the reasons for this difference are not well understood. In this study, the effects of reactor pressure and hydrogen partial pressure on silicon nanowire growth using an aluminum catalyst were studied by growing nanowires in hydrogen and hydrogen/nitrogen carrier gas mixtures at different total reactor pressures. Nanowires grown in the nitrogen/hydrogen mixture have faceted catalyst droplet tips, minimal evidence of aluminum diffusion from the tip down the nanowire sidewalls, and significant vapor–solid deposition of silicon on the sidewalls. In comparison, wires grown in pure hydrogen show less well-defined tips, evidence of aluminum diffusion down the nanowire sidewalls at increasing reactor pressures and reduced vapor–solid deposition of silicon on the sidewalls. The results are explained in terms of a model wherein the hydrogen partial pressure plays a critical role in aluminum-catalyzed nanowire growth by controlling hydrogen termination of the silicon nanowire sidewalls. For a given reactor pressure, increased hydrogen partial pressures increase the extent of hydrogen termination of the sidewalls which suppresses SiH4 adsorption thereby reducing vapor–solid deposition of silicon but increases the surface diffusion length of aluminum. Conversely, lower hydrogen partial pressures reduce the hydrogen termination and also increase the extent of SiH4 gas phase decomposition, shifting the nanowire growth window to lower growth temperatures and silane partial pressures.

Numerical study of non-equilibrium condensation and shock waves in transonic moist-air and steam flows

Transonic condensing/evaporating moist-air flow through converging-diverging nozzles is investigated numerically using non-equilibrium thermodynamic model. In this study, the results of moist-air and pure steam flows through nozzles are compared, in other words, carrier gas effects are investigated numerically. It is observed that, under similar operating conditions for steam, the wetness fraction and droplet nucleation rate along the nozzle in the case of moist-air flow is more than pure steam case. That is due to the internal flow of heat from steam portion towards the air that enhances the wetness fraction and droplet nucleation rate in moist-air case. In this study, the influence of the normal aerodynamic shocks is also studied. It is interestingly observed that, although the entropy of the mixture (steam+air) and steam portion increases along the shock, the entropy of the air portion can be reduced in response to evaporation of the liquid phase. Validation of the results is performed versus the experimental data for pure steam and moist-air flows, which show relatively good agreements.

Effect of different carrier gases and their flow rates on the growth of carbon nanotubes

The present paper examines the effect of different carrier gases and their flow rates on the growth of carbon nanotubes (CNTs). A theoretical model is developed incorporating the charging rate of the carbon nanotube, kinetics of all the plasma species, and the growth rate of the CNTs because of diffusion and accretion of ions on the catalyst nanoparticle. The three different carrier gases, i.e., argon (Ar), ammonia, and nitrogen, are considered in the present investigation, and flow rates of all the three carrier gases are varied individually (keeping the flow rates of hydrocarbon and hydrogen gas constant) to investigate the variations in the number densities of hydrocarbon and hydrogen ions in the plasma and their consequent effects on the height and radius of CNT. Based on the results obtained, it is concluded that Ar favors the formation of CNTs with larger height and radius whereas ammonia contributes to better height of CNT but decreases the radius of CNT, and nitrogen impedes both the height and radius of CNT. The present work can serve to the better understanding of process parameters during growth of CNTs by a plasma enhanced chemical vapor deposition process.

Bio-oil production from Colombian bagasse by fast pyrolysis in a fluidized bed: An experimental study

We present experimental results of fast pyrolysis of sugarcane bagasse in a fluidized-bed reactor, in which temperature, biomass feed rate, carrier gas flow, biomass, and effects of inert material particle size on global product distribution were evaluated. For this, changes in the fluid dynamic parameters were made (fluidizing gas flow between 20 and 60L/min, biomass feed rate between 2.0 and 5.3kg/h, and inert material particle size between 0.20 and 0.5125mm). Experimentally, we found that the highest yield of bio-oil was obtained when the reactor was operated at 500°C, with a carrier gas flow (nitrogen) of 50L/min, particle size of the inert material and biomass both between 0.600 and 0.425mm, and biomass feed rate of 2kg/h. Under these conditions, yields of 72.94% (w/w), 23.28% (w/w), and 3.79% (w/w) for bio-oil, biocarbon, and permanent gases were reached, respectively. Our results show synergic effects between reactivity and fluid dynamics on a fluidized bed, which ensures an efficient, fast pyrolysis process. Therefore, there are two competitive effects related to the particle diameter: first, the yield increases due to heating severity; second, the yield decreases due to entrainment of the smallest particles.

Effects of Carrier Gases on the Microstructures and Properties of Ti Coating Layers Manufactured through the Cold Spraying

This study investigated the effects of carrier gases (He and N2) on the microstructure and properties of Ti coating layers to manufacture high-density Ti layers using the cold spraying. Cold spray coating layers manufactured using He had denser and more homogenous microstructures than those produced using N2. Layers manufactured using He gas showed porosity of 0.02% and hardness of 229HV, which are better properties than the porosity (0.4%) and hardness (177HV) of N2 coating layers. The bond strength of coating layers manufactured using He recorded higher value of 74.28MPa than that manufactured using N2. This could be attributed to the fact that, when coating layers are manufactured using He gas, the powder can be easily deposited because of its high particle impact energy, facilitating the plastic deformation of the particles.