Decreasing Gas Flow Rate Research Articles

Indicator of abnormal cathode electron emission state with gas flow in Hall thrusters

The accurate diagnosis of abnormal electron emission state in hollow cathodes is crucial for the stable operation of Hall electric propulsion systems. In this study, a method of reducing the cathode working gas flow rate was used to simulate abnormal working conditions in which the cathode electron emission state (CEES) was deteriorating. By analyzing and comparing the oscillation signals under abnormal and steady-state working conditions, it was found that as the CEES deteriorated, the power content of the breathing oscillation decreased in the 1–40 kHz frequency band, and the main frequency decreased; in contrast, the power content of the transit-time oscillation increased in the 100–500 kHz range, and the main frequency was on the rise. Combined with the current growth rate analysis of breathing and transit-time oscillations, when the cathode gas flow rate decreases, the CEES deteriorates, the coupling voltage drop increases, and the potential drop in the channel decreases. The electron temperature and nonlinear power absorption of the electrons decrease, leading to a decrease in the growth rate of breathing oscillations and the breathing oscillation weakens; however, the time-averaged ion velocity and ion sound velocity in the channel decrease simultaneously, but the ion velocity decreases significantly faster than the ion sound velocity, leading to an increase in the growth rate of the transit-time oscillation, and the transit-time oscillation strengthen. Through comparison of the oscillation signals under different working conditions, such as varied anode flow rate, anode voltage, magnetic induction, it was proven to be a unique feature of CEES deteriorates, and can be used as an indicator of CEES deteriorates during the on-orbit operation of the Hall-effect thrusters.

A simulation model for ruthenium-catalyzed dry reforming of methane (DRM) at different temperatures and gas compositions

Dry reforming of methane (DRM) is an environmentally friendly technology for producing syngas while consuming CO2. However, the short lifespan of catalysts due to metal sintering, coke deposition, and sulfur poisoning hinders its widespread adoption. To address such issues, perovskite catalysts, which have shown superior performance and resistance to coke formation and poisoning, were developed. In this study, a comprehensive simulation model of a DRM reactor that employs Sr0·92Y0·08Ti0·95Ru0·05O3-d (SYTRu5) using COMSOL Multiphysics software was developed. The objective of this study is to contribute to the understanding of the intricate dynamics of DRM process via utilizing simulation models. The simulation model considered five main reactions and calculated the properties of the gas mixture considering temperatures and compositions. Using the simulation model, the distribution of gas mole fractions and temperatures were obtained. According to the results, the H2 yield and CO2 conversion rate increased with increasing operating temperature. The temperature of the catalyst bed decreased rapidly owing to the endothermicity of the reaction. Additionally, the CH4 conversion rate increased with increasing proportion of CO2, whereas the reaction converged to an equilibrium state and the temperature difference in the catalyst bed decreased with decreasing gas flow rate.

Effects of gas flow speed on bead geometry and optical emissions during laser powder bed fusion additive manufacturing

PurposePowder bed fusion processes are common due to their ability to build complex components without the need for complex tooling. While additive manufacturing has gained increased interest in industry, academia and government, flaws are often still generated during the deposition process. Many flaws can be avoided through careful processing parameter selections including laser power, hatch spacing, spot size and shielding gas flow rate. The purpose of this paper is to study the effect of shielding gas flow on vapor plume behavior and on final deposition quality. The goal is to understand more fully how each parameter affects the plume and deposition process.Design/methodology/approachA filtered-photodiode based sensor was mounted onto a commercial EOS M280 machine to observed plume emissions. Three sets of single tracks were printed, each with one of three gas flow rates (nominal, 75% nominal and 50% nominal). Each set contained single-track beads deposited atop printed pedestals to ensure a steady-state, representative build environment. Each track had a set power and speed combination which covered the typical range of processing parameters. After deposition, coupons were cross-sectioned and bead width and depth were measured. Finally, bead geometry was compared to optical emissions originating in the plume.FindingsThe results show that decreasing gas flow rate, increasing laser power or increasing scan speed led to increased optical emissions. Furthermore, decreasing the gas cross-flow speed led to wider and shallower melt pools.Originality/valueTo the best of the authors’ knowledge, this paper is among the first to present a relationship among laser parameters (laser power, scan speed), gas flow speed, plume emissions and bead geometry using high-speed in situ data in a commercial machine. This study proposes that scattering and attenuation from the plume are responsible for deviations in physical geometry.

Dynamics of bubble formation in yield stress fluids in parallelized microchannels

The bubble formation in yield stress fluids in parallelized microchannels is investigated experimentally. Nitrogen and Carbopol gel are used as the dispersed and continuous phases, respectively. Due to the feedback effect of the downstream microchannels, the uniformity and stability of bubble formation strongly depends on the properties of gels and operating conditions. The effect of yield stress on the interface evolution during bubble formation is investigated under different mass factions of Carbopol (0.2 %, 0.13 %, 0.05 %) and flow rates of gas (0.1–400 mL·min−1) and liquid (0.03–0.2 mL·min−1). The activation rate of parallel microchannels for bubble production increases with the decrease in the concentrations of Carbopol. The increase of liquid flow rate and the decrease of gas flow rate benefit the uniformity of bubble formation frequency. However, under the double-channel bubble-generation flow pattern, reducing the liquid flow rate significantly improves the stability of bubble formation.

Modeling of CO2 absorption into 4-diethylamino-2-butanol solution in a membrane contactor under wetting or non-wetting conditions

In this work, 4-diethylamino-2-butanol (DEAB) as a new type of alkanolamine solvent is used for CO2 capture in a hollow fiber membrane contactor (HFMC). A model describing the gas and liquid reactions and transport inside the membrane contactor under the wetting or non-wetting conditions was built. The countercurrent flow of natural gas and solvent was considered in the model. To investigate the influence of solvent type on decarburization efficiency, DEAB was used and compared with other common solvents such as potassium carbonate (K2CO3), triethylamine (TEA) and diethanolamine (DEA). Under the same operating conditions, the impact of parameters such as humidity, gas flow rate, liquid concentration, membrane length on the decarburization performance was examined. The results indicate that DEAB solvent had the best overall performance especially under the wetting conditions. It was noted that increasing liquid concentration, membrane length and decreasing gas flow rate enhanced decarburization.

CFD analysis of steam condensation with air in the tubes bundle channel under natural convection conditions

The condensation heat transfer characteristics of steam with the non-condensable gases (NCGs) in the tubes bundle channel are quite different from those in the simple geometry structure, such as the single tube and flat plate. In the present work, to evaluate the thermal characteristics of steam condensation with NCGs in the vertical tubes bundle channel, the numerical model of steam condensation was established based on the CFD code ANSYS FLUENT, which combined the gas component transport equations and the diffusion balance model. And several conditions with different thermal parameters were simulated, the simulation results are in good agreement with the experimental data. The condensation heat transfer in a hexagonal 7-tubes bundle channel with various tube pitches (from 1.5d to 5d) is investigated. The results indicate that the distribution of typical thermal parameters, such as velocity, air mass fraction, temperature and density, is quite different from that in the single tube due to the cross and mixture in each condensation tube boundary layer. As the condensation length increases, the air mass fraction rises, the gas flow rate decreases and the sub-cooling decreases, resulting in a lower natural convection intensity. When the tube pitch is less than 4d, the condensation heat transfer capacity in the tubes bundle channel is weakened obviously, and the heat transfer coefficient with the tube pitch 1.5d is only about 32% of that in a single tube. The air mass fraction and pressure have a significant positive effect on the heat transfer coefficient, and the wall sub-cooling has a significant negative effect on that.

Investigation on influences of loose gas on gas-solid flows in a circulating fluidized bed (CFB) reactor using full-loop numerical simulation

Abstract The influences of loose gas on gas-solid flows in a large-scale circulating fluidized bed (CFB) gasification reactor were investigated using full-loop numerical simulation. The two-fluid model was coupled with the QC-energy minimization in multi-scale theory (EMMS) gas-solid drag model to simulate the fluidization in the CFB reactor. Effects of the loose gas flow rate, Q, on the solid mass circulation rate and the cyclone separation efficiency were analyzed. The study found different effects depending on Q: First, the particles in the loop seal and the standpipe tended to become more densely packed with decreasing loose gas flow rate, leading to the reduction in the overall circulation rate. The minimum Q that can affect the solid mass circulation rate is about 2.5% of the fluidized gas flow rate. Second, the sealing gas capability of the particles is enhanced as the loose gas flow rate decreases, which reduces the gas leakage into the cyclones and improves their separation efficiency. The best loose gas flow rates are equal to 2.5% of the fluidized gas flow rate at the various supply positions. In addition, the cyclone separation efficiency is correlated with the gas leakage to predict the separation efficiency during industrial operation.

High Efficiency Operation Conditions in Polymer Electrolyte Fuel Cell System with Hydrogen Circulation

IntroductionWater management is an essential problem to achieve PEFC’s maximum performance. Hydrogen circulation is one of methods to humidify the cell with water produced in oxygen reduction reaction (ORR), while the overall hydrogen utilization can be 100 %. Additionally, by controlling the operation conditions such as gas flow direction, one-pass conversion and humidifying temperature, the cell performance can be improved. The purpose of this study is to investigate the effects of these parameters, and to optimize the cell performance. Water transport in the PEFC system is analyzed in the through-plane direction at steady state, when the dry hydrogen and humidified air are supplied to an 80 oC isothermal system, and the molar flowrate ratio of hydrogen to oxygen at cell inlet is 2.Numerical SimulationGas channels were regarded as straight lines and the gas flow inside was plug flow. The water permeation flux through PEM, which is determined by electroosmosis and back diffusion, was calculated by Eq. (1) [1]. The properties of PEM were assumed as constants, and the equilibrium moisture content λ was assumed and calculated by Springer’s equation [1].Local current density i was calculated by Eq. (2) [2], where k vcm represents 1st-order cathode reaction rate constant per layer volume, which is the function of IR-corrected cell voltage E cm expressed by Eq. (3), p Oc represents partial pressure of oxygen at cathode catalyst layer (CCL) - gas diffusion layer (GDL) boundary and F e is effectiveness factor of CCL, represents the ratio of observed rate to intrinsic rate. According to our previous work, F eis only determined by 4 dimensionless moduli M Om , M pm , P Om and y Oc [2]. M Om represents the ratio of oxygen diffusion resistance to ORR resistance (Thiele modulus). M pm represents the ratio of proton transport resistance to ORR resistance (our modulus). P Om represents the ratio of convection to oxygen diffusion (Péclet mumber).Results and DiscussionFig. 1 shows the distribution of relative humidity (RH) along gas channels, and water permeation flux through PEM in cases of co-current and countercurrent at the fixed one-pass conversion and current density. The total water permeation rate is 0 since the make-up H2 supplied into the system is dry and no water leaves the cell at steady state. The RH in cathode gas channel increases monotonically in case of countercurrent; the RH has a maximum value in case of co-current, since the water permeation flux varies in a greater region than co-current.The effect of one-pass conversion on performance is the competition of mass transport and reaction. As shown in Figs. 2 and 3, when the one-pass conversion increases at the fixed cell voltage, the average RH in gas channels increase, due to the decrease in gas flowrate in the gas channels. However, the inflection points in Fig. 2 exist around x H = 0.3, which indicates when the one-pass conversion is lower than 0.3, the gas flowrate is too high for water produced in ORR to humidify anode gas sufficiently. As the RH increasing, the average proton conductivity of PEM increases and average oxygen partial pressure in cathode gas channel decreases, as shown in Figs. 4 and 5, which indicates the proton transport is enhanced due to the humidification by water produced in ORR, and the reaction rate is reduced since the concentration of reactant decreases. As the result, by increasing the one-pass conversion, the current density firstly increases and then decreases, as shown in Fig. 6.In addition, when the one-pass conversion is high enough, the RH in gas channel will reach 1, and flooding will happen more likely inside the cell than at the exit in case of countercurrent, since RH has a maximum value in gas channel. To prevent flooding, the maximum operation conversion should be lower than the value calculated by Eq. (4), according to the material balance, where the RH2 [C] represents the cathode outlet RH, which is 1 for co-current and lower than 1 for countercurrent.ConclusionsThe optimized one-pass conversion is determined by the competition of mass transfer and reaction. As the one-pass conversion increases, the proton transfer resistance decreases due to the humidification by water produced in ORR, and reaction rate decreases due to the consumption of oxygen. The optimized one-pass conversion should be higher than 0.3 to ensure the sufficient humidification, and lower than the value calculated from Eq. (4) to prevent flooding.

A Characterization of the Performance of Gas Sensor Based on Heater in Different Gas Flow Rate Environments

The performance of gas sensors based on micro-heater is highly dependent on the environment temperature, heater temperature, and gas flow rate. The performance fluctuation of gas sensors induced by environment temperature drift can be reduced in different ways. In this article, different sizes and shapes of obstacles are placed around the sensitive component of the thermal conductivity gas sensor to study the effect of gas flow rate on the gas sensor performance. Both the simulation and experiment results indicate that the obstacle design can reduce the interference of gas flow rate on gas sensor performance. As the obstacle size increases, the influence of gas flow rate decreases and the dynamic detection accuracy of the gas sensor increases at the same gas flow rate, and the voltage variation of the sensor with quadrangular prism obstacle shape is minimal, and the gas velocity reduction effect is 1.77% better than cylinder obstacle shape. The effect of gas flow rate on the gas response is also investigated by detecting the voltage response of the MG811 gas sensor with and without thermostatical control. The result shows that the gas flow rate not only reduces the temperature of the sensor (direct influence), but also promotes the chemical reaction of the sensor, which releases a large amount of heat (indirect influence). The corresponding relationship between voltage response and gas flow rate is obtained through controlling the temperature of sensitive components thermostatically. This article provides a new angle for improving the accuracy of the gas sensor in different gas flow rate environments, which can improve the detection rate of the wireless monitoring system.

The role of heterogeneous catalysts in the plasma-catalytic ammonia synthesis

Ammonia, being the second largest produced industrial chemical, is used as a raw material for many chemicals. Besides, there is a growing interest in the applications of ammonia as electrical energy storage chemical, as fuel, and in selective catalytic reduction of NOx. These applications demand on-site distributed ammonia production under mild process conditions. In this paper, we investigated 16 different transition metal and oxide catalysts supported on γ-Al2O3 for plasma-catalytic ammonia production in a dielectric barrier discharge (DBD) reactor. This paper discusses the influence of the feed ratio (N2/H2), specific energy input, reaction temperature, metal loading, and gas flow rates on the yield and energy efficiency of ammonia production. The optimum N2/H2 feed flow ratio was either 1 or 2 depending on the catalyst – substantially above ammonia stoichiometry of 0.33. The concentration of ammonia formed was proportional to the specific energy input. Increasing the reaction temperature or decreasing gas flow rates resulted in a lower specific production due to ammonia decomposition. The most efficient catalysts were found to be 2 wt% Rh/Al2O3 among platinum-group metals and 5 wt% Ni/Al2O3 among transitional metals. With the 2 wt% Rh catalyst, 1.43 vol% ammonia was produced with an energy efficiency of 0.94 g kWh−1. The observed behaviour was explained by a combination of gas-phase and catalytic ammonia formation reactions with plasma-activated nitrogen species. Plasma catalysts provide a synergetic effect by activation of hydrogen on the surface requiring lower-energy nitrogen species.

Cell viability and measurement of reactive species in gas- and liquid-phase exposed by a microwave-excited atmospheric pressure argon plasma jet

A microwave-excited atmospheric pressure plasma jet (ME-APPJ) was generated utilizing coaxial transmission line resonators with the resonance frequency of 788 MHz. We investigated the effects of the operating parameters such as input power and gas flow rate on the electron excitation temperature and electron density using optical emission spectroscopy. The amounts of various reactive species in the plasma-activated media (PAM) exposed by the ME-APPJ were estimated using colorimetric methods. The PAM was applied to A549 cultured cells and subsequently incubated for a given duration. The concentrations of NO2− and H2O2 in the PAM incubating A549 cells were monitored until 24 h. The reduced cell viability rate was observed on A549 cells incubated in the PAM. The concentrations of NO2− and H2O2 and the viability of A549 cells depended on the operating conditions of ME-APPJ. The cell viability rate exhibited a decrease with increasing power and decreasing gas flow rate. Correlation between the concentrations of gaseous reactive species in the plasma and in the PAM and the cell viability is discussed.

Effect of multiphase flow on natural gas hydrate production in marine sediment

Natural gas hydrates (NGHs), regarded as an alternative future energy source. Currently, tests for hydrate exploitation from marine sediment have been performed in the Nankai Trough of Japan and the Shenhu area of the South China Sea. Hydrate exploitation is influenced by water-gas flow in the sediment, and considering the huge seawater reserves in hydrate accumulation areas, an experiment of seawater-gas flow was performed to dissociate hydrate. The effects of seawater-gas flow rates and initial hydrate saturation on methane hydrate (MH) production were analyzed. The results showed that seawater-gas flow efficiently promotes hydrate dissociation and inhibits hydrate reformation. Moreover, there was a faster heat and mass transfer with increasing seawater flow rates and decreasing gas flow rates, which enhanced the average MH dissociation rate. In addition, the variation time of the flow channel increased with higher initial hydrate saturation. Additionally, seawater-gas flow promotes MH dissociation stronger than deionized water-gas flow.

Application of microwave heating for methane dry reforming catalyzed by activated carbon

The effect of activated carbon as catalyst on methane dry reforming is investigated in this work. Gases conversions in CH4 decomposition, carbon gasification and CH4 dry reforming are also compared. It is compared wood-derived activated carbon exhibits better catalytic effect on methane reforming. The results indicate CH4 conversion in the reforming reaction is higher than that in the decomposition reaction, with a maximum difference of 37.9%. CO2 conversion in the reforming reaction is lower than that in carbon gasification reaction by 18.4%. Various variables are employed to determine the optimum conditions for reforming reaction. The results reveal the enhanced conversions of CH4 and CO2, accompanied by a decreased H2/CO ratio can be achieved through increasing microwave power, reducing CH4/CO2 ratio or decreasing gas flow rate. Furthermore, migration amount of carbon is calculated. It is obtained carbon migration rate reduces with the increase of microwave power or decrease of CH4/CO2 ratio. At last, catalytic activity of wood-derived activated carbon is tested. It is noticed the catalyst presents high catalytic activity at the beginning, followed by a sharp loss of catalytic activity after 40 min. This caused the decrease of CH4 and CO2 conversions nearly by 56.6% and 36.6% after the test, respectively.

Effect of microchannel junction angle on two-phase liquid-gas Taylor flow

Two-phase liquid-gas Taylor flow triggered by blocking-squeezing mechanism was studied with different junction angle θ microchannels, i.e. 20°, 45°, 90°, 135° and 160°, at various liquid (ethanol) and gas (He) flow rates. We experimentally investigated the effects of flow rates and θ on the gas bubble VB and liquid slug VS volumes. A theoretical model was formulated for the quantitative predictions of bubble and slug sizes for different θ and flow rates. Good agreements were obtained between theoretical predictions and experimental observations. The unit cell volume VU (VB + VS) decreased pronouncedly for the 20° channel with decreasing liquid or increasing gas flow rate, due to the slight increase in VB and large decrease in VS. In comparison, for the 45°, 90°, 135° and 160° channels with increasing liquid or decreasing gas flow rate, VU were less sensitive to fluid flow rate changes, due to the approximate cancellation between VB decrease and VS increase. For the 20° and 45° channels, it produced larger VU, due to larger VB and VS, when compared to the 90° channel. This is caused by the larger gas bubble throat width DN at the junction when θ < 90°. As for the 135° and 160° channels (θ > 90°), DN is approximately equal to the gas channel width, with VB, VS and VU approximately the same as the 90° channel. With θ ≥ 90° (i.e. 90°, 135° and 160° channels), as evident from the smaller VU, higher gas bubble density can be obtained when compared to θ < 90° (i.e. 20° and 45° channels). Hitherto, this observation has not been realized, and the mechanics is first investigated here with the employment of extreme θ (i.e. 20° and 160°). A thorough understanding of the underlying mechanics affecting Taylor flow can facilitate its exploitation for controlled gas bubble and liquid slug generation. Our theoretical model facilitates the tuning of the channel designs and fluid flow rates to achieve the desired gas bubble and liquid slug sizes for specific applications.

Characterizing thermal-oxidation behaviors of nuclear graphite by combining O2 supply and micro surface area of graphite

The effects of different parameters on oxidation rate are non-linear, interactive and diversified in which the change of adequacy of O2 supply is an important indicator. The influence of microstructure on oxidation rate became stronger worsening the fitting linearity to calculate the activation energy based on present method with the decreased adequacy of O2 supply due to the increase of temperature, the decrease of gas flow rate, etc. Here, we proposed a method to characterize thermal-oxidation behaviors of nuclear graphite by combining O2 supply and micro surface area of graphite. The proposed method improved the linearity and reduced the standard error of Arrhenius plots of oxidized graphite IG-110 (10 L/min reactant gas) and ET-10 (0.2 L/min reactant gas). The value of activation energy of graphite IG-110 oxidized under ASTM D7542 condition is calculated as 220 kJ/mol by this method echoing the results of previous studies with sufficient O2 supply. For the conditions with less O2 supply at low gas flow rate and/or high temperature, the change of microstructure of oxidized graphite should be obtained as an important factor influencing oxidation rate of graphite.

Experimental and modeling studies on the prediction of liquid loading onset in gas wells

Liquid loading is a major problem that limits production of gas wells. When liquid loading occurs, the gas well will suffer a rapid decrease in gas flow rate and eventually cease. An accurate prediction of liquid-loading onset is vital for operators to optimize production or take other measures in time. Through a careful review of previous studies, it's more reasonable to relate liquid-loading onset to liquid-film reversal rather than liquid-droplet reversal. However, few mechanistic approaches based on liquid-film reversal are available to predict the critical gas velocity. Furthermore, these models have complicated calculation and conservative results. This paper develops a more comprehensive and simpler analytical model for prediction of liquid-loading onset on the basis of liquid-film-reversal criterion. To reach this goal, experimental investigation has been conducted to analyze the effect of inclined angle and liquid velocity on the critical gas velocity. The Belfroid et al. (2008) angle-correction term has been adopted in the new model to predict critical gas velocity in inclined pipes. After validation against laboratory and field data from the published literature, this model has better performance compared with other models. Considering its simple form and high accuracy, the new model can provide a convenient approach for gas production engineers to predict critical gas flow rate.

Quantitatively Assessing Hydrate-Blockage Development During Deepwater-Gas-Well Testing

Summary Hydrate-associated problems pose a key concern to the oil and gas industry when moving toward deeper-offshore reservoir development. A better understanding of hydrate-blockage-development behavior can help flow-assurance engineers develop more-economical and environmentally friendly hydrate-management strategies for deepwater operations. In this work, a model is proposed to describe the hydrate-blockage-formation behavior in testing tubing during deepwater-gas-well testing. The reliability of the model is verified with drillstem-testing (DST) data. Case studies are performed with the proposed model. They indicate that hydrates form and deposit on the tubing walls, creating a continuously growing hydrate layer, which narrows the tubing, increases the pressure drop, and finally results in conduit blockage. The hydrate-layer thickness is nonuniform. At some places, the hydrate layer grows more quickly, and this is the high-blockage-risk region (HBRR). The HBRR is not located where the lowest ambient temperature is encountered, but rather at the position where maximum subcooling of the produced gas is presented. As an example case—a deepwater gas well with a water depth of 1565 m and a gas-production rate of 45 × 104 m3/d—the hydrate blockage first forms at the depth of 150 m. In the section with a depth from 50 to 350 m, hydrates deposit more rapidly and this is the HBRR. As the water depth increases and/or the gas-flow rate decreases, the HBRR becomes deeper. Inhibitors can delay the occurrence of hydrate blockage. The hydrate problems can be handled with a smaller amount of inhibitors during deepwater well-testing operations. This work provides new insights for engineers to develop a new-generation flow-assurance technique to handle hydrate-associated problems during deepwater operations.

Experimental investigation of gas flow rate and electric field effect on refractive index and electron density distribution of cold atmospheric pressure-plasma by optical method, Moiré deflectometry

Nowadays, cold atmospheric-pressure (CAP) helium plasma jets are widely used in material processing devices in various industries. Researchers often use indirect and spectrometric methods for measuring the plasma parameters which are very expensive. In this paper, for the first time, characterization of CAP, i.e., finding its parameters such as refractive index and electron density distribution, was carried out using an optical method, Moiré deflectometry. This method is a wave front analysis technique based on geometric optics. The advantages of this method are simplicity, high accuracy, and low cost along with the non-contact, non-destructive, and direct measurement of CAP parameters. This method demonstrates that as the helium gas flow rate decreases, the refractive index increases. Also, we must note that the refractive index is larger in the gas flow consisting of different flow rates of plasma comparing with the gas flow without the plasma.

A novel process for oxygen absorption from air using hollow fiber gas-liquid membrane contactor

Abstract In this study, the absorption of oxygen from air flowing through polypropylene hollow fiber membrane contactor was investigated using slaughterhouse wastewater, including about 90% (v/v) blood, as an absorbent. The effect of operating parameters on process performance was examined in two modes of absorbent flowing through both the lumen and shell of the membrane contactor. In addition, some experiments were carried out to examine the long term performance of the system. Removal efficiency and absorption flux were determined for investigation of the process performance. Results showed decrease in gas flow rate and increase in liquid flow rate resulted in higher removal efficiency, respectively. Moreover, absorption flux was increased by augmenting both gas and liquid flow rate. Furthermore, the removal efficiency of near 78% was obtained for mode of wastewater flowing through the lumen side. No considerable variations in removal efficiency were observable for long term operation.

Mathematical modeling of CO2 absorption into novel reactive DEAB solution in hollow fiber membrane contactors; kinetic and mass transfer investigation

In this study, 4−diethylamino−2−butanol (DEAB) has been applied as a novel amino alcohol absorbent in a gas–liquid hollow fiber membrane contactor (HFMC) for CO2 separation from a CO2/N2 gas mixture. A comprehensive 2−D mathematical model based on the finite element method (FEM) was developed to solve the applied partial differential equations for the shell, tube and membrane sides of a gas–solvent HFMC. The proposed model was validated using the available experimental data in the literature and the modeling results were in consistent with the experimental data. To investigate the influence of solvent on separation performance of a non−wetted mode of HFMC, the absorption of CO2 using DEAB is compared with other common industrial solvents such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA) and methyldiethanolamine (MDEA). Under moderate operating conditions, the impact of parameters such as liquid and gas flow rates, concentration, temperature and CO2 partial pressure on the performance of a HFMC have been examined. Sensitivity analysis of operating conditions reveals that mass transfer resistance of gas phase is more significant than mass transfer resistance of liquid phase and the major mass transfer resistance is located in the gas phase. The modeling results indicated that the percentage absorption of CO2 into DEAB solution was competitive with MEA solution, however much higher than DEA, MDEA and TEA solutions in all range of liquid and gas flow rates and also partial pressure. It was concluded that increasing temperature, absorbent concentration, liquid flow rate and also decreasing gas flow rate enhance the removal of CO2.