Inlet Gas Flow Research Articles

The gas flow dynamics in a separator with coaxially arranged pipes

In order to increase the efficiency of gas purification from the particles of up to 20 microns and to increase the service life of bag and electrostatic filters, the authors propose to use a centrifugal separation device with coaxially arranged pipes to be installed before the fine purification devices. The numerical studies of gas dynamics in a separation device were conducted in ANSYS Fluent software package. As a result of conducted numerical studies, it was found that the pressure loss in the centrifugal separation device is not more than 70 Pa at the inlet gas flow rate from 1 to 15 m/s and the width of rectangular hole within the range from 10 to 15 mm. The low pressure losses are caused by the design features; in particular, the resulting vortices in the inter-cylindrical space practically do not contact the wall surfaces of device. The equations of pressure loss depending on the width of rectangular holes and the hydraulic resistance coefficient of separation device depending on the inlet gas flow rate were obtained. The design coefficient of hydraulic resistance of separation device was equal to 0.45.

Multiscale modeling of chemical vapor infiltration process for manufacturing of carbon-carbon composite

Abstract Producing large parts by chemical vapour infiltration (CVI) process is quite challenging due to non-uniform nature of temperature and gas precursor distribution. Many a times repeated experiments are required to optimize the process parameters for manufacturing composites with isotropic properties. This is not only cumbersome but also cost intensive. To address this critical issue, we develop a multiscale mathematical model for thermal gradient forced chemical vapour infiltration (TG-FCVI) process considering only heterogeneous decomposition of propylene on carbon preform. The model takes account of the flow field, mass transport, reaction kinetics and the transient nature of porosity to identify the optimum process parameters. As the time taken in deposition is very large, the flow in free channel is much faster than the pores and therefore the flow equations are solved coupling both the domains in steady state (low Mach number flow). The effect of various process parameters on composites homogeneity like temperature, temperature gradient, inlet precursor concentration and inlet gas flow rate were studied. The model was validated with the available experimental data. It has been observed that high temperature gradient and inlet concentration favours homogeneous C-C composite with high final bulk density. However, increasing temperature of reactor and reducing inlet reagent concentration causes surface pore blockage and resulting in inhomogeneity in direction of axial flow

Power plants of mobile agricultural machinery using vortex exhaust ejectors

Environmental protection is one of the most important problems of the modern world, since life on Earth, the health and well-being of mankind depend on its solution. Every year the world economy emits into the atmosphere 350 million tons of carbon monoxide, more than 50 million tons of various hydrocarbons, 150 million tons of sulfur dioxide. Carbon dioxide is accumulated in the atmosphere and at the same time, the amount of oxygen decreases, and the «contribution» of motor vehicle emissions to the atmosphere is up to 90 % for carbon monoxide and 70 % for nitric oxide. A vortex exhaust ejector allows to improve the parameters of internal combustion engines (ICE) and diesel engines of mobile agricultural machines: their power increase and fuel consumption, as well as toxicity and noise reduce. Due to the aerodynamics and flow characteristics of the swirl flow, a vortex ejector is capable of creating a higher zone of reduced pressure in the near-axial area of the flow than a straightjet one, and it is capable to operate in a wide range of pressures of the gas inlet flow, and has all the modes. Constructive options of a vortex exhaust ejector for various types of power plants of mobile agricultural machinery are proposed. The experimental bench and field studies of various vehicles confirmed an increase in the effective power of ICE and diesel engines by 12 %, a decrease in hourly fuel consumption of up to 20%, and a decrease in toxicity of exhaust gases by 10-15 %

Visualization of two-phase gas-liquid flow in a radial centrifugal pump with a vaned diffuser

The operation of centrifugal pumps with gas-liquid mixtures is a common problem in the oil and gas industry. The main problem is related to the accumulation of gas inside the Electric Submersible Pump (ESP) impellers, which causes degradation of the pump pressure-rise. Literature about global performance parameters of centrifugal pumps operating with gas-liquid flows is limited, and studies focused on understanding the complex flow patterns occurring inside impellers are even scarcer. In this scenario, this work presents an experimental work developed to carry out, simultaneously, head evaluation and high-speed flow visualization in a two-stage centrifugal pump with radial-type impellers and a vaned diffuser. The pump casing and the first stage impeller were replaced by equivalent pieces reproduced with great fidelity using a transparent material in order to allow flow visualization while minimizing the effect of non-original pump parts on performance. Results show flow pattern transitions in the impeller channels when the rotating speed, the inlet gas flow rate and the liquid flow rate are changed, whereas only a single flow pattern was observed in the diffuser for the whole range of tested operating conditions. In addition, increasing the rotating speed causes, in general, a decrease of the bubble diameters inside the impeller, improving the pump's ability to handle higher gas flow rates and ultimately extending the operational window of the pump. This analysis can provide a source of data that can be useful to support theoretical models or to validate numerical simulations.

CFD investigation of [formula omitted] absorption/desorption by a fluidized bed of micro-encapsulated solvents

Micro-encapsulated solvents (MECS) have been proposed for flue gas CO2 capture. However, relatively little is known about the collective behavior of MECS in fixed or fluidized beds. Therefore, we extended our model for microcapsule CO2 capture (Finn and Galvin, 2018) to a CFD-DEM framework. Temperature and CO2 absorption measurements for microcapsules with catalyzed, aqueous, sodium carbonate solution in a small (order 20 g) bed were used for validation. The influence of inlet gas temperature, relative humidity, and gas flow rate on absorber/regenerator performance was explored. The bed averaged CO2 mass transfer rates were largely insensitive to inlet gas velocity over the time considered. The direction and magnitude of capsule water flux was very sensitive to changes in inlet gas temperature/relative humidity. Precise control of temperature/humidity may be needed if sodium carbonate capsules are to be deployed in fixed/fluidized beds at larger scales.

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900 °C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates.

Modeling and Simulation of CO2 Absorption Enhancement in Hollow-Fiber Membrane Contactors using CNT–Water-Based Nanofluids

Absorption of CO2 from a gas mixture containing CO2 and nitrogen by water-based CNT nanofluids in gas–liquid hollow fiber membrane contactor was modeled and solved using COMSOL Multiphysics 5.4. The model assumed partial wetting of the membrane, along with diffusion in the axial and radial directions. In addition, Brownian motion and grazing effects were both considered in the model. The main contribution to the mass transfer resistance for the case of external diffusion-controlled adsorption is the stagnant liquid layer around the particles, despite the layer being very thin. Accordingly, the nanofluid flows in the lumen tube side of the hollow fiber membrane was modeled as a solid-free zone and dense solid phase. The simulations were performed using 7% wetting of the membrane thickness. The results showed a significant increase in CO2 absorption with increasing concentration of carbon nanotubes (CNT). At a fixed inlet gas flow rate (20 L/h), increasing the CNT concentration from 0.1 wt.% to 0.25 wt.% increased the CO2 removal from around 20% to 45%. Comparison of the model predictions with experimental data available in the literature confirmed the validity of the developed model.

Ethanol recovery from a model broth by the fermentation-extraction-distillation coupling process

The fermentation-extraction-distillation coupling (FEDC) process for ethanol recovery from a simulated model broth using 1-dodecanol as an extractant was studied by varying distillation temperature, inlet gas flow rate, extract height and feed concentration. Results showed that the temperature field was strongly impacted by the inlet gas flow rate and the distillation temperature, but the concentration field was almost not affected by these two factors. The distillate flux was greatly influenced by the distillation temperature, the inlet gas flow rate and the feed concentration. The ethanol concentration in the distillate was increased with the increasing of all the four factors. The distillate flux and the separation factor were respectively up to about 720 g/(m2·h) and 20.4, which were respectively comparable to the permeation flux and the separation factor of pervaporation.

Experimental study of carbon dioxide absorption by mixed aqueous solutions of methyl diethanolamine (MDEA) and piperazine (PZ) in a microreactor

In this study, chemical absorption of carbon dioxide (CO2) was performed by using MDEA+PZ (aMDEA) solvent. A T-shaped microreactor mixer was used as the mass transfer device to improve the absorption rate. Operating conditions used in this study were operating temperature (15–55°C), input solvent flow rate (0–0.4lmin−1), inlet gas flow rate (1-9lmin−1), and amine concentration in the solvent (0–40 weight percent). All the experiments were carried out at atmospheric pressure and CO2 concentration of 10% in the feed gas. The central composite design method was used to set an experimental design. The results of optimization showed that the use of a microreactor for CO2 adsorption using aMDEA solvent significantly increased the total coefficient of mass transfer in the gas phase, as compared with other mass transfer devices. The maximum value obtained through the model within the range of operating variables for the response (total mass transfer coefficient in the gas phase) was 1769kmolm−3h−1kPa−1.

Experimental studies and neural network modeling of the removal of trichloroethylene vapor in a biofilter

In this study, bamboo carrier based lab scale compost biofilter was evaluated to treat synthetic waste air containing trichloroethylene (TCE) under continuous operation mode. The effect of inlet TCE concentration and gas flow rate and its removal was investigated. Maximum TCE removal efficiency was found to be 89% under optimum conditions of inlet 0.986 g/m3 TCE concentration corresponding to a loading rate of 43 g/m3 h and 0.042 m3/h gas flow rate at empty bed residence time (EBRT) of 2 min. For the first time, Artificial Neural Network (ANN) was applied to predict the performance of the compost biofilter in terms of TCE removal. The ANN model used a three layer feed forward based Levenberg-Marquardt algorithm, and its topology consisted of 3-25-1 as the optimum number for the three layers (input, hidden and output). An excellent match between the experimental and ANN predicted the value of TCE removal was obtained with a coefficient of determination (R2) value greater than 0.99 during the model training, validation, testing and overall. Furthermore, statistical analysis of the ANN model performance mediated its prediction accuracy of the bioreactor to treat TCE contaminated systems.

CO2 capture efficiency in post‐combustion using MWNT‐PAA in a packed bed column

The adsorption capacity of polyaspartamide (PAA) and multi‐wall carbon nanotubes with polyaspartamide (MWNT‐PAA) was investigated through a packed bed column with the flowing of flue gas composed of 15 % CO2, 5 % O2 and the balance N2. The adsorption performed at 25 °C, 110 kPa and inlet gas flow rate of 60 mL/min resulted in high CO2 adsorption capacity of 5.70 and 10.20 mmol‐CO2/g for PAA and MWNT‐PAA, respectively. The adsorption kinetics was very high, so 7 min were enough for the effluent gas to reach the breakthrough after saturation. The consistency of adsorbents in recurring regeneration was successful through a continuous TSA system of 10 cycle adsorption‐desorption with temperatures of 25–100 °C. The evaluation of heat through differential scanning calorimetry (DSC) resulted in exothermic adsorption with heat release of 45.14 kJ/mol and 124.38 kJ/mol for PAA and MWNT‐PAA, respectively. The heat release was found favourable to promote the desorption as the temperature could rise after adsorption. This is an advantage for energy efficiency, as it depicts the potential of energy recovery. Thus, both adsorbent PAA and MWNT‐PAA were demonstrated to be promising for CO2 adsorption capture in post‐combustion.

Mathematical modeling of regeneration of coked Cr-Mg catalyst in fixed bed reactors

On the base of two-dimensional (bed length and pellet radius coordinates) two-temperature (gas and catalyst phases) mathematical model the coked CrF3/MgF2 catalyst regeneration process in the adiabatic reactor of gas-phase perchloroethylene hydrofluorination to pentafluoroethane (Freon 125) is studied. The parameters of the mathematical model such as coke burning rate constant, temperature of the coke burning beginning T* (ignition point), heat of the reaction and activation energy were determined from experiments in lab-scale reactor and from the thermal analysis data. The influence of process parameters, e.g. oxygen and coke concentrations, initial gas and catalyst temperatures and pellet size was investigated. The simulation was carried out under conditions of low oxygen concentration (oxygen shortage) and showed that if the inlet gas temperature Tgo is lower than initial catalyst temperature Tp0 (Tgo<Tp0, Tpo≥T*), the coke burning occurs only near the outer surface of catalyst pellet, because the bed is “cooled” by the inlet gas flow. This leads to the dramatic rise of temperature in a narrow “peak burning wave” and to an unexpected bed overheating that exceeds the adiabatic heating. This effect was not discussed in publications but was detected in industrial reactor during the coked chromium–magnesium catalyst regeneration. This result is very significant for industrial applications since it helps to avoid the catalyst overheating and the following catalyst activity decreasing during the regeneration.

Modeling and Simulation of the Absorption of CO2 and NO2 from a Gas Mixture in a Membrane Contactor

The removal of undesirable compounds such as CO2 and NO2 from incineration and natural gas is essential because of their harmful influence on the atmosphere and on the reduction of natural gas heating value. The use of membrane contactor for the capture of the post-combustion NO2 and CO2 had been widely considered in the past decades. In this study, membrane contactor was used for the simultaneous absorption of CO2 and NO2 from a mixture of gas (5% CO2, 300 ppm NO2, balance N2) with aqueous sodium hydroxide solution. For the first time, a mathematical model was established for the simultaneous removal of the two undesired gas solutes (CO2, NO2) from flue gas using membrane contactor. The model considers the reaction rate, and radial and axial diffusion of both compounds. The model was verified and validated with experimental data and found to be in good agreement. The model was used to examine the effect of the flow rate of liquid, gas, and inlet solute mole fraction on the percent removal and molar flux of both impurity species. The results revealed that the effect of the liquid flow rate improves the percent removal of both compounds. A high inlet gas flow rate decreases the percent removal. It was possible to obtain the complete removal of both undesired compounds. The model was confirmed to be a dependable tool for the optimization of such process, and for similar systems.

Electrochemical Characterization and Performance Assessment of SOC Stacks in Electrolysis Mode

High temperature electrolysis (HTE) of steam, CO2, and steam and CO2 for highly efficient generation of hydrogen, carbon monoxide as well as syngas was investigated for four solid oxide cell stacks, all supplied by different stack manufacturers. The SOCs employed within the stacks were planar, and electrolyte or electrode supported with an industrial size between 80 and 128 cm². A comprehensive electrochemical characterization of both stacks and individual cells within the stacks was conducted by means of electrochemical impedance spectroscopy and polarization curve measurement. Detailed performance analyses showed the highest efficiency when operating the stack under H2O electrolysis, followed by co-electrolysis and eventually CO2 electrolysis. Subsequently, the stacks were operated under reversible system-relevant steady-state conditions, thus varying the working temperatures, the current density and the gas inlet flow. For that purpose both the conversion rate and fuel utilization were set to be between 70% and 80%. All stacks were operated for long-term periods of >1,000 h, during which degradation monitoring was applied. The results obtained within the present study allow a better understanding of the electrochemical processes that occur during reversible operation and especially HTE, and provide a guideline for optimized operation of a fully autonomous rSOC system.

Influence factors and health risk assessment of bioaerosols emitted from an industrial-scale thermophilic biofilter for off gas treatment

Bioaerosols emissions from an industrial-scale thermophilic biofilter (TBF) for sludge drying exhaust treatment were investigated by varying the inlet gas flow rate and water containing rate (WCR) of the packing materials (polyurethane foam cubes, PUFCs). Both bacteria and water-soluble ions (WSIs) were detected in bioaerosols. When the WCR of PUFCs was 37%, with the increase of flow rate from 1500 to 3500m3/h, concentrations of bacteria in bioaerosols increased from 449±27 to 643±46 CFU/m3. Variation in flow rates had similar effects on WSIs. At a constant flow rate of 3500m3/h, bacterial emissions increased from 1112±314 to 1778±157 CFU/m3 when the WCR of PUFCs increased from 44% to 65%. Similarly, the total concentrations of WSIs emissions also increased from 19.21 to 30.57μg/m3 with the rising of WCR. The bacterial populations in bioaerosols were determined via polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technology. Source apportionment results showed that more than 80% of the bacteria in bioaerosols originated from PUFCs. At the TBF outlet, health risks were associated with gaseous compounds (e.g. SO2, H2S, and 1,2-dichlorobenzene) rather than bioaerosols. Appropriate management and control measures are required to reduce the risks of these compounds.

Understanding the occurrence of the individual CO2 electrolysis during H2O-CO2 co-electrolysis in classic planar Ni-YSZ/YSZ/LSM-YSZ solid oxide cells

Commercialized Ni-YSZ/YSZ/LSM-YSZ solid oxide cells with the dimension of 10 cm × 10 cm are investigated in the H2O-CO2 co-electrolysis mode at 800 °C. The aim is to understand the occurrence of the individual CO2 electrolysis during polarization. The electrochemical impedance spectroscopy is combined with the online gas chromatography in order to reveal the possible processes. Several inlet gas flow scenarios are selected and tested at various current density. As a theoretical evidence, the electrolysis voltage comparison of H2O/H2 and CO2/CO is presented as well. The results suggest the co-electrolysis process starts with the individual H2O electrolysis which has a relatively lower reaction barrier. The higher-reaction-barrier CO2 electrolysis is activated and concurrent with the H2O electrolysis if more electric energy is applied and that's when the real sense of H2O-CO2 co-electrolysis occurs.

NGHIÊN CỨU TÍNH TOÁN TRẠNG THÁI NHIỆT VÀ ỨNG SUẤT NHIỆT TRÊN CÁNH PHUN TUABIN CAO ÁP

The high-pressure nozzle blade works under very harsh conditions, the average temperature as well as the local temperature of the inlet gas flow are the highest in the entire engine. Using ANSYS CFX and Structural packages, the paper examines themal distribution and thermal stress when accounting for the thermal distribution of radial inlet hot-airflow. The outcome shows that the maximum temperature and stress are observed at the region of blade suction and pressure sides and the values vary propotionally according to the engine loading conditions (throttle position).

Investigation of hydrodynamic behavior in random packing using CFD simulation

Computational fluid dynamics (CFD) simulations of countercurrent gas–liquid flow in random packings of Raschig rings were carried out in this study. This model used gravity simulation to construct the random packing structure, and a volume expansion-recovery method to improve the meshing quality. A simple feedback control scheme was applied to control the gas inlet flow rate so that pressure drop can be estimated. The generated characteristics of the packing structure such as the number of packing elements, dry surface area and porosity were found to be close to experiments. CFD predictions of hydrodynamics properties are also validated by the experimental data using a small column section. The results indicate that our CFD model was able to capture the essential hydrodynamics behavior of the gas–liquid countercurrent flow. Hence, the approach presented in this study can be used as a basis for studying the effect of detailed packing-geometry design on hydrodynamic and mass transfer characteristics.

Experimental Investigation of Proton Exchange Membrane Fuel Cell with Metal Foam Flow Field

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Compared with conventional flow field, metal foam has been increasingly used for gas distributor in the PEM (proton exchange membrane) fuel cell due to its high porosity and conductivity, which significantly enhances the species transport under high current density condition. In this study, the cell performances with metal foam and graphite parallel flow field are compared under normal and subzero temperature conditions. Besides, electrochemical impedance spectroscopy (EIS) is recorded to characterize the Ohmic, polarization and polarization resistance. Under normal condition, the cell with metal foam exhibits three times better performance than the one with parallel flow field. Meanwhile, the effects of inlet gas humidity and flow rates on cell performance are also studied, indicating that the cathode flooding easily occurs due to its difficult water removal. However, the high flow rate can greatly ease the cathode water flooding. Under subzero temperature condition, metal foam cell shows higher startup voltage and better ice storage capability. In addition, the effects of start-up temperature and current density on cold start performance of PEM fuel cell are studied and the high frequency resistance (HFR) is also utilized to characterize the water content and ice formation/melting in cell. The experimental results show that low initial water content, high startup temperature, and low startup current density are beneficial to PEM fuel cell cold start performance. Overall, the results shown in this study will facilitate a further understanding of the PEM fuel cell with metal foam flow field.&lt;/div&gt;&lt;/div&gt;

Fabrication and characterization of poly(vinylidene fluoride)–polytetrafluoroethylene composite membrane for CO2 absorption in gas–liquid contacting process

ABSTRACTThe wetting resistance of poly(vinylidene fluoride) (PVDF) membrane is a critical factor which determines the carbon dioxide (CO2) absorption performance of the gas–liquid membrane contactors. In this study, the composite PVDF–polytetrafluoroethylene (PTFE) hollow fiber membranes were fabricated through dry‐jet wet phase‐inversion method by dispersing PTFE nanoparticles into PVDF solution and adopting phosphoric acid as nonsolvent additive. Compared with the PVDF membrane, the composite membranes presented higher CO2 absorption flux due to their higher effective surface porosity and surface hydrophobicity. The composite membrane with addition of 5 wt % PTFE in the dope gained the optimum CO2 absorption flux of 9.84 × 10−4 and 2.02 × 10−3 mol m−2 s−1 at an inlet gas (CO2/N2 = 19/81, v/v) flow rate of 100 mL min−1 by using distilled water and aqueous diethanolamine solution, respectively. Moreover, the 5% PTFE membrane showed better long‐term stability than the PVDF membrane regardless of different types of absorbent, indicating that polymer blending demonstrates great potential for gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47767.