Inlet Gas Research Articles

Evaluation of Effective Interfacial Area in a Rotating Packed Bed Equipped with Dual Gas Inlets

This study investigates the effective interfacial area in a novel rotating packed bed (RPB) equipped with dual gas inlets instead of the conventional single-gas-inlet RPB. The aim is to enhance the mass transfer efficiency of gas-liquid contacting processes in RPBs by increasing the number of gas inlets to improve the spread of gas supply into the packing. The RPB is a promising gas-liquid contactor configuration known for its intensified mass transfer characteristics. However, the impact of additional gas inlets on the effective interfacial area of the packing remains unexplored. An experimental method assessed the interfacial area under varying operational conditions which include a liquid flow rate of 0.30-0.60 m3/h, a gas flow rate of 100-300 Nm3/h, and a rotation speed of 600-1000 rpm. At operating conditions covering the maximum rotation speed of 1400 rpm, gas flow and liquid flow rates of 300 Nm3/h and 0.60 m3/h respectively, the results showed that on average, 55 to 97% of the 2400m2/m3 specific packing area can be effectively utilized for gas-liquid mass transfer during separation operations using the RPB. Compared to results reported for single-gas-inlet RPBs using similar packings, the RPB with double gas inlet proved to provide higher utilization of the packing. By simply doubling the number of gas inlets, the findings provide valuable insights into optimizing RPB designs and operations which could enhance mass transfer efficiency for various chemical and environmental applications.

Theoretical model for predicting bubble formation from submerged orifices

Bubble diameter formed at submerged orifices is crucial and challenging to predict with a reliable universal model. A theoretical model covering a wide range of pore structures, operating conditions, and liquid properties for predicting bubble diameter based on bubble force equilibrium at the bubble detachment moment was proposed and verified with good prediction accuracy. The bubble-induced liquid velocity was incorporated to improve the prediction accuracy, and its underlying mechanism on bubble formation diameter was revealed. Additionally, the influencing mechanisms of orifice size, gas inlet velocity, and principal fluid properties on bubble formation diameter were elaborated systematically based on the new mathematical model, and the abnormal phenomenon of bubble formation under high temperatures and elevated pressures is clarified. Based on the proposed high-precision mechanistic model, the theoretical foundations for designing and scaling up industrial aerated reactors and scientific boundary conditions for numerical simulation are provided.

Numerical modeling of heat transfer behavior for two-phase flow in a nozzle considering phase change

The heat transfer and phase change of alumina particles in the gas-particle flow of the nozzle plays an important role in solid rocket motors (SRM) due to the coupling between the heat transfer and two-phase flow. However, it lacks precise modeling of the heat transfer behaviors of condensed particles in the nozzle, especially the phase change effect. In this article, we determine that the Drake model has the highest accuracy in calculating the convective heat flux between two phases, and propose a correlation to obtain radiative heat flux between the particle and walls. Then, a one-dimensional two-phase non-equilibrium model is established to consider the effects of heat transfer and solidification of particles on the two-phase flow in the nozzle. The results show that considering the phase change of particle improves the outlet thrust of the nozzle, but such increment decreases with the gas inlet temperature. When the supercooling phenomenon is considered, the nozzle thrust is reduced by 1.14% compared with that considering no supercooling. As the particle size increases, the outlet temperature of the particle phase rises and can even surpass the solidification temperature of particles and the velocity of the particle phase decreases significantly.

A coupled modeling framework for investigating flow maldistribution in cross-flow-corrugated plate heat exchangers

Accurate prediction of the impact of flow maldistribution on the thermo-hydraulic behavior of plate heat exchangers is important for thermal design and optimization in a number of practical applications. In this paper, a coupled modeling framework, consisting of a heat transfer model and a hydraulic model, is proposed for quantitatively evaluating the impact of maldistribution on the thermo-hydraulic performance of a cross-flow-corrugated plate heat exchanger. The numerical results of the proposed approach are validated by comparison with experimental data. Using the coupled model, the flow distribution nonuniformity, heat exchanger effectiveness deteriorations, and pressure drop deviations are analyzed. Furthermore, the combined effects of side stream maldistribution are investigated for different inlet Reynolds numbers and inlet temperatures. The results demonstrate that when the inlet gas Reynolds number is in the range of 1100–2700, nonuniform distribution of the gas side will cause air maldistribution, and a 10%–30% effectiveness deterioration rate. It is found that air maldistribution will not result in gas maldistribution when the inlet air Reynolds number is in the range of 6000–18 000, but increasing air nonuniformity. Will lead to increasing deterioration in heat exchanger effectiveness. In the presence of air and gas flow maldistribution, the pressure drops on the gas and air sides increase by 5% and less than 12.4%, respectively. This work provides a computational framework for optimization of cross-flow-corrugated plate heat exchangers to achieve desired thermo-hydraulic performance.

Quantifying the effects of inlet gas and collision models in direct metal deposition using a CFD-DEM approach

Simulations of the powder jet in direct metal deposition (DMD) are often made with significant simplifications such as being incompressible, steady-state, or single-component, and do not provide explanation for the choice of parameters in the collision model. This work presents a coupled Computational Fluid Dynamics–Discrete Element Method model for the powder jet in DMD that considers all of the following features: compressibility effects, particle–wall and particle–particle collisions, turbulence, gas mixing, and melt pool boundaries. The goal of the simulation is to optimize the operating conditions and to predict the outcomes of experiments. After effective validation against experimental results, the effects of inlet gas, collision models and different boundary conditions in DMD have been comprehensively studied. It is demonstrated that gases with higher diffusivities, such as helium, are less effective shielding gases than those with lower diffusivities, such as argon. The increased wall temperature arising from the melt pool and track has little influence on the particle distribution.

Investigation on the pressure pulsation characteristics in a twin-screw multiphase pump

A three-dimensional gas–liquid two-phase transient numerical model for a twin-screw multiphase pump based on dynamic grid technology was established and validated with experiments. The pump's simulated pressure distributions, velocity fields, and pressure pulsations were analyzed to reveal the mechanisms of pressure transmission and pressure pulsation characteristics. The results indicated that the flow rate of the pump fluctuated twice due to the discharge of the male and female rotors in one cycle. As the inlet gas volume fractions increased, the flow rate decreased, but the pressure pulsations increased. At the engaging positions of the two rotor tips, a sudden pressure drop happened due to the combined effect of both tooth-tip and tooth-flank leakage. When the discharge port opened, the backflow happened; the flow rate and the pressure in the discharge chamber decreased, but the pressure in the working and suction chambers increased. When the suction port closed, a slight compression of the fluid in the low-pressure working chamber occurred, causing a pressure increase in the working chamber. The working chambers inhaled and discharged once in one cycle, so the first harmonic of pressure pulsations at the suction and discharge chamber was two times the running speed. The transient flow due to the simultaneous closing and opening of the suction and discharge ports at both sides of the male and female rotors generated a harmonic of four times the running speed. This study would help to improve the operational stability of twin-screw multiphase pumps.

Modeling and Simulation of Drilling Gas Mixing Process with Various Conditions in Oil and Gas Pipeline Network

This research aims to model and simulate the gas drilling mixing process with various conditions in the inlet gas flow. This mixing process is very crucial because it can affect the phase stability in the storage tank. Based on this, the gas that has been mixed must be ensured that it is in a perfectly mixed condition before entering the storage tank. The simulation method used in this research is Computational Fluid Dynamics (CFD) with ANSYS Fluent software. The data used as input in this simulation includes flow velocity, temperature, pressure and drilling gas composition. The simulation results are expected to show that flow velocity and pressure have a significant effect on the drilling gas mixing process in the pipe flow. In addition, the differences in the composition of the drilling gas also have an impact on the mixing process, where the more diverse the composition of the drilling gas, the more difficult it is to mix the gas homogeneously. However, by using baffle plates as a barrier and agitator in the pipe, the simulation results show that the mixing of drilling gas can be significantly increased.

Control of spout deflection in dry and wet spouted beds using vibration

Spout deflection is a common instability phenomenon observed in spouted beds which decreases control over the spouted bed and worsens particle recirculation efficiency. Prior work has mitigated spout deflection using electromagnetic fields, inlet gas treatment, and baffles. Here, we demonstrate experimentally that spout deflection can be mitigated through the use of vertical vibration, which can be applied in circumstances which prior methods may not be possible. Spout deflection was mitigated for cases of non-uniform gas flow in a dry spouted bed and particle agglomeration in a wet spouted bed. Furthermore, the particle recirculation rate was found to increase significantly with increasing vibration strength in a wet spouted bed. Thus, we show that vertical vibration can significantly enhance the spout stability in both dry and wet spouted beds, without compromising recirculation rate.

Degradation performance rapid prediction and multi-objective operation optimization of gas turbine blades

The performance degradation of high-temperature blades will affect the safety and efficiency of operation. In response to issues such as ignoring strength characteristics, slow degradation performance prediction, insufficient applicability and accuracy of traditional proxy models, and long operation optimization cycle, a degradation performance prediction model of turbine blades based on the back propagation neural network is established in this research. Furthermore, the efficiency-stress multi-objective operation optimization method based on genetic algorithm is proposed. The results show that the R-square value of the degradation performance neural network prediction model is greater than 0.9 for predicting characteristic parameters. The prediction speed is improved by 104 orders of magnitude compared to the traditional computational fluid dynamics method. The influence mechanisms of turbine outlet flow rate, cooling gas inlet total temperature, and cooling gas flow rate on the degradation performance are revealed. Under fouling extreme conditions and corrosion/wear extreme conditions, the operating parameters of turbine blades are optimized. The maximum values of the efficiency improvement, power increase and maximum von Mises stress reduction are 0.74 %, 2.13 MW and 43 MPa, respectively. This study can provide an effective and novel method for real-time degradation performance prediction and rapid operating condition optimization of turbine blades.

<span>Effect of limited oxygen gas flux on properties of Al-doped ZnO films</span>

In this study, Al-doped ZnO thin films were sputter deposited on glass substrate as a function of limited oxygen gas inlet. The crystal structure, optical, and electrical properties of the films were characterized using X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy, and Hall measurement. High crystallinity was found in all AZO samples. Surface morphology presented small grain size of ~ 50 – 100 nm, and thickness of AZO thin films were maintained approximately at 280 nm. Average optical transmittance of AZO films was about 90% in the 450 – 600 nm region, and optical band-gap values varied from 3.327 to 3.380 eV. The electrical resistivity of AZO films decreased with an increasing amount of oxygen flux. These AZO films are quite appropriate for the perspective development of UV photodetectors as a central role absorbing components or n-type semiconducting layers.

Gas and powder flow characteristics of packed bed: A two-way coupled CFD-DEM study

A two-way coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) calculation was performed to numerically investigate the gas and powder flow characteristics within a packed bed. The analysis and discussion focused on the effects of gas phase velocity, particle shape, and size on the flow behavior of the powders. The results revealed that the average absolute velocity of the powder increased with an increase in the inlet gas flow rate. Conversely, the average dimensionless velocity exhibited the opposite trend. Particle shape significantly impacted the flowability of the powders. A critical value of sphericity equal to 0.96 was observed. For powders with sphericity less than 0.96, the average velocity fluctuated around a progressively decreasing value over time, and the powders tended to accumulate in the inlet region. In contrast, powders with a sphericity greater than 0.96 exhibited average velocities fluctuating around a constant value throughout the simulation. Additionally, a smaller number of these particles remained within the fluid domain, indicating a higher flow rate through the packed bed and ultimately exiting the fluid domain. Regarding the influence of particle size, the flowability reached a minimum value at a radius of 0.14 mm, with the average powder velocity mirroring this trend. Powders with a radius exceeding 0.14 mm demonstrated increasing flowability and average velocity. The observed impact on flowability was likely due to a combination of mechanisms. The findings presented in this paper offer valuable insights into the dynamics of powders within a packed bed. This knowledge can be instrumental in the design and analysis of packed bed reactors.

Influence of Yttria content in YSZ: An evaluation of water-based SPS coatings and spark plasma sintered pellets

The inherent phase instability of the state-of-the-art 7–8 mol% partially stabilised Yttria-Stabilised Zirconia (YO1.5, 8 YSZ, tetragonal) under a molten CMAS attack lacks the technological readiness needed to increase the gas inlet temperatures for more thermally efficient gas turbine engines. In this study, the concentration of Yttria in YSZ was systemically increased to impart CMAS resistance and their applicability via emerging Suspension Plasma Sprayed (SPS) coatings and Spark Plasma Sintered (SpPS) pellets under simulated conditions was evaluated. The fully stabilised higher Yttria YSZ compositions (21.4 mol% and 50.2 mol%, cubic) severely restricted the CMAS infiltration and interaction areas, with the later composition forming an apatite layer and the trans-granular cracking and chipping of YSZ into layers reduced with an increase in Yttria content. However, their application into water-based SPS coatings resulted in a complete coating failure following the high-temperature CMAS tests. During Furnace Cycling Test (FCT) tests, the 8 YSZ coating survived 34 thermal cycles compared to just one on the 50.2 mol% YSZ coatings. The premature delamination of the higher Yttria coating seems to have been caused by the spallation associated with horizontal cracks within the coating. The YSZ composition could be modified into CMAS-resistant chemistry; however, their applicability as a functioning TBC with inherent microstructural features, such as the Dense Vertically Cracked (DVC) coating strategy examined in this study, requires new coating design strategies that impart sustainable thermal cycling performance.

Optimal Dynamic Regimes for CO Oxidation Discovered by Reinforcement Learning.

Metal nanoparticles are widely used as heterogeneous catalysts to activate adsorbed molecules and reduce the energy barrier of the reaction. Reaction product yield depends on the interplay between elementary processes: adsorption, activation, desorption, and reaction. These processes, in turn, depend on the inlet gas composition, temperature, and pressure. At a steady state, the active surface sites may be inaccessible due to adsorbed reagents. Periodic regime may thus improve the yield, but the appropriate period and waveform are not known in advance. Dynamic control should account for surface and atmospheric modifications and adjust reaction parameters according to the current state of the system and its history. In this work, we applied a reinforcement learning algorithm to control CO oxidation on a palladium catalyst. The policy gradient algorithm was trained in the theoretical environment, parametrized from experimental data. The algorithm learned to maximize the CO2 formation rate based on CO and O2 partial pressures for several successive time steps. Within a unified approach, we found optimal stationary, periodic, and nonperiodic regimes for different problem formulations and gained insight into why the dynamic regime can be preferential. In general, this work contributes to the task of popularizing the reinforcement learning approach in the field of catalytic science.

Enhancing the efficiency of two‐stage cyclones without increasing pressure drop by optimizing inlet and outlet dimensions

AbstractEfforts to enhance cyclone separators aim to minimize gas energy consumption while improving separation efficiency. This study attempts to achieve this goal for cyclones arranged in series using straightforward methods. Experimental and numerical simulation analyses were performed to study the effect of matching inlet and outlet diameters on the performance of a two‐stage tandem cyclone separator. The results show that the matching method, in which the inlet gas velocities of both stages are higher than the outlet gas velocity, has a better separation efficiency. The efficiency and pressure drop models of the two‐stage cyclones in series were constructed using the response surface methodology (RSM) to obtain the optimal combination of inlet size and exhaust pipe diameter. Experimental tests showed that the accuracy of this model was reasonable. At different permitted pressure drops, the optimized structure revealed that: (1) The inlet area should be smaller than the outlet area for each cyclone stage. (2) The secondary inlet size (KA) should be as large as possible. (3) dr decreases while KA increases in each step.

Numerical study of uranium hexafluoride desublimation process based on Eulerian two-phase model

This paper presents a numerical study on the condensation process of uranium hexafluoride (UF6) in the supply and extraction system of a uranium enrichment plant. The numerical study was conducted using a standard UF6 receiving container with a nominal diameter of 127 mm and a volume of 8L under constant temperature boundary conditions. A phase change heat and mass transfer model for the desublimation process of uranium hexafluoride gas was established, and this model was combined with the Euler two fluid model to predict the distribution of key parameters such as temperature, pressure, and volume fraction of each phase during the UF6 cooling process, as well as the gas flow characteristics inside the container. In addition, this study also investigated the influence of various factors on the cooling rate. The research results indicated that UF6 gas initially condensed on the container wall and gradually diffused inward, with the highest solid density observed on the wall. Furthermore, increasing the inlet gas temperature, inlet mass flow rate, and reducing the cooling temperature, initial pressure inside the container could all enhance the desublimation rate to various degrees. The optimization plan proposed based on the above influencing factors could increase the yield of UF6 solid by 64.20% in 2 h, compared to the basic operating conditions.

Dynamic characteristics of the tip leakage vortex in an oil–gas multiphase pump based on vorticity decomposition theory

AbstractThe paper combines experimental and numerical simulation methods to investigate the tip leakage vortex (TLV) in an oil–gas multiphase pump. The study aims to understand the evolution and dynamic characteristics of the TLV. The vorticity decomposition theory is used to analyze the spatial–temporal evolution, transient behavior, and rigid vorticity of the TLV. The findings reveal that the TLV is formed near the pressure surface when the tip clearance jet passes through the shear layer. In one impeller rotation period, transient fluctuations of the TLV are attributed to pressure differences and velocity changes across the tip clearance, and the TLV undergoes two split–dissipation–recurrence processes within one impeller rotation cycle. The presence of the gas phase enhances the scale and strength of the TLV while prolonging its existence in the flow channel. Analysis based on the rigid vorticity transport equation shows that the growth of the TLV and collapse are primarily governed by the rigid vortex generation term. The Coriolis force term contributes to stabilizing the TLV, while the rigid vorticity stretching term affects its shape. Furthermore, the gas phase significantly increases the value of the Rigid vorticity Curl of pseudo‐Lamb vector Term (RCT), which plays a crucial role in the prolonged existence of the TLV under gas–liquid two‐phase conditions. From an inlet gas void fraction of 0%–20%, the RCT value increases by 4.8 × 106/s2, the entropy production value increases by 75.55%, and the hydraulic efficiency decreases by 16.29%.

Combined radiation and convection in developing flow in a parallel plate channel with real gas behavior: Contrast between gas cooling and heating

Laminar thermally developing gas flow in a two-dimensional parallel plate channel with real gas radiation has been investigated numerically. Real gas spectral radiation effects are accounted for by using the Spectral Line Weighted-sum-of-gray-gases model. Gas mixtures of H2O and CO2, either alone in mixture with N2 or as a mixture of H2O and CO2 are considered. The phenomena are investigated for a range of differences between wall and inlet gas temperature, mole fraction of the radiating species, and total pressure. Predictions for the cases of gas heating and gas cooling are contrasted with results presented by the classical no-radiation case, commonly known as the Graetz solution. The impact of gas radiation on the local mean temperature, convective and radiative wall heat fluxes, and the convective, radiative, and total local Nusselt numbers are studied.The predictions reveal that the inclusion of participating gas radiation results in a much more rapid change in temperature of the gas in the channel than for the convection-only case, for both the gas heating and gas cooling cases. Further, unique differences in the heat transfer behavior for gas cooling (wall temperature below the inlet gas temperature) and gas heating (wall temperature above the inlet gas temperature) scenarios are shown. However, significant differences between the cases of heating and cooling exist. In the classical Graetz solution, for constant thermophysical properties and using appropriately nondimensionalized heat transfer parameters (e.g., Nusselt number, inverse Graetz number) the predictions for fluid heating and cooling are identical. However, the results of this study including the influence of gas radiation demonstrate that the heat transfer behavior depends heavily on whether the gas is heated or cooled. An apparent thermally fully developed condition may exist for the case of gas cooling, whereas the variation in local Nusselt number with dimensionless axial location exhibits a local minimum for the case of gas heating. Further, the case of gas heating results in a more rapid streamwise change in mean temperature in the channel than for the cooling case. The thermal physics of the developing flow for combined convective-radiative transfer with real gas effects are explored for a range of wall and gas inlet temperatures, radiating species mole fractions, and total pressures.

Effect of number of channels on the fluctuations and distribution of humid-nitrogen condensing flow in a parallel flow field

Pressure drop and flow rate fluctuations of condensation-induced gas–liquid two-phase flow through a single microchannel have been widely recognized, which are quite different from that through parallel-connected multiple microchannels, as in the flow field of proton exchange membrane fuel cells and heat exchangers. This work investigates the effects of the number of channels on the fluctuations of the humid-nitrogen condensing flow and the uniformity of the flow rate distribution across the channels. A parallel flow field with eight channels is designed; the arrangement of these channels is axisymmetric, ensuring identical flow routes and thermal boundary conditions among individual channels. The number of open channels in the flow field could be adjusted from one to eight. The observed pressure drop fluctuated between 0.20 kPa and 0.68 kPa in the single-channel flow field, compared to 0.22 kPa to 0.43 kPa in the two-channel flow field and 0.28 kPa to 0.48 kPa in the eight-channel flow field. This indicates that the amplitude of pressure drop fluctuations decreases as the number of channels increases. In contrast, both the flow rate fluctuation and maldistribution are most significant in the eight-channel arrangement. It is also found that the effect of channel number on condensing flow dynamics is noticeable when both the velocity and humidity of the inlet gas are low.

Demonstration of CO2 capture with CaO and Ca(OH)2 in a countercurrent moving bed carbonator pilot

Decoupling the carbonation and calcination stages of Calcium Looping (CaL) facilitates the capture of CO2 from small point sources, or even the atmosphere, by transporting CO2 as CaCO3 to centralized calcination plants to obtain pure CO2 and regenerate the Ca-sorbent. In this work, we provide the experimental proof of a novel countercurrent moving bed carbonator particularly suited for such applications. We conducted experiments in a 3-meter-long moving bed reactor with an internal diameter of 0.15 m, using Ca-sorbent particles of varying sizes (in the mm and cm scale). Simulated flue gases with varied concentrations of CO2 (up to 8.5 %v), superficial gas velocities (0.5–2 m/s) and inlet gas temperatures (250–630 °C) have been tested. The temperature profiles we observed along the axial direction confirm the formation of a carbonation zone at optimum temperatures (i.e., 550–700 °C), together with a CO2 polishing region towards the gas exit that leads to CO2 capture rates over 99 % in some cases. Using Ca(OH)2 as a CO2 sorbent, we achieved a molar conversion to CaCO3 of approximately 0.7.

Numerical study on the filtration characteristics of fine particles in granular bed filter at high temperature

Granular bed filter (GBF) has become one of the current research hot topics due to its excellent performance in removing fine particles. In this paper, a three-dimensional fixed bed GBF filtration model was established and its accuracy was verified. Then, the GBF filtration performance at high temperature were studied. The results demonstrate that elevating the temperature diminishes the filtration efficiency, albeit to a limited extent. The increasing of inlet gas velocity can significantly improve pressure drop for GBF and the filtration efficiency for fine particles of sizes larger than 5 μm. As the diameter of stacked granular particle diameter grows, the filtration efficiency and pressure drop drops. The density of fine particles almost does not affect the filtration efficiency for fine particles of 1∼7 μm, but a higher density leads to a higher filtration efficiency for fine particles of sizes bigger than 9 μm. Additionally, as the fine particles size increases, the change of the filtration efficiency roughly goes through three stages: Stage 1: the filtration efficiency is basically unchanged; Stage 2: the filtration efficiency increases rapidly; Stage 3: the filtration efficiency increases steadily, but the rate of increase slows down. With the increase of the fine particles Stokes number, the filtration efficiency of GBF will pass through two phases of stabilization and rapid increase.