High Gas Flow Rates Research Articles

A Three-Dimensional Conjugate Heat Transfer Model of a Turbocharger Turbine Housing

The turbine housing is subjected to thermal load which is essential to be taken into account in the design process. In this paper, a three-dimensional conjugate heat transfer simulation of a wastegated turbine housing has been performed. The model has been validated with data from thermocouple measurements and thermography pictures. Moreover, the effect of ventilation speed on temperature distribution of turbine housing is investigated. As the air velocity increases from 8 to 20 m/s, the turbine housing temperature decreases about 114 K. The wastegate valve could be gradually opened by stepping-up the speed of the engine. The ratio of wastegate flow to the turbine housing gas flow is near 30% for the high rotational speeds and loads. Therefore, the exhaust gas passes through the wastegate channel and the velocity reaches 538 m/s for 2° opening of the wastegate valve. Simulation results show that 1.5 mm decreasing the wall thickness of the volute wall causes 30 Kelvin higher temperature in the turbine housing wall. According to the results of the simulation, the impeller specific work of high gas flow condition was observed to be up to 2.5 times of low mass flow rate operation. Furthermore, the specific amount of gas heat transfer at a closed wastegate condition is significantly higher in comparison to the high gas flow rate and open wastegate condition. In addition, the results show that at low speed and closed wastegate condition, 15 percent of the specific heat transfer occurs before the turbine wheel.

Experiments on water vapour condensation within supersonic nozzle flow generated by an impulse tunnel

An impulse facility for analysis of water vapour nozzle flows using both shock tunnel and Ludwieg tube operating modes has been developed and tested at the University of Southern Queensland. Unique high-speed flow visualisation of the water vapour condensation shock has been acquired in the throat region of a nominally two-dimensional convergent-divergent nozzle with a 120 mm2 throat area. This paper presents the facility performance and the time-resolved visualisation results for the nozzle flow, and the results are analysed with the aid of image post-processing tools and quasi-one-dimensional (Q1D) thermodynamic calculations. The experiments have produced qualitative and quantitative data on the flow conditions at four different relative humidity values from 25% to 100%, and over a range of nozzle supply temperatures between 293 K and 343 K. The direct measurement of the pressures and wave speeds within the tunnel resulted in a good agreement with the ideal gas Q1D calculations, particularly for the first incident shocks and expansion waves. Differences progressively increased with the number of reflections, due to the effect of viscous dissipation and the non-ideal end-wall interaction caused by the presence of the nozzle inlet. Moreover, flow visualizations of the location and orientation of both the weak disturbance waves and the condensation shock enabled the investigation of the supersonic water vapour condensation within the nozzle of this impulse facility. Based on these measurements, the nozzle flow downstream of the condensation shock was demonstrated to have a lower Mach number relative to the dry nitrogen flow case. This phenomenon is due to the phase change heat release, which appeared to be more significant when the condensation shock intensity was higher. Although further development of the apparatus is possible, the impulse test-rig configuration that we have developed permits a relatively high flow rate of test gas for a short period of time, leading to significantly reduced operating expenses relative to a continuous flow facility with the same mass flow rate. It is therefore suggested that future studies further improve and test the impulse facility techniques for studying condensation phenomena as a potential alternative to high-power, continuous flow facilities.

Experimental analysis of gas phase dynamics in a lab scale bubble column operated with deionized water and NaOH solution under uniform bubbly flow conditions

In this study we present an investigation on the impact of sparger configuration and fluid properties on the local gas phase dynamics for up to 17% total gas holdup. Experiments in a bubble column with 100 mm inner diameter were conducted with deionized water and NaOH solution of up to cNaOH = 32 mmol·l−1. Ultrafast X-ray computed tomography (UFXCT) was applied to obtain local hydrodynamic parameters, such as gas holdup distribution, bubble sizes and average bubble rise velocities. Radial gas holdup profiles show wall peaking, which is attributed to the uniform bubbly flow regime generated by the needle sparger used in this study. The addition of NaOH leads to similar gas holdup values but significant changes on local bubbly dynamics, such as bubble size distribution and axial gas phase velocity. The Sauter mean diameter was found to decrease with increasing concentration of NaOH, whereby the decrease is larger at higher gas flow rate.

Interfacial structure of upward gas–liquid annular flow in inclined pipes

Temporal and spatial-resolved data on the interfacial structure in upward vertical and inclined two-phase annular flows were accumulated using a novel non-intrusive multilayer conductance sensor. The sensor provides simultaneous measurement of the film thickness across the entire pipe circumference, enabling a three dimensional reconstruction of the wavy interface. Measurements were performed for two liquid (water) flow rates and a single high gas (air) flow rate. Three types of interfacial waves were identified, including ripples, disturbance and rogue waves. Rogue waves can be described as an infrequent solitary disturbance wave propagating over a ripple-dominant interface. Detailed statistical properties of the interfacial shape, such as the mean film thickness, wave height distribution, wave frequency spectra, wave propagation velocities and more, were obtained as a function the pipe inclination and azimuthal angle. The statistical analysis of the wavy interface presented in this study sheds light on a complex flow pattern of annular flow in inclined pipes, which has remained relatively unstudied experimentally.For inclined pipes, gravity imposes an asymmetric film distribution resulting in the thickest film at the bottom of the pipe. At this location, waves attain larger amplitudes while maintaining slower propagation velocities as compared to smaller amplitude waves at the top of the pipe. Generally, the wave frequency throughout the pipe circumference increases with inclination angle. For a larger liquid flow rate, the interface was found to be primarily dominant by disturbance waves. For a lower liquid velocity, the interfacial structure was found to be highly dependent on both the azimuthal and the inclination angles. An interface wave type map is presented as a function of those angles.

A novel perspective on the performance analysis and design of an injection cooling system for liquid storage

Injection cooling has been used to store liquefied cryopropellants by reducing or eliminating the liquid boil-off due to ambient heat inleak. It involves subcooling of liquid by bubbling a gas through it. Previous studies on injection cooling attributed the cooling effect on liquid evaporation into the injected bubbles. However, a closer look into the process indicates that much higher gas flow rates than those used in the experiments are necessary to cause the observed liquid cooling. Hence, it is envisaged that the liquid evaporation into the ullage also dictates the liquid cooling. A novel theoretical approach has been presented to analyze the injection cooling system by developing a lumped parameter model that considers the liquid evaporation into both the bubbles and the ullage. Satisfactory validation of the proposed model, and a comparison between the surface evaporation and the bubble evaporation corroborate the significance of surface evaporation. Thus the present approach provides a better understanding of this process. To the authors’ best knowledge, the effect of the liquid evaporation into the ullage is being considered for the first time in analyzing this system. This finding is of critical importance in the design and development of injection cooling systems for liquid storage.

Novel Core-Shell (ε-MnO2/CeO2)@CeO2 Composite Catalyst with a Synergistic Effect for Efficient Formaldehyde Oxidation.

A novel core-shell (ε-MnO2/CeO2)@CeO2 composite catalyst with a synergistic effect was prepared by hydrothermal reaction and thermal decomposition and its application to high-efficiency oxidation removal of formaldehyde (HCHO) was systemically investigated. The (MnCO3/CeO2)@CeO2 precursor was prepared first by the one-pot hydrothermal reaction of Mn2+ and Ce3+ solutions with a CO2-storage material (CO2SM) without any external templates or surfactants required. The thermal decomposition of the precursor afforded the core-shell (ε-MnO2/CeO2)@CeO2 composite catalyst with excellent catalytic performance. HCHO in the feed gas (180 ppm HCHO, 21% O2, N2 balanced) at a gas hourly space velocity of 100 L/(gcat h) is 100% converted over the catalyst at 80 °C. The conversion rate remains above 95% in 72 h and above 73.8% in 140 h, suggesting the strong stability of the catalyst at high gas flow rates and relatively low temperatures. The synergistic mechanism of the catalyst was explored by X-ray diffraction, Raman, Brunauer-Emmett-Teller, transmission electron microscopy, and X-ray photoelectron spectroscopy. The number of defects in the catalyst and the strength of the Mn-O bond in ε-MnO2 can be tuned by adjusting the synthesis conditions. More oxygen vacancies on the surface of CeO2 can make the synergistic effect of the catalyst stronger, which significantly improves the lattice oxygen (Olatt) activity on the surface of ε-MnO2. Our work has provided new insights into the preparation of the desired composite catalysts with excellent performances.

CO2 Capture in A Bubble-Column Scrubber Using MEA/CaCl2/H2O Solution—Absorption and Precipitation

This study used the solvent monoethylamine (MEA)/CaCl2/H2O to investigate CO2 absorption and CaCO3 crystallization in a bubble column scrubber. The variables explored were pH, gas flow rate, gas concentration, the liquid flow rate of the solution to absorb CO2, and CaCO3 crystallization. Under a continuous mode, the solution of CaCl2 was fed continuously, and the pH dropped after CO2 absorption. To maintain the set pH value, there was an automatic input of the MEA solvent into the bubble column. In addition to maintaining the pH, the solution could also absorb CO2 and produce CaCO3 crystals, which served two purposes. The results showed that there were mainly vaterite crystals. At different pH values, the lower the pH, the higher the precipitation rate of vaterite (Fp), and vice versa. However, under different gas flow rates, the Fp decreased as the pH value increased. Additionally, the process variables also affected the absorption rate (RA) and the overall mass-transfer coefficient (KGa) generally increased with increasing pH, gas concentration, and gas flow rate. However, it slowed down under operating conditions at high pH and high gas flow rate. Finally, correlation equations for RA, KGa, and Fp were also obtained and discussed in the study.

Investigation on the influence of the gas flow mode around substrate on the deposition of diamond films in an overmoded MPCVD reactor chamber

In an overmoded home-made MPCVD reactor, the influence of gas flow mode on the deposition of diamond films was investigated with H2/CH4 gas mixtures at the microwave power of 5800 W. The simulation results show that the diamond films can be grown in the environment filled with the gas mixture with relative high gas flow rate when an improved gas flow mode is established around the substrate. The scanning electron microscope and Raman spectra indicate that the improved gas flow mode plays a role in the growth of well-faceted crystals at the edge area of the diamond films. The quality, growth rate and uniformity of the diamond films can be significantly improved when introducing the improved gas flow mode. To explain the experimental results, the plasma is measured by optical emission spectrometer. It is shown that in the improved gas flow mode, the activated species of C2 and H in the plasma exhibit a uniform distribution. Furthermore the improved gas flow mode enlarges the area of the region where the concentrations of activated C2 and H are coupled. The diamond films with 50.8 mm and 101.6 mm in diameter have been finally deposited in the improved gas flow mode.

Subsea natural gas dehydration in a membrane contactor with turbulence promoter: An experimental and modeling study

Subsea natural gas reservoirs are usually saturated with water vapor that causes corrosion in pipelines and forms hydrates blocking pipes and installations. In this work, the viability of the subsea natural gas dehydration in a non-porous membrane contactor was evaluated experimentally and by modeling.A flat sheet composite membrane is employed as the membrane interface and a structured packing turbulence promoter was installed at the gas side. The water flux and the outlet dew point were measured at different operating conditions (e.g., pressures, liquid and gas flow rates). To estimate simultaneously the permeability, overall mass transfer coefficient, and outlet water content, a systematic approach was applied and a 1D-2D model was developed bypassing the liquid phase mass transfer resistance and solved numerically coupled with a developed correlation for axial dispersion coefficient. The results show an increase in transmembrane water flux to the highest values of 72 g/m2h and 53 g/m2h with increasing gas flow rate and pressure to 500 ml/min and 11 bara, respectively. The effect of using a turbulence promoter was evaluated, and a good agreement between the simulated and experimental results was obtained. The mass transfer resistance of a dense layer was found to be dominating compared to that of gas and liquid phase and the high pressure and high gas flow rate are favored in this process. This study shows that membrane contactor enables effective water separation under subsea conditions. Installation of a turbulence promoter in the gas phase significantly reduced the water content in the outlet gas stream.

Numerical Modeling of Equal and Differentiated Gas Injection in Ladles: Effect on Mixing Time and Slag Eye

Ladle refining plays a crucial role in the steelmaking process, in which a gas stream is bubbled through molten steel to improve the rate of removal of impurities and enhance the transport phenomena that occur in a metallurgical reactor. In this study, the effect of dual gas injection using equal (50%:50%) and differentiated (75%:25%) flows was studied through numerical modeling, using computational fluid dynamics (CFD). The effect of gas flow rate and slag thickness on mixing time and slag eye area were studied numerically and compared with the physical model. The numerical model agrees with the physical model, showing that for optimal performance the ladle must be operated using differentiated flows. Although the numerical model can predict well the hydrodynamic behavior (velocity and turbulent kinetic energy) of the ladle, there is a deviation from the experimental mixing time when using both equal and differentiated gas injection at a high gas flow rate and a high slag thickness. This is probably due to the insufficient capture of the velocity field near the water–oil (steel–slag) interface and slag emulsification by the numerical model, as well as the complicated nature of correctly simulating the interaction between both gas plumes.

Numerical and Physical Investigation of the Mixing Process in Gas Stirred Ladle System

Secondary steelmaking or ladle metallurgy is one of the important processes that adjust and homogenize the chemical compositions and the temperature. In this process, argon gas is injected into the melt through porous plugs to accelerate the chemical reaction and the mixing. One of the indicators for the mixing efficiency is “the mixing time”. The purposes of this study were to investigate the effects of gas flow rate and purging system on the mixing time and flow characteristics by using numerical and physical investigation and to predict the velocity magnitude acting on the refractory wall by analyzing the effects of gas flow rate. A 1:5 scaled water model and a full-scale ladle model of Millcon steel PLC were used in the study. The numerical simulation modelling was carried out by using CFD commercial software Flow-3D. The results from the numerical simulation were in consistence with the experiment results. The simulation results showed that with the highest gas flow rate the reduction of the mixing time was around 36% and the velocity magnitude increased to approximately 44% in comparison with the lowest gas flow rate in the full-scale model. The area at the ladle wall near the liquid surface has a higher chance of the damage than other areas. Besides, employing the dual-plugs system led to approximately 33–49% shorter mixing time compared to the single-plug system. The results show that the gas flow rate affects the turbulent kinetic energy directly. However, high turbulent kinetic energy leads to open-eye size which results in re-oxidation and contamination. Therefore, it is important to optimize the flow rate to achieve both productivity and steel cleanliness.

Influence of Pressure on Gas/Liquid Interfacial Area in a Tray Column

The influence of pressure on the gas/liquid interfacial area is investigated in the pressure range of 0.2–0.3 MPa by using a tray column test rig. A simulated waste gas, which consisted of 30% CO2 and 70% air, was used in this study. Distilled water was employed as an absorbent. The temperature of the inlet water was 19 °C. The inlet volumetric flow rate of water was 0.17 m3/h. Two series of experiments were performed; the first series was performed at inlet gas flow rate 15 Nm3/h, whereas the second series was at 20 Nm3/h of inlet gas flow rate. The results showed that the gas/liquid interfacial area decreases when the total pressure is increased. The effect of pressure on the gas/liquid interfacial area at high inlet volumetric gas flow rates is more significant than at low inlet volumetric gas flow rates. The authors studied the effect of decreasing the interfacial area on the performance of a tray column for CO2 capture.

Study on thermodynamic equilibrium and character inheritance of cobalt carbonate decomposition

Presently, the main cobalt powder production method is the reduction of cobalt carbonate, and the decomposition process significantly influences the properties of the ensuing cobalt powder. Thus, the objective of this study was to investigate CoCO3 decomposition using thermodynamic simulations and calculations, as well as experiments. The results obtained led to the conclusion that in the absence of oxygen, CoCO3 primarily decomposes into CoO and CO2. However, in the presence of oxygen, it preferentially undergoes oxidation decomposition, generating Co3O4 and CO2, while the unreacted CoCO3 subsequently decomposed forming more CoO when O2 was exhausted. Additionally, Co3O4 decomposed to CoO and O2 at high temperatures. TG-DSC-MS analyses showed that the temperature at which CoCO3 decomposed into CoO was 332 °C. The analysis of the CoCO3 decomposition process performed in an inert atmosphere showed that the decomposition product, CoO was generated at temperatures above 300 °C. Furthermore, SEM results showed that the morphology of the CoO obtained depends on that of the raw material (CoCO3), and a higher temperature induced agglomeration; thus, increasing CoO size. Lower decomposition temperatures, higher gas flow rates, and lower heating rates resulted in a decrease in CoO particle size.

Preliminary evaluation of the use of high-flow nasal cannula oxygen therapy during recovery from general anesthesia in dogs with obstructive upper airway breathing.

Brachycephalic airway syndrome can pose a risk of complicated recovery from anesthesia as a result of irritation to the excess pharyngeal andlaryngeal tissue present in affected dogs. High-flow nasal cannula (HFNC) oxygen therapy is a respiratory support modality that offers provision of continuous positive airway pressure via high gas flow rates. The HFNC system actively warms and humidifies inspired gases, which improves comfort and facilitates tolerance of the high flow rates in people and dogs. HFNC oxygen therapy was applied to brachycephalic dogs that developed increased work of breathing or hypoxemia in the recovery phase of anesthesia to determine if this device would be tolerable and effective for relief of upper respiratory difficulty. The HFNC nasal prong interface is well suited to the brachycephalic facial structure. The application of HFNC was found to reduce dyspnea scores in patients with signs of upper airway obstruction after general anesthesia. Aerophagia and changes in PCO2 were noted. Application of HFNC in the recovery period may result in improved airflow during times of somnolent obstructive breathing, not unlike the use of continuous positive airway pressure therapy in sleep-disordered breathing in people.

Are high fresh gas flow rates necessary during the wash-in period in low-flow anesthesia?

In low-flow anesthesia (LFA), there is a wash-in period in which usually high fresh gas flow (FGF) rates are used to achieve the required initial concentration of anesthetic agent in the alveoli. The aim of this study was to compare the efficiency, safety and the consumption of desflurane in LFA using constant FGF (1 L/min) and conventional LFA using high FGF (4 L/min) during the wash-in period. Eighty patients, who were scheduled for elective surgery under general anesthesia with endotracheal intubation, were enrolled in the study. Wash-in was accomplished with 1 L/min FGF (50% O2, 50% air) and 18% desflurane in group 1; and by 4 L/min FGF (50% O2, 50% air) and 6% desflurane in group 2. Throughout the surgery, the vaporizer was adjusted to maintain 0.6 to 0.8 minimum alveolar concentration (MAC). The time required to reach 0.7 MAC was shorter in group 1 (160 seconds [135-181] vs 288 seconds [240-500], P < .001). In 6 patients in group 1 and 13 in group 2, vaporizer settings were adjusted to maintain 0.6 to 0.8 MAC (P = .048). Desflurane consumption in the first hour and total desflurane consumption were higher in group 2 (P < .001 and P = .012, respectively). The efficiency of anesthesia in both the first hour and in total was higher in group 1 (P < .001). It is safe, more efficient, and economical to use 1 L/min FGF during the wash-in period in LFA.

Comparison of Two Gas Injection Methods for Generating Bubbles in a T-junction

In this work, we compare the performance of two different methods for generating bubbles in conditions relevant to microgravity. A T-junction formed by two cylindrical (1 mm of internal diameter) and perpendicular channels is used to generate trains of non-wetting bubbles. Air and distilled water are used as dispersed and continuous phases, respectively. The difference between both methods lies in the strategy used to inject the fluids. In one case (here referred to as TJ-A configuration), the gas is injected into the side channel. In the other case (referred to as TJ-B), the gas is injected into the main channel. Bubble size dispersion is analyzed and quantified with the polydispersity index. The increase of the capillary number (based on the continuous phase) has shown a strong influence on the regularity of the bubble generation process. The TJ-A method can produce monodisperse bubbles at higher capillary numbers than configuration TJ-B. The limits of monodispersity, as far as the capillary number is concerned, are studied. These limits determine the optimal operating range of the T-junction for generating highly monodisperse bubbles. Beyond these limits, polydispersity increases, although much more abruptly in TJ-B than in TJ-A. The bubble generation frequency is also studied, with special attention to the two main regimes that characterize the frequency, i.e. the linear regime (at very low gas flow rate) and the saturation regime (at high gas flow rates). A new dimensionless expression of the bubble generation frequency is proposed in this work.

Investigation of the inner structure of gas–liquid flow in airlift pumps by laser‐high speed visualization technology

AbstractExperiments were conducted to investigate the inner structure of gas–liquid flow in airlift pumps by a laser Doppler velocimetry (LDV) system and a laser‐high speed photography. The measured central plane of the riser pipe was illustrated by a laser device, and the corresponding gas–liquid flow in this plane was recorded by a high speed camera. The results showed it was the wispy annular flow, rather than the annular flow, dominated the pump performance under a high gas flow rate. This wispy annular had a thick film with a maximal value 0.2 times of pipe diameter, and it kept pump working with a high output liquid flow rate at large gas flow rates. Moreover, new flow regime maps were presented with a function of accurately estimating the flow regime transition and presenting the airlift pump performance.

Experimental and simulation research on the interface instability in gas jet forming

The phenomenon of interface instability occurred in the gas jet forming of mirror blank has been analysed in this research. Through numerical simulation and the theoretical calculation, the critical velocity of interface instability between epoxy resin and gas jet is 4.855 m/s. Through experiments and surface morphology tests, the influence of interface instability on mirror blank forming is analysed. It is concluded that the interface instability at a low gas flow rate will lead to the increase of the surface roughness of mirror blank, while the interface instability formed at a high gas flow rate will bring a periodic surface wave of epoxy resin, which makes it difficult for the mirror blank to form an expected curved surface. By calculating the gas jet rate when the interface instability occurs, this research aims to examine the causes and critical conditions of interface instability, to prevent it from happening in the process of gas jet forming.

Feeding spent coffee grounds into reactors: TFM simulation of a non-mechanical spouted bed type feeder

Due to the increasing coffee production, Spent Coffee Grounds’ (SCGs) generation has grown dramatically, hence appropriate management of this solid biomass waste is imperative. SCGs can be used as feedstocks for renewable energy and fuel generation provided that a stable feeding of powders to reactors is maintained. Recently, a non-mechanical spouted bed feeder proved itself an excellent alternative in feeding SCGs to a pilot-scale circulating fluidized bed reactor. Nonetheless, further studies are necessary for the feeder’s implementation in commercial applications. Here the feeding of SCGs with the spouted bed feeder is addressed by using Computational Fluid Dynamics. Firstly, a Two-Fluid Model (TFM) is validated against experimental data, and then the effects of five operating and design parameters were analyzed aiming at improving the handling of SCGs. The solids flowrate (WS) in the reactor could be stably controlled from 4 to 30 g/s depending on the settings. The feeder performance is enhanced by operating it under high gas flowrate (Q), high entrainment length (z), and high mass of solids in the feeder (HS). Using feeders with low cone angle (γ) or reactors with large diameter (DR) increases WS, which is appealing for the operation of medium-to large-scale units. The proposed TFM is a cost-effective tool for implementing spouted bed feeders in commercial applications. With the feeder coupled to the process, SCGs are treated continuously in the reactor for energy generation, thus reducing the disposal problems associated with this waste and improving the management of SCGs globally.

Optimization-based approach for CO2 utilization in carbon capture, utilization and storage supply chain

Carbon dioxide (CO2) is one of the primary anthropogenic greenhouse gases (GHGs), and its increasing emission has drawn wide attention from the international community. Among the strategies for CO2 diminishment, carbon capture, utilization and storage (CCUS) is considered as the key option. The objective of this work is to develop an optimization-based assessment framework that aims to incorporate CO2 storage and CO2 utilization into an integrated framework. To achieve this goal, a superstructure network including all the sections of CCUS supply chain is proposed, which includes CO2 capture, transportation, storage and utilization with 15 candidate conversion process paths. Based on this superstructure, a mathematical model for the optimal design of a supply chain of CCUS is developed. CO2 would be stored underground and/or utilized to produce chemical products through candidate conversion paths. Finally, a case with real data of large emission sources in Northeast China is studied. Three different scenarios are investigated, according to key constraints on CCUS network: CO2 emission source, raw material limits and products demands limits. Results show that adsorption is the preferred capture technology at relative high flue gas flow rate and high CO2 concentration. Storing CO2 is the recommended approach compared with utilization from the point of economy, however, carbon utilization could be a more sustainable option and may generate a carbon-neutral cycle. With the increase of CO2 utilization, the cost of CCUS supply chain also increase (Scenario A: 2.49 billion $/y, Scenario B: 2.76 billion $/y, Scenario C: 2.85 billion $/y).