Increase In Operating Pressure Research Articles

The physics of twin-fluid jet-in-crossflow at atmospheric and jet-engine operating conditions

Efforts to mitigate jet engine emissions produced a class of swirl-stabilized combustors in which a rich pilot-flame in the center of the swirl-cup anchors an outer-annulus of lean-premixed main-flame. Fuel distribution within the annulus must be carefully controlled to allow stable combustion while avoiding excessive swirl-cup heating and flashbacks. This was traditionally achieved by placing plain jet-in-crossflow (JICF) fuel injectors around the swirl-cup; however, a recent increase in engine operating pressure and temperature along with demand for leaner fuel-air mixtures made the traditional approach untenable. Hence, modern swirl-cup designs begin to adopt a new fuel-injection technique called the “twin-fluid JICF (TF-JICF)” where a sleeve of air is co-injected with the liquid jet to modify its spray-pattern. TF-JICF is a nascent variation of the JICF that is not well understood, especially at elevated pressures. Hence, an experimental investigation of TF-JICF spray behaviors was performed by our group, covering the operating conditions of 1.5–9.5 atm in crossflow pressure, 175–1050 in crossflow Weber number, 5–40 in momentum flux-ratio, and 0%–150% in air-nozzle pressure-drop, at the crossflow temperature of 150 °C and velocity of 75 m/s. Part 1 of the investigation’s results, which identified four distinct flow regimes and nonmonotonic penetration trends in TF-JICF, was published in the work of Tan et al., “The regimes of twin-fluid jet-in-crossflow at atmospheric and jet-engine operating conditions,” Phy. Fluids 30, 025101 (2018). The current paper expands upon the previous report by elucidating key spray features and potential mechanisms (e.g., transitions between crossflow-driven atomization, air-driven shear-atomization, and air-driven prompt-atomization) within each TF-JICF regime, thereby providing a conceptual framework of TF-JICF for future studies.

Optimal design for real-time quantitative monitoring of sand in gas flowline using computational intelligence assisted design framework

Abstract Global demand for oil and gas is still increasing rapidly. The direct consequence of this is the increased operating pressure amid concerns over increasing sand production. According to the Society of Petroleum Engineers (SPE), 70% of the world's hydrocarbon reserves are contained in reservoirs situated on unconsolidated formations. Given the reality of these formations, sand production will certainly be a problem of significant concern particularly during the later life of the fields when they become more ‘mature’. However, to monitor sand and optimise its production for improved recovery and safety, life extension and economy of the fields and ensured reliability, the automatic detection and prediction of sand flow characteristic measurements; sand flow rate (SFR), sand concentration (SC), line pressure drop (PD), and gas velocity (GV), has become an important research topic of great interest. Despite this importance, discussion of the topic is still lacking in the literature. This paper proposes a novel and robust architecture of intelligent real-time sand flow characteristic measurement using an acoustic sensor and computational intelligence assisted design (CIAD) framework. It fully incorporates acoustic signal processing and analysis, prediction algorithms and optimisation algorithms in the design. Acoustic features based on acoustic signal processing techniques are extracted to reduce the dimensionality of the acoustic signals. A classical Artificial Neural Network (ANN) is used to model the non-linear relationships between the acoustic signal characteristics and the flow characteristics measurands. In addition, the ANN algorithm adapts its weights and biases using the Grey Wolf Optimiser (GWO) through minimisation of the cost function during the training phase. Preliminary results obtained on a laboratory test rig demonstrate that an acoustic sensor coupled with CIAD may provide simple and robust practical solution to the measurement problem of particle-laden gas flow characteristics in real-time.

Illustrative Case Study on the Performance and Optimization of Proton Exchange Membrane Fuel Cell

Modeling is a powerful tool for the design and development of proton exchange membrane fuel cells (PEMFCs). This study presents a one-dimensional, two-phase mathematical model of PEMFC to investigate the two-phase transport process, gas species transport flow and water crossover fluxes. The model reduces the computational time for PEMFC design with guaranteed accuracy. Analysis results show that the concentration and activation overpotentials of the cell decrease with the increase of operation pressure, which result in enhanced cell performance. Proper oxygen stoichiometry ratio in the cathode decreases the cell activation overpotential and is favorable for performance improvement. The cell ohmic resistance correspondingly increases with the increase of catalyst layer thickness, which leads to a deteriorated cell performance. The improvement on cell performance could be facilitated by decreasing the membrane thickness. Predicted results show that the present model is a useful tool for the design optimization of practical PEMFCs.

NUMERICAL INVESTIGATION OF EFFECTS OF WORKING CONDITIONS ON PERFORMANCE OF PEM FUEL CELL

In this study, the effects of the working pressure and temperature on the performance of the PEM fuel cell were investigated numerically. Non-isothermal, steady - state and single-phase model was used to examine the behaviour of the proton exchange membrane (PEM) fuel cells in the three-dimensional condition. The three-dimensional single-cell model has been developed within FLUENT 6.3 software by utilizing the PEMFC module. The results of polarization (voltage) variation curves and current density distribution were given and compared with each other. According to the results obtained, by keeping humidification and cell temperatures in equilibrium, the performance of the cell improves with the increasing cell temperature. In addition, the current density of the cell increases with the increasing operating pressure.

Combustion wave of metalized extruded double-base propellants

Aluminum metal fuel, with combustion heat of 32,000 J/g, is of interest as high energy density material. Aluminum is able to react not only with free oxygen but also with inert combustion gaseous products. This study reports on the impact of ultrafine aluminum particles on combustion characteristics of double-base propellant. Metalized double-base propellant formulations were developed by solventless extrusion process. Combustion characteristics were evaluated using small-scale ballistic evaluation test motor. There was an increase in average operating pressure, burning rate, and characteristic exhaust velocity C∗ with aluminum content. Even though there was no oxidizer available for aluminum oxidation; aluminum alone offered 7.6% increase in average operating pressure, 24.6% increase in burning rate, 7.8% increase in C∗. The main outcome of this study is that this superior performance was achieved at 4 wt% solid loading level. Aluminum particles could alter the combustion wave by increasing the combustion flame temperature, average operating pressure inside the combustion chamber, thermal conductivity of DB propellant. All these combustion criteria could decrease the thickness of the dark zone, allowing the luminous flame to be more adjacent to the burning surface; therefore the reaction could proceed faster. Even though the developed metalized DB formulations were found to be more energetic with an increase in calorific value by 4.6%; they demonstrated good thermal behavior to reference formulation using DSC. These findings confirmed that aluminum is an outstanding energetic ingredient for solid rocket propulsion. It has unique ability to react with inert gases generating substantial heat output.

Optimal working fluid charge and degradation thresholds for a closed-circuit intermediate natural circulation heat transport loop

The study derives the optimal working fluid charge of a closed-circuit intermediate natural circulation heat transport loop based on the passive residual heat removal system (PRHRS) of SMART (System-integrated Modular Advanced ReacTor). The study finds that efficient natural circulation flow and heat transfer regimes can be maintained in a narrow band of working fluid charge mass owing to the small secondary side volume of the once-through helical-coil steam generator design of SMART. Overcharging condition is a severe passive system degradation mode that quickly leads to system failure. Overcharging is characterized by sustained two-phase flow instabilities, mainly liquid slugging in the hot leg of the PRHRS, and an increased operating pressure of the PRHRS coupled with a compensating increase in the operating pressure of the reactor coolant system (RCS). Increased pressures maintain the required temperature differential across the steam generator tubes and heat sink heat exchanger to achieve a prescribed quasi-steady state heat removal rate capacity. Undercharging condition is a benign degradation mode relative to overcharging and is characterized by a slow upward drift of the RCS pressure and temperature of the liquid water entering the primary side of the steam generator. Only the undercharged case of a completely dry steam generator secondary side leads to PRHRS failure-to-start via vapor lock.

Novel Application of a Polyurethane Membrane for Efficient Separation of Hydrogen Sulfide from Binary and Ternary Gas Mixtures

AbstractRecently we introduced a new polyurethane (PU) membrane synthesized from polypropylene glycol (PPG), hexamethylene diisocyanate (HDI), and 1, 4‐butane diol (BDO), and then studied the performance of the membrane for CO2 removal. This paper presents a novel application of the PPG‐HDI‐BDO membrane for separation of H2S in binary and ternary gas mixtures. The gas transport properties of the membrane in binary H2S/CH4 and ternary CH4/CO2/H2S gas mixtures at different temperatures, pressures, and gas compositions are investigated. Permeation tests show that the membrane has a high H2S/CH4 selectivity (27.2), an outstanding H2S permeability of 790 Barrer, and a remarkable CO2 permeability of 473 Barrer. The H2S permeability of 790 Barrer is the highest reported to this date for all PU membranes. The H2S permeability and H2S/CH4 selectivity of the membrane increases with temperature. As the operating pressure increases, the CO2/CH4 and H2S/CH4 selectivities of the membrane increases. H2S and CO2 permeabilities and H2S/CH4 and CO2/CH4 selectivities increase, as the H2S content of the feed increases. Solubility is most likely the dominant mechanism of gas permeation in this membrane. As the CO2 content of the feed stream increases, the H2S permeability and H2S/CH4 selectivity of the membrane decreases. The membrane has maximum H2S/CH4 selectivities of 27.4 in binary H2S/CH4 (with 0.075 mol% H2S) and 27.2 in ternary CH4/CO2/H2S (with 0.66 mol% H2S).

Transient analysis of subcritical/supercritical carbon dioxide based natural circulation loop with end heat exchangers: experimental study

Carbon dioxide (CO2) based natural circulation loops (NCLs) has gained attention due to its compactness with higher heat transfer rate. In the present study, experimental investigations have been carried out to capture the transient behaviour of a CO2 based NCL operating under subcritical as well as supercritical conditions. Water is used as the external fluid in cold and hot heat exchangers. Results are obtained for various inlet temperatures (323–353 K) of water in the hot heat exchanger and a fixed inlet temperature (305 K) of cooling water in the cold heat exchanger. Effect of loop operating pressure (50–90 bar) on system performance is also investigated. Effect of loop tilt in two different planes (XY and YZ) is also studied in terms of transient as well as steady state behaviour of the loop. Results show that the time required to attain steady state decreases as operating pressure of the loop increases. It is also observed that the change in temperature of loop fluid (CO2) across hot or cold heat exchanger decreases as operating pressure increases.

Removal of high concentration CO2 from natural gas using high pressure membrane contactors

The feasibility of removing high concentration CO2 from natural gas using membrane contactors at elevated pressures was preliminarily investigated in this study. CO2-CH4 gas mixture and activated methyldiethanolamine (aMDEA) solution were used as simulated natural gas and absorbent, respectively. The stability of poly(vinylidene fluoride) (PVDF) hollow fiber membranes in aMDEA solution at room temperature was first investigated through Fourier transform infrared spectroscopy (FTIR) and contact angle (CA) analyses. The effect of operation pressure, membrane area and feed gas flow rate on CO2 removal performance as well as CH4 loss was studied. The results indicated that the CO2 removal efficiency was significantly improved with increasing operation pressure. For 70% CO2 in feed, the removal efficiency of CO2 increased from 33.3% at 1bar to 91.3% at 60bar under the experimental conditions. Meanwhile, the overall mass transfer coefficient (KOG) gradually decreased due to the decrease of CO2 diffusion coefficient. The CO2 outlet concentration, CO2 flux and CH4 loss were also affected by membrane area and feed gas flow rate. This study provides a reference for the understanding of removal of high concentration CO2 from natural gas using membrane contactors at elevated pressures.

Transient responses of turbulent heat transfer of cryogenic methane at supercritical pressures

A numerical study has been conducted to analyze transient responding behaviors of fluid flow and heat transfer of the cryogenic methane at supercritical pressures, the physical phenomena closely related to the regenerative rocket engine cooling application. A steady-state cold flow is instantly enforced with a constant surface heat flux to activate the transient heat transfer process. The effects of surface heat flux, inlet flow velocity, and pressure on transient responses are studied in detail to obtain fundamental understanding of the underlying physical mechanisms. Results indicate that the increased fluid temperature during the heat transfer process leads to the significantly decreased fluid density at a supercritical pressure and consequently causes strong fluid thermal expansion, which results in flow oscillations. The strong pressure effect on thermophysical property variations in the supercritical-pressure heat transfer process, particularly in the trans-critical region, can lead to further extension of the transient responding process at a low inlet flow velocity and/or under a high surface heat flux. Flow oscillations become stronger and last longer under a higher surface heat flux and/or at a lower inlet flow velocity. An increased operating pressure slightly decreases the transient responding time. Under the tested conditions in the present work, the maximum transient response time is around 20ms.

WATER DISTRIBUTION UNIFORMITY FOR MINI-SPRINKLER IRRIGATION SYSTEM

The change of world climate and its attendant effect on scarce water resources have further reduced the availability of water for agriculture. Under this circumstance, the use of pressurized irrigation systems can be an option of enhancing the efficiency of water consumption. This study was therefore conducted to evaluate the performance of mini-sprinkler irrigation system and to determine optimum operating conditions that achieve high coefficient of uniformity (CU). An experiment was conducted on the experimental farm of faculty of Agricultural, Suez Canal Univ. Egypt. Four different commercially available makes of mini-sprinklers MSP1, MSP2, MSP3 and MSP4 of different nozzle sizes 0.85, 1.35, 1.5 and 2.0 mm, respectively were tested at 75 cm stake height for their hydraulic performance in terms of pressure-discharge, pressure-wetting diameter and pressure-average precipitation rate of single mini-sprinkler head relationships. The experiment was conducted at six different operating pressures of 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 bar. Polynomial equation of the form Q = aP2 + bP + C were developed for all types of four mini-sprinklers to describe the pressure-discharge relationship. On the basis of this relationship MSP4 was found to be superior over other three nozzles. Pressure- wetting diameter relationships was very well established by polynomial type equation of the form WD = aP2 + bP + C and MSP4 was to be superior over other three nozzles. Average precipitation rate was found to be decreases with increase in operating pressure. For all tested operating pressures and nozzle size, the CU increased with increased operating pressure until its maximum at 2.0 bar.

Thermal effects during biomass pyrolysis

The influence of process conditions on the overall heat demand during the pyrolysis of biomass was investigated. The results show that increasing the vapour residence time by an increasing initial sample weight or an increasing operating pressure results in an increasing char yield and in a decreasing heat demand. Lumped reaction schemes were used for data interpretation. They suggest that only an exothermic char formation process may justify the experimental results obtained. Influence of pressure, residence time and initial sample mass on biomass heat demand were correlated to the final char yield, confirming that the formation of char during pyrolysis is an exothermic process, independently of operating conditions.

Computational Investigation of the Splashing Phenomenon Induced by the Impingement of Multiple Supersonic Jets onto a Molten Slag–Metal Bath

This paper presents a study of the splashing phenomenon caused by the impingement of supersonic jets onto the slag–metal molten bath under real oxygen steelmaking conditions using numerical simulations. The validity of the mathematical model has been verified through different applications. The time-sequenced occurrence process and generation mechanism of splashing are revealed, and the splashing rate is determined with respect to lance height and operation pressure by combining the multifluid volume of fluid model with the blowing number theory. The results show that the generation of splashing is a result of the collective effects of the direct ejection of individual droplets and the tearing of “splash sheets” or “large tears”. It is also found that the splashing process is unstable and normally irregular during the blowing, and the splashing is enhanced in terms of the tearing of splash sheets or large tears with declining lance height or increasing operation pressure.

Precombustion CO2 capture using a hybrid process of adsorption and gas hydrate formation

In this study, a fixed bed of pulverized coal particles was employed to enhance the precombustion CO2 capture from fuel gas (40 mol% CO2/H2). The performance of the HAHF (hybrid adsorption-hydrate formation) process occurred in the fixed bed was evaluated at different liquid saturations and operation pressures. The experiments were carried out at 274.2 K with the pressure varying from 3.0 MPa to 6.0 MPa. 1.0 mol% THF (tetrahydrofuran) solution instead of liquid water was used to saturate the fixed bed and reduce the hydrate phase equilibrium conditions. The results indicated that gas hydrate nucleation in the fixed bed was quickly induced by gas adsorption in coal particles. The HAHF process was dominated by hydrate formation as the fixed bed saturation increased, and the CO2 recovery and separation factor were increased. Gas consumption during the HAHF process was promoted with the increase of operation pressure, but the CO2 recovery and separation factor decreased. In the fixed bed of coal particles saturated by 1.0 mol% THF solution the highest gas uptake obtained was 51.9 mmol of gas/mol of water, which was comparable with that obtained in the fixed bed of silica sand in the presence of 5.53 mol% THF. Therefore, compared with the hydrate based gas separation process, the hybrid adsorption-hydrate formation process proposed in this study could be a viable option for CO2 capture from fuel gas.

Selectivity and Mass Transfer Limitations in Pressure-Retarded Osmosis at High Concentrations and Increased Operating Pressures.

Pressure-retarded osmosis (PRO) is a promising source of renewable energy when hypersaline brines and other high concentration solutions are used. However, membrane performance under conditions suitable for these solutions is poorly understood. In this work, we use a new method to characterize membranes under a variety of pressures and concentrations, including hydraulic pressures up to 48.3 bar and concentrations of up to 3 M NaCl. We find membrane selectivity decreases as the draw solution concentration is increased, with the salt permeability coefficient increasing by a factor of 2 when the draw concentration is changed from 0.6 to 3 M NaCl, even when the applied hydraulic pressure is maintained constant. Additionally, we find that significant pumping energy is required to overcome frictional pressure losses in the spacer-filled feed channel and achieve suitable mass transfer on the feed side of the membrane, especially at high operating pressures. For a meter-long module operating at 41 bar, we estimate feedwater will have to be pumped in at a pressure of at least 3 bar. Both the reduced selectivity and increased pumping energy requirements we observe in PRO will significantly diminish the obtainable net energy, highlighting important new challenges for development of systems utilizing hypersaline draw solutions.

Preparation and arsenic adsorption assessment of PPESK ultrafiltration membranes with organic/inorganic additives

In this paper, the effects of PPESK concentration, and additives of PEO–PPO–PEO, oxalic acid/PEO–PPO–PEO, nano-TiO2/oxalic acid/PEO–PPO–PEO on membrane performances and arsenic adsorption properties were investigated. Compared with single additive of PEO–PPO–PEO, oxalic acid/PEO–PPO–PEO or nano-TiO2/oxalic acid/PEO–PPO–PEO had better pore-forming ability. It was found that PPESK membranes with additives of PEO–PPO–PEO or oxalic acid/PEO–PPO–PEO had no arsenic adsorption capability. For optimized PPESK membrane (14.0wt.% PPESK/1.2wt.% nano-TiO2/3.0wt.% oxalic acid/3.0wt.% PEO–PPO–PEO), with the contact time increasing, the arsenic adsorption efficiency decreased from 100 to 73.7%; with the increase of operation pressure, the efficiency of arsenic adsorption led a light decrease which ranged from 86.6 to 70.8%; when the arsenic (V) concentration increased from 0ppb to 500ppb, the arsenic adsorption efficiency reduced from 100 to 8.3%; the effect of feed temperature on arsenic adsorption was indistinctively; as the pH increasing from 3 to 11, the efficiency of arsenic adsorption first kept stable at 85.0%, and then decreased to 63.4%.

Experimental study on activated carbon–nitrogen pair in a prototype pressure swing adsorption refrigeration system

Pressure swing adsorption of nitrogen onto granular activated carbon in the single-bed adsorber–desorber chamber has been studied at six different pressures 6–18 kgf/cm2 to evaluate their performance as an alternative refrigeration technique. Refrigerating effect showed a linear rise with an increase in the operating pressure. However, the heat of adsorption and COP exhibited initial rise with the increasing operating pressure but decreased later after reaching a maximum value. The COP initially increases with operating pressures however, with the further rise of operating pressure it steadily decreased. The highest average refrigeration, maximum heat of adsorption and optimum coefficient of performance was evaluated to be 415.38 W at 18 kgf/cm2, 92756.35 J at 15 kgf/cm2 and 1.32 at 12 kgf/cm2, respectively. The system successfully produced chilled water at 1.7 °C from ambient water at 28.2 °C.

Transferring Characteristics of Momentum/Energy during Oxygen Jetting into the Molten Bath in BOFs: A Computational Exploration

This paper presents a numerical study of transferring characteristics of momentum/energy during oxygen jetting into the slag–metal molten bath in basic oxygen furnaces by a multi-fluid volume of fluid model. The evolution of the momentum/energy and turbulence of jets along their axial travel were studied. The results were quantitatively compared within a wide range of oxygen supply pressures, at which the jets may be at under- or over-expanding state. The efficiency of the momentum/energy transfer from the jets to the molten bath was also assessed with respect to lance height and operation pressure. The numerical results show that the momentum and kinetic energy for the jets suffering from shock waves likely cause more intensive damping compared to the jets with expansion waves. The turbulence kinetic energy and turbulence dissipation rate are observed to firstly increase and then decrease. This effect is more pronounced at a lower operation pressure. Based on these results, the optimum lance height was identified for a rapid slagging operation. It is also shown that the efficiency of the energy transfer from the jets to the molten bath is very low. Decreasing lance height or increasing operation pressure promotes the efficiency of the momentum transfer from the jets to the molten bath but lowers the efficiency of the kinetic energy transfer.

Hydrate Formation and Decomposition of CH4 and N2 in Ordered Mesoporous Carbon CMK-3 in the Presence of Tetrahydrofuran

The use of hydrate formation in porous media is an effective method for gas storage and separation. The equilibrium isotherms of CH4 and N2 in CMK-3, a mesoporous carbon material, were measured under different tetrahydrofuran (THF) concentrations and temperatures. The higher is the temperature required, the greater is the formation pressure needed, but the presence of THF significantly reduces the hydrate formation pressure. When THF exists, both CH4 and N2 form structure II (sII) hydrate; however, the amount of hydrate generation is lower than the theoretical value. As the operating pressure increases, some of the sII CH4 hydrate may transform into structure I (sI) and the amount of hydrate generation increases. The desorption isotherms showed that the gas hydrate decomposed completely when the operating pressure was below the hydrate decomposition pressure. In addition, it is feasible to separate gas mixtures via hydrate formation using the different gas hydrate formation pressures.

Study on Recycling Alkali from the Wastewater of Textile Mercerization Process by Nanofiltration

This study has researched the treatment ability of nanofiltration technology in printing and dyeing mercerization process alkali wastewater and investigated the effect of different pressures and alkalinities on membrane flux. The effect of different operating conditions on COD removal rate and alkali penetration rate has been also investigated in this study. The experimental results show that nanofiltration technology can remove the COD in printing and dyeing mercerization process wastewater effectively and the removal rate is above 80%. We conclude that the membrane flux tends to increase as the operating pressure increases, and decrease as the concentration of alkali in feed liquor and COD increases. The infiltration liquor through membrane can be satisfactorily reused by the method of concentration, and the final recovery efficiency of alkali by nanofiltration membrane treatment is above 90%.