Partial Flow Rate Research Articles

High performance symmetric supercapacitors based on Au incorporated CrN thin films fabricated by reactive magnetron sputtering

Recently, transition metal nitrides are being investigated extensively as potential supercapacitor material. In the present study, Au incorporated CrN (Au_CrN) thin films have been synthesized using reactive magnetron co-sputtering technique for application as supercapacitor electrode material. Films have been prepared at different Ar to N2 flow rates keeping total deposition pressure constant to achieve the required structural phase in the sample. Electrochemical properties of the deposited materials have been investigated with a three-electrode system in 0.5 M H2SO4 aqueous electrolyte. The CrN thin film deposited under 3:1 Ar: N2 partial pressure or flow rate ratio shows the highest specific capacitance. Upon Au incorporation, the film shows an areal capacitance of 56.8 mFcm−2 at 1.0 mAcm−2discharge current density which is an almost nine-fold enhancement in specific capacitance value compared to pristine CrN sample. Symmetric supercapacitors have also been developed by sandwiching two identical Au_CrN thin film electrodes, which have found to deliver excellent specific capacitance of 86.03 mFcm−2at 1.0 mAcm−2 discharge current density with no decline in capacitance value till 20,000 cycles. Furthermore, it can deliver a high energy density of 52.02mWhcm−2and a power density of 0.12mWcm−2. The electrochemical properties of the supercapacitors fabricated with the Au_CrN thin film electrodes are found to be better than most of the results reported so far in the literature with CrN electrodes. Results of the present study clearly demonstrate that these Au enhanced CrN films prepared by easily scalable and highly reproducible magnetron sputtering technique have great potential as a high capacitance supercapacitor electrode material.

Investigation of the kinetics of methanation of a post-coelectrolysis mixture on a Ni/CZP oxide catalyst

The use of synthetic natural gas (SNG) as a plug-and-play fuel coming from renewables can help to overcome the limitations given by the intermittency of renewable energy. A way to implement the production of SNG pass through the co-electrolysis of CO2 to a mixture of hydrogen, carbon monoxide and carbon dioxide, steam and small amounts of methane, followed by CO and CO2 methanation. The presence of different reactants and processes requires the comprehension and quantification of the kinetics of the reactions involved with the aim of optimizing methanation. In this work a kinetic model that considers both the direct CO2 methanation and the indirect RWGS + CO methanation pathways has been developed over a Ni(10 %wt)/Ce0.33Zr0.63Pr0.04O2. The kinetic study made it possible to understand the influence of the reactants and products on the reactions through the calculation of reaction rates. This allowed to test, by linearization, the models found in the literature and their adjustment permitted to calculate sixteen kinetic parameters (activation energies, heats of adsorption and pre-exponential factors) present in the rate laws of methanation of CO2, CO and the Reverse Water Gas Shift reaction. The models then made it possible to simulate the evolution of partial flow rates in an isothermal plug flow reactor and were compared to experimental data.

Impact of multi-factor coupling on the corrosion behavior of 254SMo stainless steel in an aggressive oilfield environment containing CO2 and H2S

The passivity and corrosion behavior of 254SMo stainless steel in aggressive oilfield environments containing both carbon dioxide (CO2) and hydrogen sulfide (H2S) were investigated using weight-loss and surface analyses. The results indicated that the corrosion rate increased with the increase in temperature, CO2/H2S partial pressures, tensile stress and flow rate. Compressive stress led to a reduction in sulfide compound contents and promoted the formation of protective oxide films, while tensile stress had an opposite effect. Furthermore, a synergistic effect of stress and flow was observed.

Study on the Unsteady Flow Characteristics of a Pump Turbine in Pump Mode

Extensive research has been conducted on the performance of pump turbines, particularly focused on understanding the generation mechanism of S-shaped characteristics. However, there has been a lack of research on unsteady flow characteristics in hump characteristics with small guide vane openings. This study focuses on the hump characteristics of a pump turbine in pump mode. The unsteady numerical simulation method is used along with experimental testing to examine the internal flow characteristics and induced pressure fluctuations under pump operating conditions. The results indicate that flow separation occurs in the impeller when the flow rate decreases to the valley operating condition, and recirculation flow occurs near the impeller inlet at the partial flow rate. Moreover, the unstable flow on the positive slope exhibits a low-frequency characteristic of 0.15fn. The pressure fluctuation from the hub to shroud areas of the guide vane region diminishes sequentially. Notably, distinct vortex structures emerge at the draft tube cone section under the valley operating condition. These structures extend toward the elbow section of the draft tube as the flow rate decreases. This phenomenon generates low-frequency pressure fluctuation originating from the primary frequency of the vortex and dean vortex on the surface, located at 0.4 D of the draft tube under conditions of low flow rate.

Thermodynamic analysis on CSP integrated cerium oxide (CeO2 − CeO1.72/1.83) water splitting cycle for hydrogen production

Solar thermochemical CeO2-based H2O splitting cycle was thermodynamically analyzed to ascertain the optimal thermal reduction (TH) and re-oxidation (TL) temperatures and evaluate the solar-to-fuel conversion efficiency (ηsolar−to−fuel) of the cycle. The equilibrium composition of CeO2, CeO1.72,CeO1.83 and O2 exhibited that the thermal reduction initiated at 1400 K thereby attaining 100 % TR at 2734 K. The observed variations in Gibbs free energy (ΔG) correspond to the feasibility of the re-oxidation step of CeO1.83 and CeO1.72 at 1050 K and 1200 K respectively. It was reported that the absorption efficiency of solar reactor (ηabs−solar−reactor−WS) decreases from 95.6 % to 37 %, as the TH increases from 1400 K to 2734 K. The results show that ηsolar−to−fuel reached the maximum value of 7.45 % for CeO1.72 and 7.69 % for CeO1.83 at 61.72 % TR of CeO2 without heat recuperation. Further, the ηsolar−to−fuel attained the maximum value of 14.92 % and 13.54 % for CeO1.83 and CeO1.72, respectively at the %TR of CeO2 of 80 % with 50 % heat recuperation. The solar-to-fuel conversion efficiency (ηsolar−to−fuel) further can be increased with the optimization of oxygen partial pressure (PO2) and molar flow rate of reduction regents (Ar or N2).

Evaluating the influence of Ar/N2 flow rate and pressure on the conversion efficiency of a solar-assisted Fe2O3 – FeO WS cycle for hydrogen production: A thermodynamic approach

A thermodynamic analysis is carried out to evaluate the effects of oxygen partial pressure (PO2) and molar flow rate of reduction agents (m˙N2/Ar) on the performance of Fe2O3−FeO solar thermochemical cycle (STC|Fe2O3−FeO). The chemical equilibrium and efficiency analysis parameters such as enthalpy, Gibbs free energy and entropy are calculated as a function of thermal dissociation temperature (TH). The chemical equilibrium analysis suggests that the thermal dissociation step is feasible above 1250 K while the re-oxidation step is practicable at 550 K. The efficiency analysis revealed that the highest value of conversion efficiency (ηsolar−to−fuel) reached up to 44.42% for N2 based cycle and 45.46% for Ar based cycle without using the recuperation technique. However, the conversion efficiency (ηsolar−to−fuel) attained the highest value of 57.84% for N2 based cycle and 59.14% for Ar based cycle with 50% heat recuperation.

Performance and unsteady flow characteristic of forward-curved impeller with different blade inlet swept angles in a pump as turbine

As an economical energy recovery device, a pump as turbine (PAT) is widely used in micro hydropower and energy recovery fields. Compared with an original impeller, a special impeller with forward-curved blades can dramatically enhance a PAT's efficiency and broaden its high-efficiency range because the blade angles created by the latter more effectively match the PAT's operating mode. The shape of blade curve and sweep has obvious influence on the performance of a PAT. To investigate how the inlet swept angle of forward-curved blade influences the performance of PAT, five different forward-curved impellers with different inlet swept angle blades were designed and numerically investigated based on a verified computational fluid dynamics (CFD) method. The effects of blade inlet swept angles on the external characteristics, energy loss and unsteady characteristics of PAT are analyzed. Compared with the blade whose inlet swept angle is 0°, the maximum efficiency of back-swept PAT with swept angle of −8° increases by 0.58% while the head decreases by 0.49 m. However, the efficiency of forward-swept PAT of 8° reduces by 0.9%, and the head increases by 0.68 m. The maximum reduction rates of the main frequency amplitude of pressure pulsation in the volute, impeller and draft tube of back-swept PAT are 35.2%, 45.47% and 67.24%, respectively, indicating that the back-swept blade can contribute to improve the operation stability of PAT. Moreover, the vortex in PAT with back-swept blade is greatly improved under partial and design flow rate, which can improve the unsteady flow characteristics of PAT.

Influence of CO2 partial pressure and flow rate on the corrosion behavior of N80 steel in 3.5% NaCl

In this paper, weight loss and in situ electrochemical measurements were carried out to investigate the influence of CO2 partial pressure and flow rate of corrosive media on the corrosion of N80 steel in 3.5% NaCl at 120 ℃. The corrosion product films obtained at different conditions were also analyzed by SEM and EDS. The results showed that with the increase of CO2 partial pressure, the corrosion rate decreases significantly. EIS results showed that the total resistance and charge transfer resistance of the film under all soaking times increased gradually with the increase of CO2 partial pressure, which indicates that the product film formed at high CO2 partial pressure was denser and had better protection to the matrix. Flow rate has limited influence on corrosion rate of N80 steel at tested conditions. EIS revealed that at different flow rates, the protection of corrosion product films increased with the soaking time. High flow rate is not favoarable to the formation of corrosion product film, or it is easy to break corrosion product film. And wall shear stress (WSS) is generally considered to be the main cause of failure, thus resulting in high corrosion rate of N80 steel.

Comparative studies on the propagation of rotating stall in a liquefied natural gas cryogenic submerged pump-turbine in both pump and turbine mode

With the tightening of liquefied natural gas (LNG) supply, unsteady stall flow under partial flow rate will likely cause significant difficulties with respect to the application of a cryogenic submerged pump-turbine (PT) at LNG-receiving terminals. In this study, the unsteady propagation characteristics of stall cells in pump mode (PM) and turbine mode (TM) of the PT are investigated numerically using the timescale-based hybrid turbulence model. The predicted performance curves show good consistency with on-site experimental data. As the rotating speed and fluid undercooling increase, the triggering of stall flow tends to a lower flow rate in PM, but this is reversed in TM. Under the superimposed action of separation and backflow vortex, stall flow in the impeller suffers from dynamic emergence to dissolution in PM, but quasi-static stall vortex is dominant in TM, benefiting from the rectification of the guide vane. By comparison, running in PM is prone to severe deep stall, and the stall cells have a higher propagation frequency and strength, which also induces greater local energy loss than in TM.

In Situ IGZO/ZnON Phototransistor Free of Persistent Photoconductivity with Enlarged Spectral Responses

We present comprehensive studies on ZnON thin films deposited by radio-frequency (RF) magnetron sputtering using a ZnO target under various nitrogen plasma conditions. A ZnON thin film grown under the highest nitrogen partial flow rate exhibits the lowest optical bandgap of 1.84 eV, excellent stability upon air exposure, an amorphous/nanocrystalline structure, and the strongest stoichiometric Zn3N2 chemical states. The highest field-effect mobility of 4.28 cm2 V–1 s–1, the largest responsivity, and the negligible persistent photoconductivity (PPC) effect against visible light are also realized by the thin-film transistor (TFT) configuration. The device performance of the ZnON phototransistor is compared to those of other oxide semiconductors of ZnO and InGaZnO (IGZO). Finally, an IGZO/ZnON phototransistor, where ZnON was deposited on top of IGZO by an in situ process, demonstrates high specific detectivities (1.65 × 1013, 1.35 × 1013, and 2.0 × 1014 Jones against red, green, and blue photons, respectively) without the PPC effect. We examined the photoluminescence (PL) spectra of ZnON with respect to nitrogen-associated defects, which are yet to be discussed, and emphasize that our optimum deposition process is free of the poisoning effect. To our knowledge, this is the first report on a ZnON phototransistor in which the channel was prepared by reactive sputtering of a ZnO target.

An infrared spectral database for gas-phase quantitation of volatile per- and polyfluoroalkyl substances (PFAS)

We report the construction of a database of quantitative infrared spectra specifically targeting volatile fluorocarbon gases that may be emitted during thermal treatment of per- and polyfluoroalkyl substances (PFAS) to assist understanding of treatment processes and improve quantification. To populate this database, protocols derived from the Pacific Northwest National Laboratory infrared spectral database have been employed. Each spectrum in the database is a weighted average derived from 10 or more individual measurements at different partial pressures (static method) or flow rates (dissemination method) to yield good fidelity for both strong and weak infrared signatures, with each composite spectrum ranging from ≥ 6500 cm−1 to ≤ 600 cm−1 at an apodized resolution of 0.112 cm−1. This resolution was chosen to fully resolve all spectral features, recognizing that atmospheric pressure broadening results in nearly all ro-vibrational lines having linewidths ≥ 0.1 cm−1. As an example case, application of the database is demonstrated via identification and quantification of dominant 1H-perfluoroheptane and perfluorohept-1-ene fluorocarbon products resulting from thermal decomposition of perfluorooctanoate (PFOA) below 450 °C.

Experimental investigation of cavitation-induced noise and vibration in a centrifugal pump

Cavitation has become a serious concern threatening operational stability as the need for high-speed machinery has grown. In this study, noise (sound pressure level) and vibrations (structural) were measured in a radial flow centrifugal pump for design and off-design conditions under cavitation. Because the structure of a particular noise/vibration spectrum (as well as its total level) is affected by the operating conditions and stage of cavitation within the pump, a detailed analysis the noise/vibration spectra during the pumping process was carried out to detect of the cavitation phenomenon's progression. We aim to identify the association between noise/vibration and the corresponding net positive suction head value at different flow rates. The results showed that the cavitation structure affects the vibration/noise behavior of the pump. Moreover, total noise level measurements at partial flow rates cannot be used to diagnose full cavitation breakdown, whereas total noise level measurements can be used to detect cavitation intensity at higher flow rates than the optimum operating point.

Effect of blade curve shape on the hydraulic performance and pressure pulsation of a pump as turbine

As an economical and convenient device, a pump as turbine (PAT) is widely preferred in the energy recovery process and micro-hydropower plants. To study the operational stability of a PAT, a forward-curved impeller and a back-curved impeller were designed in this paper. A verified computational fluid dynamics technique is used to compare the two different impellers in terms of the external characteristics, energy loss, and pressure pulsation under the partial load flow rate (0.8Qr), design condition (1.0Qr), and overload flow rate (1.2Qr). The results show that the total entropy generation power of the forward-curved impeller is 41.6%, 49.2%, and 53.6%, respectively, which are lower than that of the back-curved impeller. At the best efficiency point, the head, shaft power, and efficiency of the forward-curved impeller are 9.8%, 18.4%, and 13.1%, respectively, which is obviously better than that of the back-curved impeller. Similarly, the main frequency of the pressure pulsation in volute is the blade-passing frequency, and that of the impeller is the shaft frequency. Compared with the back-curved PAT, the pressure pulsations of the forward-curved PAT are decreased by 92.24%, 73.18%, and 62.22% in volute, impeller, and draft tube, respectively. This paper reveals that the forward-curved impeller not only obviously improves hydraulic performance but also significantly improves pressure pulsations within a PAT.

A Review on CO2 Absorption using Chemical Solvents at Low and High CO2 Partial Pressure Conditions in a Packed Column

CO2 removal is important for industrial flue gas treatment, biogas enhancement, and natural gas (NG) processing applications. Chemical absorption using an amine-based solvent is a proven technology for CO2 removal from various gases. In recent years, various promising amine solvents have been investigated, either as single or blended solutions, to enhance the CO2 absorption process at low and high CO2 partial pressure conditions. Low CO2 partial pressures (1 – 47 kPa) have been utilized in numerous research works focusing on flue gas treatment and biogas enhancement applications. On the other hand, high CO2 partial pressures were instead applied in NG processing ranging between 750 and 1600 kPa. To provide more insight into the current trends, existing research on CO2 absorption in amine-based solvents is presented in this review focusing on absorption performance in a packed column at low and high CO2 partial pressures. Reports on the effect of different parameters, namely CO2 partial pressure, gas, and liquid flow rates, amine concentrations, and liquid temperature, on the removal of CO2 in the packed column are included. Based on the review, the future direction is further highlighted in this area.

Initial High-Temperature Oxidation Behavior of Fe–Mn Binaries in Air: The Kinetics and Mechanism of Oxidation

High-temperature oxidation of steels can be relatively fast when exposed to air. Consequently, elucidating the effect of different parameters on the oxidation mechanism and kinetics is challenging. In this study, short-time oxidation was investigated to determine the oxidation mechanism, the affecting parameters, and the linear-to-parabolic growth transition of different Fe–Mn alloys in various oxygen partial pressures (10–30 kPa) and gas flow rates (26.6 and 53.3 sccm) in a temperature range of 950–1150 °C. Oxidation kinetics was investigated using a thermogravimetric analyzer (TGA) under controlled atmosphere. Linear oxide growth was observed within the first 20 minutes of oxidation. The linear rate constant was significantly increased by increasing the oxygen partial pressure or the flow rate of the oxidizing gas. The morphology of the oxide layer was determined by scanning electron microscopy (SEM). The crystal structure of the oxides formed was followed by in-situ X-ray diffraction (XRD), confirming that the growing layer consists of wustite mainly, which upon slow cooling to room temperature, transformed into magnetite. Energy-dispersive X-ray spectroscopy (EDS) showed that the atomic ratio of Fe+Mn to O was ~ 1.03:1 in the oxide scale, corresponding to Fe(Mn)O formation. Based on the characterization and a model for linear growth kinetics, it is concluded that the oxidation rate is controlled by the diffusion of oxidizing molecules through the gas layer to the sample’s surface. The findings led to a better understanding of initial oxidation behavior and provided a pathway for improved insight into the high-temperature oxidation behavior for more complex alloys.

CO2 Absorption from Biogas Using Piperazine-Promoted 2-Amino-2-methyl-1-propanol: Process Performance in a Packed Column

In this work, CO2 absorption from simulated biogas is investigated using different blends of a PZ + AMP solution in an absorption system at CO2 partial pressures ranging between 20 and 110 kPa. The collected data were presented as CO2 removal profiles along the packed column and were evaluated in terms of CO2 removal efficiency (%) and average overall volumetric mass transfer coefficient in the gas phase (KGav¯). An increased PZ concentration in the AMP solution was found to significantly increase the CO2 removal efficiency and KGav¯ values. It was observed that, when conducted at different CO2 partial pressures, gas and liquid flow rates, and chemical concentrations, the Lamine/GCO2 ratio strongly influenced the process behaviour in the packed column. Additionally, the optimal inlet liquid temperature was observed to be 35 ± 2 °C in this study.

Analysis of the transient pressure of fractured wells coupling with irregular flow fracture: Semi-analytical model and case study

A strange phenomenon happens all the time that the obtained permeability by the conventional finite-conductivity model (FC) is much larger than the actual value in tight reservoir. The conventional pressure-transient analysis models of vertical-fractured wells regard fracture as a regularly non-uniform flow rate. However, due to fracture bending, irregular proppant filling, proppant crushing, and inadequate fracturing fluid backflowing, the fracture may show an irregular flow rate in different fracture segments. An additional horizontal line or concave curve appears on the pressure derivative curve by considering the irregular flow rate in the fracture. In the past, the concave curve would be regarded as an error from field data, and the horizontal line on the pressure derivative curve would be regarded as the quasi-radial flow regime. If the horizontal line is recognized as the quasi-radial flow regime in tight reservoir, the interpreted permeability will be magnified many times. In this work, we proposed a multi-segment irregular non-uniform flow model with changing wellbore storage effect (MINFC) to characterize the pressure response of irregular fractures better, making the pressure response in the fracture more realistic. The MINFC model can correct the magnified permeability and diagnose the partial closure fracture location, length, and flow rate. Green function and Newman product method are applied to obtain the bottom-hole pressure behavior. The results demonstrate that the pressure derivative curve is not a line with a slope of 0.5 in the irregular fracture flow regime but a horizontal or concave curve. Sensitivity analysis demonstrates that the location and length of the irregular proppant filling will affect the duration of the horizontal line. In conclusion, the reservoir permeability and fracture half-length obtained by the MINFC model are closer to the actual value. The locations of irregular proppant filling and low flow rete are quantified so that researchers can take steps to improve fracture performance. Finally, the comparison between the MINFC model and the finite-conductivity model verifies the MINFC model's accuracy. The MINFC model matches field data to verify its practicability.

Multi-objective design optimization of industrial pump inducer to avoid cavitation instabilities

Abstract In this paper, important four design parameters which are sweep radius, sweep angle, solidity and incidence angle were firstly extracted for the inducer shape optimization. A multi-objective optimization method was applied to the inducer and optimal design was manufactured by 3D-Printer. Pump performance tests and cavitation performance test were conducted for both baseline inducer and optimal one. In addition, internal flow at the inlet of the inducer was measured by PIV in order to investigate the onset and the scale of backflow. As the result, it was confirmed that the cavitation performance of the optimized inducer was improved by about 23% while maintaining pump efficiency. It was also clarified that the onset of backflow at partial flow rate was shifted to lower flow rate by PIV. Furthermore, the occurrence range of cavitation surge in the partial flow rate was narrowed. Based on the sensitivity analysis result, it was found that the influence of sweep radius on both cavitation performance and backflow onset was large. Moreover, some design guidelines are suggested in conclusion.

Main control factors and prediction model of flow-accelerated CO2/H2S synergistic corrosion for X65 steel

As an important infrastructure for offshore petroleum development, submarine pipelines are the lifeline of offshore petroleum resources development. However, the medium flow containing H2S and CO2 threatens the normal production of oil fields. Based on 18 groups of orthogonal experiments, considering CO2 partial pressure, H2S partial pressure, temperature, pH, chloride concentration and liquid flow rate, the general and local corrosion rate were obtained. The corrosion products were characterized with SEM/EDS and XRD. The main controlling factors and corrosion mechanism were explored. Under the experimental conditions, CO2 and H2S were the main controlling factors of general and local corrosion. With the increase of gas partial pressure, the corrosion rate increaseed gradually. Flow accelerated the synergistic corrosion mechanism and model were established. Within the working condition range, the prediction error was less than 20%, which was better than ECE prediction model. The results can improve the integrity management of submarine pipelines.

Boosting framework via clinical monitoring data to predict the depth of anesthesia.

BACKGROUND: Prediction of the depth of anesthesia is a difficult job in the biomedical field.OBJECTIVE: This study aimed to build a boosting-based prediction model to predict the depth of anesthesia based on four clinical monitoring data.METHODS: Boosting is a framework algorithm that is used to train a series of weak learners into strong learners by assigning different weights according to their classification accuracy. The input of the boosting-based prediction model included four types of clinical monitoring data: electromyography, end-tidal carbon dioxide partial pressure, remifentanil dosage, and flow rate. The output was the depth of anesthesia.RESULTS: The boosting framework model built in this study achieved higher prediction accuracy and a lower discrete degree in predicting the depth of anesthesia compared with the DT-, KNN-, and SVM-based models.CONCLUSIONS: The boosting framework was used to set up a prediction model to predict the depth of anesthesia based on four clinical monitoring data. In the experiments, the boosting framework model of this study achieved higher prediction accuracy and a lower discrete degree. This model will be useful in predicting the depth of anesthesia.