Start-up Cycles Research Articles

Modelling and theoretical research on transient lubrication and wear coupling behavior of main bearing during start-up of low-speed diesel engine

This study endeavors to establish a transient mixed lubrication model for time-varying wear of main bearings under dynamic loading conditions during the startup process. This model accounts for variations in oil film thickness attributable to deformation, wear profiles, and journal misalignment throughout the operational cycle. The evolution of main bearing lubrication characteristics during the startup process was analyzed, as well as the evolution of wear profiles and their effects on lubricating properties under different numbers of startups. The results indicate that as the number of startup cycles increases, the wear rate gradually levels off. With increasing startup times, there is a decrease in contact pressure and a slight reduction in oil film pressure, resulting in enhanced lubricating performance. Furthermore, the influence of startup duration on wear is significantly greater than that of radial clearance.

Hydrogen in aviation: A simulation of demand, price dynamics, and CO2 emission reduction potentials

Aviation contributes to anthropogenic climate change by emitting both carbon dioxide (CO2) and non-CO2 emissions through the combustion of fossil fuels. One approach to reduce the climate impact of aviation is the use of hydrogen as an alternative fuel. Two distinct technological options are presently under consideration for the implementation of hydrogen in aviation: hydrogen fuel cell architectures and the direct combustion of hydrogen. In this study, a hydrogen demand model is developed that considers anticipated advancements in liquid hydrogen aircraft technologies, forecasted aviation demand, and aircraft startup and retirement cycles. The analysis indicates that global demand for liquid hydrogen in aviation could potentially reach 17 million tons by 2050, leading to a 9% reduction in CO2 emissions from global aviation. Thus, the total potential of hydrogen in aviation extends beyond this, considering that the total market share of hydrogen aircraft on suitable routes in the model is projected to be only 27% in 2050 due to aircraft retirement cycles. Additionally, it is shown, that achieving the potential demand for hydrogen in aviation depends on specific market prices. With anticipated declines in current production costs, hydrogen fuel costs would need to reach about 70 EUR/MWh by 2050 to fulfill full demand in aviation, assuming biofuels provide the cheapest option for decarbonization alongside hydrogen. If e-fuels are the sole option for decarbonization alongside hydrogen, which is the more probable scenario, the entire hydrogen demand potential in aviation would be satisfied according to this study's estimates at significantly higher hydrogen prices, approximately 180 EUR/MWh.

A robust tubular solid oxide fuel cell through bifunctional praseodymium oxide nanocatalyst infiltration

Due to inherent merits such as rapid start-up, easy sealing, and good thermal cycling resistance, tubular solid oxide fuel cell (SOFC) is becoming a promising alternative device for clean and efficient energy conversion; yet the lower power density is a challenging problem when compared to planar SOFC. In this study, an asymmetric infiltration of Pr6O11 nanocatalyst, a bi-functional catalyst, is innovatively proposed to enhance the electrochemical performance and prolong the cell lifespan. First, a suitable anode functional layer (AFL) based on the Ni-YSZ (yttria stabilized zirconia) anode is presented. The additional AFL results in a significantly enhanced peak power density (PPD) of 1259 mWcm−2 at 800 °C, which is 66 % higher than that of the primitive cell (756 mWcm−2). Subsequently, a new approach of asymmetric infiltration is devised in one step during the cell manufacturing procedure to simultaneously modify the anode and cathode-electrolyte interface to boost cell output power. Consequently, the nanostructure-engineered tubular cell exhibits outstanding peak power density of 1592 mWcm−2 at 800 °C, that is more than twice that of the blank cell, outperforms the majority of the Ni-YSZ supported tubular cells. Furthermore, the robust tubular cell runs on hydrogen fuels with excellent stability over more than 2000 h at a constant current density of ∼300 mAcm−2. The exceptional performance and endurance can be attributed to the rational cell design, which holds great potential for the commercialization of tubular SOFC.

Development of IrO2 Nanosheet–Pt/C Composite as Reversal Tolerant Anode Catalysts for Polymer Electrolyte Fuel Cell

Introduction: During the start-up and shutdown cycles of a polymer electrolyte fuel cell (PEFC), certain areas of the anode flow channel may not receive sufficient hydrogen due to water blockage or sluggish diffusion. This can lead to hydrogen starvation, which in turn causes a shortage of protons during cell reaction. The result is an increase in anode potential, which triggers the carbon oxidation reaction (COR) and damages the catalyst layer.Promoting the oxygen evolution reaction (OER) to alleviate the COR is a promising strategy to develop reversal-tolerant anodes (RTAs). Incorporating OER-active materials, such as IrO2, as a co-catalyst is an effective way to mitigate the rise in anode potential and prevent COR [1].In this study, a novel OER-active material, iridium oxide nanosheet (IrO2(ns)), was used as the co-catalysts and combined with commercial Pt/C in three different ways; mixing Pt/C with normal- and small-sized IrO2 nanosheets (IrO2(ns)/Pt/C), and Pt/C mixed with carbon supported IrO2 nanosheet (Pt/C+IrO2(ns)/KB). The OER activity and tolerance to cell reversal conditions were characterized using a 3-electrode rotating disk electrode (RDE) setup. Experiment: IrO2(ns)(250 nm) colloid was synthesized following literature [2]. The resulting IrO2(ns)(250 nm) colloid was subjected to ultrasonication to obtain small-sized nanosheets (IrO2(ns)(100 nm)) [3]. Nanosheet-carbon composite (IrO2(ns)(100 nm)/KB) was prepared by mixing IrO2(ns)(100 nm) colloid and KB (Ketjen black EC-300J) and physically mixed with Pt/C. Commercially available IrO2 nanoparticles (c-IrO2) were purchased from Tokuriki Honten Co., Ltd. and added to Pt/C (c-IrO2-Pt/C) and used as a reference sample.The composite catalyst was prepared by mixing Pt/C with different IrO2 nanomaterials and will be denoted as IrO2(ns)(x mass%)-Pt/C or c-IrO2 (x mass%)-Pt/C depending on the source of the IrO2 material used. RDE studies were conducted using a 3-electrode half-cell setup with 0.1 M HClO4 as the electrolyte. The counter electrode was carbon fiber, and a reversible hydrogen electrode (RHE) was used as the reference electrode.Except for the OER activity, the electrodes for all measurement were prepared with a Pt loading of 8.0 μg/cm2. For hydrogen oxidation reaction (HOR) activity measurements, the electrolyte was purged with H2. For chronopotentiometry (CP) and electrochemically active Pt surface area (ECSA) measurement, the electrolyte was purged with N2. For OER activity measurements, the electrolyte was purged with N2, and the working electrode was prepared with a Pt loading of 17.3 μg/cm2. Except for ECSA measurement, all data were accumulated at an electrolyte temperature of 60oC. Results and Discussion: Figure 1 shows the OER activity (10 mV/s) of Pt/C and composite catalysts prepared with c-IrO2(5 mass%), IrO2(ns)(250 nm, 5 mass%), IrO2(ns)(100 nm, 5 mass%), IrO2(ns)(100 nm, 2.5 mass%) and IrO2(ns)(100 nm, 1 mass%). At 1.5 V vs. RHE, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C exhibited a 2-fold increase in OER activity compared to IrO2(ns)(250 nm, 5 mass%)-Pt/C and a 25 % increase compared to c-IrO2 (5 mass%)-Pt/C. All composite catalysts displayed significantly higher OER activity than the pristine Pt/C sample.To simulate the degradation behavior in the fuel cell anode, a series of CP tests were performed at 16, 48, 80, and 112 μA/cm2. The HOR mass activity was used as a quantitative factor to present the decay caused by cell reversal degradation. The HOR activity before and after CP was evaluated using linear sweep voltammetry (LSV) from -0.08 V to 0.5 V vs. RHE. The HOR mass activity at 20 mV vs. RHE was calculated based on the Koutecky-Levich equation. After CP, the Pt/C sample showed a decrease in HOR activity from 851 A/g to 621 A/g (72% retention). In contrast, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C showed an initial HOR activity comparable to Pt/C (1420 A/g) and still retained a high HOR activity of 1400 A/g after CP (100% retention). The addition of IrO2(ns) as a co-catalyst effectively suppressed the carbon oxidation reaction under cell reversal conditions.

Synthesis of Ir Nanoparticles As Promoters for the Stabilization of Fenc-Catalysts Under Ssc Conditions

Fuel cells are promising devices for implementation in automotive propulsion. While the standard operation seems feasible, during start-up and shutdown high potentials occur on the cathodic site induced by the reverse current mode. In consequence, the carbon oxidation reaction (COR) occurs and limits the lifetime of PEMFCs. One approach suppressing carbon corrosion is the introduction of small amounts of an oxygen evolution reaction (OER) catalyst, as e.g. iridium. In our recent work we showed that in relative manner the durability was improved, however, the initial performance was less compared to the non-modified FeNC catalyst.[1 ] These NP had been prepared by a polyol approach.[2 ] However, capping agents (CA) could eventually still be present in these systems, blocking the particles in their performance.Herein, we present our results using an alternative surfactant free synthesis of Ir nanoparticles, adapted from literature,[3 ] that are then used for the modification of an FeNC catalysts. The performance of the newly prepared FeNC+Ir vs the FeNC+Ir+CA reference was evaluated employing accelerated stress tests mimicking the start-up and shut down conditions in RDE and PEMFC. It is shown that with this new approach the amount of NP on the surface can be better controlled. Beside the electrochemical testing structural characterization by X-ray-diffraction, thermogravimetric analysis and transmission-electron-microscopy was performed.It will be shown that by surfactant free synthesis Ir nanoparticles with high purity can be obtained. Due to the higher purity, an improvement of the OER activity can be achieved with the same Ir loading. In the RDE, an improvement in stability was observed by loading an FeNC catalyst with Ir nanoparticles. However, under fuel cell conditions, no improvement in stability was observed by loading Ir nanoparticles onto a FeNC catalyst.List of references[1] Prössl, C., Kübler, M., Paul, S., Ni, L., Kinkelin, S. J., Heppe, N., Eberhardt, K., Geppert, C., Jaegermann, W., Stark, R. W., Bron, M. & Kramm, U. I. (2022). Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions. Journal of Materials Chemistry A, 10(11), 6038-6053.[2] Prössl, C., Kübler, M., Nowroozi, M. A., Paul, S., Clemens, O., & Kramm, U. I. (2021). Investigation of the thermal removal steps of capping agents in the synthesis of bimetallic iridium-based catalysts for the ethanol oxidation reaction. Physical Chemistry Chemical Physics, 23(1), 563-573.[3] Bizzotto, F., Quinson, J., Schröder, J., Zana, A., & Arenz, M. (2021). Surfactant-free colloidal strategies for highly dispersed and active supported IrO2 catalysts: Synthesis and performance evaluation for the oxygen evolution reaction. Journal of catalysis, 401, 54-62.

Nitrogen removal performance and C, N, S transformation under dry-wet alterations of heterotrophic-autotrophic sequential bioretention system amended with waste reed and sulfur

Mixotrophic denitrification (combining heterotrophic denitrification and autotrophic denitrification) based bioretention system is a promising sustainable technology for nitrate nitrogen removal from stormwater runoff due to the ease of start-up and long operational cycle. However, the initial release of organic matter and ammonia nitrogen from most biomass carbon sources and the ineffectiveness for real-time treatment during rewetting period limit its engineering application. In this study, a novel heterotrophic-autotrophic sequential bioretention system was constructed by sequential packing waste reeds and sulfur in the upper and lower layers of the submerged zone. The removal of nitrate nitrogen, total nitrogen, ammonia nitrogen, and chemical oxygen demand maintained at 92.45%–99.54%, 84.80%–95.60%, 57.27%–82.86%, and 67.79%–85.82%, respectively, under different influent nitrate nitrogen loads of 20 mg/L, 14 mg/L, and 8 mg/L, respectively. The system solved the massive leaching of ammonia nitrogen and organic matter from waste reeds in the early phases and achieved low production rate of nitrite nitrogen (0.0004–0.0048 kg/(m3·d)) and sulfate (0.09–0.27 kg/(m3·d)). For 3 and 5 antecedent dry days, the real-time nitrate nitrogen removal kept at 99.66 ± 0.25% and 91.26 ± 7.91%. Microbial communities and functional genes revealed the C, N, S transformation driven by the system improved the responds to dry-wet alterations. The synergy of heterotrophic layer (heterotrophic denitrification and sulfide-driven autotrophic denitrification) and autotrophic layer (sulfur-driven autotrophic denitrification, dissimilatory nitrate reduction to ammonia, and sulfate reduction) promoted the complete denitrification and reduced by-products formation.

Fuel-Flexible Ceramic Fuel Cells at Reduced Operating Temperatures

Ceramic fuel cells are uniquely capable of generating power using a wide range of fuels, including hydrogen, hydrocarbons, and ammonia. One of the primary issues of ceramic fuel cells for large-scale power generation originates from the high operating temperature, which leads to limited material choices for interconnects and sealants, expensive balance of plants, slow start-up and shutdown cycles, and high degradation rates, inevitably limiting their scaleup and commercialization. Reducing the temperature to <600 °C could transform the architecture and operation of ceramic fuel cells. However, the internal reforming of hydrocarbons is endothermic, which is thermodynamically and kinetically unfavorable at lowered operating temperatures, necessitating the development of internal reforming catalysts to enhance the anode catalytic activity. This talk will first focus on presenting the approaches that have been validated for designing and synthesizing internal reforming catalysts, with a particular focus on internal steam reforming and dry reforming of methane. Additionally, the characterization of high-performance ceramic fuel cells equipped with these catalysts will also be discussed. The associated challenges and proposing strategies from different perspectives will also be provided in this talk.

Design of High Specific Power Solid Oxide Fuel Cells

The development of solid oxide fuel cells (SOFCs) has progressed from the early Electrolyte Supported Cell (ESC) to state-of-the-art Anode Supported Cell (ASC), which allows the implementation of thinner electrolyte layer (less than 10 micron) and reduction in the operating temperature (below 800°C). The various components of SOFC are constantly being optimized by many research groups to further improve the overall stack performance, including specific power, power density, thermal shock resistance, rapid start-up, and thermal cycling exposure.Precision Combustion, Inc. (PCI) has been working on an advanced electrochemical-based energy storage and power generator design for meeting aggressive specific-power and specific-energy targets required for mobile and transportation applications, such as all-electric propulsion of ground and air vehicles. The key drivers are an exceptionally power-dense solid oxide fuel cell design operating with energy-dense liquid fuels and a hybridized system architecture that maximizes component efficiencies for ultra-high system efficiency. This effort builds on PCI’s experience in developing groundbreaking SOFC generators for mobile and space applications.PCI has developed and demonstrated a novel design of fuel cells with high specific power, that also allows for direct internal reforming of methane and hydrocarbon fuels within a SOFC stack. The system consists of interconnected internal reforming Microlith® metal mesh catalysts strategically embedded within the solid oxide stack. The fuel cell configuration was optimized to reduce CTE mismatch and to improve area specific resistance. The resulting enhanced heat transfer design of the combined components offers the potential for higher overall system efficiency and system simplification as well as enables further compactness and weight reduction of the fuel cell while improving the conditions for long system life. The approach also offers the potential to operate with a wide range of input fuels (i.e., high hydrocarbons as well as various levels of CO2 and water in the fuel inlet) without forming carbon. Carbon formation within the stack system has been known to be detrimental to the performance and durability. Our approach allows for the operation of a modular, advanced SOFC stack for generating power directly from hydrocarbon fuels. Computational design, process simulation, and qualification testing were performed to validate the concept.In this presentation, the results from a breadboard SOFC stack system operation will be highlighted, including the power density, efficiency, and durability. An improvement in the performance as a result of the design advancement, which could improve the stack lifetime, will also be described. The carbon avoidance in the stack while operating with hydrocarbon fuels and with a low water requirement was confirmed. Sensitivity study of the concept to temperature, flow rate, and anode fuel composition was performed and will be highlighted. Finally, preliminary results from the fuel cell design optimization activities will be summarized.

Creep-Fatigue Life Property of P91 Welded Piping Subjected to Bending and Torsional Moments at High Temperature

Abstract In recent years, the role of thermal power plants has shifted from providing a baseload to providing supplemental supply to compensate for fluctuations in the output of renewable energy sources. Thus, the operation of these plants involves frequent startup and shutdown cycles, which lead to extensive damage caused by creep and fatigue interactions. In addition, the piping utilized in thermal plants is subjected to a combined stress state composed of bending and torsional moments. In this study, a high-temperature fatigue testing machine capable of generating such a bending-torsional loading was developed. Creep-fatigue tests were conducted on P91 steel piping with weldment. The results clarified that the creep-fatigue life was reduced by the superposition of the torsional and bending moments and that it was further reduced by a holding load. It was shown that the creep-fatigue life of piping with weldment can be estimated accurately using the equivalent bending moment, which is composed of the torsional and bending moments. It was also confirmed that crack occurred in the heat-affected zone (HAZ) of the welded part, which has been often observed in actual thermal power equipment. From the finite element analysis, it was identified that cracking was initiated in the HAZ due to the accumulation of creep strain and increase in the hydrostatic pressure component during a holding load.

Feasibility of low-intensity ultrasound treatment with hydroxylamine to accelerate the initiation of partial nitrification and allow operation under intermittent aeration

Partial nitrification is a key aspect of efficient nitrogen removal, although practically it suffers from long start-up cycles and unstable long-term operational performance. To address these drawbacks, this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine (NH2OH) on the performance of partial nitrification. Results show that compared with the control group, low-intensity ultrasound treatment (0.10 W/mL, 15 min) combined with NH2OH (5 mg/L) reduced the time required for partial nitrification initiation by 6 days, increasing the nitrite accumulation rate (NAR) and ammonia nitrogen removal rate (NRR) by 20.4% and 6.7%, respectively, achieving 96.48% NRR. Mechanistic analysis showed that NH2OH enhanced ammonia oxidation, inhibited nitrite-oxidizing bacteria (NOB) activity and shortened the time required for partial nitrification initiation. Furthermore, ultrasonication combined with NH2OH dosing stimulated EPS (extracellular polymeric substances) secretion, increased carbonyl, hydroxyl and amine functional group abundances and enhanced mass transfer. In addition, 16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound + NH2OH system, while Nitrosomonas gradually became the dominant group. Collectively, the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.

A model of social responsibility for start-ups: developing a cross-fertilisation of responsible innovation, the lean start-up approach, and the quadruple helix approach

ABSTRACT In this paper, we cross-fertilise responsible innovation (RI), the Lean Start-up approach (LSA) and the Quadruple Helix approach (QH) within one model: the social responsibility for start-ups model (SRSM). SRSM aims to instil responsibility into the start-up innovation process by ensuring that the voices of stakeholders from all four helices are taken into account, whilst providing an assessment of current impacts in these areas compared with the ambition of start-ups. This helps to identify room for improvement in order to provide an iterative, lean approach for start-ups to inform the strategy of the start-up cycle, which incorporates the four helices of the QH, and the four process requirements found in RI theory (anticipation, reflexivity, inclusiveness, and responsiveness). This model works as a way to operationalize responsibility in start-ups. This paper fills a gap where there is a lack of suitable approaches for start-ups to follow and implement.

Self-healing Fuel Cells by Biological Actuators

A completely novel approach aims to extend the lifetime of polymer electrolyte membrane fuel cells (PEM-FCs) many times over through a self-healing mechanism, thus contributing to the transition to a sustainable economy and mobility. Many start-up cycles in truck or car applications lead to pinholes in the proton-conducting polymer membranes (Nafion™). Since there is no way to repair this type of defect when the fuel cell is already assembled, the performance of the fuel cell stack is continuously reduced towards the end of its lifetime. The BioHealing project, an interdisciplinary consortium at the Karlsruhe Institute of Technology, investigates an innovative biohybrid technology that can repair occurring pinholes selectively in fuel cell membranes by a self-healing mechanism without disassembling the fuel cell stack. This is enabled by a biohybrid system, i.e., integrating biological and technical components. The filler-forming enzymes are functionally immobilised on the polymer membrane surface via a special peptide linker to enable site-directed filler production during membrane electrode assembly. For self-healing, a substrate is injected into the gas inlet of the fuel cell stack, the enzymatic reaction is catalysed, and the substrate is converted into the filler, a biological polymerised product that seals the existing pinholes. In this publication, the concept is presented with initial research results. The concept includes characterisation of surface properties and functional groups of the Nafion™ membrane, immobilisation of the specially designed fluorophilic peptide linker, selection of suitable enzymes to be screened for activity and stability, and investigation of the filler to be successfully esterified with the membrane.

Fatigue Strength Assessment of Single-Sided Girth Welds in Offshore Pipelines Subjected to Start-Up and Shut-Down Cycles

During the service life of offshore pipelines, many start-up and shut-down cycles take place, possibly leading to significant cyclic loads. Fatigue failure may occur, resulting in serious environmental pollution and loss of property. The study aims to assess the fatigue strength of single-sided girth welds in offshore pipelines under these specific fatigue loads. The longitudinal stress range caused by the variation of the pipeline’s internal pressure and temperature is calculated. The effective notch strain approach is used to assess the fatigue strength of welds. The plastic behaviour of the weld root is investigated for a study case to justify the use of low-cycle fatigue assessment approaches. The effect of weld root geometry on the notch stress factor is studied to identify the dominant geometrical parameters. The fatigue strength of the study case is assessed, and some limitations of the assessment are discussed. The results show that the plastic behaviour of the weld root is only significant for severe local stress concentrations, which is mainly governed by the axial misalignment, weld root angle and the weld root bead width. If the fatigue damage at failure is 0.1, a limited number of start-up and shut-down cycles are allowed during the service life of the pipeline for the study case, indicating the necessity of fatigue strength assessment.

Effect of Change in Startup Cycle Time on Transient Thermal Stresses in Steam Turbine Rotor

During the turbine start stop period, occuring at brief intervals , the temperature of the steam turbine rotor varies. Because of the significant temperature gradients, this shift in temperature causes transitory thermal stresses in the rotor. Changes in material parameters such as thermal expansion coefficient ,modulus of elasticity, thermal conductivity, specific heat, Poisson's ratio, and others cause transient stresses. Thermal and mechanical stresses are applied to the turbine rotor. Before designing the rotor, it is necessary to estimate transient thermal stresses. The finite element study of a 210 MW steam turbine rotor for transient thermal loading is investigated in this paper. 30Cr1Mo1V was used to make the rotor. CAD software (PRO-E) was used to create the high-pressure turbine model. Since the steam turbine shaft (rotor) was symmetric about the axis along which it rotates, the model was solved using a 1 Degree slice model. Ansys 11 was used to investigate the FE model for transient thermal stresses for reduced cold start up cycle. The analysis was carried out for start up cycles of 560, 440 and 320 minutes respectively. The comparative results were studied and it was observed thatalthough the transient thermal stresses in the reduced cold start up cycle of 440 minutes are higher as compared to the transient thermo-mechanical stress value for actual cold start up cycle (560 minutes) but are within safe limits of yield and tensile strength. The thermal stress values for the other reduced cold start up cycle (320 minutes) re quite higher than the allowable yield and tensile strength of the material and hence cannot be considered as feasible start up cycle. Thermal stresses in the transient state were found to be significantly higher than steady state thermal stresses.

Numerical Simulation of a Kaplan Prototype during Speed-No-Load Operation

Hydropower plants often work in off-design conditions to regulate the power grid frequency. Frequent transient operation of hydraulic turbines leads to premature failure, fatigue and damage to the turbine components. The speed-no-load (SNL) operating condition is the last part of the start-up cycle and one of the most damaging operation conditions of hydraulic turbines. Hydraulic instabilities and high-stress pressure fluctuations occur due to the low flow rate and unsteady load on the runner blades. Numerical simulations can provide useful insight concerning the complex flow structures that develop inside hydraulic turbines during SNL operation. Together with experimental investigations, the numerical simulations can help diagnose failures and optimize the exploitation of hydraulic turbines. This paper introduces the numerical model of a full-scale 10 MW Kaplan turbine prototype operated at SNL. The geometry was obtained by scaling the geometry of the corresponding model turbine as the model and prototype are geometrically similar. The numerical model is simplified and designed to optimize the numerical precision and computational costs. The guide vane and runner domains are asymmetrical, the epoxy layer applied to two runner blades during the experimental measurements is not modelled and a constant runner blade clearance is employed. The unsteady simulation was performed using the SAS–SST turbulence model. The numerical results were validated with torque and pressure experimental data. The mean quantities obtained from the numerical simulation were in good agreement with the experiment. The mean pressure values were better captured on the pressure side of the runner blade compared to the suction side. However, the amplitude of the pressure fluctuations was more accurately predicted on the suction side of the runner blade. The amplitude of the torque fluctuations was considerably underestimated.

Entrepreneurial Intention and Delayed Job Satisfaction From the Perspective of Emotional Interaction: The Mediating of Psychological Capital.

The coronavirus disease 2019 (COVID-19) pandemic has exacerbated the labour shortage, and promoting entrepreneurship to spur job creation is one of the most effective strategies to address this problem. Entrepreneurs must lengthen their employment or start-up cycles due to COVID-19 normalisation. Consequently, the impact of career willingness to delay satisfaction on entrepreneurial ambition is investigated in this research via an online survey in Jiangsu Province, China. The findings show that students with a high level of career delayed contentment has a higher level of entrepreneurial intention (EI), implying that career delayed contentment intention influences EI positively. Psychological capital (PC) modifies this process, increasing the influence of job delayed satisfaction on EI by strengthening PC. PC’s significant components are self-efficacy, hope, optimism, and flexibility. This study combines the willingness to wait for satisfaction with the willingness to start a business, providing a valuable reference for reducing the work condition caused by the COVID-19 epidemic.

Dual inner circulation and multi-partition driving single-stage autotrophic nitrogen removal in a bioreactor

The single-stage autotrophic nitrogen removal (ANR) process is impeded by a long start-up cycle and unstable operation performance. In this study, an airlift inner-circulation partition bioreactor (AIPBR) was operated continuously for 215 days to explore methods of strengthening the performance and stable operation of the single-stage ANR system. AIPBR start-up period took around 38 days, the total nitrogen removal efficiency was > 85% on day 35. With the decrease of hydraulic retention time and the increase of aeration rate, the nitrogen removal rate increased to 0.85 ± 0.02 kg-N/m3/day. The sludge morphology gradually changed into dark-red floc-coupled granular sludge. Nitrosomonas (9.95%) and Candidatus Brocadia (6.41%) were dominant in the sludge. During long-term operation, AIPBR achieved the dual inner circulation of sewage and sludge and then formed effective dissolved oxygen and sludge partitions to provide a suitable growth environment for various functional bacteria, promote synergy between them, and strengthen the ANR performance.

Novel GaPtMnP Alloy Based Anodic Electrocatalyst with Excellent Catalytic Features for Direct Ethanol Fuel Cells

AbstractAlthough considerable effort has been devoted to developing bifunctional electrocatalysts with enhanced atomic utilization in ethanol fuel cells, significant progress in this field has been hindered by notable drawbacks of the electrocatalysts, such as low stability, poor activity, and inefficient repeatability for multiple startup and shutdown cycles. Considering these issues herein, a novel nanosized GaPtMnP alloy anchored on N‐doped multiwall carbon nanotubes (MWCNTs) is developed. The average size of the spherical GaPtMnP alloy nanoparticles is ≈3.5 nm. The atomic structure and d‐band shift of Pt in the GaPtMnP alloy are demonstrated using state‐of‐the‐art density functional theory calculations. Cyclic voltammetry analysis revealed that GaPtMnP/N‐MWCNT delivered high mass and specific activities of 9.16 A mgPt−1 and 10.4 mA cm−2, respectively, in 0.3 m H2SO4 + 0.5 m ethanol, values that are ≈13‐ and 8‐fold higher than the corresponding values for Pt/C. In addition, it exhibits long‐term stability and durability even after 3000 cycles. A single cell based on the GaPtMnP/N‐MWCNT anodic electrocatalyst exhibits a peak power density of 86.64 mW cm−2, which is approximately fourfold higher than that of Pt/C at 70 °C. Furthermore, the performance of a fuel cell comprising the GaPtMnP/N‐MWCNT catalyst remained constant even after multiple startup–shutdown cycles.

Performance and stability of a critical raw materials-free anion exchange membrane electrolysis cell

A water electrolysis cell based on anion exchange membrane (AEM) and critical raw materials-free (CRM-free) electrocatalysts was developed. A NiFe-oxide electrocatalyst was used at the anode whereas a series of metallic electrocatalysts were investigated for the cathode, such as Ni, NiCu, NiMo, NiMo/KB. These were compared to a benchmark Pt/C cathode. CRMs-free anode and cathode catalysts were synthetized with a crystallite size of about 10 nm. The effect of recirculation through the cell of a diluted KOH solution was investigated. A concentration of 0.5–1 M KOH appeared necessary to achieve suitable performance at high current density. amongst the CRM-free cathodes, the NiMo/KB catalyst showed the best performance in the AEM electrolysis cell achieving a current density of 1 A cm−2 at about 1.7–1.8 V/cell when it was used in combination with a NiFe-oxide anode and a 50 µm thick Fumatech FAA-3–50® hydrocarbon membrane. Durability tests showed an initial decrease of cell voltage with time during 2000 h operation at 1 A cm−2 until reaching a steady state performance with an energy efficiency close to 80%. An increase of reversible losses during start-up and shutdown cycles was observed. Appropriate stability was observed during cycled operation between 0.2 and 1 A cm−2; however, the voltage efficiency was slightly lower than in steady-state operation due to the occurrence of reversible losses during the cycles. Post operation analysis of electrocatalysts allowed getting a better comprehension of the phenomena occurring during the 2000 h durability test.

Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions

Ir modification of FeNC catalysts improves the durability of the catalysts, but causes electronic changes that are disadvantageous for the activity.