Severe Operating Conditions Research Articles

Energy and environmental performance of vapor injection heat pumps using R134a, R152a, and R1234yf under various injection conditions

Vapor injection heat pumps have been used to mitigate performance degradation under severe operating conditions. Low-global-warming-potential (GWP) refrigerants have been used to replace R134a in heat pumps to comply with F-gas regulations. However, experimental and optimization analyses of vapor-injection heat pumps with low-GWP refrigerants are limited in terms of injection conditions. In this study, the energy and environmental performance of vapor-injection heat pumps containing low-GWP refrigerants were experimentally investigated under various injection conditions. The capacity and coefficient of performance (COP) of the vapor-injection heat pumps using R152a and R1234yf were optimized and compared to those using R134a under various injection conditions. The optimized vapor-injection heat pump using R152a increased the heating and cooling COPs by 5.7% and 1.3%, respectively, compared to those using R134a because of its lower power consumption. In addition, the life-cycle climate performance (LCCP) of the optimized vapor-injection heat pumps using R152a and R1234yf were 4.7% lower and 3.0% higher, respectively, than those using R134a under practical conditions. Overall, R152a is recommended as a preferred alternative for vapor-injection heat pumps because of its high COP and low LCCP.

Enhancing the performance of Ni-rich lithium metal batteries through the utilization of amine-functionalized 1D/3D nano shields and additives in high-voltage operation

The development of high-energy–density lithium metal batteries (LMB) is of paramount importance for various emerging energy storage applications, and high-voltage operating system based on high-capacity nickel-rich layer LiNixCoyMn1−x−yO2 (Ni-rich NCM, x ≥ 0.6) cathode combined with a Li metal anode is a representative promising solution. However, it is challenging to stabilize the lithium metal anodes with severe operating conditions, mainly because dissolved transition metal (TM) ions from the cathode trigger harmful side reactions, such as electrolytic decomposition and the growth of dendritic Li structures, resulting in serious safety hazards. In this study, we fabricated an ion-entrapping functional separator using amine-functionalized 1D or 3D inorganic particles confirmed by DFT calculation. Then, we applied in the Ni-rich LMB, demonstrating suppression of TM ion cross-over of 47% compared to conventional PE separators leading to improved cycle numbers and capacity retention at high-voltage operation. Further, combining functional additive introduction with the transition metal cross-over shielding separator resulted in synergistic ion capturing up to 84%. The results of this study provide new insights into the design of advanced LMB for high-energy–density.

Failure analysis of an aero-engine inter-shaft bearing due to clearance between the outer ring and its housing

The inter-shaft bearing is a critical but vulnerable component of dual rotors, because of the severe operational conditions and loads. This paper investigates the failure mechanism of a fractured inter-shaft bearing belonging to a high thrust-weight ratio turbofan engine. Fractographic and microscopic analyses of the fracture surfaces were conducted, followed by vibration signal processing. Finite element analyses of the outer ring were also performed considering the centrifugal, thermal, and roller-raceway loads. What’s more, using the linear elastic fracture mechanics theory, the crack growth path simulation was obtained, whose result showed good agreement with the real fracture morphologies. The results indicated that due to the clearance between the outer ring and its housing during the operation, the anti-rotation tabs of the outer ring were subjected to non-uniform load, thus several tabs might suffer large stress concentrations at the root fillets, which could lead to the crack initiation. During the following operation of the aero-engine, the crack propagated through the outer ring and cause the fatigue fracture of tabs. The investigation provided herein suggests that the outer ring and its housing should be redesigned to eliminate the clearance during the operation, an outer ring formed integrally with the bearing housing flange is one of the failure preventions of this failure mode.

Investigation of Microstructure and Magnetic Properties of HP40-Nb Reformer Tubes

In this paper, the results of nondestructive evaluation, structure characteristics, and magnetic properties of HP-Nb steam reformer tubes of a direct reduction unit are presented. An eddy current testing technique based on a special normal probe was performed to estimate the service life of the outer surface of the reformer tubes at a frequency of 60 kHz. The magnetic properties were investigated by vibrating sample magnetometer testing. Microstructural transformations of reference samples were performed by an optical microscope equipped with image analysis software and scanning electron microscopes. With exposure to severe operational conditions in oxidizing atmospheres and high temperature, microstructural changes such as oxidation and transformation of M23C6 and M7C3 carbide in the carburization zone, and chromium depletion in the austenite matrix, can be intensified. The tubes were inspected on a point basis and the eddy current data were presented as an impedance map. The results of the eddy current testing and vibrating sample magnetometer showed that microstructural changes due to operational conditions affect the electromagnetic response of the tubes.

Thermal characteristics of a 90-mm bore cylindrical roller bearings for aerospace applications: All-steel versus hybrid bearings

Modern aircraft engines have to meet rigorous requirements such as thrust to weight ratio, efficiency and new regulations related to environment protection. These requirements affect all engine modules and components, including rolling element bearings. The latter have to withstand severe operating conditions because of the high thermal impact due to elevated rotational speeds and loads. In this study, two test campaigns were carried out under realistic operating conditions of load, speed, and oil flow rate to investigate and compare the thermal characteristics of two distinct cylindrical roller bearings: a hybrid bearing featuring silicon nitride (Si3N4) rollers and an all-steel bearing. Each bearing was instrumented with an array of thermocouples around its circumference to determine temperature profile under various test conditions. In addition, oil supply and drain temperatures were also measured to estimate the power loss. The experiments were conducted on a high-speed rolling-element test rig operating at speeds up to 30,000 rpm and under radial loads of up to 4500N.

A Short Literature Review on Turning and Milling of Cobalt Alloys

Among the existing machining processes, turning and milling are characterized as the most used and consequently are considered the most important. Machining moves a market estimated at around 10% of gross national production. Many industrial components and parts are subjected to severe operating conditions, in corrosive environments, high temperatures what causes wear. With the development of industries, there is a need for steel alloys with different properties, to meet different purposes. Cobalt alloys, as well as others, arose from the need to develop metals that would meet the growing demand in applications with high temperatures and high working stress in gas turbine components. Due to their high mechanical and thermal resistance, these alloys are difficult to machining, a situation that requires in-depth studies to reduce process costs and improve the surface quality of machined parts. Machined surfaces may have different textures depending on the process. Turning and milling generate grooved profiles due to tool/part interaction. In many cases, roughness is used as an output parameter to control the process. Another important factor is the wear of cutting tools, which must be selected according to the material properties of the workpiece, machine tool and other parameters that influence its wear. Controlling the useful life of the tool is a decisive factor when you want to avoid loss of productivity, with fewer stops for changes, consequently, you have a more effective and economical production. The present study presents a brief review of the literature regarding turning and milling of cobalt alloys, regarding the optimization of machining parameters, tools used and the use of lubri-cooling techniques, with the objective of reducing the roughness of the parts, the tool wear, improve surface integrity and contribute to the sustainability of manufacturing processes when machining difficult-to-cut materials. In this review, a comparative analysis of the results is presented, indicating the gaps in research such as classification and processing of alloys, formation of carbides with non-uniform distribution, which impairs the performance of the tools. Some suggestions for future work indicate the absence of studies on the use of diamond and CBN tools, clarify the interaction medium lubricant-coolant-coating of the tools-alloy chemical composition and cutting parameters, in addition to dynamic analyzes in the cutting of hardened materials.

Single-step conversion of ethanol into n-butene-rich olefins over metal catalysts supported on ZrO2-SiO2 mixed oxides

With airlines committed to drastically reduce their carbon footprint by 2050, producing jet fuel from renewable ethanol is of particular interest. Recently, we reported on an Ag/ZrO2/SBA-16 catalyst that is very effective for directly converting ethanol into to n-butene-rich olefins jet fuel precursors (i.e., 88% at full conversion). Here, we report on a Cu/ZrO2/SBA-16 catalyst that presents remarkable olefins selectivity (i.e., 89% at 96% conversion) and enhanced stability as compared to Ag/ZrO2/SBA-16 catalyst. Under severe operating conditions a conversion loss < 10% was observed with the Cu/ZrO2/SBA-16 catalyst as compared to a 50% loss of conversion with the Ag/ZrO2/SBA-16 catalyst. Combined experimental and computational tools revealed that replacing Ag with Cu shifts the reaction pathway of crotonaldehyde hydrogenation from 1,3-butadiene (i.e., coke precursor) production to butyraldehyde formation. Experiments conducted with 4%Cu/4%ZrO2 supported on SBA-16, dealuminated zeolite Beta, and aluminum silicate revealed the performance and stability advantage of the SBA-16-supported catalyst.

Electrified four-ball testing – A potential alternative for assessing lubricants (E-fluids) for electric vehicles

The increasing worldwide demand for hybrid and electric vehicle technology has brought new challenges for the global lubricant industry. The new lubricants for electric vehicles, also called E-fluids or EV-fluids, are expected to meet a new set of requirements including withstanding the much severe operating conditions of EV powertrains. High starting torques, high RPMs and uncontrollable shaft currents passing through the contact interfaces are some of the most challenging powertrain conditions that can impact the performance of these lubricants. Although there have been some papers already reporting on significant alteration of tribological properties of lubricants under electrification, so far there are no standard test protocols aimed at the fast and reliable screening of base oils, additives and formulated lubricants under such conditions. Thus, this research work focuses on exploring the popular four-ball ASTM-D4172 standard method to evaluate the tribological behavior of lubricants under electrified conditions. Specifically, a conventional four-ball tester was instrumented with a DC power source and a resistance data logger was used to explore the friction and wear performance of various lubricants (including a neat base oil, two automatic transmission fluids (ATF-3 and ATF-5) and a gear oil) with different dielectric strength under the conditions of ASTM-D4172 standard with and without DC currents (0, 1.5 and 3 A). The changes in average wear scar diameter, specific wear modes and mechanisms, friction coefficients, electrical contact resistance and temperature were analyzed and reported. Besides, the chemical changes in oils during the electrified tests were evaluated via IR spectroscopy. The main findings suggest that passing current through the four-ball contact interfaces significantly alters friction, wear and temperature in comparison to the conventional standard method without electrification. Thus, the proposed test method with electrification could be a potential new alternative for testing E-fluids under electrical environments.

High-efficiency perovskite photovoltaic system performance by molecular dynamics method: Optimizing electron transport thicknesses, hole transport, and anti-reflector layers of the sustainable energy materials

The perovskite solar cell was modeled with the assistance of the molecular dynamics (MD) method to propose a superior configuration for perovskite solar cells and high efficiency for longtime use under severe or unsafe operating conditions. To achieve this aim, several materials and alignments were examined. The whole thickness of this device was kept small enough (≦1 µm). Inorganic materials were used as selective compartments. Perovskite solar cells may have the performance of their photovoltaics improved by optimizing certain parameters. When selecting the materials, several criteria were taken into consideration, including thicknesses, cost, stability, efficiency, and compatibility with wearable Photovoltaic (PV). To model this construction, the electro-physical characteristics of the components were considered, and the findings were compared to those obtained by other studies.

Glass-ceramics for joining oxide-based ceramic matrix composites (Al2O3f/Al2O3-ZrO2) operating under direct flame exposure

This work focuses on the joining processes of oxide-based ceramic matrix composites (Al2O3f /Al2O3-ZrO2), which are used as radiant tube furnace components in the steel industry. These components have to operate in harsh environments, and under high temperatures, and they therefore have to resist corrosion, humidity, and combustion. Two glass-ceramics systems, which have Y2Ti2O7 as their main crystalline phase, as well as specific and optimized properties to withstand severe operating conditions, including temperatures of 900 °C, are here proposed as joining materials. The adhesion of the glass-ceramics to the composite was found to be excellent after mechanical and thermal tests in which they were in direct contact with a 900 °C flame and thermal cycling of between 400 °C and 900 °C.

High‐Temperature Behavior of the Heat‐Treated and Overaged AlSi10Mg Alloy Produced by Laser‐Based Powder Bed Fusion and Comparison with Conventional Al–Si–Mg‐Casting Alloys

In recent years, the AlSi10Mg alloy produced by laser‐based powder bed fusion (L‐PBF) has gained more attention for increasing the strength‐to‐weight ratio in structural parts subjected to severe operating conditions. Herein, the effects of thermal exposure (0–48 h at 200, 210, and 245 °C) on the metastable microstructure of the L‐PBF AlSi10Mg alloy and the high‐temperature (200 °C) tensile properties post‐overaging (41 h at 210 °C) of the heat‐treated alloy is investigated. In particular, two specific heat treatment conditions, currently neglected in the literature, are analyzed: i) T5 heat treatment (direct artificial aging: 4 h at 160 °C), and ii) the innovative T6R heat treatment (rapid solution: 10 min at 510 °C, and artificial aging: 6 h at 160 °C). The T5 shows a lower decrease in mechanical properties after thermal exposure and during the high‐temperature tensile test than the T6R. This behavior is related to the higher efficiency of the submicrometric cellular structure in hindering the dislocation motion. In addition, the T5 has good tensile properties compared to high‐temperature Al–Si–Mg‐ and Al–Si–Cu–Mg‐casting alloys, representing an attractive option in future industrial applications characterized by operating temperatures up to 200 °C.

Railway Noise Reduction at the Source only. Is this possible or mandatory?

Climate change urges CO2 reduction also in traffic. Electrified Railways are a powerfull CO2 free and energy and space efficient traffic mode already today. Modal shift is demanded but environmental noise of railway hinder rail traffic growth significantly. Noise tunnels are not only expensive but also reduce energy efficency and increase interior noise. Noise barriers are very costly and optical obstacles. TSI-Noise values have many criticisms. They do not cover the most bothering situations, curve running and severe other critical operation conditions are missing. The noise limit values are very high. Many standard measures in all other technical fields, construction machines or road vehicles do not exist in the railway context. Even worse is the situation of the track noise. There are nearly no measures except the demand for smooth surfaces. But the noise radiation of rails and sleepers is not constant but can be reduced significantly. Even good railway practice in other countries does not push the noise reduction without legislatve demands. Exemple are quiet high speed pantographs and tamping machines in Japan. With general measures and low noise barriers and skirts on each track side the immision limt even at densly operated lines of LDEN 55 dBA is possible.

Improving the Usage Properties of Steel Using Cold Spray Deposition: A Review

In this paper, the improvement of the characteristics of different steels that are subjected to extreme operating conditions, including the steels used in the manufacture of various military components, the AISI 52100, the manufacture of bearings, and other types of parts that are also subjected to severe operating conditions were analyzed regarding cold spraying, which uses different types of powders to increase the performance of the materials. The cold, thermal spraying technology “Cold Spray” is a method of processing particles in a solid state. Thermal spraying, based on the dynamic increase in gas acceleration up to supersonic speeds, leads to the obtainment of high kinetic energies, and the accelerated particles are deposited at values that are below their melting point. Research conducted through cold spray technology has seen a significant improvement in material properties; when processing the particles in a solid state, they adhere to the surface instead of eroding it. Cold spraying has proven to be an effective technique for improving material properties, as confirmed by its integration into different fields and industries, becoming competitive by being the only method for depositing particles below their melting point.

Effect of surface termination on the balance between friction and failure of Ti3C2Tx MXenes

Reactive molecular dynamics simulations of Ti3C2Tx with three different surface terminations were used to understand friction and failure of MXenes during sliding at normal pressures from 2–20 GPa and temperatures from 300–1100 K. The O-terminated MXene had the smallest shear stress at low pressures and temperatures, but failed at more severe conditions due to interlayer bonding and the formation of Ti–O–Ti bridges between MXene layers. Failure was not observed for the OH-terminated MXene or a heterostructure combining O- and OH-terminations. For these, at less severe operating conditions, shear stress was smaller for the OH-terminated MXene, while the opposite was observed at higher temperatures and pressures. These trends were explained in terms of adhesion and the complex effect of hydrogen atoms that can either facilitate or hinder sliding, depending on the termination and conditions. Results show that friction and failure are affected by and potentially tunable via MXene surface termination.

An Experimental Investigation on Welding of 5Cr- 0.5Mo Material for Heat Exchanger Application

Chromium-Molybdenum (Cr-Mo) steels are widely used in oil refineries, petrochemical industries and power plants forvarious applications, including heat exchangers, pressure vessels and piping. The main advantage of these steels are theimproved creep strength due to addition of Molybdenum and enhanced corrosion resistance imparted by chromium.5Cr-0.5Mo steels are extensively used in seamless tubing in petroleum industry because of their corrosion resistanceagainst oils and crude containing hydrogen sulphides and other corrosive agents. The main advantage of 5Cr-0.5Mo steelsis the improved oxidation resistance because of increased Chromium content. In modern refineries, a more recent andcommon application of this steel grade is in the fabrication of desulphurization plants used for the production of cleanlow Sulphur petrol and diesel fuels.In recent past, L&amp;T heavy engineering received a challenging project for manufacturing of 2 nos.of high-pressure exchangersinvolving 5Cr-0.5Mo material having a wall thickness of 85 mm. The severe operating conditions also demanded a stainlesssteel347 weld overlay on inner surface of the vessel. Producing crack-free weldments in 5Cr-0.5Mo which are adequate fora given service would conventionally entail correct choice of filler metal, stringent welding conditions including preheat,proper welding technique and post-weld heat treatment (PWHT). This paper describes about development of weldingprocedures for this material and our experience in successful fabrication of high pressure exchangers with 5Cr-0.5Mo asthe material of construction.

Boosting Carbon Nitride Photoactivity by Metal-Free Functionalization for Selective H2O2 Synthesis under Visible Light

Carbon nitride (CN) is a polymer-based material thoroughly studied for different photocatalytic applications due to its optical, electronic, and chemical properties. Its main limitation is fast electron/hole recombination. To overcome this drawback, several functionalization methods have been applied using organic solvents and severe operating conditions. In the present work, a thermally exfoliated CN was functionalized for the first time via a hydrothermal route using glucose (G), perylene (P), and anthraquinone (A) by implementing water as solvent at a mild temperature (120 °C). The materials were tested for the photocatalytic production of hydrogen peroxide (H2O2) in aqueous solutions saturated with dissolved oxygen and in the presence of a sacrificial agent (isopropyl alcohol). Improved evolution rates of H2O2 were confirmed from 9.7 mmol g–1 h–1 for the unmodified CN material, up to 11.1, 14.2, and 25.0 mmol g–1 h–1 for the functionalized photocatalysts CN-G, CN-P, and CN-A, respectively. The surface chemistry studied by XPS, EDX, and FTIR revealed the specific functionalities allowing for improved energy transfer, faster redox reactions, and enhanced photoactivation. The optical and electrochemical characterizations corroborate the photocatalytic results since photoluminescence was severely quenched after functionalization, and the electronic properties were enhanced, both indicating reduced recombination of charge carriers. The band structure was also investigated, proving that the generation of H2O2 was thermodynamically favored for the functionalized materials, while H2O2 decomposition was suppressed.

Performance analysis of a double-effect absorption refrigeration cycle using a low-temperature ethanol solution as the working pair

In this paper, a double-effect absorption refrigeration system using a low-temperature working pair, lithium bromide (LiBr)+1-butyl-3-methylimidazolium bromide ([BMIM]Br)/ethanol (C2H5OH), was proposed to reduce the driving heat source temperature and enlarge the operation range to subzero temperatures. Based on the measured thermal properties, the thermodynamic performance of the double-effect absorption refrigeration cycle under different working conditions was calculated by Matlab and compared with that using LiBr/H2O working pair. Results showed that the generation temperature of the refrigeration system using LiBr-[BMIM]Br/C2H5OH was reduced by about 30 K in comparison to LiBr/H2O under the same operating condition. The temperature in the absorber with LiBr-[BMIM]Br/C2H5OH was 40 K higher than its crystallization temperature, whereas LiBr/H2O was only less than 20 K. Moreover, the system using LiBr-[BMIM]Br/C2H5OH was able to successfully work under 273.15 K without crystallization. At a typical operating condition, the COP of the double-effect absorption refrigeration cycle with LiBr-[BMIM]Br/C2H5OH reached 1.47, which was 0.10 higher than that using LiBr/H2O. As a low-temperature working pair, LiBr-[BMIM]Br/C2H5OH showed a great potential in utilizing solar energy and the low-temperature waste heat under severe operating conditions. Furthermore, compared with LiBr/H2O, the refrigeration system had a better economic performance with LiBr-[BMIM]Br/C2H5OH working pair.

Design of novel fractional order FPGA based reactor protection and safety controllers for ACP1000 nuclear power plant in LabVIEW

In this research work, an advanced most modern ACP1000 Nuclear Power Plant is addressed. An enhanced fractional order model of ACP1000 nuclear power plant is adopted with an addition of protection and safety systems. The whole plant model is developed by using innovative hybrid technology of Visual Basic, LabVIEW, Fractional Order and Field Programmable Gate Array (FPGA). A reactor trip system is designed and modeled using FPGA technology in LabVIEW. Plant parameters are systematically modeled and panels are designed in LabVIEW for reactor protection controllers. Twenty one reactor trip controllers are designed and modeled based on complex digital logics using FPGA programming in LabVIEW. Two fractional order trip controllers are designed for over temperature protection and over power protection in LabVIEW. FPGA based safety controllers are designed for Engineered Safety Features (ESF) in LabVIEW. For enhanced model of ACP1000 nuclear power plant, 374 systems are modeled in modular form in Visual Basic Environment. Nine process controllers are configured in ANFIS framework in LabVIEW. In this research work, process controllers are used in conjunction with protection and safety controllers using FPGA. The parametric display of simulations is carried out in Visual Basic. The closed loop performance of proposed protection controllers is evaluated under reactor trip and turbine trip while that of safety controllers are evaluated under inadvertent opening of safety valves of pressurizer. Various parameters are simulated for severe transient conditions and the results are evaluated and validated against reference design data and Final Safety Analysis Report (FSAR) of ACP1000 nuclear power plant. All the results are well within the trip and safety systems design bounds under abnormal and severe operating conditions.

Fabrication and characterization of RF magnetron sputtered composite MoS2 and ZrN coatings on Ti3SiC2 max phase for space applications

The lubrication effect of solid-based materials has been recognized for centuries, but their use as lubricants dates back to only about 50 years. Solid lubricants are used in applications where parts operate under severe operating conditions such as extreme temperatures and very high vacuum. Solid lubricants replace liquid based lubricants for operation under extreme environmental conditions that are beyond the capability of a liquid-based lubricant such as high or very high vacuum, high and cryogenic temperatures, radiation, corrosive gases, and fretting wear. Applications such as space mechanisms, satellites, space vehicles, turbopumps, nuclear reactors, refrigeration plants, etc are examples of such operating conditions. In this research, nano scale composite coatings of MoS2with varied proportions of ZrN (5%, 10% and 20%) were deposited on Ti3SiC2 Max phase substrate using Physical Vapour Deposition (PVD). The PVD technique used was the RF magnetron sputtering process. Material characterization was carried out using Field Emission Scanning Electron Microscope (FESEM) Spectroscopy and Energy Dispersive X-Ray Spectroscopy (EDS). Addition of ZrNis observed to reduce the porosity of the self-lubricating MoS2 coating.

ВЛИЯНИЕ КАЛЬЦИЙ-СТРОНЦИЕВОГО КАРБОНАТА И УСЛОВИЙ ОХЛАЖДЕНИЯ ПРИ ЗАТВЕРДЕВАНИИ НА СТРУКТУРУ И СВОЙСТВА КОМПЛЕКСНО-ЛЕГИРОВАННЫХ БЕЛЫХ ЧУГУНОВ СИСТЕМЫ Fe–C–Cr–Mn–Ni–Ti–Al–Nb

Under severe operating conditions, such as aggressive abrasives, high temperatures and harmful working environments, machine and equipment parts are favoured that are made mainly of white cast irons. The structure and the amount of carbide phase in these cast irons influence their mechanical properties and their ability to resist wear at elevated temperatures. White cast irons owe their particular wear resistance to the high content of primary MC carbides and eutectic carbides such as M7C3 in the matrix, which is mainly composed of austenite or austenite and ferrite. There is a wide variety of technological methods that are designed to improve the special characteristics of cast irons, centred mainly on improving the structure of the materials. The most effective methods for improving the mechanical and special properties of foundry alloys are refining and complex modification. The heat resistance of cast iron is improved as a result of removal of harmful impurities from the melt and formation of refractory inclusions such as SrO and available MgO, Al2O3, SiO2 in carbonate. These inclusions serve as crystallisation centres, which leads to melt supercooling and structure refinement. The modifying effect of carbonate is due to the formation of SrO oxide, these inclusions act as modifiers of the second kind. When cast iron is heated, an oxide film of strontium chromate (SrCrO4) is formed on the surface of castings, which has a higher density and better adhesion to the metal base than spinel oxide (FeO·Cr2O3). This results in better resistance to scale formation.