Pressure Gap Research Articles

Some problems of heat and mass transfer during the operation of engineering systems in multiphase environments

Three types of problems related to problems of heat and mass transfer in the soil are considered. The first class of problems deals with the diagnostics of damage of underground pipelines by thermal fields on the soil surface. The second type studies the dynamics of changes in the temperature of a geothermal reservoir depending on the temperature of the water entering this reservoir and the pressure gap between injection and production wells. The third-type problems consider the propagation of non-stationary thermal fields in the soil from operated engineering systems in the permafrost. The main attention is paid to long-term forecasting of the propagation of non-stationary thermal fields in the frozen soil between operating production wells of northern oil and gas fields. In problems of the first two classes, which served as a basis for the development of problems of the third type, water filtration in the soil is considered, and thermal fields propagate in single-phase media. The third-class problems take into account possible phase transitions in the soil when describing non-stationary thermal fields in permafrost soils, leading to Stefan-type problems. Accounting for water migration for the specific third-type problems on the determination of the radius of frozen soil thawing from production wells in northern oil and gas fields does not significantly affect this process since lateral water migration above the groundwater level is minimal. Therefore, only the latent heat of the initial water content is taken into consideration. This paper discusses a mathematical model containing the most significant physical and climatic data affecting the distribution of thermal fields in permafrost rocks and presents the results of numerical calculations.

Scanning tunneling microscopy under chemical reaction at solid–liquid and solid–gas interfaces

The task of bridging the pressure gap between ideal ultrahigh vacuum conditions and more realistic reaction conditions involving gas and liquid phases is crucial in surface and interfacial chemistry. Scanning tunneling microscopy (STM) has played a key role in addressing this challenge by enabling atomic-scale probing of the interface. STM enabled us to study surface structure, electronic structure, atomic manipulation, dynamics of molecules and atoms, and chemical properties of the surface at the atomic scale. Over the past four decades, the field of STM has undergone explosive growth. This review article focuses on recent advances in operando STM, specifically in the study of solid–liquid and solid–gas interfaces. It highlights the latest works in ambient-pressure STM, which has enabled the observation of atomic features under various gas and reaction conditions. This information sheds light on the surface mobility of adsorbates and atomic structures of reaction intermediates. The review also addresses research on electrochemical STM, which investigates the evolution of surface morphology under electrochemical processes and provides insights into atomic-scale reaction mechanisms. Finally, the article outlines future challenges and perspectives for operando STM techniques.

Bridging the Pressure and Materials Gap in Heterogeneous Catalysis: A Combined UHV, In Situ, and Operando Study Using Infrared Spectroscopy

Bridging the Pressure and Materials Gap in Heterogeneous Catalysis: A Combined UHV, In Situ, and Operando Study Using Infrared Spectroscopy

Si3N4-TiN rotary EDM optimization by Mo-Jaya algorithm with Pareto optimal solution, analysis of micro-structural and geometrical tolerances

Research into rotary electrical discharge machining on high temperature with biomedical application Si3N4-TiN ceramic composite is presented in this paper. Current (I), pulse on time (Ton), pulse off time (Toff), dielectric pressure (DP), speed and spark gap voltage (Sv) are some of the many performance characteristics. Among the factors taken into account is the material removal rate, surface roughness, electrode wear rate, cylindricity, perpendicularity, top radial overcut, bottom radial over cut and run out. Multiple parameter combinations were validated experimentally and the resulting reactions were examined. Mean effects analysis and regression analysis are used to investigate the impacts of individual parameters. To comprehend the instantaneous behavior of the replies, multi-objective Jaya optimization is utilized to optimize the responses simultaneously. The multi-objective problem's outcomes are shown in 3D charts, with each showing the Pareto optimal solution. From this real conclusion, the optimal combinations of answers are extracted and reported. The aggregate optimization result was also shown, which factored in all eight responses. MRR of 0.238 g/min was obtained which is a 10.6% improvement from the experimental values. Electrode wear of 0.0028 g/min was obtained showing a 6.6% reduction. Similarly reduction in values of Surface roughness, top radial overcut and bottom radial over cut, Circularity, Perpendicularity, run out was observed and the percentages are 3.4, 4.7, 4.5, 7.8, 10.0 and 10.53 respectively. Details on the structural and morphological examinations of the various surface abnormalities that occur during the process have been presented.

Revealing CO2 dissociation pathways at vicinal copper (997) interfaces

Size- and shape-tailored copper (Cu) nanocrystals can offer vicinal planes for facile carbon dioxide (CO2) activation. Despite extensive reactivity benchmarks, a correlation between CO2 conversion and morphology structure has not yet been established at vicinal Cu interfaces. Herein, ambient pressure scanning tunneling microscopy reveals step-broken Cu nanocluster evolutions on the Cu(997) surface under 1 mbar CO2(g). The CO2 dissociation reaction produces carbon monoxide (CO) adsorbate and atomic oxygen (O) at Cu step-edges, inducing complicated restructuring of the Cu atoms to compensate for increased surface chemical potential energy at ambient pressure. The CO molecules bound at under-coordinated Cu atoms contribute to the reversible Cu clustering with the pressure gap effect, whereas the dissociated oxygen leads to irreversible Cu faceting geometries. Synchrotron-based ambient pressure X-ray photoelectron spectroscopy identifies the chemical binding energy changes in CO-Cu complexes, which proves the characterized real-space evidence for the step-broken Cu nanoclusters under CO(g) environments. Our in situ surface observations provide a more realistic insight into Cu nanocatalyst designs for efficient CO2 conversion to renewable energy sources during C1 chemical reactions.

Effects of plasma treatments on the surface wettability properties of PTFE polymeric films

A cold cathode plasma source is constructed for modifying PTFE surface characteristics. The source was easily built, had a consistent plasma discharge medium and acceleration system. A cylindrical Langmuir probe is also used to evaluate plasma parameters like density, temperature or even plasma potential. This probe is designed to be moveable so that it may approach any desired position in the plasma volume. The influences of nitrogen pressure and probe-cathode gap on plasma parameters were investigated. The electron temperature [Formula: see text] fluctuated from [Formula: see text] to [Formula: see text][Formula: see text]eV as the pressure rises from 0.2 to 0.4[Formula: see text]mbar. Further, by increasing the cathode-probe gap from 0.4 to 2[Formula: see text]cm, the electron densities increased from [Formula: see text][Formula: see text]cm[Formula: see text] to [Formula: see text][Formula: see text]cm[Formula: see text]. Furthermore, the contact angles, work of adhesion and surface free-energy of pristine as well as irradiated PTFE films, were estimated. The results demonstrated that by extending the plasma exposure duration from 0 to 12[Formula: see text]min, the water contact angle is lowered from 82.2∘ to 30.5∘. At these conditions, the work of adhesion is raised from 81.9 to 134.1[Formula: see text]mJ/m2, as the surface free energy is increased from 29.8 to 71.8[Formula: see text]mJ/m2.

Scanning photoelectron spectromicroscopy: From static to operando studies of functional materials

The scanning photoelectron microscope (SPEM), developed more than 30 years ago, has undergone numerous technical developments, providing an incredibly vast kind of feasible sample environments, which span from the traditional high spatial resolution core level based chemical analysis to insitu and operando complex experiments, including also electrochemical setups and operational electronic devices at various temperatures. Another important step ahead is overcoming the so-called pressure gap for operando studies, recently extended to near ambient values by building special environmental cells. Using recent results of conventional and unconventional experiments, obtained with SPEM at the ESCA Microscopy beamline at Elettra Sincrotrone Trieste the present review demonstrates the current potential of this type of photoelectron spectromicroscopy to explore the interfacial properties of functional materials with high spatial resolution.

Integration of organic Rankine open cycles to alkanes’ fractional distillation: Process design and techno-economic assessment

Large thermal energy is used by the petrochemical industry to ensure the unfolding of its separation processes, characterized by low grade heat waste. Organic Rankine cycles (ORC) are effective technologies which have been confirmed to be trustworthy for waste heat recovery (WHR). Applications require reliable ORC to be integrated to specific processes in order to boost its technical and economic metrics, leading to ORC modules innovation. In the present work, process design and economic evaluation of organic Rankine open cycle (OROC) integration to alkanes’ fractional distillation is addressed. The integration is optimized within pinch technique framework, and practically ensured by using distillation process fluid mixtures of light, medium and higher alkanes as working fluids in open cycles, taking advantage of the pressure gaps within the distillation system and the final utilization of the pre-mentioned fluids. Compared to n-pentane ORC, the results indicate that OROCs could deliver 3 MW of power at 23, 27% reduced specific investment and operating costs, respectively. Economic indices for this integration are found to be highly dependant on electricity prices. OROCs project could detain a positive net present value at 0.065 $/kWh with a payback period of 7.3 years.

Improving Etched Flatness by Micro Airflow Array Pressurization in ITO Glass Laser Machining.

In laser etching of ITO glass, the warpage due to workpiece positioning causes breakpoint or deformation of micron-scale etching circuits. Based on traditional laser etching, a micro-airflow array pressurization is proposed by using a micro-flow air bearing through airflow positioning. The objective is to achieve high-precision laser etching by pressurized micro-deformation of ITO glass during positioning. First, the micro-air flow and pressurized micro-deformation were modelled in relation to the airflow pressure and etching gap in order to analyze the flatness variation behavior. Then, the surface flatness was investigated in relation to the airflow parameters and relative bearing location. Finally, the critical value of the pressurization parameter were calculated using a data-twin and were applied to industrial ITO glass etching. It is shown that the uniform flow pressure distribution and surface central micro-deformation were formed by positive airflow pressure in the airflow area. The airflow pressure and etching gap could promote surface flatness, while excessive values could result in excessive deformation. Under the micro flow pressure, the initial flatness of the workpiece was able to be compensated within the critical pressurization parameter. By controlling the micro flow stress, the micro-airflow array pressurization could reduce the flatness to 22 μm with stress of 10.7-12.6 Pa. In industrial production, the surface fine circuits can be laser etched with an optimized micro flow pressure, which solves the problems of local breaks or deformed circuits due to the conventional etching process and the structural layout.

Si3N4–TiN conductive ceramic composites: topography on EDMed surfaces and precise drilled holes

In this study, it is challenging to drill a 5 mm hole in a Si3N4–TiN conductive ceramic composite, specifically when attempting to identify an association between EDM machining inputs such as current, pulse on-time, pulse off-time, dielectric pressure and spark gap and performance parameters like as Material Removal Rate, Electrode Wear Rate, Average Surface Roughness, and geometrical tolerances such as Cylindricity, Circularity and perpendicularity. The study examines the surface deformations of a composite comprising EDAX report, machined electrode and molybdenum wire following WEDM machining. Current of 5A, Pulse on-time of 9µs, Pulse off-time of 7µs, spark gap of 0.15 mm, dielectric pressure of 21.0 kg/cm2, material removal rate of 0.004214 g/min, electrode wear rate of 0.000245 g/min and surface roughness of 0.349 µm were found to be optimal. The experimental findings show that good surface finish may be attained on a copper electrode-machined surface, along with improved machining accuracy, closer geometrical tolerances and lesser anomalies.

ATHENA Main Heat Exchanger Conceptual Design and Thermal-Hydraulic Assessment With RELAP5 Code

Abstract Among the envisaged experimental infrastructures supporting ALFRED reactor development, Fostering Alfred Construction consortium identified ATHENA as one of the facilities to address the pool thermal-hydraulic challenges and demonstrate the feasibility of the revised ALFRED configuration, along with the thermal-hydraulic performances of its main components. ATHENA is a large pool-type lead-cooled multipurpose experimental facility featuring a large size vessel (3.2 m diameter, 10 m in height), conceived to host almost 800 tons of lead to test ALFRED relevant scaled components. The test section to be installed in the main vessel includes an electrically heated core simulator (CS), made of 7 FAs, which delivers to the primary coolant a nominal thermal power of 2210 kW, a main coolant pump for lead circulation, and a countercurrent shell and tubes main heat exchanger, which tube bundle is fed by pressurized water by a dedicated secondary circuit. A preliminary analytical calculation has been performed to identify the most suitable configuration for the ATHENA heat exchanger, as well as to achieve a preliminary sizing of the component. The final layout foresees a bundle of 91 bayonet tubes, arranged in a cylindrical geometry, having an active length of 3000 mm and adopting an external double wall tube with a pressurized helium gap. A numerical model of the heat exchanger has been developed using the thermal-hydraulic system code RELAP5/Mod3.3, and a numerical sensitivity analysis on the geometrical and operating parameters has been carried out to verify the performances of the component.

Research on Improvement of Clamping Device for Online Nondestructive Tensile Testing of Braided Wire Rope

The online nondestructive tensile testing machine can crush wire ropes, during the safety tension test of braided wire ropes. To solve this problem, this paper analyzes the reasons for crushing phenomena from the aspects of static simulation and geometric analysis of wire ropes. In terms of static simulation of the tensile process, the equivalent stress, contact pressure and contact gap cloud map of the wire rope in the clamping jaw range are obtained. It is found that both equivalent stress and contact pressure of the wire rope reach maximum values at the transition section between the adjacent peak and trough of the sinusoidal curve, while both reach minimum values at the position of the peak and trough, where the wire rope is in a non-contact state. Concerning the geometrical analysis of the clamping surface of the jaws, the results show that the normal distance between the sinusoidal curves of the movable jaw and the fixed jaw is not constant in one period, which is the smallest at the transition section between the peak and the trough. Therefore, our group determine the destruction resulted from the unreasonable curve shape of the clamping surface, further improve the jaw curve and realize the non-damaged safety tension test of wire ropes.

Uniform Catalytic Nanocrystals: From Model Catalysts to Efficient Catalysts

ConspectusSolid catalysts play a key role in the chemical industry, energy, and the environment. Fundamental understanding of heterogeneous catalysis exerted by solid surfaces is useful for structural designs of efficient catalysts but is challenging due to the complexity. Emerging uniform catalytic nanocrystals (NCs) with controlled and well-defined surface structures have brought new opportunities for fundamental understanding and directed explorations of efficient catalysts. In a previous Account ( Acc. Chem. Res. 2016, 49, 520−527), I postulated and exemplified a concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the “materials gap” and “pressure gap” which are often encountered using the traditional single crystal model catalysts. In this Account, I summarize our effort in fabricating efficient uniform nanocrystal catalysts based on the fundamental understanding of structure–activity relations and reaction mechanisms acquired by oxide nanocrystal model catalyst studies. Directed by the fundamental understanding that the Cu2O{110} facet is active in catalyzing propylene epoxidation with O2 and the fine Cu2O nanocube exposes high densities of Cu2O{110} edge sites, we successfully explore fine Cu2O nanocubes as a highly selective catalyst for propylene epoxidation with O2. Directed by the fundamental understanding that the Cu{100} facet is the active Cu facet in catalyzing the water–gas shift (WGS) reaction, we successfully fabricate a highly active ZnO/fine Cu nanocube WGS catalyst with enhanced ZnO-CuCu{100} active site density. Directed by the fundamental understanding of TiO2 facet effects on the surface band bending and adsorbate–surface interfacial energy level alignment, and consequent photocatalytic performance, we successfully fabricate highly active TiO2{001} NC-based photocatalysts for photocatalytic CH4 conversions. These results adequately exemplify the concept of fundamental understanding-directed explorations of efficient catalysts following a strategy of “identification of active site structure + maximization of active site density”, which, together with the advancement of controlled-synthesis methods, is expected to greatly accelerate the explorations of novel and efficient catalysts in future.

Absence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles

Understanding chemical reactivity and magnetism of 3d transition metal nanoparticles is of fundamental interest for applications in fields ranging from spintronics to catalysis. Here, we present an atomistic picture of the early stage of the oxidation mechanism and its impact on the magnetism of Co nanoparticles. Our experiments reveal a two-step process characterized by (i) the initial formation of small CoO crystallites across the nanoparticle surface, until their coalescence leads to structural completion of the oxide shell passivating the metallic core; (ii) progressive conversion of the CoO shell to Co3O4 and void formation due to the nanoscale Kirkendall effect. The Co nanoparticles remain highly reactive toward oxygen during phase (i), demonstrating the absence of a pressure gap whereby a low reactivity at low pressures is postulated. Our results provide an important benchmark for the development of theoretical models for the chemical reactivity in catalysis and magnetism during metal oxidation at the nanoscale.

Workload Indicators of Staffing Need (WISN) Method for Midwives Planning and Estimation at Asrade Zewude Memorial Primary Hospital, North west Ethiopia

BackgroundWorkforce is a crucial component of the health service delivery system. Ethiopia faces health workforce challenges when it comes to evidence based health workforce planning.Workforce planning was initially determined by comparing the health worker ratio to the general population number. Later, it was determined by standard staffing schedules for each health facility level. However, neither of these methods addressed the evidence based workload variation issue among the same level facilities all around the country. A workload indicator of staff needs (WISN) method can address these variations. Therefore this research was carried on to determine workload pressure excess or gap in midwives, thereby to promote the WISN use in health facilities, based on WISN results of midwives at Asrade Zewude memorial Hospital.MethodsA cross sectional study using WISN model was used to determine the workload excess and gap pressure in midwives at Asrade Zewude Memorial primary hospital, North West Ethiopia. Midwives were selected based on a priority point scale as outlined in the WISN method.ResultsAccording to the data obtained, midwives worked five days a week and 1030 h per year. This working time was spent on health service activities (58.4%), additional activities (36.6%) and support activities (5%). WISN calculations demonstrated a shortage of five midwives with WISN ratio of 0.8 at Asrade Zewude Memorial primary hospital North West Ethiopia.ConclusionMidwives at the study area were carrying on their routine tasks even though there was a staff gap of 5: thus, the midwives had a workload excess of 20%. Under these conditions, it may be hard for the facility to achieve universal health service goals. Therefore the hospital should institutionalize WISN method planning to objectively employ midwifery professionals. This study had limitations too as it used retrospective annual service statistics and small sample size which affects generalization of the results to other health facilities and other health worker cadres within the study hospital.

Pressure relaxation in some multiphase flow models

We consider in this paper multiphase flow models involving two, three or four fields, in total mechanical and thermodynamical disequilibrium. Thus several pressure fields arise, and we precisely focus here on the pressure relaxation process, while restricting to four distinct multiphase flow models. The first two models only involve immiscible compressible components, while the last two hybrid models involve both miscible and immiscible components. It is shown that some -weak- restrictions may occur on pressure gaps, which are unlikely to appear in practice. Evenmore, three-phase flow models may involve a non-monotone behaviour in the return to pressure equilibrium.

Influence of auxiliary mold stretch-bend forming on the forming quality for L-section aluminum alloy profile

To improve the stretch-bend forming precision of aluminum alloy profiles with complex open sections, the relationship stress–strain distribution and the spring-back radius variation were analyzed under different stretch-bend stages. Numerical simulation was performed on the auxiliary mold stretch-bend and spring-back process for the L-section aluminum alloy profile with variable curvature. The effects of cover plate pressure and baffle gap on residual stress, section deformation and spring-back value after forming were investigated. The results show that the stretch-bend warpage can be avoided by setting the cover plate on the straight section of the profile web plate. With the increase of the cover plate pressure, the section distortion of the vertical plate increases by 82%, and the maximum spring-back increases by 71%. A baffle plate was added to the outside of the vertical plate, and the baffle gap is proportional to the amount of section distortion and inversely proportional to the spring-back value. The critical cover force (1 kN) and the critical baffle gap (1 mm) obtained by numerical analysis are used in the stretch-bend forming experiment, and the maximum error between the two results is 2.39%. The numerical simulation has a certain reference value for the rational design of the auxiliary mold stretch-bend process parameters.

Diagnosing Mild Forms of Anorectal Malformation With Anorectal Manometry: A Prospective Study.

Rectoperineal congenital anorectal malformations (CARMs) are diagnosed by examining the perineum, combined with electric stimulation (ES) of the anal sphincter performed under anesthesia. This procedure may be troublesome because it is based on the observed contractibility of the sphincter. We aimed to add 3-dimensional high-resolution anorectal manometry (3D-HRAM) to the procedure and to assess its value for diagnosing rectoperineal forms of CARM. We prospectively included 66 patients younger than 24 months who presented with constipation and were suspected of CARM, idiopathic constipation, or Hirschsprung disease. The patients were assessed between 2015 and 2021 at University Medical Center Groningen, the Netherlands. All patients underwent 3D-HRAM, followed by the standard diagnostic procedure for either CARM or Hirschsprung disease. Of the 51 patients who underwent both 3D-HRAM and ES, we observed that patients with rectoperineal CARM revealed a pressure gap along the anterior part of the anal sphincter. Based on this observation, we diagnosed 35 patients with CARM. Subsequently, all 35 diagnoses were confirmed with ES. Sixteen patients were diagnosed as not having CARM, 100% of whom were in agreement with the gold standard-ES. Both the specificity and sensitivity of 3D-HRAM for diagnosing rectoperineal CARM were 100%. We consider 3D-HRAM a reliable tool for diagnosing and excluding rectoperineal CARM. Using this method in patients suspected of CARM might keep infants from undergoing unnecessary interventions requiring anesthetics, such as ES. By providing objective insight into the functional capabilities of the anal sphincter, anorectal manometry adds to the diagnosis.

Effects of Machining Parameters on Electrochemical Multi-Field Coupling

Electrochemical machining involves three couplings between electric field, flow field and thermal field. The precipitation of hydrogen on the surface of the cathode will affect the entire electrochemical machining process and the final machining quality of the workpiece. Finite element software is used to analyze the effects of different voltages, electrolyte inlet pressure and interelectrode gap on current density, hydrogen volume fraction, conductivity and temperature distribution in this article. The research results show that the increase of processing voltage will increase the current density, hydrogen volume fraction and temperature, and decrease the conductivity of the solution. As the pressure of the electrolyte increases, the current density and conductivity increase, but the hydrogen volume fraction and temperature decrease. The current density, hydrogen volume fraction and temperature decrease, and the conductivity increases when the gap between electrodes increases. At the inlet, the current density and conductivity are relatively large, and gradually decrease along the electrolyte flow direction, while the hydrogen volume fraction and temperature are the smallest at the inlet, and gradually accumulate along the electrolyte flow direction, and reach the maximum at the outlet. Through multi-physics coupling simulation, the current density, temperature, conductivity and bubble distribution in electrochemical machining can be predicted, which can provide a theoretical basis for actual electrochemical machining process parameter selection.

Mechanical Wave Propagation in Solidifying Al-Cu-Mn-Ti Alloy and Its Effect on Solidification Feeding

The wave field in solidifying metals is the theoretical basis for analyzing the effects of mechanical vibration on solidification, but there is little research on this topic. This study investigated the wave field and its effect on the solidification feeding in the low-pressure sand casting (LPSC) of Al-Cu-Mn-Ti alloy through experimental and numerical investigation. The solidification temperature field was simulated by AnycastingTM, and the wave field was simulated by the self-developed wave propagation software. The shrinkage defect detection showed that applying vibration had a greater promotional effect on feeding than increasing the holding pressure. The predicted defects under vibration coincided with the detections. The displacement field showed that the casting vibrated harmonically with an inhomogeneous amplitude distribution under the continuous harmonic vibration excitation, and the vibration energy was mainly concentrated in the feeding channel. With solidification, the ux amplitude reduced rapidly after the overlapping of dendrites, finally reducing slowly to a certain level; the uy amplitude reduced dramatically after the occurrence of a quasi-solid phase, finally reducing slowly to near zero. Mechanical vibration produced a severe shear deformation in the quasi-liquid phase—especially in the lower feeding channel—reducing the grain size to promote mass feeding. The feeding pressure and feeding gap were changed periodically under vibration, causing the vibration-promoting interdendritic feeding rate to fluctuate and eventually stabilize at about 13.4%. The mechanical vibration can increase the feeding pressure difference and change the blockage structure simultaneously, increasing the formation probability of burst feeding.