Channel Shape Research Articles

The impact of residual technological stresses on the opening and stability of through cracks in pipeline elements

The impact of residual stresses in a DN850 pipe (steel 10GN2MFA) with austenitic cladding, welding stresses in the mounting annular seam of the pipeline, and residual stresses arising in a curvilinear branch DN350 (steel 08Kh18N10T) during manufacture by plastic deformation on the opening and stability of through cracks is considered. Calculations of residual stresses are performed using the finite element method (FEM). It is shown that residual stresses cause a change in the size and shape of the outflow channel, the coolant flow rate, and the value of the J-integral at the crack tip. In case of short cracks and relatively low operating stresses, the crack edges can close on the inside of the pipe wall due to the action of residual stresses thus leading to a decrease or cessation of the leak. A reversed effect of residual stresses on extended cracks is observed at rather high operating stresses: change in the shape of the outflow channel (an increase in the opening of the crack edges on the outer surface of the pipe) leads to a decrease in the friction of the coolant flow against the crack edges and, hence, to an increase in the leak volume. The results of testing full-scale models of elements of a straight section of the pipeline with a welded seam and a curvilinear branch DN350 with artificially created defects by internal pressure and bending moment are presented. It is shown that local through cracks develop from initial defects, which remain stable at maximum design loads (normal operating conditions plus maximum design earthquake) which matches the calculation results and meets the requirements of the applicability of the concept of «leak before break».

Numerical study of time and number cycle to failure for the new bipolar plate in the PEM fuel cell used in hybrid energy storage

The operation of a fuel cell poses significant problems related to local current density and the failure rate of components. The issue results from high flow resistance and stresses that guarantee the tightness of the stack. Low flow resistance allows the stack to be used in Hybrid Energy Storage. This study shows that the selection of the best variant of the channel shape in a fuel cell should be based on more than just observing electrochemical performance. Increasing the current density flux can lead to faster component degradation. Older material degradation models based on the strain tensor will only accurately identify some risks. Thanks to the use of Perzyna's viscoplastic model, it was possible to protect the fuel cell from premature failure. Earlier studies did not indicate how the changes in the shape introduced, improving the electrochemical properties, impacted the component's service life during cyclic loads.

INVESTIGATION OF THE EFFECT OF A DIFFERENT TRAPEZOIDAL INCLINATION ANGLE IN A REVERSE TRAPEZOIDAL CROSS-SECTION FLOW CHANNEL ON THE PERFORMANCE OF THE PEM FUEL CELL WITH THE COMPUTATIONAL FLUID DYNAMIC (CFD) METHOD

In this work, a reverse trapezoidal cross-section channel shape for a single flow channel PEM fuel cell was examined with computational fluid dynamic (CFD) method. ANSYS Fluent was applied to solve electrochemical reactions, potential fields, mass, species, and energy transport equations. Species mass ratio, temperature distribution and relative humidity were obtained for the cell as well as the i-V and power density plots. The results were compared to two reference geometries with the commonly used square section shape for the channel. One reference geometry has the same channel width and height with the reverse trapezoidal cross-section channel while the other has the same cross-section area. The results indicate that the cell with reverse trapezoidal cross sectional flow channel shape has more than 32% higher power density than the cell with square cross-sectional flow channel shapes, but poor water management.

Lattice Boltzmann simulation of droplet coalescence in fuel cell flow channel with mechanical vibration

Fuel cells are the promising power source for future green vehicles and water management is an important issue for proton exchange membrane (PEM) fuel cells, which affects the lifetime and durability of fuel cells critically. In the available studies, the key parameters such as channel shape, airflow rate and material wettability have been extensively studied for water management. However, so far there is no open research on the effect of mechanical vibration on water management although most fuel cells work under vibration conditions. To bridge the knowledge gap, based on the Shan-Chen lattice Boltzmann model, this paper aims to reveal the water droplet coalescence process in an airflow channel under vibration conditions and several interesting observations are obtained for the first time. A large vibration amplitude or a small vibration frequency will not only hinder the movement of droplets, but also accelerate the coalescence of droplets. Also by comparing the simulation results it can be found that the droplet movement velocity decreases significantly after coalescence. Therefore, it is important to avoid large amplitude and small frequency for the operation of PEM fuel cells.

The Ancestral Shape of the Access Proton Path of Mitochondrial ATP Synthases Revealed by a Split Subunit-a.

The passage of protons across membranes through F1Fo-ATP synthases spins their rotors and drives the synthesis of ATP. While the principle of torque generation by proton transfer is known, the mechanisms and routes of proton access and release and their evolution are not fully understood. Here, we show that the entry site and path of protons in the lumenal half channel of mitochondrial ATP synthases are largely defined by a short N-terminal α-helix of subunit-a. In Trypanosoma brucei and other Euglenozoa, the α-helix is part of another polypeptide chain that is a product of subunit-a gene fragmentation. This α-helix and other elements forming the proton pathway are widely conserved across eukaryotes and in Alphaproteobacteria, the closest extant relatives of mitochondria, but not in other bacteria. The α-helix blocks one of two proton routes found in Escherichia coli, resulting in a single proton entry site in mitochondrial and alphaproteobacterial ATP synthases. Thus, the shape of the access half channel predates eukaryotes and originated in the lineage from which mitochondria evolved by endosymbiosis.

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Porous Medium Modeling of Catalytic Monoliths Using Volume Averaging

Catalytic monoliths are being explored in conventional catalytic processes for their ability to achieve process intensification. Scientific computing can play an essential role in this exploration. The high computational cost of the first-principles models has led to modeling these reactors as a porous medium. However, this modeling strategy is not performed in a mathematically rigorous manner. We use the volume averaging technique as a mathematical framework to convert the pointwise governing equations for a monolith into averaged equations for a porous domain. These averaged equations require the closure of several unclosed terms, which are neglected in the classical porous medium (CPM) assumption. We discuss these unclosed terms and their impact on model predictions. We show that except in the limit of negligible Damköhler number the treatment of the catalytic reactions in CPM leads to significant errors. We propose a technique to accurately calculate the catalytic reaction rates in the volume-averaging-based porous medium (VAPM) model developed here. This technique is valid for a wide range of Damköhler numbers for both linear and nonlinear kinetics. Moreover, to calculate the effective properties of the porous medium, such as thermal conductivity, we employ asymptotic averaging (numerical homogenization) that can be used for any arbitrary channel shape and size. Predictions of the proposed VAPM model are assessed against three-dimensional multichannel monolith simulations, resolving the solid and fluid phases, for elementary and complex kinetics. In addition, VAPM is validated against the experiments of steam methane reforming in a catalytic monolith. The developed methodology reduces the computational cost by 3 orders of magnitude while maintaining the accuracy of the detailed multichannel simulations.

The sensitivity analysis of dynamic electric breakdown damage model and simulation of granite by high voltage electric pulse

The use of high-voltage electrical pulse (HVEP) technology for improving the rate of penetration in deep, complex formations has been reported; however, its rock fragmentation mechanism is not fully understood, and the parametric design of electric drilling tools is not perfect. This research paper realized the whole process of single-pulse HVEP rock-breaking by using the electric breakdown model, combining circuit parameter coupling, Kirchhoff’s law, electric breakdown criterion, heat transfer process, and solid mechanical field. The sensitivity simulation of HVEP rock-breaking parameters, which considers the structural parameters of pulse power supply, the deterioration of rock during the electrical breakdown process, the correlation between dynamic dielectric strength of rock and time, and rock heterogeneity, is analyzed. The simulation results indicate that the shape of the plasma channel has little relationship with the pulse peak voltage, and the rock-breaking volume of a single pulse is positively related to the pulse peak voltage; the electrode spacing is positively correlated with the breakdown voltage of the rock in a first-order function shape and has a positive correlation with the failure volume; large electrode spacing can promote HVEP rock-breaking; electrode tilt has little effect on the minimum breakdown voltage and failure volume, and its optimal design should be combined with the flow field analysis of the electric bit structure; the heterogeneity index of granite results in breakdown voltage amplitudes within 3 kV and differences in the fragmentation effect of HVEP. The research results can be used as theoretical support for optimizing HVEP matching drilling tools.

Die-sink EDM texturing to fabricate hydrophilic and wear resistant surface

ABSTRACT The present work emphasizes the fabrication of a series of V-groove channels utilizing electrical discharge machining using a pointed tungsten tool electrode. The prepared textured surface is tested for the shape of V-groove channel, wetting behavior, and tribological aspect. A decrease in shape error of V-groove channel is observed as the peak current increases from 4 A to 10 A due to an increase in discharge energy which functions as the melting or vaporizing of machined materials. The water contact angle decreases from 61.3160 (untextured surface) to 49.5670 (sample 4) showing an increase in hydrophilic behavior for the samples having nearly a V-groove-shaped channel. Further, there is a decrease in COF value from 0.48 (untextured surface) to 0.23 (sample 4). The decreased COF value attributes to the formation of metallic bridges in the V-groove channel. The prime wear mechanism for an untextured surface is found to be ploughing whereas adhesion with ploughing is dominant for textured surfaces.

Determining technological properties of drilling muds

Purpose. To rationalize well washing by considering the influence of the annular channel limitation, granulometric composition of the mud, limitation of the joint movement of mud particles, drill string rotation, shape of the movement channel, and rheological properties of a cleaning agent. Methodology. Applied laboratory studies on the properties of drilling fluids are carried out using modern methods of analytical analysis and experimental studies, in particular, by using general principles of mathematical and physical modelling, methods of processing the results of studies in the EXCEL, MATNSAD environment, control and measuring devices of the laboratory of washing liquids of the Department of Oil-and-Gas Engineering and Drilling of Dnipro University of Technology (hydrometer, viscometer, plastometer, stalagmometer), and materials (technical water, clay bentonite powder, reagents, stabilizers and activators, surfactants as well as equipment and laboratory base of “Ukrnafta” PJSC to carry out certain stages of research. Findings. The properties of surface-active substances and activated washing liquids are analyzed. The main technological properties of drilling fluids are studied. Comprehensive information on the physical and chemical ability of flushing drilling fluids is provided. The main technological measures ensuring the stability of drilling process using activated-surfactant drilling fluids are considered in detail. The main technological principles of determining rational formulations of a selected cleaning agent in the circulation of Newtonian liquids are formulated and substantiated. A detailed description of surfactants, their properties and methods to study the formed solutions is given. Originality. The process of a rock-breaking tool on the well bottom will be stable in the conditions of dynamic equilibrium of the rock-breaking processes and removal of broken products into the annular space. Therefore, for a correct understanding of wellbore washing issues, basic regularities are established of the specified processes and the influence of various factors on these processes. Practical value. It has been proven that in order to give a drilling fluid the necessary properties that, on the one hand, will ensure an increase in the efficiency of rock breaking on the well bottom, and, on the other hand, will create favourable conditions for stable removal of cuttings onto the surface and maintenance of the well walls in a stable condition, it is necessary to apply different methods, in particular chemical activation as well as magnetic, thermal and electrochemical activation, in its different varieties.

Main Flow Migration in the Middle Yangtze River Influenced by Cascade Reservoirs: Characteristics, Controlling Factors, Trends, and Ecological Impact

The main flow migration in the middle Yangtze River occurs in most river sections and is affected by factors such as incoming water and sediment, riverbed boundaries, and channel shapes, leading to a complex riverbed evolution. Revealing the controlling factors and analyzing the developmental trends are important for addressing the adverse ecological impacts caused by these changes. Based on a large amount of observational data since the impoundment of the Three Gorges Reservoir, the characteristics of the main flow migration in the middle Yangtze River under different flow conditions were analyzed, and its correlation with the nodes and bars at the inlet, the plane shape of the river, and riverbed morphology were determined to identify the key controlling factors. The results showed that it is characterized by the displacement of the main flow zone during the middle-flow period. The key factors controlling the main flow migration include the deflecting action of the nodes and sidebars at the inlet, relaxation of the channel plane shape, and resistance difference caused by the riverbed morphology between the branches. The trend analysis suggests that the main flow migration in the middle Yangtze River may become more frequent after the operation of the cascade reservoirs in the future and may threaten the ecological environment.

Wave Energy Convertor for Bilateral Offshore Wave Flows: A Computational Fluid Dynamics (CFD) Study

Human activities have adversely affected the Earth’s habitable environment. Carbon emissions and other greenhouse gas emissions are the primary cause of climate change and ozone layer depletion. In addition, the exponential decay of fossil fuel resources has resulted in the rising demand for renewable and environmentally-friendly energy sources. Wave energy is the most consistent of all intermittent renewable energy sources and offers a promising solution to our energy needs. This study focuses on harnessing offshore wave energy resources, specifically targeting offshore conditions with the highest energy density. A novel direct drive cross-flow turbine with an improved augmentation channel shape was designed and analyzed using commercial computational fluid dynamics software. The turbine’s base model reached a maximum efficiency of 54.3%, with 33.4 kW of power output at 35 rev/min and a 3.0 m head. Bidirectional flow simulations were carried out, and the peak cyclic efficiency was recorded at 56.8% with a 36.4 kW average power output. The nozzle entry arc angle of 150 degrees was found to be the most efficient, and the numerical simulation’s fully developed solution computed the flow behavior through the runner and nozzle under steady-state conditions.

Numerical investigation of organic fluid flow boiling for proton exchange membrane fuel cell cooling and waste heat recovery

High power density is one of the competitive edges of proton exchange membrane fuel cell (PEMFC), making it a promising technology for many applications. However, its intensive heat generation leads to a high cooling burden, and a large amount of low-grade waste heat is difficult to utilize, which brings technical difficulty to the system's thermal management. In this study, the organic fluid (R245fa) with low boiling temperature is selected for the PEMFC stack's phase change cooling, and the organic Rankine cycle (ORC) is employed to recover waste heat. Four cooling channels are designed: serpentine straight, spiral straight, serpentine thin and serpentine zigzag channels. The boiling flow is simulated to reveal the effect of channel layout, sectional size and channel shape on the cooling and heat recovery performance. The results show that the cooling plates can be cooled to a reasonable temperature by the organic fluid, and the maximum surface temperature difference is within 15 K, which demonstrates the good cooling performance of flow boiling. The highest ORC thermal efficiency of 7% is achieved by the serpentine straight channel and the spiral straight channel, while the serpentine zigzag channel has the best temperature uniformity contribution resulting from its secondary circulation flow. This study demonstrates the potential of flow boiling on PEMFC thermal management and gives guidance on the cooling channel design.

Method of predicting valve seal leakage considering deflection of the spool

The small angular deflection of the spool under the action of non-equilibrium force is a main reason for valve seal failure. In the present study, a prediction model of the valve seal leakage was established considering the sectional shape and channel height of the leakage channel. The effect of spool deflection on the leakage rate was analyzed quantitatively from the results of three-dimensional finite element mechanical analysis. The microscale leakage channel of a contact deformation surface was then generated through the reconstruction of the rough surface with nanoscale precision, deterministic rough-peak contact analysis, and lattice leakage theory. The results showed that the spool deflection was the key factor affecting the leakage rate. The leakage rate was measured on a self-built experimental platform, and the experimental results verified the accuracy of the theoretical calculations.

Numerical Analysis of Liquid Potassium Flow and Heat Transfer in a Core for Space Nuclear Reactor Based on Entransy Dissipation Theory

AbstractThe research on the flow and heat transfer of alkali metals is an important technical means to strengthen the heat transfer of the core. In this paper, the 15 cooling channels with different structures are established. Under Re = 2.85 × 104–2.17 × 105, several operating parameters, such as core inlet temperature (T = 350 K, 390 K, 450 K, 550 K, 850 K), fuel rod pitch ratio (P = 1.2, 1.4, 1.6, 1.8, 2.0), and channel shape (triangle and square) on the heat transfer performance are numerically simulated. At the same time, this work introduces an evaluation criterion, entransy dissipation, to measure the irreversibility of the heat transfer process. The results show that the triangular channel has a stronger heat transfer capacity than the square. And the increase of the rod diameter ratio is a positive means to enhance the heat transfer. Among the studied channels, Model “I” (triangle channel, P = 2.0) has the best heat transfer performance. The above results have some guiding value to realize core heat transfer enhancement by adjusting fuel rod arrangement.

MP26-19 CHARACTERIZATION OF THULIUM FIBER LASER PULSES: DIFFERENCES BETWEEN SHORT AND LONG PULSE

You have accessJournal of UrologyCME1 Apr 2023MP26-19 CHARACTERIZATION OF THULIUM FIBER LASER PULSES: DIFFERENCES BETWEEN SHORT AND LONG PULSE Ron Marom, William W. Roberts, Timothy L. Hall, John Robinson, Adam J. Matzger, and Khurshid R. Ghani Ron MaromRon Marom More articles by this author , William W. RobertsWilliam W. Roberts More articles by this author , Timothy L. HallTimothy L. Hall More articles by this author , John RobinsonJohn Robinson More articles by this author , Adam J. MatzgerAdam J. Matzger More articles by this author , and Khurshid R. GhaniKhurshid R. Ghani More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003254.19AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Recent studies have shown the significance of pulse modulation in energy delivery to the stone with better ablation and less retropulsion. Thulium Fiber Laser (TFL) is a novel laser technology with a different wavelength and pulse characteristics to holmium and is increasingly used for lithotripsy. Our aim was to characterize the TFL pulse to better understand parameter selection. METHODS: Using a commercially available TFL system (Fiber Dust, Quanta) we characterized the optical (temporal) profiles of a single pulse at 1J Shortest Pulse (SP), 1J Longest Pulse (LP), 3J SP, and 2.4 LP with a photo detector. By using MATLAB we normalized the optical profiles with the average pulse energy as measured by a power meter (n=100). We then performed high-speed imaging at 50,000 frames per second on the vapor bubble generated by pulses of 1J SP and 1J LP. Using MATLAB we segmented the bubble anatomy and measured its maximal width and length at each frame to quantify bubble dimensions. RESULTS: The temporal profile of the TFL pulse is rectangular in shape with a uniform power throughout the entire pulse besides a brief initial peak (<1% of the pulse energy). The full width half max (FWHM) for 1J SP, 1J LP, 3J SP, and 2.4J LP was calculated to be 2022.5 µsec, 5995 µsec, 6025 µsec, and 11990 µsec, respectively with a peak power governed by the pulse length: 474 Watts for SP and 167 Watts for LP (Figure 1). Both SP and LP of 1J reached the same maximal vapor bubble length of 4 mm, and the same maximal width of 1.8 mm. However, SP had intermittent closure of the channel while the LP channel appeared to elongate along the pulse duration (Figure 2). CONCLUSIONS: This study quantifies some of the single pulse characteristics of a TFL. In the system tested, the peak power was a function of the pulse duration and not the pulse energy. SP had multiple generations of bubble formation, almost like a multi-pulse, while LP had a channel shape that elongated and widened along the pulse duration. Further investigation is required to understand how these impact ablation. Source of Funding: None © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e360 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Ron Marom More articles by this author William W. Roberts More articles by this author Timothy L. Hall More articles by this author John Robinson More articles by this author Adam J. Matzger More articles by this author Khurshid R. Ghani More articles by this author Expand All Advertisement PDF downloadLoading ...

A compact channel patch antenna with reconfigurable circularly polarized pattern for mobile satellite communications

A compact dual-band circularly polarized antenna with a characteristic of pattern reconfiguration is proposed for S-band satellite handsets. The antenna works as a patch antenna in a channel shape with no ground beneath reaching an overall size of 0.55λ × 0.14λ × 0.1λ. The dual-band performance is realized through multi-branch slots of the patch. The antenna mainly consists of a channel metal patch, a channel dielectric, and a simple feeding network. The overall shape of slot can be changed by the PIN diode on the patch to adjust the surface current direction, which in turn achieves 180° switching of the left-hand circularly polarized radiation beam direction. In addition, by combining the quadrifilar helical antenna, which is switchable in the end-fire beam direction, the designed antenna can realize the switching of four main beam directions to achieve 360° 3D spatial coverage. The proposed antenna is fabricated and measured to verify the proposed design. The test results show that the designed antenna obtains circularly polarized radiating characteristics in S-band with the center frequency of 1.98 GHz and 2.2 GHz, and the test results and simulation results are basically consistent, which indicates the superior performance of the designed antenna.

Rectified transport of a single vibration-driven vehicle in the asymmetric channel

The rectification transport of a single vibration-driven self-propelled vehicle in a two-dimensional left–right asymmetric channel was experimentally investigated. The rectification efficiency of the vehicle moving from the center to the exit was statistically obtained for the range of channel widths, inter-channel asymmetry degrees, and platform tilt angles. The trajectory of its movement was also analyzed. It was found that the structure of the channel provides the main influence. Different channel shapes lead to different ranges of unfavorable widths, and transport efficiency decreases when the asymmetry diminishes — the two channels converge. The addition of external gravity does not counteract the structural limitations, but only affects the probability of departure.

Macroscopic hydro-thermal processes in a large channel-type reservoir

Study regionThis study was conducted in Xiangjiaba Reservoir, located in the Jinsha River, China's upper reach of the Yangtze River. Study focusLarge channel-type reservoirs are characterized by significant runoff, deep water, and narrow-and-long channel shape, creating unique hydrodynamic and thermodynamic conditions for their eco-environmental systems. However, the hydro-thermal processes of this type reservoir are not fully known. A large channel-type reservoir was selected to investigate the macroscopic processes through a field survey and employing a three-dimensional (3D) hydro-thermodynamic model. New hydrological insights for the regionThe reservoir experienced a seasonal varying thermal stratification, with a vertical temperature difference of ∼9 °C. Meanwhile, a conjoint flow pattern was detected, consisting of an upper-layer warm water flow and a lower-layer circulation, which was very different from the lakes' wind-induced pattern. When the reservoir was stratified, the inflow warm water on the thermocline could produce a shear effect, promoting vertical mixing and further contributing to hypolimnion shrinking. The reservoir experienced a water age increase during the non-stratification period, with the near-dam age being ∼20 days. The trap effect of the lower-layer circulation retained the cold water in the hypolimnion during the stratification period, and the water age reached 115 days. The presented varying flow pattern and transport timescale have essential effects on the eco-environmental systems, providing practical insights into managing water quality and aquatic environment in reservoirs.

Study of the influence of objective functions on the topology optimization design of battery cold plate

Topology optimization design of cold plate flow channels is a potential approach to improve the performance of battery thermal management systems. In this paper, four objective functions, such as maximum heat exchange, maximum outlet enthalpy, minimum solid domain temperature, and multi-objective function, are used to investigate the effect of the objective function on the topology optimization flow channel shape and cooling performance. The results show that the cold plate channel shape can be adjusted according to the objective function. With the inlet flow rate of 0.002 kg·s−1, the inlet coolant temperature of 25 °C, the ambient temperature of 20 °C, and the 3C-rate discharge, it was found that the topology optimization cold plate with maximum outlet enthalpy as an objective function will give the best cooling performance, in which the maximum temperature of the battery is 29.65 °C, which is 0.48 °C less than the battery with convectional rectangular channel cold plate cooling. For the multi-objective function, the increase in the weighting coefficient of the heat transfer term can improve the cooling capacity of the cold plate, and the increase in the weighting coefficient of the flow term can reduce the flow resistance of the cold plate and enhance the efficiency of energy utilization. In addition, the unsteady battery temperature is calculated during the entire 3C-rate discharge process, and it is found that the topology optimization cold plate can slow down the increase of battery temperature and improve the proportion of battery discharge time at ideal temperature.