Chamber Wall Research Articles

Exploring combustion characteristics of a novel micro combustor with a fan swirler for thermophotovoltaic system

The combustion and thermal characteristics of non-premixed methane (CH4)–air flames in a swirl micro combustor are numerically investigated for potential use in a thermophotovoltaic (TPV) system. Swirling flows associated with methane–air combustion are simulated using a Reynolds stress model and detailed chemistry of GRI-Mech 3.0. The optimal condition for improved emission and combustion performance is established by taking into account six blade angles and three fuel-lean equivalence ratios, to consider among other geometric features of the fan swirler and operating conditions.The reactive swirling flows in a micro combustor with a fan swirler are modified by altering the blade angle (θb). For θb = 5°, 10°, and 15°, the swirl micro combustor with a two-vortex structure exhibits a significant enhancement of the fuel–air mixing and thermal performance compared to no-swirl combustor. As θb increases, inner vortices close to the fuel stream and outer vortices near the combustor wall behind the fan blades are developed according to the interaction of swirling flows and recirculating flows due to the blockage effect of the fan blades. For θb = 15°, the strong interaction between two vortex regions maximizes combustion efficiency. The combustion efficiency is highest at θb = 15° and lowest at θb = 75°. For three fuel-lean conditions of θb = 15°, the flame zone is enlarged towards the combustion chamber wall, resulting in a high and uniform wall temperature. The resulting radiant emitter efficiencies for a TPV system are increased by 28.3 %–35.1 % compared to that of the no-swirling micro combustor. The results indicate that the fan swirler has recirculation flows for the best emitter and combustion efficiency unlike vane-type swirlers.

Microfluidic compartmentalization of rat vagal afferent neurons to model gut-brain axis

BackgroundVagal afferent neurons represent the key neurosensory branch of the gut-brain axis, which describes the bidirectional communication between the gastrointestinal system and the brain. These neurons are important for detecting and relaying sensory information from the periphery to the central nervous system to modulate feeding behavior, metabolism, and inflammation. Confounding variables complicate the process of isolating the role of the vagal afferents in mediating these physiological processes. Therefore, we developed a microfluidic model of the sensory branch of the gut-brain axis. We show that this microfluidic model successfully compartmentalizes the cell body and neurite terminals of the neurons, thereby simulates the anatomical layout of these neurons to more accurately study physiologically-relevant processes.MethodsWe implemented a primary rat vagal afferent neuron culture into a microfluidic platform consisting of two concentric chambers interconnected with radial microchannels. The microfluidic platform separated cell bodies from neurite terminals of vagal afferent neurons. We then introduced physiologically-relevant gastrointestinal effector molecules at the nerve terminals and assessed their retrograde transport along the neurite or capacity to elicit an electrophysiological response using live cell calcium imaging.ResultsThe angle of microchannel outlets dictated the probability of neurites growing into a chamber versus tracking along chamber walls. When the neurite terminals were exposed to fluorescently-labeled cholera toxin subunit B, the proteins were taken up and retrogradely transported along the neurites over the course of 24 h. Additionally, mechanical perturbation (e.g., rinsing) of the neurite terminals significantly increased intracellular calcium concentration in the distal soma. Finally, membrane-displayed receptor for capsaicin was expressed and trafficked along newly projected neurites, as revealed by confocal microscopy.ConclusionsIn this work, we developed a microfluidic device that can recapitulate the anatomical layout of vagal afferent neurons in vitro. We demonstrated two physiologically-relevant applications of the platforms: retrograde transport and electrophysiological response. We expect this tool to enable controlled studies on the role of vagal afferent neurons in the gut-brain axis.

Analysis of the relationship between near-wall velocity distribution and wall heat flux under diesel spray flame impingement in an RCEM

To clarify the relationship between the near-wall flow and the heat flux through the wall, the velocity distribution of the diesel spray flame and the heat flux at the combustion chamber wall were measured in a rapid compression and expansion machine (RCEM), which has a twodimensional combustion chamber. The velocity distribution of the diesel spray flame near the wall was measured by the particle image velocimetry (PIV), and the heat flux through the wall where the diesel spray flame impinges was measured using a newly developed multi-point heat flux sensor. Furthermore, the velocity gradient tensor was calculated based on the measured velocity distribution results, and the effect of the shear flow characteristics on wall heat transfer was analyzed. As a result, the higher the injection pressure leads the higher the peak value of the heat flux. A fluctuation of the heat flux exhibits the same trend as the fluctuations of the velocity, and a high heat flux appeared in the high-velocity gradient tensor region, which suggests that the characteristics of shear flow near the wall can affect the heat flux.

Standard technical specifications for methacholine chloride (Methacholine) bronchial challenge test (2023)

Standard technical specifications for methacholine chloride (Methacholine) bronchial challenge test (2023)

The Effects of Syngas Composition on Engine Thermal Balance in a Biomass Powered CHP Unit: A 3D CFD Study

Syngas from biomass gasification represents an interesting alternative to traditional fuels in spark-ignition (SI) internal combustion engines (ICEs). The presence of inert species in the syngas (H2O, CO2, N2) reduces the amount of primary energy that can be exploited through combustion, but it can also have an insulating effect on the cylinder walls, increasing the average combustion temperature and reducing heat losses. A predictive numerical approach is here proposed to derive hints related to the possible optimization of the syngas-engine coupling and to balance at the best the opposite effects taking place during the energy conversion process. A three-dimensional (3D) computational fluid dynamics (CFD) model is developed, based on a detailed kinetic mechanism of combustion, to reproduce the combustion cycle of a cogenerative engine fueled by syngas deriving from the gasification of different feedstocks. Numerical results are validated with respect to experimental measurements made under real operation. Main findings reveal how heat transfer mainly occurs through the chamber and piston walls up to 50° after top dead center (ATDC), with the presence of inert gases (mostly N2) which decrease the syngas lower calorific value but have a beneficial insulating effect along the liner walls. However, the overall conversion efficiency of the biomass-to-ICE chain is mostly favored by high-quality syngas from biomasses with low-ashes content.

Formation of Extended Tubular Plasma in Argon at Low Pressure and in a Weak Longitudinal Magnetic Field

The results of experimental studies on the formation and subsequent evolution of extended (l = 300 mm) and thin-walled (Δr ≈ 10 mm) tubular (2r ≈ 110 mm) plasma in a weak longitudinal magnetic field (B = 175 G) without the use of a thermionic cathode are presented. The cylindrical chamber in which the tubular plasma was formed was pumped with high purity argon (99.998%) at an average velocity of about 1 m/s at a pressure of P = 10–3–10–2 Torr. Two methods of creating seed electrons initiating the development of ionization avalanches were used. The difference inherent to these methods has been established in the dynamics of breakdown, completing in the formation of a tubular discharge. In the first of them, a pulsed discharge preceding the high voltage supply of the main discharge created gas preionization in a small area around the sectioned cathodes. In the second method, seed electrons were created in the entire working area of the discharge chamber by an RF discharge with a frequency of 85 kHz and duration of about 1 s. High-speed shooting with a 4-frame ICCD camera allowed us to establish the dynamics of tubular discharge formation at all its stages. Measurements of the longitudinal and radial discharge current were carried out. The results we obtained showed the possibility of spatial isolation of an extended tubular plasma from the close located metal wall of the discharge chamber by using a weak longitudinal magnetic field.

Numerical implications of including drifts in SOLPS-ITER simulations of EAST

The inclusion of drifts in plasma edge codes like SOLPS-ITER is required to match simulation data with experimental profiles. However, this remains numerically challenging. In this paper, the effect of some numerical factors on the final plasma solution is investigated. This study is performed on three EAST simulations in the upper single null configuration: an attached purely deuterium case, an attached case with limited Ne-seeding, and a detached Ne-seeded case. The effects of the anomalous conductivity and anomalous thermo-electric coefficient on the plasma potential are investigated. Next, the effect of the employed grids is shown. In order to investigate these effects, accurate drift simulations are needed. Therefore, the employed time step and numerical parameters are discussed for the three studied simulations. For all presented simulations, it is verified that the restriction of the grid to the first flux surface tangent to the main chamber wall is sufficient within the context of non-extended simulations. This means that the main power dissipation takes place inside the simulated domain, and only a small fraction of the power is leaving the B2.5 grid through the grid boundary closest to the first wall. Finally, the effect of drifts on the asymmetry between the inner and outer target for EAST simulations is demonstrated.

Spatial and temporal evolution of electromagnetic pulses from solid target irradiated with multi-hundred-terawatt laser pulse inside target chamber

Giant electromagnetic pulses (EMPs) induced by high-power laser irradiating solid targets interfere with various experimental diagnoses and even damage equipment, so unveiling the evolution of EMPs inside the laser chamber is crucial for designing effective EMP shielding. In this work, the transmission characteristics of EMPs as a function of distances from the target chamber center (TCC) are studied using B-dot probes. The mean EMP amplitude generated by picosecond laser-target interaction reaches 561 kV m−1, 357 kV m−1, 395 kV m−1, and 341 kV m−1 at 0.32 m, 0.53 m, 0.76 m, and 1 m from TCC, which decreases dramatically from 0.32 m to 0.53 m. However, it shows a fluctuation from 0.53 m to 1 m. The temporal features of EMPs indicate that time-domain EMP signals near the target chamber wall have a wider full width at half maximum compared to that close to TCC, mainly due to the echo oscillation of electromagnetic waves inside the target chamber based on simulation and experimentation. The conclusions of this study will provide a new approach to mitigate strong electromagnetic pulses by decreasing the echo oscillation of electromagnetic waves inside the target chamber during laser coupling with targets.

Modification on Drying Chamber Wall of Spray Dryer Towards Better Yield

Spray drying is a widely used industrial process that converts liquid or slurry feed materials into dry powder or granules and it commonly shrouded with the stickiness problem. This study was carried out by response surface methodology (RSM) to minimize fouling during the spray drying process by optimizing the condition of the drying chamber wall of the spray dryer. The concentration (%) and exposure time (min) of polytetrafluoroethylene (PTFE) were examined as independent variables in order to modify the dryer wall. Responses including flux adhesion weight, product recovery, hygroscopicity, and moisture content of the powder were evaluated. Statistical analysis showed that experimental data were best fitted into a quadratic polynomial model with regression coefficient values greater than 0.75 for all responses. The optimum conditions in reducing fouling were discovered at PTFE concentration of 17.27% and PTFE exposure time of 6 min. These conditions would result in low flux adhesion weight (35.28 mg), high product recovery (39.38%), low hygroscopicity (6.08%) and low moisture content (7.97%). The observed outcomes aligned with the predicted values, affirming the suitability of the model in improving the flowability of the spray drying process.

Analysis and optimization of the chamfered pyramid and evaluation of geometrical parameters’ effect on its sound absorption coefficient

Since symmetrical geometry makes it easier to arrange pyramid absorbers on anechoic chamber walls compared to wedge absorbers, the goal of this paper is to present an optimal pyramid-shaped absorber which, in addition to the optimal performance in sound absorption, has other advantages such as less thickness, lower material consumption and cost, easier construction, arrangement and maintenance and occupying less space compared to wedges. The COMSOL Multiphysics software was used to simulate the optimized sound absorber by using the genetic algorithm programed in MATLAB software, with the goal of a 100 Hz cut-off frequency. The results show that the optimized chamfered pyramid at the top performs better at sound absorption compared to the complete pyramid and wedge with 18% less thickness. Furthermore, the cut-off frequency decreased to 91 Hz when a gap of up to 15 mm was created between the adjacent absorbers mounted on the surface, which is desirable.

IMPROVEMENT OF DIMENSIONS AND CHARACTERISTICS OF THE VORTEX CHAMBER PUMP FOR COAL-WATER MEDIUM DELIVERING

The vortex chamber pump combines the positive characteristics of the centrifugal pump and the jet pump, and its efficiency is much higher than that of the classical jet pump. This pump differs from the vortex injector by having the pump flow into the tangential outlet channel, which is not available in the vortex injector. The traditional bulk material pump in many aspects has certain shortcomings, these shortcomings limit its application scope and use effect, the traditional bulk material pumps mechanical parts and seals rapidly wear, resulting in short service life. Based on solving the Reynolds equations for water flow, the influence of the angle between the tangential channels of the pump on the energy characteristics is analyzed: an increase in the angle to 180° leads to a decrease in the relative efficiency by 30 %, the outlet pressure by 12 %, and the suction flow rate by 14 %. Thus, the design with a zero angle between the tangential active medium inlet and the tangential outlet channels is optimal in terms of energy-saving pumping performance. As the diameter of the vortex chamber increases, there is no significant trend in the efficiency of the pumped fluid be the vortex chamber pump. With the increase in the total supply pressure, the axial inlet flow rate increase is relatively slow, and the outlet flow rate increases in a parabolic trend. The wear of the pump vortex chamber wall depends on the mass flow rate of coal entering the vortex chamber. The larger the mass flow rate of the abrasive medium, the greater the erosion rate density and the mean volume fraction in the vortex chamber of the vortex chamber pump. The smaller the particle diameter of the coal, the larger the erosion rate density and mean volume fraction in the vortex chamber of the vortex chamber pump. Thus, an increase in particle size should be sought, which will result in less wear.

Size-dependent depositional loss of inorganic, organic, and mixed composition particles to Teflon chamber walls under various environmental and chemical conditions

Size-dependent depositional loss of inorganic, organic, and mixed composition particles to Teflon chamber walls under various environmental and chemical conditions

Multi-objective optimization of rectangular cooling channel design using Design of Experiments (DOE)

In scramjet engines, the optimal design of a regenerative cooling channel is critical for cooling, reducing pressure loss on the walls of the combustion chamber and improving heat sink utilization of fuel. In this study, thermal performance factor (η) and proportion of chemical heat sink in total heat sink (ψ) are introduced as objective functions, additionally, multi-objective optimizations are performed on a rectangular cooling channel using the DOE (design of experiments) method. Two suitable regression models for objective functions η and ψ are quantitatively generated by employing the RSM (response surface methodology), and the R-squared of the regression models are 98.34 % and 97.44 %, respectively. The precision and dependability of the models, as well as the degree of significance of the variables including the mass flow rate (ṁ), aspect ratio (AR), and wall thickness (tw) are assessed via the ANOVA (analysis of variance). The results show that the linear variables x1 (ṁ) and interaction variable x1x2 (ṁ, AR) are the most essential variables in forecasting η and ψ, respectively. The complex effects of linear and interactive variables on the objective functions are discussed. When the cracking rate is less than 40 %, the effect of x1 (ṁ) on η initially decreases and then increases. By contrast, x3 (tw) causes an increase in η initially, followed by a decrease. The variables affecting ψ are x1 (ṁ), x2 (AR), and x3 (tw), in the descending order in terms of effect degree. In addition, to optimize η and ψ simultaneously (weight distribution is equal to one-half for both sides), an optimal point with ṁ = 378.89 g/s, AR = 1, and tw = 1.5 mm is introduced, which yields η = 0.898 and ψ = 0.505. The maximum error between the value fitted using the regression model and the value calculated from simulations is 3.03 %.

Influence of cusp magnetic field configuration on plasma parameters of radio frequency driven negative ion source for CRAFT NNBI

Radio Frequency (RF) driven negative ion source is the preferred ion source for negative ion based Neutral Beam Injection system (NNBI). The plasma generator, which consists of RF driver(s) and an expansion chamber, is one of the key parts for NNBI. The distribution of cusp magnetic field which is generated by permanent magnets installed at the lateral wall of the expansion chamber is a common issue, due to the great influence on electron density, electron temperature and spatial uniformity of plasma density in the extraction area. Two kinds of configuration of cusp magnetic field (checkerboard type and symmetric type) and three types of arrangement of permanent magnets (with three, four and five rows of magnets) have been carried out with the approach of finite element and the experimental performance. On the RF negative ion source testbed, a moveable Langmuir probe has been adopted to investigate the characteristic of electron density and temperature near the extraction area. Since the symmetric type with three rows of permanent magnets generates the distribution of cusp magnetic field that contribute to extract the plasma from RF driver and improve the probability of particle collision easily, the higher electron density and the lower electron temperature was obtained via simulation. The experimental conclusion is that the symmetric type with three rows of permanent magnets leads to a higher electron density and lower electron temperature, showing a great agreement with simulation results. The results are helpful to optimize the structure and performance of high power ion source, and provide support for the development of large area RF negative ion sources with multi-driver.

Calculation of space-charge tune shift in a cylindrical chamber for bunched beams employing Green’s function formalism

When computing the space-charge tune shift for a relativistic bunched beam within a cylindrical chamber, mirror currents for a coasting beam, initially introduced to replace the chamber wall, are employed. Subsequently, the obtained result is extended to encompass the bunched beam, taking into account the bunching factor which quantifies the distribution of bunches around the accelerator ring. In the process of derivation, the terms that characterize the bunch length are intuitively integrated into the formula. As a result, the validity of this approach has never been established. This study provides the derivation of the space-charge tune shift formula for both relativistic and nonrelativistic bunched beams right from the outset, employing the Green function formalism. Subsequently, it is compared with the earlier formula derived using mirror currents. Published by the American Physical Society 2024

Throttling simulation and control of liquid oxygen/liquid methane rocket engine pressurized by the electric pump

This article presented simulation and control of a liquid oxygen/liquid methane variable thrust rocket engine pressurized by the electric pump in the throttling process. To get a proper injection pressure drop, the variation of the injection area was investigated and determined. In the control scheme, the combustion pressure and mixture ratio were the targets. To simplify the control scheme, the pressure and mixture ratio were correlated to the oxygen mass flow rate and methane mass flow rate, respectively. By controlling the propellant mass flow rate, the target engine thrust was reached. In addition, the influence of mass flow rate measurement points on the control effect was analyzed. The simulation results showed that the designed controller can reduce the overshoot of the critical engine parameters. Therefore, the maximum temperature of the thrust chamber wall after the regenerative cooling was decreased. Consequently, the thrust control errors were within 3% except for the points where the thrust changed suddenly, which can meet the mission requirements.

Suppression of runaway electrons by injection of argon gas in the low-density discharges in the STOR-M tokamak

Behaviors of runaway electrons have been investigated by injection of argon impurity gas during the low-density hydrogen discharges in the STOR-M tokamak. Argon gas is puffed using a fast electromagnetic gas puffing valve with various amounts of gas puffed at different injection times. It has been found that puffing of an appropriate amount of gas can suppress the already generated runaway electrons evidenced by the intensity reduction of the hard X-ray (HXR) radiation caused by the impact of runaway electrons on the STOR-M chamber wall. On the other hand, excessive argon gas puffing causes earlier termination of the discharge.

Disease Prognosis of Fetal Heart’s Four-Chamber and Blood Vessels in Ultrasound Images Using CNN Incorporated VGG 16 and Enhanced DRNN

Fetal Heart Disease (FHD) based Structural Heart Disorders (SHD) occur when certain features of the heart develop abnormally. These flaws may cause blood flow to circulate in the erroneous spot, slow down, or be utterly blocked. Heart Defects (HD) caused via FHD or disorders that primarily impact embryonic heart conditions are alternatively referred to as Congenital Heart Defects (CHD). Multiple prior investigation algorithms such as Multi-Resolution Convolutional Neural Network (MRCNN), Deep Convolutional Neural Network (DCNN), Faster-RCNN (FRCNN) and DANomaly Wgan-GP and Convolutional Neural Network (DGACNN) rendered in the detection of FHD. Yet, the models have endured several challenges due to fuzzy constraints and irrelevant adherence. The intended aim is to detect the dilemma of the fetal heart in UltraSound (US) images using two distinct tier methods. The initial tier detects the fetal heart chamber's walls and valves using the Convolutional Neural Network (CNN)-incorporated Visual Geometry Group 16 (VGG 16) technique for processing fetal ultrasound images, allowing it to detect and dissolve anomalies in heart walls. This initial investigation concerns improving the image's quality in each subsequent sequence, from lowest to most improved using the conventional Augmented Wiener Filtering (AWF) approach. Succeeding, an instance-level Region of Interest (ROI) segmentation for exploiting the feature mining approach will be carried out via spatial features masking and ground-truth labeling framework for septal defect diagnosis. The second tier determines the flaws in fetal heart blood flow size, structure and vessels utilizing Deep Recurrent Neural Network (DRNN) integrated with region-based texture characteristics Local-Binary-Pattern (LBP), Histogram-of-Oriented-Gradient (HOG) and the Bags Of Features (BOF) segmentation framework via image acquiring. In eventual, the histogram equalization enhancement algorithm with Median Modified Wiener Filter (MMWF) is enumerated to enhance the visual quality, tests for signal-to-noise ratio, rate of variations, and noise proportion for sorting the blood vessels of the input fetal image. The analyzed CNN’s VGG 16 and DRNN model’s efficiency via Matrix Laboratory (MATLAB) has detected the cardiac features both in normal and abnormal ranges with an overall accuracy of 99.89% and 98.7%.

Clean SiO2 atomic layer etching based on physisorption of high boiling point perfluorocarbon.

This study aimed to evaluate the SiO2 atomic layer etching (ALE) process that is selective to Si3N4 based on the physisorption of high boiling point perfluorocarbons (HBP PFCs; C5F8, C7F14, C6F6, and C7F8 have boiling points above room temperature). The lowering of the substrate temperature from 20 °C to -20 °C not only increased SiO2 etch depth per cycle (EPC) but also increased etch selectivity of SiO2/Si3N4 to near infinity. Due to the differences in fluorocarbon adsorption at a temperature during the physisorption depending on boiling points of PFCs, the desorption time and ion bombardment energy during the desorption step needed to be optimized, and higher ion bombardment energy and longer desorption time were required for higher HBP PFCs. Even though near infinity etch selectivity of SiO2/Si3N4 was obtained, for the SiO2 etching masked with Si3N4 patterns, due to the adsorption of PFC on the sidewall of the Si3N4 layer, the difficulty in anisotropic etching could be observed. By adding an O2 descumming step in ALE processes, an anisotropic SiO2 etch profile could be obtained with no adsorption of fluorocarbon on the chamber wall. Therefore, it is believed that the HBP ALE processes can be applicable for achieving high selective SiO2/Si3N4 with more stability and reliability.

Understanding the active role of water in laboratory chamber studies of reactions of the OH radical with alcohols of atmospheric relevance.

In this work, we studied the reactions of three cyclic aliphatic alcohols with OH at room temperature, atmospheric pressure and different humidities in a Teflon reaction chamber. It was determined that the lower the solubility of the alcohol in water, the larger the effect of the humidity on the acceleration of the reaction. This experimental evidence allows suggesting that the acceleration is due to the reaction of the co-adsorbed reactants at the air-water interface of a thin water film deposited on the Teflon walls of the reaction chamber, instead of between co-reactants dissolved in the water film or due to gas phase catalysis as previously suggested. Therefore, formation of thin water films on different surfaces could have some implications on the tropospheric chemistry of these alcohols in the tropical regions of the planet with high humidity.