Wall Conditions Research Articles

Stability Deterioration Analysis of Toppling Dangerous Rock Mass under the Combined Effect of Vibration and Freeze-Thaw Cycles

To investigate the degree of stability deterioration in toppling dangerous rock mass under different action times, firstly, the vibration load generated by train travel in a single action and its decay law were studied, and the theoretical relational equation of rock strength deterioration under the action of vibration loading was obtained by analyzing the increase in half axle expansion of micro fissures inside the rock. Secondly, the freezing stress of the microfissures was determined according to the rock freezing and swelling theory, and the theoretical relational equation of rock strength deterioration under the action of freeze-thaw cycles was obtained by integrating the rock confinement and moisture migration conditions of the fissures wall. The stability coefficient of the toppling dangerous rock mass exhibited a rapid and then slow decreasing trend with increasing number of actions, which was non-linearly negatively correlated with the train running speed and the initial porosity of the rock, and non-linearly positively correlated with the freezing temperature. Controlling the freezing temperature and initial porosity of rock can significantly reduce the degree of deterioration in the stability of dangerous rock mass.

Turbulent transition in a channel with superhydrophobic walls: anisotropic slip and shear misalignment effects

Superhydrophobic surfaces dramatically reduce skin friction of overlying liquid flows. These surfaces are complex and numerical simulations usually rely on models to reduce this complexity. One of the simplest consists of finding an equivalent boundary condition through a homogenisation procedure, which in the case of channel flow over oriented riblets, leads to the presence of a small spanwise component in the homogenised base flow velocity. This work aims at investigating the influence of such a three-dimensionality of the base flow on stability and transition in a channel with walls covered by oriented riblets. Linear stability for this base flow is investigated: a new instability region, linked to cross-flow effects, is observed. Tollmien–Schlichting waves are also retrieved but the most unstable are three-dimensional. Transient growth is also affected as oblique streaks with non-zero streamwise wavenumber become the most amplified perturbations. When transition is induced by Tollmien–Schlichting waves, after an initial exponential growth regime, streaky structures with large spanwise wavenumber rapidly arise. Modal mechanisms appear to play a leading role in the development of these structures and a secondary stability analysis is performed to retrieve successfully some of their characteristics. The second scenario, initiated with cross-flow vortices, displays a strong influence of nonlinearities. The flow develops into large quasi-spanwise-invariant structures before breaking down to turbulence. Secondary stability on the saturated cross-flow vortices sheds light on this stage of transition. In both cases, cross-flow effects dominate the flow dynamics, suggesting the need to consider the anisotropicity of the wall condition when modelling superhydrophobic surfaces.

The Impact of Wind-Driven Rain on Surface Waterproofed Brick Cavity Walls

Moisture ingress is a major cause of damage to masonry cavity walls. Products of various chemical compositions are available for wall surface treatment, aimed at reducing/eliminating water ingress. This study presents the results of full-scale wall tests designed to quantify water absorption into uninsulated and insulated brick masonry cavity walls exposed to wind-driven rain (WDR) with and without surface waterproofing. Two different waterproofing products were used: acrylic and silane–siloxane mixture. Untreated and treated walls were exposed to cycles consisting of 10 min wetting at 2.25 L/m2·min every 60 min. The results show that both treatments lead to a reduction in water ingress ranging from 90% to 97%. However, while a more consistent performance was obtained for the silane/siloxane-treated walls under repeated exposure, the results for the acrylic treatment were dominated by the original wall conditions, improved with a reapplication of the treatment. The testing protocol proposed in this study is effective in determining the performance of waterproofing treatments exposed to different levels of WDR. Both treatments prove to be effective in preventing moisture uptake in walls in moderate WDR exposure conditions, while in extreme WDR exposure conditions, the acrylic treatment is less effective.

Directional reverberation time and the image source method for rectangular parallelepipedal rooms.

The image source (IS) method is a commonly used geometrical acoustics simulation technique in room and virtual acoustics. In particular, it has been used in the analysis of room reverberation under different choices of geometry and wall conditions. Under a simple rectangular parallelepipedal geometry, reverberation time is known to be dependent on the direction of arrival of reflections relative to the room axes. In this article, a closed-form expression for the directional energy decay and reverberation time is derived, which is valid in the late response, and may be used in the case of either angle-independent or angle-dependent reflection. The expression reduces to an easily evaluated formula in the case of an omnidirectional energy decay curve (EDC). Various numerical results are presented, including the validation of the closed-form expression against EDCs and late reverberation times drawn directly from the IS method.

PZN-PT single crystal based high-frequency intravascular ultrasound transducers

Cardiovascular disease (CVD) is a kind of high life-threatening illness for humans. Intravascular ultrasound (IVUS) technology could highly help the physicians to know the condition of human's vessel wall. In this work, the novel lead zinc niobate-lead titanate (PZN-PT) single crystals-based IVUS transducers were prepared. The electrical properties of PZN-PT single crystals were investigated with high d33 of 2531 pC/N and dielectric constant. The high piezoelectric response could improve the transmission and receive properties of IVUS transducers. Moreover, the high dielectric constant (8050) could highly help the miniaturization of IVUS transducer. The IVUS transducers have a center frequency at 43.5 MHz and a -6dB bandwidth of 62.3%. It promising the PZN-PT based IVUS transducers are suitable for the clinical diagnosis field for CVD.

Abstract TMP4: Computational Fluid Dynamics Analysis Offers Novel Preoperative Insights for Unruptured Cerebral Aneurysms - Predicting Aneurysm Wall Thinning and Thickening -

Objective: The preoperative identification of thin-walled regions (TIWRs) and thick-walled regions (TKWRs) in cerebral aneurysms can contribute to enhancing surgical safety. Our recent computational fluid dynamics (CFD) analysis of cerebral aneurysms has demonstrated that the wall shear stress vector cycle variation (WSSVV) and the oscillatory shear index (OSI) can potentially predict TIWRs and TKWRs. This study aims to validate the accuracy of using WSSVV and the OSI to identify these areas and to report on their effectiveness in actual surgeries. Methods: Our cohort comprised 42 patients who underwent cerebral aneurysm clipping surgery at our hospital from January 2019 to September 2022. CFD analysis was performed using Hemoscope. We defined suspected TIWRs as blue regions and suspected TKWRs as red regions on both color maps. We evaluated the positive predictive value (PPV) by comparing these preoperative suspected areas with actual thin and thick areas determined intraoperatively under surgical microscopic observation. Results: Of the 42 patients, 15 were male and 27 were female. The average age was 63 years, and the average aneurysm size was 5.9 mm. The location of the aneurysms was the middle cerebral artery in 18 cases, the internal carotid artery in 15 cases, the anterior communicating artery in 8 cases, and the basilar artery in 1 case. WSSVV yielded a PPV of 83% for TIWRs and a PPV of 78% for TKWRs. In comparison, the OSI demonstrated a PPV of 77% for TIWRs and 76% for TKWRs. Spearman's rank correlation analysis revealed a strong correlation between WSSVV and the OSI; the correlation coefficient was 0.883 (p-value < 0.001). Conclusions: CFD analysis of unruptured cerebral aneurysms could be used to predict TIWRs and TKWRs using both WSSVV and the OSI with an accuracy of approximately 80%. The preoperative evaluation of the wall condition using CFD analysis appears to be highly reliable and is likely to contribute to the safety of cerebral aneurysm surgery.

Estimates of global recycling coefficients for LTX-β discharges

We report the first observation of global recycling coefficient R near 0.5 in the Lithium Tokamak eXperiment-β (LTX-β), significantly below the minimum R previously reported in other devices. In a series of experiments with varied Li wall conditioning, estimates of the recycling coefficient have been made using a Lyman-α array and DEGAS2 modeling. A progressive reduction in Lyman-α emission with increased lithium and an increase in edge electron temperature are observed. It is also observed that with increasing Li coating thickness, the effective particle confinement time τp* is reduced and approaches TRANSP calculated energy confinement time (τE), with τp* near τE,TRANSP for the lowest recycling coefficients. Edge temperatures approaching core plasma temperatures, first reported in LTX, can now be directly connected to estimates of the recycling coefficient and qualitatively agree with previous UEDGE simulations. The particle flux to the limiting surfaces appears to be significantly reduced in comparison with fluid scrape-off layer (SOL) models, indicating that a large fraction of the SOL ions are mirror trapped. SOL collisionality drops more than an order of magnitude below the banana regime boundary, indicating the importance of kinetic effects. Full-f 1x2v gyrokinetic simulations of SOL field lines with the GKEYLL code indicate that the fraction of ions trapped along field lines increases as collisionality drops, as a result of increased lithium evaporation.

Estimating the change in pleural pressure using the change in central venous pressure in various clinical scenarios: a pig model study

BackgroundWe have previously reported a simple correction method for estimating pleural pressure (Ppl) using central venous pressure (CVP). However, it remains unclear whether this method is applicable to patients with varying levels of intravascular volumes and/or chest wall compliance. This study aimed to investigate the accuracy of our method under different conditions of intravascular volume and chest wall compliance.ResultsTen anesthetized and paralyzed pigs (43.2 ± 1.8 kg) were mechanically ventilated and subjected to lung injury by saline lung lavage. Each pig was subjected to three different intravascular volumes and two different intraabdominal pressures. For each condition, the changes in the esophageal pressure (ΔPes) and the estimated ΔPpl using ΔCVP (cΔCVP-derived ΔPpl) were compared to the directly measured change in pleural pressure (Δd-Ppl), which was the gold standard estimate in this study. The cΔCVP-derived ΔPpl was calculated as κ × ΔCVP, where “κ” was the ratio of the change in airway pressure to the change in CVP during the occlusion test. The means and standard deviations of the Δd-Ppl, ΔPes, and cΔCVP-derived ΔPpl for all pigs under all conditions were 7.6 ± 4.5, 7.2 ± 3.6, and 8.0 ± 4.8 cmH2O, respectively. The repeated measures correlations showed that both the ΔPes and cΔCVP-derived ΔPpl showed a strong correlation with the Δd-Ppl (ΔPes: r = 0.95, p < 0.0001; cΔCVP-derived ΔPpl: r = 0.97, p < 0.0001, respectively). In the Bland–Altman analysis to test the performance of the cΔCVP-derived ΔPpl to predict the Δd-Ppl, the ΔPes and cΔCVP-derived ΔPpl showed almost the same bias and precision (ΔPes: 0.5 and 1.7 cmH2O; cΔCVP-derived ΔPpl: − 0.3 and 1.9 cmH2O, respectively). No significant difference was found in the bias and precision depending on the intravascular volume and intraabdominal pressure in both comparisons between the ΔPes and Δd-Ppl, and cΔCVP-derived ΔPpl and Δd-Ppl.ConclusionsThe CVP method can estimate the ΔPpl with reasonable accuracy, similar to Pes measurement. The accuracy was not affected by the intravascular volume or chest wall compliance.

Influence of randomly distributed wall roughness on the flow behaviors of liquid-liquid slug flow in a co-flowing microchannel

In present study, the influence of randomly distributed wall roughness on the flow behaviors of liquid-liquid slug flow in a co-flowing microchannel has been numerically investigated, as the manufacturing tolerance of microfluidic device in engineering application is unavoidable. A circular axisymmetric microchannel model is adopted to study the effect of roughness height and correlation length on the wall roughness generation and internal laminar flow characteristics in the microchannel. The wall roughness is modeled by well-known Gaussian distribution method. The prediction of slug velocity and liquid film thickness from numerical simulations has been well validated with the empirical and analytical correlations and experimental data in the literature. The obtained results show that the rough wall condition significantly affected the internal flow behaviors, such as slug moving velocity and slug breaking-off. According to the quantitative comparison of normalized surface areas between high (larger than 0.4 m/s) and low (smaller than 0.69 m/s) velocity region, the surface area of low velocity region under rough wall condition (wall roughness: D/l=3.333 and σ/D = 0.018) is 46 % larger than smooth wall condition, which means effective flow area of microchannel is reduced. The surface area of high velocity region under rough wall condition increases around 66 % compared with smooth wall condition. This study could be used as a promising reference and provide more understanding for roughness control in industrial microfluidic device.

Effect of surface structure on fluid flow and heat transfer in cold and hot wall nanochannels

Nanochannels consisting of hot and cold walls with periodic rectangular and triangular nanostructures were simulated by molecular dynamics in this paper, the periodic size dimensionless parameters φ was defined to describe the dimension of nanostructures on the wall. The results show that the addition of nanostructures leads to the variation of mass density distribution of fluid near the wall. A hot wall with nanostructures can promote the appearance of a fluid high-potential area near it. The discrepant attraction for fluid from the wall caused by the different wall conditions leads to different flow characteristics in nanochannels. Fluid velocity growth rate near the hot wall is 10.5% higher than that near the cold wall. Average velocity of the fluid near the hot wall is 5.1% higher than that of fluid near the cold wall. A wall with rectangular nanostructures at φ = 0.28 shows minimum flow resistance among rough hot walls, while a wall with triangular nanostructures at φ = 0.14 has minimum flow resistance among rough cold walls. Heat is transferred from the hot wall to the cold wall through fluid flow. Wall conditions impact the heat transfer situation of fluid in flow boundary by changing the fluid mass density contribution. The addition of nanostructures and decrease of nanostructures size is beneficial for heat transfer while unfavorable for fluid flow, convective heat transfer was influenced by their combination. For a wall with 300 K, the addition of rectangular nanostructures at φ = 0.07 has the best convective heat transfer performance. For a wall with 200 K temperature, increasing triangular nanostructures at φ = 0.14 on the wall can reach the best convective heat transfer capacity. This paper can provide a theoretical foundation for the optimization of nanochannels to achieve best convective heat transfer ability.

Effects of green walls on thermal perception and cognitive performance: An indoor study

In this study, 144 university students were recruited to investigate the effects of greenery dosing on emotional and physiological properties by testing neurobehavioral responses, measuring a physiological index, monitoring electroencephalogram signals, and a questionnaire survey. Where there was a non-green wall (green view index (GVI) = 0 %), a small green wall (GVI = 5 %), and a large green wall (GVI = 15 %), the mean thermal comfort vote increased by 0.02, 0.25, and 0.44, respectively, compared to pre-trial conditions. Subjects’ cognitive performance was highly improved in the presence of a large green wall. Systolic blood pressure and heart rate were reduced (1.68 and 3.14, respectively) most significantly in the presence of a large green wall. Diastolic blood pressure decreased significantly by 1.92 in the presence of a small green wall. Oxyhemoglobin saturation and eardrum temperature were not affected by indoor green wall sizes. We found no significant change in the frontal asymmetrical activity of the brain among subjects where there was a non-green wall, but it increased significantly in the event of a small (+0.12) and a large green wall (+0.14). Finally, in a non-green and small green wall conditions, the relative power of δ brain wave activity was minimized and α brain wave activity was maximized 13 and 9 min after the subjects began looking at green walls. After 7 min of exposure to a large green wall, the relative power of δ reached its minimum and α and θ both reached their maximum.

Changeover between helium and hydrogen fueled plasmas in JET and WEST

The pre-fusion power operation (PFPO) phase of ITER, as described in the ITER research plan with Staged Approach,22ITER Organization, “ITER Research Plan within the Staged Approach,” ITR-18–003, Aug. 2018. includes both hydrogen (H) and helium (He) plasma operations. In preparation for PFPO, both WEST and JET ran He plasma campaigns to study plasma-wall interactions in a tungsten environment. The campaigns included a back-and-forth transition between H or deuterium (D) and He plasma operation allowing the assessment of the achievable plasma content as well as the accessible wall reservoirs for respective species. The WEST changeovers included tokamak pulses with a fixed divertor configuration. The JET changeovers applied ion cyclotron wall conditioning (ICWC) and tokamak pulses including limiter phases and four different divertor configurations. Glow discharge conditioning (GDC) was applied to complete the changeovers. The results are characterized by subdivertor optical and mass spectrometric gas analyzers and spatially resolved optical emission spectroscopy. A He content of 96–97 % after H operations is achieved by tens of ICWC pulses (JET) and several dedicated diverted plasmas (WEST and JET), while a fivefold is estimated to be required for the back transition. Effective pumping of the wall released species is a key parameter for a fast changeover. Upon applying higher heating power, the relative content of the fueled plasma species decreases. The JET gas balance analysis indicates that He operation may increase H retention. WEST divertor spectroscopy indicates a larger He inventory near the inner divertor strike line. He GDC has a clear effect on the He recycling light at the WEST divertor while D GDC did not reduce the long lasting He content observed in D pulses after the JET He campaign.

A Fractional Study of MHD Casson Fluid Motion With Thermal Radiative Flux and Heat Injection/Suction Mechanism Under Ramped Wall Condition: Application of Rabotnov Exponential Kernel

Abstract The primary objective of this research is to extend the concept of fractionalized Casson fluid flow. In this study, a comprehensive analysis of magnetohydrodynamic (MHD) natural convective flow of Casson fluid is conducted, focusing on obtaining analytical solutions using the non-integer-order derivative known as the Yang–Abdel-Aty–Cattani (YAC) operator. The YAC operator utilized in this research possesses a more generalized exponential kernel. The fluid flow is examined in the vicinity of an infinitely vertical plate with a characteristic velocity denoted as u 0. The mathematical modelling of the problem incorporates partial differential equations, incorporating Newtonian heating and ramped conditions. To facilitate the analysis, a suitable set of variables is introduced to transform the governing equations into a dimensionless form. The Laplace transform (LT) is then applied to the fractional system of equations, and the obtained results are presented in series form and also expressed in terms of special functions. The study further investigates the influence of relevant parameters, such as α, β, Pr , Q, Gr, M, Nr and K, on the fluid flow to reveal interesting findings. A comparison of different approaches reveals that the YAC method yields superior results compared to existing operators found in the literature. Graphs are generated to illustrate the outcomes effectively. Additionally, the research explores the limiting cases of the Casson and viscous fluid models to derive the classical form from the YAC fractionalized Casson fluid model.

Impact of plasma operating conditions on the ion energy and angular distributions in dual-frequency capacitively coupled plasma reactors using CF4 chemistry

A two-dimensional hybrid model is used to simulate an industrial dual-frequency capacitively coupled plasma reactor working at closely spaced frequencies (13.56–40.68 MHz) in pure CF4 chemistry. The goal is to understand how plasma operating conditions (pressure, low-frequency and high-frequency RF powers, and chamber wall conditions) influence critical etching parameters such as the ion energy and angular distribution (IEAD) and the ion flux at the wafer. In base case conditions, the ionic and radical composition at the center of the plasma is analyzed, revealing CF3+ and F− as the primary ions, and F, CF, CF3, CF2, and F2 as the predominant radicals (by decreasing density). The impact of the surface recombination coefficient of F radicals into F2 at the reactor walls, γ(rec,F &amp;gt; F2), is then explored; it is found that increasing γ(rec,F &amp;gt; F2) has a strong impact on the final plasma composition, decreasing CF and F densities while increasing CF3, CF2, and F densities, which highlights the importance of properly considering wall conditions in CF-based plasmas simulation. The IEAD at the wafer is then characterized, showing that the total IEAD shape is affected by the plasma ion composition: heavy ions such as CF3+ (69 amu) form the core of the distribution while lighter species such as F+ (19 amu) form the wing of the distribution due to their lower mass. The low frequency (LF) power (100–900 W) is shown to substantially modify the ion energy distribution function (IEDF) owing to sheath voltage changes, but to also marginally increase the ion flux at the wafer. Conversely, the high-frequency (HF) power (100–1500 W) strongly impacts the ion flux at the wafer due to HF voltage fluctuations, while the IEDF remains mostly unaffected. This study also reveals some coupling between the effects of the LF (13.56 MHz) and HF (40.68 MHz) power, a phenomenon attributable to their proximity in frequency which should not be neglected. Finally, increasing the pressure from 30 to 200 mTorr is found to increase the electronegativity by a factor 4 and to strongly impact the plasma structure, primarily due to variations in ion mobility; it also widens the ion angular spread, potentially influencing etch uniformity. Notably, higher pressures exceeding 100 mTorr result in a decrease in the average ion density and the emergence of a low-energy peak in the ion energy distribution, attributed to charge exchange collisions.

Condition of the vascular wall and uric acid level in men with low and moderate cardiovascular risk depending on body mass index

Condition of the vascular wall and uric acid level in men with low and moderate cardiovascular risk depending on body mass index

Варианты хирургического лечения хронического ателектаза верхнечелюстной пазухи (синдрома молчащего синуса)

Silent sinus syndrome is a fairly rare ENT pathology. It is still not possible to explain the exact cause of this syndrome. Modern equipment and accurate diagnostics provide the opportunity to make a diagnosis and choose the right treatment and rehabilitation tactics. The authors analyzed 36 patients from 2008 to 2024 who were admitted to the ENT department with symptoms of different nature and clinical manifestations, allowing making diagnosis silent sinus syndrome, to confirm which data on the course of the disease, radiological and endoscopic characteristics of the maxillary sinus were used. For surgical access, three options for opening the maxillary sinuses were used: through the middle and lower nasal passages as well as through the canine fossa. Access through the canine fossa (micro maxillary sinusotomy) with the formation of a persistent anastomosis in the middle and lower nasal meatus turned out to be the most optimal. The choice of location for opening the sinus was determined by the degree of prolapse of the orbital contents into the lumen of the sinus and the condition of the bone walls of the orbit. The article also presents a clinical case of complete opening of the maxillary sinus, with correctly formed bone walls and normal aeration of the sinus in a patient with this syndrome, after treatment.

Comparative Analysis of Pelvic Floor Muscle Damage Postpartum: Vaginal Delivery vs. Cesarean Section

Background. Evaluation of pelvic floor muscle (PFM) strength damage across different delivery modes, providing insights into potential preventive measures for pelvic floor dysfunctions (PFDs) in the early postpartum period. Aim. Compare the differences in PFM strength and endurance between full‐term cesarean section (CS) and vaginal delivery (VD) in the early postpartum period of primiparous women. Methods. The assessment included stress urinary incontinence (SUI), pelvic organ prolapse (POP), and pelvic floor electromyography (PFE). Muscle fiber strength was categorized into four modes at a threshold level of 3: I &lt; 3 II &lt; 3, I &lt; 3 II &gt; 3; I &gt; 3 II &lt; 3, I &gt; 3 II &gt; 3. Multinomial logistic regression was employed for CS and VD, and a sensitivity analysis was conducted using level 2 as the threshold. Outcomes. When muscle fiber strength was categorized into four modes at a threshold level of 3, Type I, and Type II fiber muscle endurance (FME) are differences between the CS and VD groups. Results. The CS and VD groups differed significantly in SUI and anterior and posterior vaginal wall conditions. MDVP was below the normal range in both groups, and MDVP, PFM strength, and PFM endurance did not differ significantly (P &gt; 0.05). Logistic regression results indicated that higher MDVP, Type I, and Type II FME were protective factors when I &lt; 3 in the VD group. However, I &lt; 3‐II &gt; 3, higher MDVP, and Type I FME were protective factors (OR: 0.339, 95% CI: 0.223, 0.516) in the CS group. Clinical Implications. The study introduces a nuanced understanding of the impact of different delivery modes on PFM, contributing valuable insights for clinical prevention and treatment strategies in the early postpartum period. Strengths and Limitations. Muscle fiber strength was categorized into four modes and further sensitivity analysis was conducted. This study only conducted a correlation analysis of outcome variables without considering intervenable variables. Conclusions. The VD group had a higher incidence of pelvic floor dysfunction in the early postpartum period than the CS group. Both groups experienced a decline in PFM function without significant differences. CS was primarily associated with Type I muscle fiber damage, while VD was related to both Type I and II muscle fiber damage. Improving PFM endurance is beneficial for muscle strength recovery.

Theoretical analysis of radiation effects in laminar flow over a von-Kármán body of revolution

An analysis presents the impact of thermal radiation on the laminar boundary layer established due to the motion of a von-Kármán surface. The reason for choosing such a shape is its appearance in many aeronautical vehicles, especially the F-16 fighter jet nose cone. However, the transverse curvature effects are also observable in many other shapes of bodies of revolution. But considering such a practical body of revolution provides a chance to quantify the transport phenomena happening on sophisticated aerospace vehicles. As a result, a correct understanding of the momentum and the thermal process in actual situations can be achieved. Power-law form of wall temperature is assumed to cover a variety of non-isothermal wall conditions. The typical body contour of a von-Kármán surface does not allow the scaling symmetry in the longitudinal direction; thus making the flow of non-similar in nature. An efficient numerical scheme (Keller–Box) with the second order accuracy is used for the solution purposes. The results are found to be satisfactory regarding the previous published work for moving cylinder cases. This ensures the validity of the tabulated data for the von-Kármán surface case. Through numerous tables and graphs, the impacts of thermal radiation parameter, wall temperature exponent, and transverse curvature parameter have been highlighted and thoroughly analyzed. Once the radiation parameter is increased, it is noticed that the rate of heat transfer increases and the thermal thickness of the boundary layer grows, whereas the reverse behavior is seen when the wall temperature exponent is increased. Furthermore, it has been found that increasing the surface transverse curvature increases the thermal thickness of the boundary layer and the rate of heat transfer. To the considered body shape, the reported data are expected to serve as a good source for the development of approximate methods concerning complex flow geometries involving transverse curvature effects.

Al heat affected zone-less resistance element welded lap joints of Al alloy and 1 GPa class steel: Transition of microstructure and fracture with heat transfer

In this study, Al joint systems without heat-affected zones (HAZ) were developed on Al/Fe alloy lap joints fabricated by resistance element welding (REW). The robustness of the joints with and without HAZs was quantitatively evaluated to consider another side effect in REW Al/Fe alloy systems. Compared to conventional REW, removing the Al HAZ not only alters the steel properties, but also reduces the work hardening of the Al alloy due to the difference in the distinct heat transfer paths. Furthermore, the presence of Al HAZ significantly influenced the hardness characteristics of the molten steel portion. In the cold wall configuration without Al HAZ, hardness values exceeding those of the hot wall by approximately 100 Hv or more were observed. At a welding current of 10.5 kA, the hot wall configuration demonstrated an approximate 30 % increase in tensile shear load and a 66 % increase in displacement compared to the cold wall configuration without HAZ. In the cold wall conditions, interfacial failure (IF) was not attributed to microstructural disparities but was linked to the formation of an inherent notch root when S20C melted due to the absence of Al HAZ. Contrary to previous reports, the presence of HAZ in Al alloys results the production of tough steel through REW.

Studies of the material erosion and deposition during the wall conditioning processes using quartz crystal microbalance in EAST

To study material erosion and deposition during different wall conditioning processes in the Experimental Advanced Superconducting Tokamak (EAST), two newly developed quartz crystal microbalances (QMBs) at the mid-plane of port C (C-QMB) and port J (J-QMB) with the same radial radius were used for in-situ and real-time measurements during the 2021 autumn experimental campaign. It was found that the material deposition was mainly influenced by the location of the antenna and the power of the ion cyclotron range of frequency (ICRF), rather than the location of the gas inlet, during the wall cleaning with helium plasma and siliconization assisted with ICRF plasma. The higher energy and density of plasma could result in higher deposition rates near the antenna. While, during lithium (Li) coating, the material deposition was greatly influenced by the location of the Li oven due to the deposition of unionized Li atoms. The ICRF power influenced the material deposition behavior far away from the Li ovens. Besides, a stronger effect on impurity suppression was observed with a more uniform deposition trend of Li coating. This necessitates further study on the influence of factors such as the location of the Li oven and ICRF antenna, the temperature of ovens, and ICRF power on the homogeneity of wall conditioning.