Search Results (85)

Cobalt-based perovskite oxides exhibit remarkable catalytic activity owing to abundant oxygen vacancies and mixed ionic–electronic conductivity, but they suffer from structural instability. In contrast, iron-based perovskite oxides are thermochemically stable under oxidizing and reducing conditions but are catalytically limited. To combine these complementary properties, a composite perovskite oxide was designed and prepared by infiltrating Sr_0.95Ce_0.05CoO_3−δ (SCC) into Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ (BSFC). The SCC precursor solution was dropwise applied to a BSFC|SDC|BSFC symmetric cell and heat treated. Surface morphology and compositional analyses confirmed the distribution of SCC nanoparticles on the BSFC surface. High-temperature X-ray diffraction and Rietveld refinement results revealed that both BSFC and SCC retained the cubic perovskite structure (space group Pm-3m) at room temperature. No phase transition or secondary phase formation was observed during heating from 200 to 800 °C, and the peak shifts are attributed to thermal expansion and possible oxygen loss at elevated temperatures. Upon cooling, the diffraction patterns returned to their initial state, confirming a high-temperature structural stability. XPS analysis showed an increase in the satellite peak intensity associated with Fe³⁺ after SCC infiltration, and the average oxidation state of Fe decreased from 3.52 (BSFC) to 3.49 (composite perovskite oxide). The O 1s spectra revealed a higher relative content of surface-adsorbed oxygen species in the composite, indicating increased oxygen vacancy formation. Full article

The thick-walled thickness effect in layered-symmetrical structure is very important for considering the external thermal heating on the surface of functionally graded material (FGM) plates. Dynamic thermal vibration with advanced shear correction on the FGM plates are presented. The third-order shear deformation theory (TSDT) is included to calculate the values of advanced shear correction for the thick plates based on the displacement assumed in the middle symmetry plane. The values of advanced shear correction coefficient are in nonlinear variation with respect to the power-law index value for FGM. The dynamic stresses are calculated when the displacements and shear rotations are obtained for the given natural frequency of displacements, frequency of applied heat flux and time. The natural frequencies of sinusoidal displacements and shear rotations are obtained by using the determinant of the coefficient matrix in the fully homogeneous equation. Only the numerical dynamic results of displacements and stresses subjected to sinusoidal applied heat loads are investigated. The heating study in symmetry structure of FGMs to induce thermal vibration is interesting in the field of engineering and materials. The center displacements can withstand a higher temperature of 1000 K and a power-law index of 5, for which the length-to-thickness ratio 5 is better than that for 10. Full article

This paper introduces a novel MEMS-based thermal flow sensor designed for high sensitivity and linearity across a wide range of gas flow velocities. The sensor incorporates a single microheater and two pairs of thermistors symmetrically arranged around the heater, with strategically placed obstacles to enhance performance. To ensure accuracy under varying flow conditions, the sensor is divided into two functional regions: one optimized for low flow velocities (0–1 m/s) and the other for high flow velocities (1–6 m/s). Simulations conducted using COMSOL Multiphysics reveal that including obstacles improves heat transfer and increases the interaction time between the heated surface and the flow, particularly in the high-flow region. In the low-flow regime, the sensor achieves a sensitivity of 2.5 SK/m with 91% linearity. In contrast, in the high-flow regime, the sensitivity increases to 6.5 SK/m with similarly high linearity. This dual-region design highlights the sensor’s versatility in handling a broad range of flow velocities, making it suitable for applications in medical, industrial, and environmental monitoring. These findings underscore the advantages of the dual-region design and obstacle integration, providing a robust solution for accurate flow measurement under diverse operating conditions. Full article

Surface roughness plays a vital role in determining surface integrity and function. Surface irregularities or reduced quality near the surface can contribute to material failure. Surface roughness is considered a crucial factor in estimating the fatigue life of structures welded by FSW. This study attempts to provide a deeper understanding of the nature of the surface formation and roughness of aluminum joints during FSW processes. In order to form more efficient joints, the frictional temperature generated was monitored until reaching 450 °C, where the transverse movement of the tool and the joint welding began. Hardness and tensile tests showed that the formed joints were good, which paved the way for more reliable surface roughness measurements. The surface roughness of the weld joint was measured along the weld line at three symmetrical levels using welding parameters that included a rotational speed of 1250 rpm, a welding speed of 71 mm/min, and a tilt angle of 1.5°. The average hardness in the stir zone was measured at 64 HV, compared to 50 HV in the base material, indicating a strengthening effect induced by the welding process. In terms of tensile strength, the FSW joint exhibited a maximum force of 2.759 kN. Average roughness (Rz), arithmetic center roughness (Ra), and maximum peak-to-valley height (Rt) were measured. The results showed that along the weld line and at all levels, the roughness coefficients (Rz, Ra, and Rt) gradually increased from the beginning of the weld line to its end. The roughness Rz varies from start to finish, ranging between 9.84 μm and 16.87 μm on the RS and 8.77 μm and 13.98 μm on the AS, leveling off slightly toward the end as the heat input stabilizes. The obtained surface roughness and mechanical properties can give an in-depth understanding of the joint surface forming and increase the ability to overcome cracks and defects. Consequently, this approach, using adaptive thresholding image processing coupled with grayscale histogram analysis, yielded significant understanding of the FSW joint’s surface texture. Full article

The study introduces new technologies of microfinishing, which are primarily aimed at cylindrical surfaces but with machining effectiveness, precision, and surface longevity. In the newly proposed dual-zone microfinishing method, symmetrical abrasive film feeding systems are adapted with a lever mechanism and a pivoting pressing assembly to simultaneously conduct processing in two zones. With such a design, uniform force distribution is ensured, while mechanical deformation is reduced to raise the utility of the abrasive film and lower scraps for better economic performance. Also, the application of microfinishing operations combined with carbon layer deposition using graphite-impregnated abrasive films is introduced as a novel method. This process combines surface refinement and the forming of wear-resistant carbon coatings into one single operation, resulting in increased wear resistance and reduced forces of friction. Further stabilization of the conditions for microfinishing is achieved by immersing the processing zone in a fluid medium due to increased lubrication, improvement in heat dissipation, and the optimization of surface properties. It is particularly suitable for high-precision applications and a maintenance-free environment such as military, vacuum, and low-temperature systems. The experimental results show the effectiveness of the proposed methodologies, underscoring their ability to create remarkably smooth surfaces and very robust carbon textures simultaneously. Full article

Nowadays, effective thermal management is essential to prevent overheating in high-power devices. The utilization of high-emissivity materials plays a crucial role in enhancing heat transfer efficiency in both natural and mixed convection systems. This study presents an experimental investigation of a rectangular fin heat sink’s thermal performance, exploring the effect of mixed convection and radiation heat transfer on two symmetrical fins with an aspect ratio of ${\mathrm{S}}^{\mathrm{*}}=$ 0.4 and 0.8. The experiment was carried out in a laboratory-scale wind tunnel, where the inlet fluid velocity was maintained at a constant value of u = 0.3 m/s across a range of Richardson number (0.6–5) and Rayleigh number (1.09–9.15 $\times {10}^5$), corresponding to the variation of heat loads 18–100 W. High-emissivity paint (ε = 0.85) was applied to the heat sink fins and compared to a low-emissivity paint (ε = 0.05) to assess the effect of performance. The results reveal that the high emissivity fin dissipated heat more effectively, with radiation and convection contributing approximately 25% and 75%, respectively, at the highest Rayleigh number. The study also revealed that increased fin spacing enhanced the view factor, although radiation heat transfer was higher for lower fin spacing due to a greater number of fins. Additionally, fin effectiveness was influenced more by fin spacing compared to surface emissivity, with effectiveness decreasing at higher Rayleigh numbers across all conditions. Infrared (IR) imaging confirmed that the high-emissivity coating allowed the heat sink to dissipate up to 30 °C from the heated surface, underscoring the substantial impact of high-emissivity materials in thermal management applications. Full article

The main purpose of this paper was to determine and compare the boundary conditions of heat transfer on the cooled surface of a cylindrical sensor made of Inconel 600 alloy while cooling with a water jet, water spray and air-assisted water spray under high-temperature conditions. The inverse method for the heat conduction equation was used to determine the boundary conditions. Experimental tests were carried out, including temperature measurements at several points inside the cylinder while cooling with all the tested systems from a temperature of 900 °C for three values of water pressure: 0.05 MPa, 0.1 MPa and 0.2 MPa. Temperature measurements were used as the input data to identify the heat transfer boundary conditions. The temperature field of the axially symmetric sensor was determined using the finite element method. The boundary conditions were determined as average values of the heat transfer coefficient and heat flux and local values of the heat transfer coefficient. A comparison of the amount of thermal energy dissipating from the sensor surface as a result of boiling and a forced single-phase convection is also presented in the paper. The highest uniformity of cooling was obtained during air-assisted water spray-cooling. Full article

As one of the most critical components in lithium-ion batteries (LIBs), commercial polyolefin separators suffer from drawbacks such as poor thermal stability and the inability to inhibit the growth of dendrites, which seriously threaten the safety of LIBs. In this study, we prepared calcium alginate fiber/boron nitride-compliant separators (CA@BN) through paper-making technology and the surface coating method using calcium alginate fiber and boron nitride. The CA@BN had favorable electrolyte wettability, flame retardancy, and thermal dimensional stability of the biomass fiber separator. Meanwhile, the boron nitride coating provided excellent thermal conductivity and mechanical strength for the composite separator, which inhibited the growth of lithium dendrites and enabled lithium-ion symmetric batteries to achieve more than 1000 stable and long cycles at a current density of 0.5 mA cm⁻². The interwoven fiber mesh formed by the boron nitride coating and the calcium alginate provided multiple pathways for ion migration, which enhanced the storage capacity of the electrolyte, improved the interfacial compatibility between the separator and the electrode, widened the window of electrochemical stability, and enhanced ionic migration. This eco-friendly bio-based separator paves a new insight for the design of heat-resistance separators as well as the safe running of LIBs. Full article

The influences of surface layer (SL) physics schemes on the simulated intensity and structure of Typhoon Rai (2021) are investigated using the WRF model. Numerical experiments using different SL physics schemes—revised MM5 scheme (MM5), Eta similarity scheme (CTL), and Mellor–Yamada–Nakanishi–Niino scheme (MYNN)—are conducted. The results show that the intensity forecast of Typhoon Rai is largely influenced by SL physics schemes, while its track forecast is not significantly affected. All three experiments can successfully capture the movement of Rai, while CTL provides better intensity simulation compared to the other two experiments. The higher ratio of enthalpy exchange coefficient to drag coefficient (C_K/C_D) in CTL than MM5 and MYNN leads to significantly increased surface enthalpy fluxes, which are crucial for the typhoon intensification of the former. To explore the influence of SL physics on the structural evolution of the typhoon, the azimuthal-mean angular momentum (AM) budget is utilized. The results indicate that asymmetric eddy terms may also largely contribute to the AM tendencies, which are relatively more comparable in the weaker TC for MM5, compared to the stronger TC with the dominant symmetric mean terms for CTL. Furthermore, the extended Sawyer–Eliassen (SE) equation is solved to quantify the transverse circulations of the typhoon induced by different forcing sources for CTL and MM5. The SE solution indicates that the transverse circulation above and within the boundary layer is predominantly induced by diabatic heating and turbulent friction, respectively, for both CTL and MM5, while all other physical forcing terms are relatively insignificant for the induced transverse circulation for CTL, except for the large contribution from the eddy forcing in the upper-tropospheric outflow for MM5. With the stronger connective heating in the eyewall and boundary-layer radial inflow, the linear SE analysis agrees much better with the nonlinear simulation for CTL than MM5. Full article

In this study, a kind of in-fiber Mach–Zehnder interferometer (MZI) is designed and experimentally examined. The MZI is composed of two in-fiber S-shaped cores (SSCs), which enhance strain sensitivity. To prepare the SSCs, a high-frequency CO₂ laser is first utilized to polish grooves on the symmetrical surface of a single-mode fiber (SMF). The polished area is then subjected to arc-discharging by a commercial fusion splicer, and the core of the fiber bends towards the polished grooves due to the self-roundness of the cladding and the heating effect of discharge. The results of the experiments demonstrate that the sensor achieves high strain sensitivities of −66.5 pm/με and −40.1 pm/με within the strain range of 0 με to 350 με. By solving the matrix equation, simultaneous online measurements of temperature and strain can be performed. With the advantages of easy fabrication, low cost, high sensitivity, and compactness, the proposed sensor is a competitive candidate in strain sensing. Full article

The phenomenon of natural convection is the subject of significant research interest due to its widespread occurrence in both natural and industrial contexts. This study focuses on investigating natural convection phenomena within triangular enclosures, specifically emphasizing a valley-shaped configuration. Our research comprehensively analyses unsteady, non-dimensional time-varying convection resulting from natural fluid flow within a valley-shaped cavity, where the inclined walls serve as hot surfaces and the top wall functions as a cold surface. We explore unsteady natural convection flows in this cavity, utilizing air as the operating fluid, considering a range of Rayleigh numbers from Ra = 10⁰ to 10⁸. Additionally, various non-dimensional times τ, spanning from 0 to 5000, are examined, with a fixed Prandtl number (Pr = 0.71) and aspect ratio (A = 0.5). Employing a two-dimensional framework for numerical analysis, our study focuses on identifying unstable flow mechanisms characterized by different non-dimensional times, including symmetric, asymmetric, and unsteady flow patterns. The numerical results reveal that natural convection flows remain steady in the symmetric state for Rayleigh values ranging from 10⁰ to 7 × 10³. Asymmetric flow occurs when the Ra surpasses 7 × 10³. Under the asymmetric condition, flow arrives in an unsteady stage before stabilizing at the fully formed stage for 7 × 10³ < Ra < 10⁷. This study demonstrates that periodic unsteady flows shift into chaotic situations during the transitional stage before transferring to periodic behavior in the developed stage, but the chaotic flow remains predominant in the unsteady regime with larger Rayleigh numbers. Furthermore, we present an analysis of heat transfer within the cavity, discussing and quantifying its dependence on the Rayleigh number. Full article

Ice detection poses significant challenges in sectors such as renewable energy and aviation due to its adverse effects on aircraft performance and wind energy production. Ice buildup alters the surface characteristics of aircraft wings or wind turbine blades, inducing airflow separation and diminishing the aerodynamic properties of these structures. While various approaches have been proposed to address icing effects, including chemical solutions, pneumatic systems, and heating systems, these solutions are often costly and limited in scope. To enhance the cost-effectiveness of ice protection systems, reliable information about current icing conditions, particularly in the early stages, is crucial. Ultrasonic guided waves offer a promising solution for ice detection, enabling integration into critical structures and providing coverage over larger areas. However, existing techniques primarily focus on detecting thick ice layers, leaving a gap in early-stage detection. This paper proposes an approach based on high-order symmetric modes to detect thin ice formation with thicknesses up to a few hundred microns. The method involves measuring the group velocity of the S₁ mode at different temperatures and correlating velocity changes with ice layer formation. Experimental verification of the proposed approach was conducted using a novel group velocity dispersion curve reconstruction method, allowing for the tracking of propagating modes in the structure. Copper samples without and with special superhydrophobic multiscale coatings designed to prevent ice formation were employed for the experiments. The results demonstrated successful detection of ice formation and enabled differentiation between the coated and uncoated cases. Therefore, the proposed approach can be effectively used for early-stage monitoring of ice growth and evaluating the performance of anti-icing coatings, offering promising advancements in ice detection and prevention for critical applications. Full article

In this study, the combination of ordinary cement concrete (OCC) and shrinkage-compensating concrete (SCC) was utilized to pour super-long mass concrete. The temperature and strain of the concrete were continuously monitored and managed actively after pouring. The investigation focused on the temporal and spatial distribution patterns of the temperature field, the temperature difference between the core and surface, and the strain evolution. Based on the constructed hydration exothermic model of layered poured concrete, the effects of the SCC, molding temperature, and surface heat transfer coefficient on the temperature field were analyzed. The results show that the temperature of super-long mass concrete rises quickly but falls slowly. SCC exhibits higher total hydration heat than OCC. The temperature field is symmetric along the length but asymmetric along the thickness due to varying efficiency of heat dissipation between the upper and lower parts of the concrete. After final setting of the concrete, the strain varies opposite to the temperature and peaks at −278 με. A few short cracks are observed on the end of the upper surface. Moreover, the numerical simulation results are in good agreement with the measured results. Increasing the molding temperature and surface wind speed increases the temperature difference between the core and surface. Conversely, increasing the thickness of the insulation layer is an effective way to curtail this difference. Thermal stress analysis is carried out and shows that lowering the molding temperature of SCC and increasing the thickness of insulation material can effectively reduce thermal stress. Full article

In this paper, a microheater that can absorb thermal stress and has a large heating area is demonstrated by optimizing the structure and process of the microheater. Four symmetrically distributed elongated support beam structures were machined around the microheater via deep silicon etching. This design efficiently mitigates the deformation of the heated region caused by thermal expansion and enhances the structural stability of the microheater. The updated microheater no longer converts the work area into a thin film; instead, it creates a stable heating platform that can uniformly heat a work area measuring 10 × 10 mm². The microheater is verified to have high temperature uniformity and structural stability in finite element simulation. Finally, thorough investigations of electrical–thermal–structural characterization were conducted. The test findings show that the new microheater can achieve 350 °C with a power consumption of 6 W and a thermal reaction time of 22 s. A scan of its whole plane reveals that the surface of the working area of the new microheater is flat and does not distort in response to variations in temperature, offering good structural stability. Full article

The present study initially evaluates the feasibility of deep learning models to predict the flow and thermal fields of a wing with a symmetric wavy disturbance as the passive flow control. The present study developed the encoder–decoder (ED) and convolutional neural network (CNN) models to predict the characteristics of flow and heat transfer on the surface of three-dimensional wavy wings in a wide range of parameters, such as the aspect ratio, wave amplitude, wave number, and the angle of attack. Computational fluid dynamics (CFD) is used to generate the dataset of the deep learning models. Various tests are carried out to examine the predictive performance of the architectures for two deep learning models. The CNN and ED models demonstrated a quantitatively predictive performance for aerodynamic coefficients and Nusselt numbers, as well as a qualitative prediction for pressure contours, limiting streamlines, and Nusselt contours. The predicted results well reconstructed the spiral vortical formation and the separation delay by the limiting streamlines. It is expected that the present established deep learning methods are useful to perform the parametric study to find the conditions to provide efficient aerodynamic and thermal performances. Full article