Decreasing Film Thickness Research Articles

Effects of Heat Transfer Characteristics of R32 and R1234yf with Al2O3 Nanoparticle through U-Bend Tube Evaporator

This study used the Ansys Fluent® computational fluid dynamics code in conjunction with a volume of fluid multiphase model and phase-change model to analyze the flow boiling evaporation heat transfer coefficient and flow patterns of R32 and R1234yf with Al2O3 nanoparticle through the U-bend tube with a curvature ratio for downward-oriented flow. The volume of fluid (VOF) model was used to follow the patterns at the interface, while the SST k-omega model was used to simulate the gas-liquid flow. This work has been validated by utilizing a R134a refrigerant. Simulations were performed at various mass fluxes, vapor qualities, and temperatures to determine the effects of these variables on heat transfer and frictional pressure decrease in the tube. R1234yf shows much better performance than the other pure refrigerants in terms of heat transfer and vaporization. The addition of nanoparticle Al2O3 with the refrigerants R32 and R1234yf significantly improved the heat transfer coefficient and increased the vapor fraction. The frictional pressure drop increases with increasing mass flux and decreases with increasing vapor quality due to a significant decrease in the liquid film thickness. The heat transfer coefficient, on the other hand, increases with increasing mass flux and decreases with vapor quality up to a point. There are certain changes in the heat transfer coefficient at the bend. After the bend, the frictional pressure drop increased at a higher rate than before the bend, and the vapor fraction increased at a higher rate.

Modeling and analysis of 3D mixed lubrication in marine cam–tappet pair

During the operation of the marine cam–tappet pair, affected by periodic dynamic load, transient velocity, and micromorphology, it usually operates in a mixed lubrication state. Under extreme operational conditions, contact is likely to occur at the asperity of the interface, leading to problems such as stress concentration and dry contact. Considering the transient dynamics and three-dimensional roughness of cam–tappet pair, a mixed-elastohydrodynamic lubrication model is developed in this article, while the effects of surface waviness on the lubrication state are also investigated. The results show that the film thickness can be increased by 0.098 μm, and the coefficient of friction can be reduced by 10.6% when the wavelength ratio ranges from 1/6 to 6. However, when the amplitude exceeds 0.6 μm, the coefficient of friction may reach 0.10. Under conditions of low speed and high load, the film thickness decreases and contact load ratio increases. And about 30% reduction in film thickness is achieved on cam–tappet pair, potentially leading to increased wear or scuffing failure.

Simultaneous film temperature and film thickness measurements for jet impingement applications using two-color laser-induced fluorescence

The study investigates a jet impingement cooling process of a cylindrical geometry relevant for electric and electronic applications. The applied two-color detection technique enables a simultaneous determination of film temperature and film thickness. For this purpose, the heat transfer oil Marlotherm LH was doped with the temperature-sensitive fluorescence tracer nile red. The temperature determination was realized by suitable band pass filters. Preliminary spectral investigations were carried out in terms of varying dye concentration, temperature and film thickness. At high dye concentrations (up to 37.5 mg/L), reabsorption effects lead to a spectral shift toward higher wavelengths with increasing film thickness. Low dye concentrations (0.29 mg/L, 0.59 mg/L) show no film thickness dependent spectral shift. A film temperature investigation at low dye concentration showed no bias of the intensity ratio due to film thickness, i.e., no additional spectral shift toward lower wavelengths was observed. The investigations on the jet impingement setup revealed an increasing film temperature and decreasing film thickness with increasing solid temperature. The average film temperature increases with increasing solid temperature from 298 (solid temperature 298 K) to 308 K (solid temperature 398 K). At higher solid temperatures, the film temperature increases with distance to the stagnation zone. The average film thickness decreases with increasing solid temperature from 0.24 to 0.17 mm. At high solid temperatures, the film temperature increased with radial distance to the stagnation zone. This behavior is caused by the increasing temperature gradient with increasing solid temperature and decreasing viscosity with increasing film temperature.

On interaction between a bubble with evaporation and heated pillar block in microchannel

As demand for managing high heat flux in specialized applications grows, flow boiling in microchannels has received escalating attention for its high efficiency and cost-effectiveness. The complex interaction between an evaporating bubble and a heated pillar in a microchannel is governed by a confluence of transport mechanisms, including bubble morphology, fluid convection, heat transfer, and phase change phenomena. This study develops a three-dimensional mathematical model, employing the saturated-interface-volume approach to simulate the complex interaction process effectively. The results indicate that the liquid film thickness between the bubble and the heated surface is the primary factor affecting heat transfer. A reduction in the Reynolds number as well as an increase in the initial bubble diameter lead to a decrease in the liquid film thickness and an increase in the temperature gradient within the thin liquid film, which enhance both the evaporation rate and heat transfer efficiency. The temperature of the surrounding fluid is also decreased. The bubble passage disrupts the flow structure, particularly impacting the boundary layer and vortex structure. These perturbations in temperature and flow structure constitute a secondary factor influencing heat transfer. The efficiency of heat transfer varies significantly across different surfaces; surfaces with a larger thin liquid film region exhibit the most significant improvement, followed by the downstream surface where the flow and temperature fields are most affected. This study advances the fundamental comprehension of the complex interaction between an evaporating bubble and a heated pillar in a microchannel, integrating a detailed analysis of the relevant transport mechanisms.

Water Film Structure and Wettability of Different Quartz Surfaces: Hydrogen Bonding Across Various Cutting Planes.

Quartz is ubiquitous in subsurface formations. The crystal faces have different atomic arrangements. Knowledge of the molecular structures on the surface of quartz is key in many processes. Molecular dynamics simulations are conducted to investigate the atomic arrangement effect on the water film structure, ion adsorption, and wettability at three different α-quartz surfaces. The interfacial structures depend on the quartz surface. Intrasurface hydrogen bonding between surface silanols differs in the α-quartz surface. At the (0001) surface, the OH density is 9.58 nm-2, consisting of Q2 units with two hydroxyl groups per silicone atom. At the (101̅0)-β surface, the OH density is 7.54 nm-2, consisting of Q3 units with one hydroxyl group per silicone atom; there is significant intrasurface hydrogen bonding. At the (101̅0)-α surface, the OH density is 7.54 nm-2, consisting of Q2 units; however, there is little intrasurface hydrogen bonding. The intrasurface hydrogen bonding results in the exposure of hydrogen-bond acceptors to the aqueous phase, causing water molecules to have an H-up (hydrogen toward surface) orientation. This orientation can be found at the (0001) and (101̅0)-β surfaces; it is related to the degree of ordering at the surface. The ordering at the (0001) and (101̅0)-β surfaces is higher than that at the (101̅0)-α surface. In aqueous systems with ions, cation adsorption is the most dominant at the (0001) surface due to the largest surface density of the intrasurface hydrogen bonding, providing interaction sites for cations to be adsorbed. We observe a pronounced decrease in water film thickness from the ions at the (0001) surface only, likely due to significant cation adsorption. In this work, we demonstrate that the hydrogen-bond network, which varies from the plane cut, affects the water film structure and ion adsorption. The contact is nearly zero despite the changes in the film thickness and molecular structure at the temperature of 318 K.

Ultrathin Limit on the Anisotropic Superconductivity of Single-Layered Cuprate Films

Exploring dimensionality effects on cuprates is important for understanding the nature of high-temperature superconductivity. By atomically layer-by-layer growth with oxide molecular beam epitaxy, we demonstrate that La2–x Sr x CuO4 (x = 0.15) thin films remain superconducting down to 2 unit cells of thickness but quickly reach the maximum superconducting transition temperature at and above 4 unit cells. By fitting the critical magnetic field (μ 0 H c2), we show that the anisotropy of the film’s superconductivity increases with decreasing film thickness, indicating that the superconductivity of the film gradually evolves from weak three- to two-dimensional character. These results are helpful to gain more insight into the nature of high-temperature superconductivity with dimensionality.

Study on Urea Crystallization Risk Assessment and Influencing Factors in After-Treatment System of Diesel Engines

In order to meet the increasing pollutants discharge standard, the selective catalytic reduction (SCR) module in the diesel engine after-treatment system is an important means to reduce nitrogen oxide (NOx) emissions. SCR systems are prone to urea crystallization at lower temperatures, especially during the cold-start conditions of diesel engines. In this study, we use the diesel engine after-treatment system test bench to obtain the boundary parameter of the simulation modules, and the urea crystallization risk assessment model of the diesel SCR system is established. Comparing the computational fluid dynamics (CFD) results with the test bench results, it is shown that the predicted urea film distribution of the assessment model is in good agreement with the experimental results. In order to clarify the various factors that affect the urea crystallization risk, this paper conducts a simulation analysis on a nozzle and mixer structure and operating parameters. The CFD results indicate that the increase in urea spray time will increase the maximum urea film thickness on the SCR system mixer surface. Exhaust temperature is the most important influencing factor. When the diesel engine exhaust temperature increases from 190 °C to 300 °C, the maximum urea film thickness decreases by 32 and the urea film mass accumulation decreases by 5%. Exhaust flow has a small impact on urea crystallization risk. When the exhaust flow increases from 300 kg/h to 600 kg/h, the maximum urea film thickness decreases by 39% and the urea film mass accumulation decreases by about 1%. In addition, urea spray rate, nozzle numbers, spray angle, and spray cone angle are also factors that affect urea crystallization risk.

Spatiotemporal mapping of nanotopography and thickness transitions of ultrathin foam films.

Freshly formed soap films, soap bubbles, or foam films display iridescent colors due to thin film interference that changes as squeeze flow drives drainage and a progressive decrease in film thickness. Ultrathin (thickness <100 nm) freestanding films of soft matter containing micelles, particles, polyelectrolyte-surfactant complexes, or other supramolecular structures or liquid crystalline phases display drainage via stratification. A fascinating array of thickness variations and transitions, including stepwise thinning and coexistence of thick-thin flat regions, arise in micellar foam films that undergo drainage via stratification. In this tutorial, we describe the IDIOM (interferometry digital imaging optical microscopy) protocols that combine the conventional interferometry principle with digital filtration and image analysis to obtain nanometer accuracy for thickness determination while having high spatial and temporal resolution. We provide fully executable image analysis codes and algorithms for the analysis of nanotopography and summarize some of the unique insights obtained for stratified micellar foam films.

Axial and azimuthal development of disturbance waves in annular flow in a horizontal pipe

Transformation of gas-liquid flow in a horizontal pipe is investigated during the transition from stratified to annular flow pattern. Using Brightness-Based Laser-Induced Fluorescence technique, spatiotemporal evolution of liquid film thickness is analyzed over the downstream distance range of about 900 mm (45 pipe diameters), starting from the inlet. The measurements are carried out for three values of azimuthal angle θ: 0 (pipe bottom), 90°, and 180°, to track the circumferential spreading of liquid film and disturbance waves. At large gas velocities, thin liquid film is dragged upwards before the formation of large waves. The disturbance waves are created at the pipe bottom and spread circumferentially as they propagate downstream, over the already-wetted pipe walls. At large enough liquid flow rates, the spreading disturbance waves reach the pipe ceiling and form full rings around the circumference. The frequency and velocity of the disturbance waves eventually become the same around the pipe circumference; the disturbance wave amplitude and the base film thickness decrease with θ. The base film is more uniform around the circumference compared to the wave amplitude. At lower liquid flow rates, the disturbance waves cover only a part of pipe circumference. Their edges demonstrate oscillatory circumferential spreading, which ends by deceleration and decay of the edges. The upper part of the pipe may be wetted by a thin base film layer, covered only with ripples, or remain dry. At low gas speeds and large liquid flow rates, occasional splashing of large waves over the pipe ceiling without pre-wetting by the thin film is possible; however, the remaining film drains downward and no stable annular film is maintained. Liquid droplets, entrained from the pipe bottom and depositing in the upper parts of the pipe, are gathered in trains of creeping pendant droplets at the very top part of the pipe; no continuous wetting is achieved due to droplet deposition.

Influence of Heat Source on Thin Film Flow of Ferrofluid Past an Unsteady Stretching Sheet

In this work, the impact of a heat source on the thin-film ferrofluid flow over an unstable stretching sheet in the presence of an external magnetic field has been examined. The governing partial differential equations are transformed into a system of ordinary differential equations by similarity transformation. The resultant system of ordinary differential equations is solved numerically through shooting technique involving Runge-Kutta-Fehlberg (RKF45) method. To improve the initial guess values, the Newton-Raphson method is used. The significance of magnetization parameter, Prandtl number and heat source parameter on the flow and heat transmission process have been graphically analysed. The decrease in film thickness is observed for growing values of heat source parameter.

Numerical investigation and analysis of heat transfer and thin film flow of Fe3O4 and Al2O3 nanoparticles dispersed in H2O over vertical stretching sheet

Purpose This article presents a numerical investigation of thin film flow and heat transfer for lamina, tetrahedron, and hexahedron-shaped nanomaterials of F e 3 O 4 and A l 2 O 3 over a time-dependent radially vertical stretching surface. Moreover, magnetohydrodynamics and viscous dissipation effects are also incorporated. Thin-film treatment is especially beneficial in nanotechnology. As a result, the current study’s findings will be useful in a variety of thin film phenomena involving nanoparticles. F e 3 O 4 thin films have considerable potential in a variety of applications, including sensors and batteries. Aluminum oxide nanoparticles have two key applications: medicines and the materials manufacturing industries. Methodology A similarity transformation is employed to produce the nonlinear governing system of equations, which is numerically solved using the BVP4C method in MATLAB. As film thickness depends on the unsteadiness parameter, with an increase in the parameter causing a decrease in film thickness ( β ) , velocity, and temperature. Findings The lamina and hexahedron shapes provide maximum and minimum film thickness for F e 3 O 4 and A l 2 O 3 both nanoparticles, while the hexahedron and lamina shapes generate maximum and minimum skin friction. The Nusselt numbers exhibit the opposite effect. The highest and lowest heat transfer rates are noticed for lamina and hexahedron-shaped nanoparticles of A l 2 O 3 .

Direct measurement and modeling of viscoelastic-viscoplastic properties of freely standing thin polystyrene films.

The demand for applications, such as coatings, separation filters, and electronic packaging, has greatly driven the research of polymer films. At nanometer scale, mechanical properties of thin polymer films can significantly deviate from bulk. Despite outstanding progresses, there still lack deep discussions on nonlinear viscoelastic-viscoplastic response and their interactions under nanoconfinement. In this work, by conducting measurements via the bubble inflation method and modelling using Schapery and Perzyna equations, we demonstrate nonlinear viscoelastic-viscoplastic properties of freely standing thin polystyrene (PS) films. The results show the unchanged glassy compliance and the rubbery stiffening phenomenon for thin PS films, where the lower rubbery plateau in rubbery stiffening may originate from the induced molecular orientation by plastic deformation. With decreasing film thickness, viscosity and yield stress in viscoplasticity increase in an exponential and a linear trend, respectively, indicating the significant role of nanoconfinement effect on viscoplastic properties. These findings may reveal that there are many properties from linear viscoelasticity to nonlinear viscoelasticity-viscoplasticity that need to be explored and unveiled for sufficient understanding of the nanoconfinement effect on altering mechanical behavior of polymers.

Scalable ferroelectricity of 20 nm-thick (Al0.8Sc0.2)N thin films sandwiched between TiN electrodes

Ferroelectric (Al, Sc)N thin films have the potential for use in low-power memory applications. This study demonstrates the thickness scalability of ferroelectricity down to an approximately 20 nm-thick (Al0.8Sc0.2)N film sandwiched between microfabricable TiN electrodes. The impact of the deposition gas atmosphere during the sputtering process and the top electrode materials on the crystal structures and ferroelectric properties was investigated for 20–30 nm-thick (Al0.8Sc0.2)N thin films deposited on Si substrates covered with a TiN layer by radio frequency magnetron sputtering. The deposition atmosphere did not strongly affect the crystal structures of the 30 nm-thick (Al0.8Sc0.2)N films but significantly affected their ferroelectric properties. The leakage current density decreased for films deposited under pure N2 gas compared to the films deposited under a gas mixture of 0.67Ar + 0.33N2. The ferroelectric properties of 20 nm-thick (Al0.8Sc0.2)N films were changed by the top electrode materials; both the switching electric field and its maximum applicable electric field increased for the TiN top electrodes compared with the Pt top electrodes, improving the saturation characteristics of the remnant polarization (Pr) against the applied electric field. Consequently, the 20 nm-thick (Al0.8Sc0.2)N film sandwiched between the microfabricable TiN top and bottom electrodes showed ferroelectricity without noticeable degradation with decreasing film thickness; the film maintained large Pr values of over 100 μC/cm2 in the temperature range from room temperature to 150 °C. The present data open the door to scalable ferroelectric random-access memories using almost thickness-degradation-free thin (Al, Sc)N films with microfabricable TiN electrodes.

Phonon thermal transport in ferroelectric α-In2Se3 via first-principles calculations

Two-dimensional (2D) ferroelectrics are promising candidates in the field of microelectronics due to their unique properties such as excellent photoelectric responsiveness. However, the thermal properties of 2D ferroelectrics are less investigated. Here, the thickness dependent thermal conductivity in ferroelectric α-In2Se3 is systematically investigated by the first-principles method combined with the phonon Boltzmann transport equation. On this basis, the strain and oxidation effects on the thermal conductivity of monolayer α-In2Se3 is further studied. The calculation results show that the thermal conductivity has a significant reduction with decreasing film thickness or increasing tensile strain, and the anharmonic phonon–phonon scattering rate is the intrinsic mechanism for the reduction in thermal conductivity. On the other hand, the replacement of Se atoms by O atoms can achieve a bidirectional and wide-range (12×) tuning of thermal conductivity. The increase in specific heat and phonon group velocity is responsible for the thermal conductivity enhancement at high doping levels while that in phonon–phonon scattering rate is responsible for the thermal conductivity reduction at low doping levels. In all cases, acoustic phonons dominate the in-plane thermal transport behavior. These findings broaden our understanding of phonon transport and its control in ferroelectric semiconductor α-In2Se3.

Stability analysis of near-field acoustic levitation considering misalignment and inclination

The near-field acoustic levitation (NFAL) technique is attracting increasing attention because of its compact design and environmental friendliness. An intriguing aspect of NFAL is the restoring performance when the levitated object is misaligned with the radiator. While numerous studies have proposed models to predict this performance, they typically consider only the misalignment of the levitated object and disregard its inclination. Consequently, this paper presents a numerical model that accounts for both misalignment and inclination to investigate the stability of NFAL systems. First, the Reynolds equation, which describes the variation in pressure distribution, is introduced. Due to the misalignment, a hypothetical reflector with a groove is applied to conveniently express the film thickness. The Reynolds equation is then solved using the eight-point discrete method in conjunction with the boundary equations, and spline interpolation is used to determine the inclination angle. This approach yields the relationship between the restoring force and the eccentricity, which is validated experimentally. Furthermore, parametric studies reveal that increasing the radiator vibration amplitude or the reflector weight enhances the stability. It is also observed that air provides higher stability compared to hydrogen, and a flexible radiator exhibits higher stability compared to a rigid radiator. With decreasing film thickness (e.g., by reducing the vibration amplitude or increasing the weight of the reflector), the stability in the inclination direction is improved at the cost of increased probability of levitation failure.

A lubrication model for bubbly oil lubrication with interfacial effect and thermal effect using the theory of multiphase mixtures

Bubbly oil lubrication is a type of lubrication method. However, the lubrication model of the bubbly oil has not been thoroughly considered. This paper aims to investigate the modelling for bubbly oil lubrication considering the interfacial effect and thermal effect, and a theoretical model is established based on the theory of multiphase mixtures. The interfacial and thermal effects on the static characteristics of a thrust bearing are analyzed. A test rig for the thrust bearing is developed to measure the static characteristics of the bearing under bubbly oil lubrication. The results show that the bearing static characteristics, i.e. bearing temperature rise, film thickness, friction torque, and volume flow, increase with consideration of three interfacial effects; the bearing temperature rise increases but the film thickness, friction torque, and volume flow rate decrease with consideration of the three thermal effects; the thermal effect on the bearing static characteristics is greater than the interfacial effect.

Surface scattering-dependent electronic transport in ultrathin scandium nitride films

With the constant miniaturization of device technologies, it has become essential to understand and engineer the electronic properties of semiconductors in nanoscale dimensions. Scandium nitride (ScN), an emerging rock salt indirect bandgap semiconductor, has attracted significant interest for its interesting thermoelectric, plasmonic, neuromorphic computing, and Schottky barrier device applications. However, an in-depth understanding of the electronic transport, carrier scattering mechanism, and optical properties in ultrathin ScN films is still missing. Here, we show surface-scattering dominant electronic transport in epitaxial ScN films at nanoscale thicknesses. At the ultrathin dimensions, surface scattering increases significantly due to the large surface-to-volume ratio and growth-induced texturing. As a result, mobility decreases, and resistivity increases drastically with decreasing film thickness. Temperature-dependent electronic transport shows that the mobility of the ultrathin films decreases with increasing temperature due to the ionized-impurity and dislocation scattering. Electronic transport properties are further rationalized with x-ray diffraction and pole-figure analysis that shows that while the ultrathin films maintain their predominant 002 texture, their quality degrades with decreasing thickness. However, no significant changes are observed in the electronic structure of the films, as evidenced by x-ray photoelectron spectroscopy, photoemission measurements, and first-principles density functional theory calculations. Our results elucidate the impact of surface scattering on the ultrathin ScN films and would lead to miniaturized devices with improved efficiencies.

Research on limestone calcined clay cement-based ultra-high performance concrete with high cement substitution: Mixture design and engineering properties

Limestone calcined clay cement (LC3) is believed to be able to substitute Portland cement and promote low-carbon development in the concrete industry. Ultra-high performance concrete (UHPC) features high proportions of cement. Herein, an LC3-based UHPC with high cement substitution was designed and optimized based on the D-optimal method, and its engineering properties, including workability, mechanical properties, hydration process, microstructural evolution, and carbon emission were evaluated. Results show that with an increase in LC3, the dynamic yield stress increases and the water film thickness decreases, which indicates that the workability of LC3-based UHPC reduces. When the substitution ratio is about 55 percent, the optimized LC3-based UHPC achieves the maximum compressive strength, about 146.05 MPa. XRD and TG results show that LC3 consumes portlandite by the pozzolanic reaction, which generates additional gel products. However, as the substitution ratio exceeds 55 percent, the degree of pozzolanic reaction drops, resulting in a decrease in the count of hydration products and compressive strength. The pore structure of LC3-based UHPC is refined, with fewer air voids and a larger percentage of gel pores compared to the normal UHPC. The optimized LC3-based UHPC with a substitution ratio higher than 50 percent in this study achieves high integrated performance with engineering applications and low carbon environmental value.

CO gas sensing characteristics of BaSnO3 epitaxial films prepared by PLD: The effect of film thickness

In the present work, perovskite Barium Stannate (BaSnO3) thin films of varying thickness were investigated for carbon monoxide (CO) gas sensing application. Epitaxial BaSnO3 thin films of thickness (90, 270 and 360 nm) were grown on MgO substrates by using pulsed laser deposition technique. The enhanced electrical properties of the films with decreasing thickness can be attributed to the increased amount of Sn4+ ions in the film. An increase in CO gas sensing response of thin films was observed with decreasing film thickness. BaSnO3 thin film having 90 nm thickness exhibits a higher gas sensing response of 58% at 400 °C, which is a quite lower temperature as compared to the previous works in similar systems. This high value is attributed to the presence of large number of grains and grain boundaries providing easy adsorption and desorption of oxygen species at the surface, confirmed by the atomic force microscopy and X-ray photoelectron spectroscopy, respectively.

300 mm CMOS-compatible superconducting HfN and ZrN thin films for quantum applications

The rising interest in increased manufacturing maturity of quantum processing units is pushing the development of alternative superconducting materials for semiconductor fab process technology. However, these are often facing CMOS process incompatibility. In contrast to common CMOS materials, such as Al, TiN, and TaN, reports on the superconductivity of other suitable transition-metal nitrides are scarce, despite potential superiority. Here, we demonstrate fully CMOS-compatible fabrication of HfN and ZrN thin films on state-of-the-art 300 mm semiconductor process equipment, utilizing reactive DC magnetron sputtering on silicon wafers. Measurement of mechanical stress and surface roughness of the thin films demonstrates process compatibility. We investigated the materials phase and stoichiometry by structural analysis. The HfN and ZrN samples exhibit superconducting phase transitions with critical temperatures up to 5.84 and 7.32 K, critical fields of 1.73 and 6.40 T, and coherence lengths of 14 and 7 nm, respectively. A decrease in the critical temperature with decreasing film thickness indicates mesoscopic behavior due to geometric and grain-size limitations. The results promise a scalable application of HfN and ZrN in quantum computing and related fields.