Large Film Thickness Research Articles

A time-resolved investigation at multiple-length scales of the structure of liquid foam stabilized by albumins from pea

HypothesisThe structural details of foams made with pea albumins are affected by the pH of the initial solution and followed heat treatment. ExperimentsAn in situ, time-resolved investigation of foams prepared with pea albumins was conducted using small-angle neutron scattering (SANS) in combination with imaging and conductance measurements. Solutions were tested at pH three pH values (3, 4.5, and 8) before and after heating (90 °C for 1 and 5 min). FindingsThe characteristic structures present in the foam from the nano to the meso-scale differed during drainage depending on solution pH. Foams obtained at pH 3, had the largest bubble radius and thinnest plateau border, as well as the highest extent of liquid drainage. At pH 4.5, close to the isoelectric point of the proteins, foams displayed similar bubbles’ behavior to those at pH 8, but with the largest film thickness. In this case, the proteins were extensively aggregated. Heating of the solutions prior to foaming did not significantly affect the foam aging regardless of pH. The quantification of specific surface areas and film thickness over time without sample disruption shows to be a powerful approach to designing foam structures.

Experimental Investigation of Film Thickness in Wastewater Airlift Pumps by an Image Processing Method

The airlift pump is a key part of wastewater treatment and is employed as an innovative and feasible collection tool. However, as one of the key factors in the lifting capability of airlift pumps, film thickness in the gas–liquid two-phase flow operating in pumps is still an unknown topic because it is difficult to measure. This paper proposes a visualization method for measuring film thickness and investigates the film thickness when operating under gas flow with a high rate in airlift pumps using experiments. Firstly, a simulation experiment platform was built, and the images of the film structure were acquired by a high-speed camera. Then, image-processing technology and an image distortion correction were proposed to extract the gas–liquid interface for studying the thickness of the film. The experimental results demonstrated that a large film thickness ranging from 0.15 D to 0.24 D was found in airlift pumps and that its film thickness kept a constant value, even under a high gas superficial velocity, maintaining a large output liquid flow from airlift pumps. As wastewater was carried by wastewater treatment, a larger film thickness of the annular film will benefit the high lifting rate of wastewater. The works in this paper offer valuable insights for the higher performance of working airlift pumps and wastewater treatment efficiency.

Optimizing Load Capacity Predictions in Gas Foil Thrust Bearings: A Novel Full-Ramp Model

Gas film thickness significantly influences the performance prediction of Gas Foil Thrust Bearings (GFTB). However, the Classical Model (CM) for GFTBs exhibits inaccuracies in describing gas film thickness. In this paper, we explore the differences in the details of gas film thickness modeling and propose a Parallel Segmentation Model (PSM), which fixes the errors of the CM in describing the gas film thickness in the ramp section, and a Full-Ramp Model (FRM), to which a more realistic description of the gas film in the flat section is also added. Comparative analysis, utilizing a publicly available test dataset based on the open-source GFTB structure, establishes that the FRM surpasses the CM and PSM in accurately predicting load capacity. In-depth analysis shows that the location of the minimum gas film thickness for determining the load capacity is located at the innermost circle of the free end of the top foil, whereas the FRM is subjected to the same load with a larger film thickness at this location, which may be due to the unique geometry of the top foil of the FRM. Subsequently, employing the FRM, a parametric study explores load capacity in GFTB, considering variables such as ramp height, top foil thickness, bump foil stiffness, ramp section extent, and top foil area. The results demonstrate that GFTB load capacity exhibits a linear increase with the expansion of the top foil area. Moreover, the load capacity increases with augmented top foil thickness and bump foil stiffness, albeit at a decreasing rate. Additionally, an increase in ramp section extent initially enhances load capacity, reaching a maximum value before declining. Similarly, an increase in ramp height initially augments load capacity, attaining a maximum before subsequent diminution.

Study on characteristics and mechanism of re‐entrainment in intake filtration components of the gas turbine

AbstractAiming at the problem that the droplet re‐entrainment in the intake filtration components affects the gas intake quality and the safe operation of gas turbines, the characteristics and mechanism of the re‐entrainment in a marine double‐hook inertial stage filter are studied, and the distribution of liquid film and re‐entrainment under different inlet air velocities and droplet size distributions are compared. The results show that, due to the influence of inertia and turbulent dispersion, droplets tend to deposit on draining hooks and the lower surface of the leeward side of the blade to form a liquid film. Film stripping is the main form of re‐entrainment under ship‐driving conditions. Due to the high airflow velocity and the large film thickness, hook peaks are the most prone to film stripping, and the critical airflow for film stripping velocity is 14.8 m/s. With the increase of the inlet air velocity, the film thickness at the draining hooks increased first and then decreased, and the film stripping positions were extended from the hook peaks to the rear. Different droplet size distributions mainly affect the liquid film thickness at the draining hook and leeward side of the blade, which in turn affects the film stripping mass.

Ultrasonic measurement for lubricant film thickness with consideration to the effect of the solid materials

An improved ultrasonic reflection coefficient phase model is proposed for lubricant film thickness measurement with consideration to the influence of the solid layers. In the model, the theoretical relation of the lubricant film thickness to ultrasonic reflection coefficient phase is established, which is used for effectively determining the lubricant film thickness. Furthermore, the proposed model is verified by both the finite element analysis and experiments. The results show that the lubricant film thickness ranges between 2 μm and 45 μm can be measured by using the proposed model, which covers both the spring model region and the blind region. In addition, at a small film thickness, the reflection coefficient phase is significantly affected by the acoustic impedances in both solid layers. However, the reflection coefficient phase is dominantly affected by the solid layer in the neighbourhood of the incidence source at a large film thickness.

Far‐ and Near‐Field Heat Transfer in Transdimensional Plasmonic Film Systems

AbstractA confinement‐induced nonlocal electromagnetic response model is applied to study radiative heat transfer processes in transdimensional plasmonic film systems. The results are compared to the standard local Drude model routinely used in plasmonics. The former predicts greater Woltersdorff length in the far‐field and larger film thicknesses at which heat transfer is dominated by surface plasmons in the near‐field, than the latter. The analysis performed suggests that the theoretical treatment and experimental data interpretation for thin and ultrathin metallic film systems must incorporate the confinement‐induced nonlocal effect in order to provide reliable results in radiative heat transfer studies. The fact that the enhanced far‐ and near‐field radiative heat transfer occurs for much thicker films than the standard Drude model predicts is crucial for thermal management applications with thin and ultrathin metallic films and coatings.

Elastohydrodynamic lubrication analysis of tapered roller bearing considering effect of free ends

The EHL model of tapered roller bearing considering free ends is established and the effect of force on the large end is also considered. The free ends are constructed through the overlapping method, and the distribution of pressure and film thickness are obtained with the unified Reynolds equation. The effect of force and distance between two neighboring free ends are investigated, based on which the proper contact case is selected. The EHL of tapered roller bearing with different fillets and Lundberg profile are discussed. The results show the length and radius of roller fillet and the modification of Lundberg profile roller should be carefully selected to improve lubrication performance with low pressure, large minimal film thickness and low stress concentration.

Decagonal Sn clathrate on d -Al-Ni-Co

Decagonal quasiperiodic ordering of Sn thin films on $d$-Al-Ni-Co is shown based on scanning tunneling microscopy (STM), low-energy electron diffraction, and density functional theory (DFT). Interestingly, the decagonal structural correlations are partially retained even up to a large film thickness of 10 nm grown at $165\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The nucleation centers called ``Sn white flowers'' identified by STM at submonolayer thickness are recognized as valid patches of the decagonal clathrate structure with low adsorption energies of these motifs. Due to the excellent lattice matching (to within 1%) between columns of Sn dodecahedra in the clathrate structure and pentagonal motifs at the $d$-Al-Ni-Co surface, the interfacial energy favors clathrate over the competing Sn crystalline forms. DFT study of the Sn/Al-Ni-Co composite model shows good mechanical stability, as shown by the work of separation of Sn from Al-Ni-Co slab that is comparable to the clathrate self-separation energy. The relaxed surface terminations of the ${\mathrm{R}}_{2}{\mathrm{T}}_{4}$ clathrate approximant are in self-similarity correspondence with the motifs observed in the STM images from monolayer to the thickest Sn film.

Study on Tribological Characteristics of Textured Surface under Convergent Oil Film Gap

Under the condition of convergence, a textured non-parallel 2D slider bearing model was established, and the tribological properties of textured surface under the convergence gap were numerically studied with the load-carrying capacity as an indicator. Firstly, whether the convergence ratio parameter can accurately characterize the joint effects of film thickness difference and oil film thickness on the surface tribological properties was verified, and the effects of film thickness difference and oil film thickness on the load-carrying capacity of textured and non-textured surface were studied, respectively. The results show that the efficiency of improving the load-carrying capacity of the surface structure first increases and then decreases with the increase of the oil film thickness. In the case of large film thickness difference, the surface texture will reduce the efficiency of improving the load-carrying capacity. In addition, the effects of texture depth, texture width, and sliding velocity on the load-carrying capacity under the convergence gap are also studied. In particular, an optimal texture width to maximize the load-carrying capacity exists.

Transient mixed-lubrication analysis of low-viscosity lubricated bearings under impact load with consideration of turbulence

For heavy-duty bearings with low-viscosity lubricant, asperities may contact near the minimum nominal film thickness, while turbulence may develop in the area with large film thickness. When bearings encounter transient impact or unsteady loads, the influence of turbulence and surface roughness is relatively complex. To investigate transient lubrication and dynamic characteristics of mixed-lubricated bearings with turbulent flow, a transient mixed-lubrication model considering turbulence is proposed in this paper. A transient generalized average Reynolds equation is derived based on the Ng-Pan turbulence model. The transient journal center positions are obtained by solving the journal's dynamic equation. The numerical procedure is established. Based on the proposed model, the effect of turbulence, surface roughness, and transient impact load direction as well as the magnitude on transient lubrication and dynamic characteristics of mixed-lubrication bearings is analyzed. The results show that turbulence increases the transient minimum nominal film thickness and may decrease the transient friction force in the mixed-lubrication regime. Surface roughness modifies the dynamic trajectory of the journal center and increases both the transient minimum nominal film thickness and the friction force in the mixed-lubrication regime. The impact load direction significantly affects transient characteristics of the bearing. An increase in the load-deflection angle destabilizes the bearing operation state.

Effect of reversing duration time and commutation meshing state on the elastohydrodynamic lubrication of reciprocating spur gear rack

AbstractReciprocating spur gear rack is prone to lubrication failure near the reversing dead center position. Ree‐Eyring lubrication fluid, multigrid method and multigrid integral method were used to calculate the pressure profile, film thickness and oil temperature rise. Compared with linear motion, the process of reciprocating commutative movement is more complicated and the lubrication state are more unstable. The effects of different reversing duration time and commutation meshing state on lubricant film were analysed. The results show that, the oil thickness during the gear reversing process is significantly reduced. While shortening the reversing time can improve the lubricating film thickness, it causes the instantaneous oil temperature to rise. Therefore, the gear tooth damage caused by high temperature can be avoided by prolonging the reversing duration time properly. The longer the reversing duration time, the minimum value of central film thickness and central pressure is closer to the meshing outlet area. No matter what the reversing time change, the minimum lubrication film thickness is in the reversing dead center position. So the reversing dead center is still the dangerous point for the lubrication failure of the spur gear rack mechanism. When the reversing dead center is in the leading tooth of double‐tooth meshing, the gear has the largest film thickness and the largest contact area. In addition, the synthetic radius of curvature and entrainment velocity become larger so the lubrication conditions have been improved. The results provide the theoretical basis and guidance for the reasonable design of the spur gear rack and the improvement of its lubricating performance.

Linear stability of a thin fluid film interacting with its surrounding bulk fluid

Thin films can become unstable when attractive van der Waals forces overcome the stabilizing effects of surface tension and viscous forces. In many applications, the effect of the surrounding bulk fluid cannot be neglected when considering a thin film subject to perturbations. In this work, we examine the two limits of potential flow and Stokes flow in the surrounding bulks to derive dispersion relations in each limit. We show that the effect of the surrounding bulks cannot be ignored for many film–bulk fluid pairings and film thicknesses and present conditions for the validity of each regime. In particular, the potential-flow regime exists when van der Waals forces are sufficiently strong, while the Stokes-flow regime exists when the bulk dynamic viscosity is sufficiently large. Due to the nature of the dispersion relation in the Stokes-flow limit, several distinct scenarios are identified in the corresponding stability diagram, each involving the interplay of different forces. For example, a novel instability regime involving capillary–viscous interactions is identified for large film thicknesses. Finally, by enlisting multiple realistic fluid pairings and film thicknesses wherein such instabilities can occur, we demonstrate the practical relevance of our theoretical findings. This work enables the extension of thin film stability theory to the analysis of antibubbles, splashing molten metals and ionic liquids, Mesler entrainment of microbubbles in breaking waves, and emulsion stability.

Structural and Electric Properties of Epitaxial Na0.5Bi0.5TiO3-Based Thin Films

Substantial efforts are dedicated worldwide to use lead-free materials for environmentally friendly processes in electrocaloric cooling. Whereas investigations on bulk materials showed that Na0.5Bi0.5TiO3 (NBT)-based compounds might be suitable for such applications, our aim is to clarify the feasibility of epitaxial NBT-based thin films for more detailed investigations on the correlation between the composition, microstructure, and functional properties. Therefore, NBT-based thin films were grown by pulsed laser deposition on different single crystalline substrates using a thin epitaxial La0.5Sr0.5CoO3 layer as the bottom electrode for subsequent electric measurements. Structural characterization revealed an undisturbed epitaxial growth of NBT on lattice-matching substrates with a columnar microstructure, but high roughness and increasing grain size with larger film thickness. Dielectric measurements indicate a shift of the phase transition to lower temperatures compared to bulk samples as well as a reduced permittivity and increased losses at higher temperatures. Whereas polarization loops taken at −100 °C revealed a distinct ferroelectric behavior, room temperature data showed a significant resistive contribution in these measurements. Leakage current studies confirmed a non-negligible conductivity between the electrodes, thus preventing an indirect characterization of the electrocaloric properties of these films.

Influence of anodization parameters on film thickness and volume expansion of thick- and large-sized anodic aluminum oxide film

Anodic aluminum oxide (AAO) film with a thickness ranging from 20 to 100 μm was prepared using a large-sized Al plate (4 cm × 10 cm) to investigate the anodization parameter effect on the film thickness and volume expansion factor. A corrosion treatment (voltage = 0 V) was performed to investigate the film dissolution caused by acid. The actual anode surface temperature was also measured to confirm the field-assisted nature of AAO dissolution. The film thickness increases exponentially with temperature, and increases approximately linearly with voltage, duration or concentration. The volume expansion factor gives a first rising and then falling trend with temperature or duration, while it has a nearly linear trend with voltage or concentration. The volume expansion factor increases with the intensified electric field, while its decrease is attributed to the Joule heat-enhanced dissolution. In the case of large film thickness (> 20 μm), the pore confinement effect may be one of the reasons for the change of volume expansion factor. In addition to the conventional parameters, the heat transfer-related parameters (for example, sample size) also greatly affect the AAO film growth.

Influence of power-law fluid on transient performance of liquid film seal based on the time-dependent non-Newtonian dynamic Reynolds equation

The effects of lubricant's non-Newtonian property on dynamic characteristics of spiral groove liquid film seal are presented in this paper. The modified dynamic Reynolds equation for non-Newtonian fluid is derived, which is solved simultaneously with the kinematic equation. The transient response to the rotor's axial runout and angular misalignment, such as the axial and angular movement of stator ring, the transient film thickness, are presented for different power-law indexes, as well as the transient performance parameters. The results indicate that the seal has larger film thickness under the lubrication condition with dilatant lubricant while the stator ring has better tracking property operating with shear-thinning lubricant. Overall, the non-Newtonian property should be considered in the design of liquid film seal.

Numerical simulation on partial coalescence of a droplet with different impact velocities* *Project supported by the National Natural Science Foundation of China (Grant No. 51876102) and the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant No. 51621062).

Partial coalescence is a complicated flow phenomenon. In the present study, the coalescence process is simulated with the volume of fluid (VOF) method. The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence. The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off. The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off. With the droplet impact velocity increasing, the droplet shape will get close to a sphere before the pinch-off. When the shape gets close enough to a sphere, the partial coalescence shifts to full coalescence. The effect of film thickness on the coalescence process is also investigated. With large film thickness, partial coalescence happens, while with small film thickness, full coalescence happens. In addition, the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter. And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.

Experimental study of droplet impact on superheated cylindrical surfaces

In this study, droplet impact dynamics on superheated cylindrical surfaces are investigated experimentally, through high-speed imaging. The outcome regimes of impacting droplets observed in the experiments are mapped and described. Four distinguishable regimes are identified, namely rebound-transition boiling, rebound-film boiling, breakup-transition boiling, and breakup-film boiling. In addition, the effects of Weber number, surface temperature and curvature diameter on boiling mode, film thickness, droplet spreading and contact time are examined. The scaling laws of maximum spreading ratio and liquid film thickness with the impact Weber number are established. The larger film thickness on the concave surface reduces the dynamic Ledifenfrost temperature, meanwhile improves the critical Weber number for droplet breakup. Under the effect of the tangential gravity component, the spreading of droplets in the circumferential direction is suppressed on the concave surface, while is promoted on the convex surface. Increasing the curvature diameter, the maximum spreading increases on the concave surface, but decreases on the convex surface. The maximum spreading on both surfaces decreases with the wall temperature in the transition boiling state. Noticeable reduction in the contact time of droplets in the rebound regimes are observed on both surfaces, especially on the concave surface. The contact time is shown to generally decrease with the wall temperature, but increase with the curvature diameter.

Bulk-like dielectric and magnetic properties of sub 100\xa0nm thick single crystal\xa0Cr2O3\xa0films on an epitaxial oxide electrode

The manipulation of antiferromagnetic order in magnetoelectric Cr2O3 using electric field has been of great interest due to its potential in low-power electronics. The substantial leakage and low dielectric breakdown observed in twinned Cr2O3 thin films, however, hinders its development in energy efficient spintronics. To compensate, large film thicknesses (250 nm or greater) have been employed at the expense of device scalability. Recently, epitaxial V2O3 thin film electrodes have been used to eliminate twin boundaries and significantly reduce the leakage of 300 nm thick single crystal films. Here we report the electrical endurance and magnetic properties of thin (less than 100 nm) single crystal Cr2O3 films on epitaxial V2O3 buffered Al2O3 (0001) single crystal substrates. The growth of Cr2O3 on isostructural V2O3 thin film electrodes helps eliminate the existence of twin domains in Cr2O3 films, therefore significantly reducing leakage current and increasing dielectric breakdown. 60 nm thick Cr2O3 films show bulk-like resistivity (~ 1012 Ω cm) with a breakdown voltage in the range of 150–300 MV/m. Exchange bias measurements of 30 nm thick Cr2O3 display a blocking temperature of ~ 285 K while room temperature optical second harmonic generation measurements possess the symmetry consistent with bulk magnetic order.

Squeeze Film Force Modeling with Considering Slip and Inertia Effects Between Hydrophobic Surfaces Within Submillimeter Clearance

Squeeze film force exists but is undesirable in some engineering applications such as immersion lithography and micro-electro mechanical systems. The dynamic characteristics of such systems can be improved by adopting hydrophobic surfaces. In addition to squeeze film damping effects, slip effects are prominent and the inertial effects can be neglected with small film thickness, while inertial effects are prominent and slip effects can be neglected with large film thickness. Existing squeeze film force models that ignore inertia effects will cause unacceptable deviations between hydrophobic surfaces with clearance from dozens to hundreds of microns. In this paper, the squeeze film force model is formulated based on Navier–Stokes equations and two parameters slip boundary conditions while simultaneously considering slip and inertia effects. Experiments using different squeeze film thicknesses and squeeze amplitudes are conducted with parallelism between two specimen surfaces of less than 0.01°. The experimental results show that the slip and inertia effects are critical for accurately predicting the squeeze film force between hydrophobic surfaces under moderate film thickness. The predicted errors of the proposed model can be significantly reduced to less than 0.5% after proper fitting of the two slip parameters under all the test conditions. The method can be adopted for the identification of slip parameters and derivation of kinetic models for systems with squeeze film.

Templated Growth of Metastable Polymorphs on Amorphous Substrates with Seed Layers

Metastable inorganic materials with unique properties are important in many practical applications, but their synthesis is often challenging. In physics, epitaxial stabilization, also known as pseudomorphic growth, is used to synthesize metastable polymorphs, but usually only as very thin films and on expensive single-crystal substrates. In chemistry, the templated growth of inorganic solid-state materials on self-assembled monolayers of organic molecules is reported. Bridging these two fields, here, we show that the synthesis of metastable polymorphs is possible up to large film thickness on amorphous substrates covered with thin inorganic seed layers that serve as templates. The stabilization of a 500-nm-thick metastable wurtzite (WZ) $\mathrm{Mn}\mathrm{Te}$ film by a 5-nm-thick $\mathrm{Zn}\mathrm{Te}$ seed layer sputtered on amorphous glass substrates is experimentally demonstrated. Theoretical calculations explain this experimental observation by the small WZ polymorph energy relative to that of the ground-state nickeline (NC) structure of $\mathrm{Mn}\mathrm{Te}$ and a large lattice constant difference of the two. The resulting metastable WZ-$\mathrm{Mn}\mathrm{Te}$ polymorph exhibits a wide band gap of 2.7 eV and a low hole density of ${10}^{12}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, which is relevant to optoelectronic applications. These properties are in sharp contrast to those of the narrow-band-gap highly doped NC-$\mathrm{Mn}\mathrm{Te}$ with 1.3 eV band gap and ${10}^{19}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ hole density. The difference in hole density is due to the calculated difference in the formation energy of manganese vacancy acceptor defects. Overall, these results suggest that templated growth on amorphous substrates with seed layers can be used to synthesize metastable polymorphs of other materials, without the need for expensive single-crystal substrates.