Film Rupture Research Articles

Contact Time of Droplet Impact on Superhydrophobic Cylindrical Surfaces with a Ridge.

This study investigates whether adding ridges to a superhydrophobic cylindrical surface can reduce contact times compared to those of ridged flat or cylindrical surfaces, inspired by the shortened contact time achieved by adding ridges to flat surfaces. The study focuses on studying azimuthal ridges on the cylinder through experimentation, emphasizing the impact dynamics and contact time characteristics under varying We (Weber number) and D* (dimensionless droplet diameter). Within the ultralow Weber number range (ULWR), low Weber number range (LWR), and medium Weber number range (MWR), the contact time is longer than on ridged flat surfaces. In the high Weber number range (HWR), the opposite is observed: increased inertial forces lead to the rupture of the liquid film above the ridges due to Rayleigh-Plateau instability. As a result, the primary droplet splits into two sections with curvature effects promoting its recoiling and rebounding. This study introduces a criterion, defined as C = We/D*, and finds that when C exceeds 2.42, not only is the contact time shorter than on ridged flat or cylindrical surfaces, but it also further decreases with an increase in We or a decrease in D*. The contact time characteristics observed in the HWR offer potential applications in areas such as anti-icing.

Negatively correlated corrosion and stress corrosion cracking of Mg-Al-Mn-Ca based alloys

A negative correlation between corrosion and stress corrosion cracking (SCC) for Mg-Al-Mn-Ca-(Ce/Y) alloys is revealed. Specifically, high-level Al solute and trace Ce/Y alloying enhance the corrosion resistance via reducing Volta potential difference and forming dense corrosion product film. However, the compact film breaks severely during SCC, aggravating the initiation of cracks. Meanwhile, the numerous second phases facilitate H diffusion and adsorption, exacerbating the hydrogen enhanced decohesion in Ce/Y-containing alloy. The film rupture induced anodic dissolution and hydrogen enhanced decohesion dominate the SCC. This work shed light on fundamental understanding of the relationship between corrosion and SCC.

Stability of an aqueous foam lamella at simulated fire conditions containing surfactants relevant to firefighting foams

To better understand interactions between firefighting foams and a fire environment, we isolated interactions to a single surfactant containing bubble lamellae. A horizontal thin liquid film experiment was designed to study film rupture in the presence of heated air and heptane vapors. Thin films were formed from aqueous solutions of alkylpolyglycosides (APGs, G215 and G225), trisiloxane (502W and L77), and fluorinated (Cap) surfactants and their mixtures. The Cap surfactant film was the most stable to heat but in the presence of heptane, the surfactant film had a comparable (and the Cap:G215 mixture had a shorter) rupture time to the fluorine-free surfactant films. APG films showed the least destabilization with heptane followed by the trisiloxane films and the Cap film which was the most destabilized by heptane. L77, Cap, and their respective mixtures formed possible emulsions with the fuel vapors, turning cloudy with vapor introduction. The correlation between film rupture behavior and fuel induced foam lifetime may be better defined by minimizing error in lifetime and producing longer film lifetimes. This thin film experiment represents a new way of observing surfactant/fuel interactions that may elucidate important surfactant properties for firefighting foams.

Molecular-level study of hydrophobic interactions during low-rank coal particle-bubble attachment

Particle-bubble attachment is a crucial part of coal and mineral flotation processes. The attachment of two different hydrophobic low-rank coal particles to bubble surface were simulated by a non-equilibrium molecular simulation method. Both particles were subjected to water film drainage resistance when approaching the bubble. Eventually, CPC (low-rank Coal Particle with mixed Collector adhered) jumped in and attached to bubble, but CP (low-rank Coal Particle) had only repulsive effect with bubble. The surface water film of CPC generated tiny hole under the entropy effect of water molecule rearrangement, and the presence of gas–water and oil–water interfacial tension promoted the rapid expansion of the hole until the water film rupture. The critical rupture thickness of the water film on CPC surface was about 1 nm and the rupture was completed in a very short time of 0.4 ns. The CPC jumped in and attached to the bubble surface under the action of oil–water interfacial tension. This suggests that the long-range hydrophobic force originates from the combined action of various interfacial tensions. Our results demonstrate the important role of interfacial tension in the attachment of hydrophobic particle to bubble, and contribute to the connection between microscopic and macroscopic mechanism of particle-bubble attachment.

Effect of particle shape on bubble-particle attachment behavior: Roles of surfaces, edges, and vertexes

It has been understood through many studies that particle shape is important in terms of particle adhesion to air bubbles in flotation. However, there are many questions yet to be answered. Whether the surface of the particle or its sharp corners is effective is only one of the issues that need to be better understood. Therefore, this study aims to delve deeper into the fundamental studies on the role of particle's geometry (surface, edges, and vertex) in their flotation behavior by investigating the attachment of spherical, cylindrical, triangular prismatic, and cubic particles to air bubbles based on their attachment efficiency, settling velocity, collision efficiency, and induction time. Bubble-particle attachment test results inferred that the attachment efficiency was in the order of cubic > triangular > cylindrical > spherical. In addition, it was found that the induction time of the spherical surface decreased from 37 ms to 15 ms with increasing collector concentration, while the induction time of the edged cubic particle decreased from 8 ms to 2 ms. This was attributed to the fact that the edge facilitates the drainage, thinning, and rupture of the water film between the bubble and the particle, thereby increasing the attachment efficiency. Finally, it has also been observed that the three-phase contact line of the cube particle is larger than that of the spherical particle, which improves the attachment stability and reduces detachment efficiency. The results obtained in this study shed light on the fact that the shape of the particles fed to flotation can be produced by using a suitable mill and thus higher flotation efficiency can be achieved with lower collector concentration.

Клинико-функциональные результаты комплексного лечения синдрома сухого глаза на фоне хронического периферического увеита

Relevance. Inflammation and impaired stability of the pre-corneal tear film are central to the pathogenesis of dry eye disease (DED). Signs of ocular surface irritation and symptoms characteristic of DED accompany intermediate uveitis in 28–57 % of cases. Purpose. To evaluate clinical and functional results of treatment of DED and intermediate uveitis, including tear replacement and anti-inflammatory therapy in combination with laser retinal coagulation at the extreme periphery of the ocular fundus. Materials and methods. The results of treatment of 78 patients with DED and intermediate uveitis were analyzed. The effectiveness of the developed method of treatment of combined pathology was evaluated after 3, 6, 12, 18 months based on the dynamics of OSDI index, hyperemia of bulbar conjunctiva, LIPCOF test, Schirmer I test and Norn's test. Results. Application of complex treatment of DED in patients with intermediate uveitis promotes statistically significant (p≤ 0.05) decrease of discomfort signs according to OSDI results up to 34.7 %, decrease of bulbar conjunctiva hyperemia index up to 50 %, decrease of LIPCOF test index up to 27.2 %, increase of tear film rupture time up to 31.6 % and total tear production up to 89.7 % with stable cure of intermediate uveitis during 18 months of observation. Conclusions. Tear replacement and anti-inflammatory therapy in combination with laser retinal coagulation at the extreme periphery of the ocular fundus is an effective method of treatment of DED and intermediate uveitis, providing stable clinical and functional results for a long time. Keywords: dry eye disease, intermediate uveitis, laser coagulation of the extreme periphery of the retina

Проявления синдрома сухого глаза у детей с сахарным диабетом 1-го типа в зависимости от уровня гликированного гемоглобина

Introduction. Diabetes mellitus is one of the serious diseases that leads not only to restrictions on physical activity, but also changes the social and psychological spheres of life of patients. The purpose of the studyis to evaluate the results of functional methods for studying tear production function in children with type 1 diabetes mellitus. Materials and methods of research. The study included 240 children registered at the Children's City Endocrinology Center in Almaty. There were 133 boys (55.42 %), 107 girls (44.58 %). The examined children were divided into 6 groups depending on the level of glycated hemoglobin (HbA1c). The control group consisted of 52 people. All patients were assessed for the severity of blockage of the breast ducts, the state of total tear production (Schirmer test 1), the state of the tear meniscus (biometry of the tear meniscus), the time of tear film rupture, and the state of the conjunctiva. Patients with dry eye syndrome were prescribed softdrops and the dynamics of the process were monitored. Research results. In patients with type 1 diabetes mellitus, in 69.6 % of cases there were manifestations of breast dysfunction of varying severity. From 17 % to 39.8 % of patients in the main groups had manifestations of hyperemia and 28 % mild conjunctival edema, which is clinically a sign of the presence of an irritating factor, possibly due to an increase in tear hyperosmolarity. The Schirmer test showed a decrease in tear secretion function, a decrease in tear film rupture and a decrease in the level of menisci in comparison with the control. The use of softdrops eye drops helps to stabilize the tear film, increase tear secretion and tear production functions in children with signs of dry eye syndrome due to type 1 diabetes mellitus. These studies should be taken into account when prescribing pathogenetic therapy for the correction of dry eye syndrome in these groups of patients. Keywords: diabetes mellitus, ophthalmological manifestations of diabetes mellitus, dry eye syndrome, dry eye disease

Stabilization mechanism of viscoelastic polymer microspheres on N2 foam system

Foam assisted flooding for crude oil displacement has been used as a commercially viable method for gas-enhanced oil recovery (EOR) processes, due to its outstanding ability in flow rate controlling. Micron-sized particles were continuously applied as the stabilizer for foam fluids, which can adsorb at the water–gas interface to increase interfacial elasticity, as such to prevent foam film rupture during bubble collisions. Current work synthesized two viscoelastic polymer microspheres by inversing emulsion polymerization, and evaluated their effectiveness as the foam fluids additives from the aspects of particle sizer and interfacial viscoelasticity. Furthermore, the ability of polymer microspheres to stabilize foam fluids was qualitatively analyzed according to the dynamics light scattering method and microscopic inspection. When containing 0.8 % SDS + 0.4 % polymer microspheres, the N2 foam system represented the most stable status for both viscoelastic polymer microspheres. The adsorption of microspheres at foam interface significantly increased the foam film strength that prevented lamella rupture when bubbles collision during the flooding process. Moreover, the sustained release property of viscoelastic polymer microspheres helped the fluid to be gradually released from the lamella, which further decreased the thinning speed of the liquid film between bubbles and to increase the foam stability.

Modern diagnosis of dry eye syndrome on MEDI WORKS S390L slit lamp

In recent years, in conditions of increased work with gadgets and computers, the prevalence of dry eye syndrome has increased dramatically. The presented article is devoted to the modern diagnosis of dry eye syndrome.25 patients (50 eyes) participated in the study, which was conducted at the ophthalmological center of Astana Vision Pavlodar LLP in Pavlodar. Of these, 7 patients after laser vision correction, 4 patients suffering from myopia, wore contact lenses, locally applied medications for the treatment of dry eye syndrome. The examination included a Schirmer test, a tear film rupture time test (NIBUT, VRSP), filling out the questionnaire «Ocular Surface Disease Index» (OSDI) and determining the height of the lacrimal meniscus.The author of the article concluded that noninvasive research methods used for the diagnosis of SSG are more acceptable, since they do not violate the integrity of the tear film.

Mechanism Study of Stress Corrosion Behavior under Tensile and Compressive Stresses for Welded Joint Used in Nuclear Turbine Rotor.

Stress corrosion damage containing pitting and cracking was investigated for NiCrMoV steel-welded joint used in nuclear turbine rotor in 3.5% NaCl solution. The U-bend specimen containing tensile face and compressive face was adopted which was conducive to study the effects of stress on pitting and stress corrosion cracking. On tensile surface of U-bend specimen, pit grew in open environment and was converted into crack covered with passivated film. Interestingly, corrosion pit was also found on compressive surface, which might attribute to this location creating enclosed environment causing Cl- to diffuse hardly. Then, pit grew under the occluded oxide crust composed of special crystalline corrosion products. When pit approached to critical size, crack initiated from it. The critical size of pit for crack initiation from pit was 35 μm on tensile surface and 95 μm on compressive surface. The sensitivity of crack initiation in tensile surface was higher than that in compressive surface. Then, cracking on compressive surface was controlled by slip dissolution mechanism, that is, dislocation outcrop generated through plastic deformation during manufacturing and absorbed Cl- in enclosed environment to accelerate metal dissolution and film rupture. Thereupon, the stress corrosion cracking on compressive surface was able to be maintained. The findings compared corrosion damage modes caused by the two kinds of stress and emphasized the nonignorable role of compressive stress on stress corrosion damage.

Клиническая эффективность селективной IPL-терапии пациентов с синдромом сухого глаза, сочетанным с дисфункцией мейбомиевых желез

Purpose. To evaluate functional and clinical parameters characterizing dry eye syndrome (dES) before and after selective IPL therapy. Material and methods. The study involved 19 patients (38 eyes). Inclusion criteria: dry eye syndrome associated with meibomian gland dysfunction (mgd). The age of the study participants ranged from 23 to 75 years, on average 53.2 ± 14.5; women - 68 %, men - 32 %. the evaluation of the data was carried out at the initial visit, after each session of treatment and in the long-term period - after 3 months. Evaluated features: norn tear film stability scores (time to first tear film break, mean tear film break time), tear meniscus height, tear film lipid layer thickness. The assessment of the patients’ conditions according to biomicroscopy data, the condition of the meibomian glands, the eyelid margin, redness of the eye was performed at the initial visit and after each session of hardware treatment. The treatment included: 3 sessions of selective IPL therapy on the lumenis m22 optima IPL device with an interval of 1 time in 3 weeks. Results and discussion. The mean time to first tear film (tF) rupture in study participants before selective IPL therapy was 0.2 (0.1–0.5) seconds, after treatment it increased to 1.6 (0.3–5.4) seconds. The average value of the average tear film rupture time in patients before treatment was 4.7 (1.5–7.8) seconds, and after treatment it increased to 8.6 (4.4–12.0) seconds. Conclusion. The time of the first tF rupture and the average time of tF rupture in patients after the treatment increased. After the treatment, the following statements were reliably established: an increase in the proportion of patients with a lacrimal meniscus height of more than 0.2 mm; increase in the thickness of the lipid layer of the tear film; improvement in the proportion of patients with eyelid border disorders; reduction in the proportion of patients with eye redness. Keywords: selective IPL therapy, dry eye syndrome, meibomian gland dysfunction

Heat flux from the surface in the process of the rupture of a thin liquid film by an electric field

In this article, the cooling of a solid surface by an evaporating film of a dielectric liquid and the influence of an electric field on this process are studied. The mesoscopic lattice Boltzmann method is applied to simulate the fluid flow with phase transitions and the heat transfer. The cases without electric field, with initially uniform electric displacement field, and with non-uniform electric field are considered. A uniform field enhances the cooling slightly. Non-uniform field leads to the rupture of the film. In this case, the local heat flux in local regions increases significantly when the film becomes thin and effectively evaporates. After the rupture of the film, the heat flux from a dry spot decreases abruptly. The formation of a dry spot can be prevented by switching off the electric field before the film rupture. Thus, we demonstrate the possibility of enhanced cooling of local regions at a surface using pulses of non-uniform electric field acting on a thin film of dielectric liquid placed at the surface. If the inflow of liquid to the film could be provided, it is in principle possible to realize a periodic process of application of voltage pulses to electrodes and to enhance the cooling of surface by the evaporation of a film of dielectric liquid.

Rimming flow in a rotating horizontal cylinder with phase change at the interface

The two-dimensional solutions and stability analysis are presented for an evaporating thin viscous liquid film flowing inside a uniformly heated rotating horizontal cylinder. A non-linear, fourth-order, partial differential evolution equation is obtained by simplifying mass, momentum, and energy conservation equations within the lubrication approximation. The effect of evaporation, gravity, viscous drag, surface tension, thermocapillary stress, and intermolecular forces has been taken into account. The numerical solutions of the model are validated against the existing experimental as well as the numerical results, along with the analytical result for the limiting cases of the present model. The film thickness model is solved to elucidate two-dimensional spatiotemporal solutions and their stability for a wide range of thermal and other parameters. The evaporative mass flux at the liquid–air interface results in unsteady solutions which are oscillatory in nature, and the amplitude of the oscillations increases with an increase in the evaporative flux. The film ruptures after some time and the rupture time is found to be inversely proportional to the evaporation number, a non-dimensional number quantifying the rate of evaporation. The linear stability analysis shows that the thermocapillary stresses as well as the long-range molecular forces destabilize the film. A negative disjoining pressure is shown to reduce the rupture time and vice versa. Evaporation (condensation) plays a destabilizing (stabilizing) role in the thin film flow. Non-linear computations are carried out for the steady profiles, validating the growth rates obtained from the linear stability analysis.

Lubrication analysis of low-speed and heavy-load journal bearing in wind turbine gearbox under different operating conditions

Aiming at the working conditions of frequent starting, low speed and heavy load, and yaw tilting of radial sliding bearings in wind turbine gearboxes, a numerical analysis model of the lubrication performance coupled with instantaneous starting and operating conditions of radial sliding bearings was established based on the average Reynolds equation, and the start-up phase was analyzed. The motion trajectory of the shaft diameter and the axis center was used to obtain the change state of the bearing film thickness from the start-up to the stable stage; the influences of the comprehensive surface roughness, the journal inclination angle, and the journal rotation speed on the lubrication performance of the bearing during the whole stage of start-up and stable operation were studied respectively. The results show that the eccentricity has a maximum value in the starting stage, and the risk of film rupture caused by rough contact is the greatest. With the increase of the comprehensive surface roughness, the bearing capacity and friction coefficient both increase, and the maximum bearing capacity and friction coefficient in the starting stage are higher than those in the stable stage, which increase by about 13.62% and 131.58% respectively. With the increase of the inclination angle of the shaft diameter, the bearing capacity and friction coefficient both increase, and the maximum load capacity and friction coefficient in the starting stage are about 30% and 116% higher than those in the stable stage on average. With the increase of the speed, the bearing capacity of the bearing increases and the friction coefficient decreases, which is beneficial to improve the bearing performance. The calculation results provide an important basis for evaluating the wear risk of sliding bearings under frequent starting conditions, and provide a reference for the structural design and selection of sliding bearings, operating temperature, oil film pressure, etc.

Stress Corrosion Cracking of Copper–Nickel Alloys: A Review

Under the combination of certain corrosive ions and stress, Cu-Ni alloys may experience severe stress corrosion cracking (SCC), which causes premature failure and hinders their further applications as crucial construction materials in various engineering fields. To reveal the origin of such failure, minimize the related negative impacts, and achieve economic and social benefits, this review summarizes all SCC-related issues by making a brief introduction to Cu-Ni alloys, reporting the SCC behavior in various environments, identifying the effects of different factors during SCC, and revealing the SCC degradation mechanisms. S2− and NH4+ are the prominent SCC initiators since the former can combine with Cu+ to form Cu2S as a non-protective corrosion product, while the latter has a great tendency to react with Cu2O/Cu and accelerate the general or local dissolution. Their combination has the most detrimental effect. The SCC mechanisms of Cu-Ni alloys are summarized as film rupture theory and dealloying theory. The related SCC mitigation strategies, including using inhibitors, tailoring alloying elements, and removing/reducing the stress are also discussed. In addition, future directions are made at the end of this paper.

Rogue nanowaves: A route to film rupture

Rogue nanowaves: A route to film rupture

Research on pitting corrosion characteristics of X90 steel based on acoustic emission and electrochemistry methods

The X90 pipeline steel pipe is expectedto become the standard steel in future pipeline construction due to its high transmission efficiency and lower cost. However, little study has been conducted on corrosion on-line monitoring of X90 steel. To investigate the pitting development of X90 steel, a combined electrochemical device and acoustic emission (AE) system was set up in this work. The results reveal that the pitting process can be divided into three stages: activation response and passive film rupture, and corrosion pit propagation, and pitting reaction. In addition, the corrosion rate of metal is quite high during the activation reaction and passivation film rupture stage, and the characteristic parameters of the AE signal are very large. In the frequency domain, the frequency range is mostly centered between 100 and 200 kHz, with a peak frequency of about 150 kHz. The corrosion pit propagation stage is the transition stage from metal oxidation to metal pitting reaction. The activity of the signal is low, and the characteristic signal is diminished, and the frequency domain characteristics are comparable to the preceding stage. The signal activity rises, the total signal intensity increases, and several signals exceeding 55 dB arise during the pitting response stage.

Experimental study of the flow dynamics and thermodynamic properties of a tube in vertical falling film evaporator for data center cabinets

This study presents an innovative integrated structure that combines a cabinet with a vertical falling film evaporator, enabling efficient natural evaporative cooling and effectively reducing energy loss in data centers. To in-depth understand the proposed structure's cooling mechanism, a novel inserted liquid film distributor is initially devised in the experiment, which can make the water flowing into the tube form an intact liquid film. Then, the visualization experiments are carried out in the tube to observe the water film flow dynamics, demonstrating that a minimum spray density of 0.048 kg·m−1·s−1 can be attained while maintaining liquid film integrity. Meanwhile, when the vibration frequency reaches 2700 Hz, a significant water film rupture in the tube occurs. Finally, building upon the experimental result analysis, at a spray density increment of 0.024 kg·m−1·s−1, the maximum increments of heat transfer rate and heat transfer coefficient corresponding to the intact liquid film are 16.2% and 23.3%, respectively. By contrast, those two indexes corresponding to the ruptured liquid film are 63.4% and 50.9%, respectively. This research provides reliable guidance and valuable insights for the design and efficient operation of natural evaporation falling film evaporators.

Evaluation of corrosion resistance of 316L stainless steel by laser ultrasonic nondestructive testing technology

At present, the corrosion resistance of materials such as 316L stainless steel is mainly tested by electrochemical testing, which is time-consuming, laborious and environmentally unfriendly. In this paper, the laser ultrasonic detection technology, which is a rapid, non-destructive, pollution-free microstructure and corrosion resistance evaluation method is used for the detection of 316L stainless steel, and the ultrasonic signals are filtered by the wavelet threshold denoising method. The results show that the laser ultrasonic attenuation coefficient obtained by the wavelet threshold denoising signal processing method has a good correlation with the corrosion resistance of 316L stainless steel. A laser ultrasonic potential evaluation model was established based on the passivation film rupture potential and ultrasonic attenuation coefficient. The average relative error of the evaluation model for corrosion resistance of 316L stainless steel is less than 5.00%. The relative error of corrosion resistance evaluated by the laser-receiving method is lower than that by the probe-receiving method. It is feasible to nondestructive evaluation of the corrosion resistance of 316L stainless steel by laser ultrasonic technology.

Statistical in situ scanning electron microscopy investigation on the failure of oxide scales

AbstractOxide scales play a pivotal role in obstructing surface chemical and electrochemical reactions, hence hindering chemo‐mechanical effects such as liquid metal embrittlement of steels. Therefore, the critical conditions and failure mechanism of the oxide film are of major interest in the safe service of steels. Though in situ microscopic methods may directly visualize the failure mechanism, they are often challenged by the lack of statistically reliable evaluation of the critical conditions. Here, by combining in situ scanning electron microscopy with a tapered specimen tensile test in a single experiment, we uniquely achieve a mechanistic study with statistically reliable quantification of the critical strains for each step of the dynamic process of film rupture. This is demonstrated with the oxide films formed on a ferrite–martensite steel in liquid lead–bismuth eutectic alloy at elevated temperatures, with in situ results falling right into the predictions of the statistical analysis. Explicitly, the integrated experimental methodology may facilitate the materials genome engineering of steels with superior service performance.