Film Height Research Articles

English

BACKGROUND Dry eye is an important factor affecting the quality of life especially elderly. The major cause of adult blindness in India is cataract. After cataract surgery many are beleaguered by dry eye symptoms. Since small incision cataract surgery remains the most commonly performed surgical procedure for cataract in India the ocular surface and tear film changes occurring in patients after cataract surgery in our hospital was studied. METHODS A prospective observational study was conducted among 120 patients who underwent uncomplicated cataract surgery at RIO, Thiruvananthapuram for a period of 12 months from July 2019 - June 2020 to assess the changes that occur in ocular surface and tear film after small incision cataract surgery. The dry eye status was measured using Schirmer tests, tear film breakup time, tear film height, fluorescein and lissamine green staining and finally graded using OSDI score. The score was assessed preoperatively & postoperatively at 1 week, 4 weeks & 12 weeks. RESULTS Pre & postoperative OSDI score showed that 1 week after surgery only 5 % patients remained with no dry eye changes. 4 weeks after the surgery mild dry eye was found in 35 %, moderate dry eye in 40 % & severe dry eye in 23 % patients. 12 weeks after surgery mild dry eye was found in 53.3 %, moderate in 33.3 % & severe in 1.7 %. The occurrence of dry eye was seen to increase 1wk postoperatively & peak around 4weeks postoperatively. CONCLUSIONS Small incision cataract surgery induces significant dry eye changes in patients whose ocular surface & tear film was normal preoperatively. The dry eye changes were noted to worsen maximum at 4 weeks after surgery & these changes persisted in low grade even at 12 weeks after surgery. KEYWORDS Dry Eyes, Small Incision Cataract Surgery (SICS), OSDI (Ocular Surface Disease Index) Score

Assessment of acne vulgaris and its association with ocular dryness

Background: Acne vulgaris is a chronic inflammatory disease of the pilosebaceous unit resulting from several interacting pathophysiologic factors. The present study was conducted to assess Acne vulgaris and its association with ocular dryness. Materials & Methods: 86 patients with acne vulgaris underwent assessment of Schirmer's test, tear film breakup time (TBUT), tear film height, presence of conjunctival injection, punctate epithelial erosions (PEE), and meibomian gland dysfunction (MGD). Results: Out of 86 patients, males were 56 and females were 30. Common complaints were watering & burning eyes in 42, foreign body sensation in 14, itching in 20, redness in 6 and on off vision blurring in 4 patients. The corneal findings were lustureless in 64, clear cornea in 12 and punctate lesions & lustureless cornea in 10 patients. The difference was significant (P

Geometrical Optimization of the EHL Roller Face/Rib Contact for Energy Efficiency in Tapered Roller Bearings

In the context of targeted improvements in energy efficiency, secondary rolling bearing contacts are gaining relevance. As such, the elastohydrodynamically lubricated (EHL) roller face/rib contact of tapered roller bearings significantly affects power losses. Consequently, this contribution aimed at numerical optimization of the pairing’s macro-geometric parameters. The latter were sampled by a statistical design of experiments (DoE) and the tribological behavior was predicted by means of EHL contact simulations. For each of the geometric pairings considered, a database was generated. Key target variables such as pressure, lubricant gap and friction were approximated by a meta-model of optimal prognosis (MOP) and optimization was carried out using an evolutionary algorithm (EA). It was shown that the tribological behavior was mainly determined by the basic geometric pairing and the radii while eccentricity was of subordinate role. Furthermore, there was a trade-off between high load carrying capacity and low frictional losses. Thereby, spherical or toroidal geometries on the roller end face featuring a large radius paired with a tapered rib geometry were found to be advantageous in terms of low friction. For larger lubricant film heights and load carrying capacity, spherical or toroidal roller on toroidal rib geometries with medium radii were favorable.

Enhancement of vapor condensation heat transfer on the micro- and nano-structured superhydrophobic surfaces

Recently, micro- or nano- structured surfaces haven been developed to enhance condensation heat transfer, water harvesting and self-cleaning. However, at large subcoolings, condensate floods the subcooled substrate, thus deteriorating the heat transfer efficiency. Here, the superhydrophobic surfaces with micropillared and nanopillared structures are proposed to enhance heat transfer at large subcoolings. The influence of micropillar spacing and surface subcooling on the droplet dynamics and heat transfer performance is experimentally investigated using microscopic visualization techniques. In addition, the microscopic modeling of condensation heat transfer on the microstructured surfaces is performed using the mesoscopic lattice Boltzmann method. The results demonstrate that the droplet size distribution on the micropillared surface is significantly smaller over that of the nanostructured surface. The heat transfer coefficient decreases with the increase of micropillar spacing. As the subcooling rises, although the condensate floods the substrate, the heat transfer coefficient of the S10R30 (S10R30 represents the micropillar arrays with s = 10 μm and 2r = 60 μm) surface is enhanced by 26.4% compared to the hydrophobic nanostructured surface. This is because the height of liquid film is the same of order of magnitude as the micropillars, reducing the thermal resistance caused by the liquid layer. Combining environmental scanning electron microscope (ESEM) observations and LB simulation results, it is concluded that the droplets first nucleate at the bottom corner of micropillars. In addition, the condensate droplets merge to form a film, fill the micropillar gaps, and cover the entire micropillars, leading to a sharp decrease in heat flux. These findings provide a theoretical and experimental guidance for the development of condensing surfaces to enhance heat transfer.

Water film area and dust removal efficiency of string grilles: a theoretical analysis

Based on multiphase flow theory and capillary mechanics, the dimensionless bond number expression of the influence of string grille wire spacing on droplet spreading is derived. Taking a liquid film formed by spreading droplets based on Kelvin correlation, the Young–Laplace equation, and the Hagen–Poiseuille law, an equation for calculating the thickness and height of the liquid film is established with temperature, relative humidity and molar volume of liquid phase as independent variables. According to the theory of string grille filtration and dust removal, a dust removal efficiency calculation model covering the wet string grille wire group is constructed based on the liquid film thickness, height, wire diameter, water film area, and vortex shedding frequency. Finally, a theoretical analysis of the influence of water film area on the efficiency of wet string grille dust removal is carried out based on the spray pressure and the ratio of string grille wire distance to wire diameter. It is found that the effect of spray pressure on water film area and dust removal efficiency is more significant than the string grille wire distance diameter ratio. Moreover, the optimized combination of wet string grille wire distance diameter ratio 0.84, wind speed 3 m/s and spray pressure 0.8 MPa is found, which could provide an important reference for engineering applications.

Achieving Stable Patterns in Multicomponent Polymer Thin Films Using Marangoni and van der Waals Forces.

Liquid-air interfaces can be deformed by surface-tension gradients to create topography, a phenomenon useful for polymer film patterning. A recently developed method creates these gradients by photochemically patterning a solid polymer film. Heating the film to the liquid state leads to flow driven by the patterned surface-tension gradients, but capillary leveling and diffusion of surface-active species facilitate eventual dissipation of the topography. However, experiments demonstrate that using blends of high- and low-molar-mass polymers can considerably delay the decay in topography. To gain insight into this observation, we develop a model based on lubrication theory that yields coupled nonlinear partial differential equations describing how the film height and species concentrations evolve with time and space. Incorporation of a nonmonotonic disjoining pressure is found to significantly increase the lifetime of topographical features, making the model predictions qualitatively consistent with experiments. A parametric study reveals the key variables controlling the kinetics of film deformation and provides guidelines for photochemically induced Marangoni patterning of polymer films.

CFD analysis of blade coating from a reservoir onto a horizontal substrate using a homogeneous two‐phase model

AbstractA two‐phase numerical analysis is performed of two‐dimensional, laminar, liquid flow from a reservoir onto a horizontal, rigid, moving substrate. The homogeneous two‐phase model in commercial CFD code CFX is used to model the liquid plus a region containing both liquid and air near the phase interface and downstream of the blade region. Slow convergence due to surface tension modelling required initialization from intermediate results omitting surface tension. Comparisons made with two previous numerical analyses demonstrate the performance of this approach. For a particular upstream reservoir geometry, the effects of changing the substrate speed and the liquid properties from a Newtonian fluid to a Carreau‐Yasuda non‐Newtonian fluid on the pressure field and the downstream film height are studied. The details of the liquid recirculation in the reservoir and the overall pressure distribution are discussed. New results are presented for the meniscus position and contact angle, which are fully predicted by the two‐phase approach. The meniscus position was strongly influenced by substrate speed and liquid properties, whereas the contact angle did not change significantly with changes in substrate speed and dynamic viscosity for the Newtonian fluid nor with changes in the functional parameters for the non‐Newtonian fluid.

Optical modeling of cellulose nanofibril self-assembled thin film with iridescence

Nanostructure-induced structural coloration and bio-invisibility are important for camouflaging as it displays color and can be tuned and imparted in a more environmentally friendly manner. However, even though many new camouflage fabrics and technologies are invented, there is a lack of numerical electromagnetic and optical approaches to analyze the phenomenon of light scattering of camouflaging materials from nanostructures. In this study, we built and presented a successful simulation of physical coloration caused by multilayer membrane interference. We created this model based on surfactant-like cellulose nanofibrils (CNFs) that tightly stacked into photon-active microstructure and surface topology for light reflection, thus affecting the film gloss. Incident light coming at a defined wavelength or angle was studied. The effects of film height, high microstructure, and curvature on the optical properties of ITO/PET substrates were investigated. These showed the coloration is highly dependent on the nanostructure’s characteristics. This study provides a general prediction model to deal with optical multilayer systems where interference plays a vital role in optical camouflaging, etc.

Dielectrowetting of a thin nematic liquid crystal layer.

We consider a mathematical model that describes the flow of a nematic liquid crystal (NLC) film placed on a flat substrate, across which a spatially varying electric potential is applied. Due to their polar nature, NLC molecules interact with the (nonuniform) electric field generated, leading to instability of a flat film. Implementation of the long wave scaling leads to a partial differential equation that predicts the subsequent time evolution of the thin film. This equation is coupled to a boundary value problem that describes the interaction between the local molecular orientation of the NLC (the director field) and the electric potential. We investigate numerically the behavior of an initially flat film for a range of film heights and surface anchoring conditions.

Tear evaluation by anterior segment OCT in dry eye disease

Objective.Dry Eye Disease (DED) is a multifactorial disorder, centered by loss of tear homeostasis. The diagnosis represents a challenge in the absence of a gold standard, so different questionnaires and techniques are combined. Considering that a low lacrimal secretion and a high rate of evaporation can determine changes in the tear film, the question that arises is if there are differences between the tear film thickness and the tear meniscus values of patients with DED compared to healthy volunteers, and if so, if they can be proposed as an objective diagnosis technique using Optical Coherence Tomography (OCT).Materials and methods.Ocular Surface Disease Index (OSDI) was used together with examiner confirmation for the diagnosis of DED. All the images were acquired using anterior segment Spectral Domain - OCT. Measurements were calculated using ImageJ. IBM SPSS Statistics was used for data analysis. Statistical significance was achieved if p value was <0.05, with 95% confidence intervals.Results.There were no statistically significant differences between the two groups concerning tear film thickness for the right or left eye (p=0.895 and p=0.178, respectively, p >0.05) or the difference between them (p=0.858, p >0.05). Tear meniscus area and height for each eye and the difference between the eyes reported no significant difference between the healthy and the DED volunteers.Conclusion.Tear film thickness does not record statistically significant differences between the DED and the healthy group, and neither does the sagittal area, the tear film height, or the difference between them when acquired with OCT.Abbreviations: DED = dry eye disease, ASOCT = anterior segment optical coherence tomography, REFT = right eye tear film thickness, LEFT = left eye tear film thickness, DifFT = difference between the two eyes for tear film thickness, RETMA = right eye tear meniscus area, LETMA = left eye tear meniscus area, DifTMA = difference between the two eyes for tear meniscus area, RETMH = right eye tear meniscus height, LETMH = left eye tear meniscus height, DifTMH = difference between the two eyes for tear meniscus height

Experimentally testing a generalized coarsening model for individual bubbles in quasi-two-dimensional wet foams.

We present high-precision data for the time evolution of bubble area A(t) and circularity shape parameter C(t) for several bubbles in a quasi-two-dimensional foams consisting of bubbles squashed between parallel plates. In order to fully compare with earlier predictions, foam wetness is systematically varied by controlling the height of the sample above a liquid reservoir which in turn controls the radius r of the inflation of the Plateau borders. For very dry foams, where the borders are very small, classic von Neumann behavior is observed where a bubble's growth rate depends only on its number n of sides. For wet foams, the inflated borders impede gas exchange and cause deviations from von Neumann's law that are found to be in accord with the generalized coarsening equation. In particular, the overall growth rate varies linearly with the film height, which decrease as surface Plateau borders inflate. More interestingly, the deviation from dA/dt∝(n-6) von Neumann behavior grows in proportion to nCr/sqrt[A]. This is highlighted definitively by data for six-sided bubbles, which are forbidden to grow or shrink except for the existence of this term. It is tested quantitatively by variation of all four relevant quantities: n, C, r, and A.

Streamlines in the Two-Dimensional Spreading of a Thin Fluid Film: Blowing and Suction Velocity Proportional to the Height

The two-dimensional spreading under gravity of a thin fluid film with suction (fluid leak-off) or blowing (fluid injection) at the base is considered. The thin fluid film approximation is imposed. The height of the thin film satisfies a nonlinear diffusion equation with a source/sink term. The Lie point symmetries of the nonlinear diffusion equation are derived and exist, which provided the fluid velocity at the base, vn satisfies a first order linear partial differential equation. The general form has algebraic time dependence while a special case has exponential time dependence. The solution in which vn is proportional to the height of the thin film is studied. The width of the base always increases with time even for suction while the height decreases with time for sufficiently weak blowing. The streamlines of the fluid flow inside the thin film are plotted by first solving a cubic equation. For sufficiently weak blowing there is a dividing streamline, emanating from the stagnation point on the centre line which separates the fluid flow into two regions, a lower region consisting of rising fluid and dominated by fluid injection at the base and an upper region consisting of descending fluid and dominated by spreading due to gravity. For sufficiently strong blowing the lower region expands to completely fill the whole thin film.

Streamlines in the Two-Dimensional Spreading of a Thin Fluid Film: Blowing and Suction Velocity Proportional to the Spatial Gradient of the Height

The aim of this investigation is to determine the effect of fluid leak-off (suction) and fluid injection (blowing) at the horizontal base on the two-dimensional spreading under the gravity of a thin film of viscous incompressible fluid by studying the evolution of the streamlines in the thin film. It is assumed that the normal component of the fluid velocity at the base is proportional to the spatial gradient of the height of the film. Lie symmetry methods for partial differential equations are applied. The invariant solution for the surface profile is derived. It is found that the thin fluid film approximation is satisfied for weak to moderate leak-off and for the whole range of fluid injection. The streamlines are derived and plotted by solving a cubic equation numerically. For fluid injection, there is a dividing streamline originating at the stagnation point at the base which separates the flow into two regions, a lower region consisting mainly of rising fluid and an upper region consisting mainly of descending fluid. An approximate analytical solution for the dividing streamline is derived. It generates an approximate V-shaped surface along the length of the two-dimensional film with the vertex of each section the stagnation point. It is concluded that the fluid flow inside the thin film can be visualised by plotting the streamlines. Other models relating the fluid velocity at the base to the height of the thin film can be expected to contain a dividing streamline originating at a stagnation point and dividing the flow into a lower region of rising fluid and an upper region of descending fluid.

Design of experiments to systematically classify the collision behaviors of a droplet and liquid film composed of different types of liquids

The impingement of a single droplet on a liquid film is observed using a high-speed video camera. Specifically, an experiment is conducted to simulate the impingement behaviors of a fuel droplet on an engine oil film in a real engine. The droplets are composed of n-heptane and ethanol. The films pertain to engine oils with two viscosities. The impact of the engine oil type, droplet liquid type, droplet release height, and temperature and thickness of the oil film on the collision phenomenon is evaluated. The design of experiments scheme is used to identify the dominant parameters affecting the crown height and splash generation. The dominant parameters for the crown height are the oil film temperature, which affects the oil viscosity; droplet release height, which is related with the impinging velocity, and oil film thickness. The splash phenomena can be divided into two types, specifically, splash phenomena with split early type and crown break type, which are affected by the droplet release height and oil film temperature, respectively. The results demonstrate that the design of experiments scheme can help evaluate the dominant parameters in impingement phenomena.

Electrocapillary effect in liquid films with an electrically charged interface

Abstract The electrocapillary effect is the change in interfacial tension between two immiscible liquids when subjected to an electric field across the interface. The change in interfacial tension occurs due to variations in the surface charge density of adsorbed ions or polar species at the interface. In the present work, we provide fluid mechanical insights into electrocapillarity-based dynamics of an interface between a passive air layer and a thin liquid film that has small, but finite electrical conductivity. We formulate and solve mathematical equations that model the situation in which a liquid film bounded by an air layer of controllable thickness is sandwiched between two electrode plates, and an electric field is applied across the layers. As the liquid and air have different conductivities, free charges would accumulate at the liquid–air interface to ensure that current is conserved across the layers. In our model, the interfacial tension is assumed to vary as per the classical Lippmann’s equation. The present mathematical model describes spatiotemporal variation of the film height and interfacial charge density as a function of the applied potential, air layer width, and the sensitivity of interfacial tension to the electric potential. Our results show that ultrathin liquid films (

A study on the high-efficiency mixer of the SCR system

A new mixer for a diesel engine after-treatment system is developed to meet the requirements of China VI emission regulation. As for the structure of the mixer, it is surrounded by spiral blades, and the center is staggered with small blades, which is conducive to the crushing of urea droplets and can make the droplets fully mixed with air, improve the conversion efficiency of nitrogen oxides (NOx) and reduce ammonia leakage. The numerical analysis, engine bench test, and vehicle road test were carried out on the after-treatment system equipped with the new mixer. The numerical calculation results show that the velocity uniformity index of the selective catalytic reduction (SCR) carrier can reach 0.98, as well as the ammonia uniformity can reach 0.95, meanwhile, the low wall film height shows excellent anti-crystallization properties. engine bench test results are consistent with numerical results. The crystallization status of the mixer after the vehicle durability test is acceptable and well performed.

The Formula for Best Sunscreen Performance: Beer-Lambert's Law Under the Microscope.

Sunscreens used for the protection of human skin work by attenuating the potentially harmful solar UV radiation. In recent years, the quantitative understanding of this attenuating effect has grown tremendously, enabling model calculations of sunscreen performance. Such calculations are based on the simulation of the UV transmission of the sunscreen film applied on human skin. However, there are 2 prerequisites assumed to hold. The first prerequisite is the applicability of the Beer-Lambert law for sunscreen films, and the second is that the thickness variation of the sunscreen film can be described with a gamma distribution of film heights. There is strong evidence from recent experimental work that both assumptions are correct. For several applications, calculations of sunscreen performance have been shown to be useful, for instance, in the design of new sunscreen formulations aiming for a certain sun protection factor or other characteristics, prediction of pre-vitamin D production in the skin in the presence of sunscreen, in vitro measurement of water resistance, and assessment of the ecotoxicological profile of a sunscreen formulation or the influence of oil polarity on UV-filter absorbance and the consequence for sunscreen performance.

Randomized controlled trial of trehalose: An efficient autophagic bioprotectant in the management of dry eye disease.

PURPOSE:To compare the therapeutic effect of sodium hyaluronate (SH)–trehalose (Trehalube, Microlabs, Bangalore, India, SH 0.1% and trehalose 3%) or SH (0.1% Hylotears, Raymed, Chandigarh, India) alone in patients with dry eye disease (DED).MATERIALS AND METHODS:Patients were randomized into two groups: SH-trehalose (SH 0.1% and trehalose 3%) or SH (0.1% Hylotears) alone. The Ocular Surface Disease Index (OSDI) questionnaire was used to assess patient's symptoms. Patients were followed up at 4 and 8 weeks, and OSDI score, tear film break-up time (TBUT), tear film height (TFH), Schirmer's test, and conjunctival staining were evaluated at each visit.RESULTS:A total of 384 patients were included in the study, 192 patients in each arm. The mean age of participants was 37.62 + 14.4 years and 225 were women (56%). The improvement in Schirmer's test was significantly better in the SH-trehalose group at 8 weeks (5.26 + 4.3 mm, 95% confidence interval = 4.6–5.9 mm) compared to the SH group (3.71 + 3.9, 95% confidence interval = 3.15–4.28 mm). The TBUT and TFH showed slight improvement at 4 weeks in both groups, but not at 8 weeks. There were no group differences at all-time points in terms of conjunctival staining and OSDI-based grades of DED.CONCLUSION:It was found that treating dry eye with SH-trehalose leads to greater improvement in the Schirmer's values and TBUT after 8 weeks of sustained use in patients with DED, and this was more pronounced in those with severe DED.

Emergence and breakup of a cluster of ordered microparticles during the interaction of thermocapillary and thermogravitational convection

Local laser heating of the liquid film leads to simultaneous self-organization of both cellular convective structures and a cluster of micron-scale particles. The cluster is formed on the free surface of the layer and consists of hexagonal structures with a size of 50-100 μm. The height of the liquid film (0.5 mm) is ten times the diameter of the convective cells. Experimental data on the distribution of particle sizes and sizes of hexagonal cells in the cluster are presented. The cluster shape may be either a circle with a diameter of 110-140 μm, or an ellipse. Due to the instability of the velocity field, the toroid is not formed, and convective cells are formed only near the heating center. Self-organization of a cluster of particles and cellular structures using local heating can be effectively used to create new promising materials, as well as in micro-biology and medicine.

A Mathematical Model of Intermittent Gas Lift in Elevation-Production Operation with Line-Pack and Line-Drafting Phenomena in a Gas Line

This paper discusses a transient model of the intermittent gas lift technique in an oil well. The model is developed in the gas line, in the tubing-casing annulus, and the tubing. The line-pack and line-drafting phenomena in the gas line are considered in the model. A numerical approach will be used to solve the mathematical model that represents fluid flow during intermittent gas lift injection. The dynamics of important variables in the intermittent gas lift are investigated and analyzed to determine the best production strategy for intermittent gas lift. The variables are film thickness and velocity, slug height and velocity, and gas height and velocity. The relationships between surface injection control parameters (gas injection pressure and gas injection rate) and the velocity and height of film, gas, and liquid are shown in one cycle of the gas lift intermittent process. The higher the gas injection pressure, the faster the gas injection velocity, and the thinner the film thickness in the tubing. In order to obtain clean tubing from film thickness, the gas injection pressure needs to be optimized, which will lead to maintaining compressor discharge pressure availability. Detailed observation of the dynamic performance inside the tubing production well will give the optimum oil production rate for oil wells under a gas lift intermittent production strategy for field application.