Annular Thin Film Research Articles

Drastic Microbial Count Reduction in Soy Milk Using Continuous Short-Wave Ultraviolet Treatments in a Tubular Annular Thin Film UV-C Reactor.

Vegetative cells of Listeria monocytogenes and Escherichia coli and spores of Bacillus subtilis and Aspergillus niger were inoculated in soy milk at an initial concentration of ≈5 log CFU/mL. Inoculated and control (non-inoculated) soy milk samples were submitted to three types of treatments using a tubular annular thin film short-wave ultraviolet (UV-C) reactor with 1 mm of layer thickness. Treatments applied depended on the flow rate and the number of entries to the reactor, with UV-C doses ranging from 20 to 160 J/mL. The number of entries into the reactor tube (NET) was established as the most determining parameter for the efficiency of the UV-C treatments. Conidiospores of A. niger were reported as the most resistant, followed by B. subtilis spores, while vegetative cells were the most sensible to UV-C, with Listeria monocytogenes being more sensible than Escherichia coli. Treatments of just 80 J/mL were needed to achieve a 5 log CFU/mL reduction of L. monocytogenes while 160 J/mL was necessary to achieve a similar reduction for A. niger spores.

Comparison and prediction of UV-C inactivation kinetics of S. cerevisiae in model wine systems dependent on flow type and absorbance

UV-C (254 nm) treatment can be an alternative or supplement method to adding sulfite to wine for stabilization. There are various types of UV-C reactors using different flow types. However, literature data often refer to specific microorganisms in specific food using specific UV-C reactors. Therefore, a statement about the influence of the flow conditions on the inactivation of microorganisms is difficult. This study examined the inactivation of Saccharomyces cerevisiae dependent on the flow conditions. Different flow conditions were realized in three UV-C reactor types. In order to minimize the influence of the natural fluctuations of the ingredients in wine, a model medium was introduced and validated to mimic the inactivation of S. cerevisiae in wine. The absorbance of the model solution was adjusted to resemble wine available on the market by applying variable concentration of food coloring (sunset yellow). These model solutions with inoculated microorganisms were UV-C treated using different flow conditions (Dean vortices, turbulent and laminar tube flows, and laminar annular thin film flows with a 3 mm and a 0.6 mm gap). Mathematical models were established to predict the inactivation of S. cerevisiae dependent on the flow type, the absorbance of the (model) wine and the UV-C dose.

A Further Theoretical Study of Capacitive Pressure Sensors Based on Thin Film Elastic Deflection and Parallel Plate Capacitor: Refined Closed-Form Solution and Numerical Calibration.

The capacitive pressure sensor based on thin film elastic deflection and a parallel plate capacitor uses a non-conductive elastic annular thin film centrally connected to a conductive, rigid, flat, concentric-circular thin plate as a pressure sensing unit. On application of pressure, the non-conductive thin film deflects elastically, which in turn moves the conductive thin plate (as a movable upper electrode plate of the parallel plate capacitor) towards the lower electrode plate, resulting in a change in the capacitance of the capacitor. Therefore, the applied pressure can be determined by measuring the capacitance change, based on the closed-form solution for the elastic behavior of the annular thin film under pressure. Such capacitive pressure sensors are more suitable for large-sized sensors such as those used for building-facade wind pressure measurements, etc. In this paper, a further theoretical study of such capacitive pressure sensors is presented. The newly presented, more refined closed-form solution can greatly reduce the output pressure error under the same input capacitance, in comparison with the previously presented closed-form solution. A numerical example of how to use the resulting closed-form solution to numerically calibrate input–output characteristics is given for the first time. The variation trend of pressure operation ranges and input–output characteristics with important parametric variations, which can be used for guiding the design of such capacitive pressure sensors, is investigated.

Improvement of an annular thin film UV-C reactor by fluid guiding elements

In this paper special elements are inserted into an annular thin film UVC reactor to guide the laminar flow. These “Fluid Guiding Elements” (FGE) divide the flow into three separated laminar currents that are alternatingly directed through a small gap of 0.6 mm facing the UV source by turns. Computational fluid dynamic simulations have been used to visualize the flow dynamics inside the reactor.The residence time distribution and the Bodenstein number show an increase of back mixing in the reactor with the elements. An Iodide/iodate actinometry comparison has shown a better dose distribution throughout the treated volume based on the FGE. The inactivation of E. coli DH5α as an exemplary organism could be improved by more than 4 log levels after 5 passes through the reactor using the FGE independent of the flow rate. The absorbance of a model solution was varied by different dye concentrations and the use of FGE improve the inactivation of Saccharomyces cerevisiae. Industrial relevanceThe stabilization of liquid foods before bottling is a crucial aspect. The consumers often do not accept a chemical additive like sulphites in wine or dimethyl carbonate in juices. A physical alternative is the UV-C Treatment. In contrast to a turbulent flow a laminar flow has a far lower pressure drop. Therefore, a lower amount of energy is needed to pump the liquid. This study shows that with fluid guiding elements a sufficient inactivation can be achieved with laminar flow.

On-route to dryout through sequential interfacial dynamics in annular flow boiling around temperature and heat flux controlled heater rod

A numerical methodology is used to track the interfacial dynamics of the dryout mechanism for flow boiling around the heated cylindrical rod. The mathematical model is based on the Volume of Fluid interface capturing technique for two-phases of fluids. A single set of Navier-Stokes equations with an added source term to take care of vapor mass flux generation due to phase change is utilized. The simulations are carried out for various combinations of flow parameters and heating conditions at a representative higher working pressure of 40 bar, which is usually observed in Boiling Water Reactors (BWR). Various mechanisms of dryout, such as disturbance wave generation, droplet entrainment, deposition, rewetting, nucleation beneath the thin annular film, and its dynamics are illustrated with pictorial representations. The liquid phase fraction distribution across radial and axial planes, wall temperature, and heat transfer coefficient are used to quantify the dryout characteristics.

Modelling of the breakup process of viscous fluids by a high-speed rotary atomizer

Spray drying is a preferred method of drying and successful agglomeration of various materials and is widely used in the chemical, food, pharmaceutical and in the power industry, e.g. to produce polymers, dairy products, foodstuff, pharmaceutics or for flue gas cleaning, etc. In spray drying applications very often rotary atomizers are used for atomization of highly viscous and rheologically complex liquids. The resultant droplet size distribution has to be adapted to customer needs, since it directly influences the resultant powder size distribution and the morphology, porosity and packing density of the powder particles. In the present experimental and theoretical study, the size and the velocity of drops generated by a rotary atomizer is measured using a phase Doppler instrument for Newtonian liquids of different viscosities. A theoretical model is developed for the liquid flow through the radial openings of the atomizer wheel, considering a thin annular film flow and a rivulet-type flow. These two types of flow have also been observed in the experiments. Finally, a semi-empirical model for the average diameter of drops in the spray is developed, accounting for the different mechanisms of atomization of the rivulet and the thin film flows.

Partial and complete wetting in a micro-tube

This study investigates the flow of a thin annular film driven by an axial force in a micro-tube. Partial wetting is taken into account using the diffuse interface theory and the film dynamics is approximated by a long-wave mesoscopic model. One of the goals is to understand the transition between partial wetting and complete wetting when the driving force increases. Two scenarios, depending on the curvature, lead to complete wetting. For low curvature, complete wetting arises by ridge spreading, whereas for a sufficiently large curvature, it arises via coating of the sliding ridge. The latter regime has no equivalent for plane substrates. The transition between the two scenarios is explained as an exchange of solution branches involving a solution composed of merged ridges.

A theoretical study of an improved capacitive pressure sensor: Closed-form solution of uniformly loaded annular membranes

In this study, the conductive diaphragm in conventional capacitive pressure sensors with dual function (the deformable element and the upper electrode plate of a non-parallel plate capacitor) was modified into a non-conductive elastic annular thin-film (as the deformable element) centrally connected with a conductive rigid circular plate or alternatively with a non-conductive rigid circular plate adhered by a conductive thin-film (as the upper electrode plate of a parallel plate capacitor). This modification brings two advantages: the parallel plate capacitor is more convenient in the accurate calculation of capacitance than a non-parallel plate capacitor; it is easier to select a deformable element with good elastic behavior in non-conductive elastic thin-films than to select such a deformable element in conductive diaphragms. These advantages could provide convenience for further improving the performance of sensors. The presented closed-form solution can meet the needs of the research and development of this improved capacitive pressure sensor.

Post-wrinkling analysis of a torsionally sheared annular thin film by using a compound series method

This paper investigates the torsional wrinkling behavior of an annular thin film. Non-dimensional nonlinear von Karman buckling equations are established, which are solved by introducing a compound series method to acquire the post-wrinkling characteristics. The proposed theoretical model can accurately predict the critical wrinkling behavior and post-wrinkling characteristics of the annular thin film, which are verified by the experimental measurement based on the digital image correlation (DIC) technique. The theoretical results show that the post-wrinkling stress is intimately associated with the wrinkle configuration in the post-wrinkling stage. The hoop post-wrinkling stress along the wrinkle texture direction of the annular thin film dictates the wrinkle evolution. The wrinkle number remains constant in the elastic regime, which is determined by the critical buckling load factor. The results provide good guides to tune or control the wrinkles in the thin film.

Free transverse vibration of a wrinkled annular thin film by using finite difference method

This paper investigates the free transverse vibration of a wrinkled annular thin film. The non-dimensional Hamilton motion equation of the wrinkled annular thin film is established, which is solved by using the finite difference method to acquire the vibration frequency and mode. The predicted vibration characteristics are verified by the experimental measurements based on the digital image correlation (DIC) technique. The results show that wrinkles have great effects on the vibration of the annular thin film. Especially for the heavily wrinkled cases, the local–global interactive mode dominates the vibration of the annular thin film. The frequency increases as the wrinkling level increases which is mainly due to the increased nonlinear geometric stiffness. The results provide favorable supports for understanding the role of nonlinear wrinkling on the vibration of thin films.

The effect of total reflection in PLIF imaging of annular thin films

Planar laser-induced fluorescence (PLIF) imaging techniques are increasingly used to study wavy annular flows in vertical and horizontal pipes. We present a ray-tracing study that analyzes the imaging properties of the PLIF technique for uniform and wavy annular films. Part of the emitted fluorescence will hit the water–air interface at angles greater than the critical angle of total reflection. As a consequence, PLIF imaging probes the film twice: From bottom to top and then again from top to bottom. Deflected fluorescence widens PLIF images of uniform films by about 30%. Surface waves further increase the contribution of deflected rays to the overall signal. At the steep slopes of large amplitude axial waves, total reflection might widen PLIF signals by up to a factor of two.

Regularity analysis of wrinkles under the action of capillary force in an annular thin film

The wrinkling law of annular sheet which is induced by capillary force with inner liquid film is analyzed in this paper. The results show that the inner liquid film can wrinkle the annular sheet when the surface tension of the liquid film reaches a critical value, and the critical value can be dramatically altered by changing the geometry and properties of the annular sheet. The results obtained in this article may hold potential applications in generating three-dimensional structures through capillary effects.

Wrinkles as the Result of Compressive Stresses in an Annular Thin Film

It is well‐known that an elastic sheet loaded in tension will wrinkle and that the length scale of the wrinkles tends to 0 with vanishing thickness of the sheet [Cerda and Mahadevan, Phys. Rev. Lett. 90, 074302 (2003)]. We give the first mathematically rigorous analysis of such a problem. Since our methods require an explicit understanding of the underlying (convex) relaxed problem, we focus on the wrinkling of an annular sheet loaded in the radial direction [Davidovitch et al., Proc. Natl. Acad. Sci. 108 (2011), 18227]. Our main achievement is identification of the scaling law of the minimum energy as the thickness of the sheet tends to 0. This requires proving an upper bound and a lower bound that scale the same way. We prove both bounds first in a simplified Kirchhoff‐Love setting and then in the nonlinear three‐dimensional setting. To obtain the optimal upper bound, we need to adjust a naive construction (one family of wrinkles superimposed on a planar deformation) by introducing a cascade of wrinkles. The lower bound is more subtle, since it must be ansatz‐free. © 2014 Wiley Periodicals, Inc.

Combining ultraviolet light and mild temperatures for the inactivation of Escherichia coli in orange juice

It is difficult to guarantee the effectiveness of UV technology to reach 5Log10 cycles of inactivation of Escherichia coli in a large amount of fruit juices with high absorption coefficients and turbidities, such as orange juice. The aim of this work was to overcome this limitation by combining UV light and mild temperatures. UV treatments were carried out in an equipment with eight individual annular thin film flow-through reactors connected sequentially and submerged in a thermostatic water bath. A treatment of 13.55J/mL reached 0.25±0.04, 0.41±0.13, 0.84±0.32, 0.96±0.12, 2.57±0.05, 5.41±0.23, and more than 6Log10 cycles of inactivation of E. coli STCC 4201 suspended in commercial sterilized orange juice at 25.0, 40.0, 50.0, 52.5, 55.0, 57.5, and 60.0°C, respectively. The comparison of UV resistance at 25°C with heat resistance at mild temperatures demonstrated a synergistic effect of both technologies applied simultaneously. The maximum synergistic lethal effect was reached at 55°C (68.03%).A UV light treatment (23.72J/mL) at 55°C (3.6min) of freshly squeezed orange juice allowed reaching more than 5Log10 cycles of inactivation of a E. coli cocktail (STCC 4201, STCC 471, ATCC 27325, ATCC 25922, and O157:H7 Chapman strain). The selected treatment did not affect the pH, acidity, Brix, and color, and decreased 16.45% ascorbic acid content and 63.96% the Pectinmethylesterase activity.

Angular velocity detector, method of detection of angular velocities using angular velocity detector, and method of fabricating angular velocity detector

An angular velocity detector using a vibrator made of an annular thin film. The detector also has electrodes arranged ingeniously to have high detection sensitivity for angular velocities. The detector can detect angular velocities in two axial directions simultaneously. The detector has support portions ( 1105 ), ( 1106 ) which are formed over a first substrate ( 1123 ) and poised above the surface of the first substrate ( 1100 ) at a certain spacing therefrom. Resilient support bodies are supported to the support portions and include outer springs ( 1102 ) and inner springs ( 1103 ). A vibrator ( 1101 ) is mounted via the resilient support. An exciting means consisting of a magnet ( 1124 ) and an exciting electrode ( 1108 ) excites the vibrator to vibrate in a certain direction of vibrations. When the vibrator ( 1101 ) is excited to vibrate in the direction of vibrations by the exciting means and an angular velocity acts from the outside, a displacement detection means consisting of a detection electrode ( 1109 ) and electrodes ( 1120 ) detects the displacement of the vibrator ( 1101 ) in a direction perpendicular to the direction of vibrations in response to the angular velocity. The vibrator ( 1101 ) or an angular velocity detection portion including the vibrator ( 1101 ) is electromagnetically driven to vibrate.

Annular Thin-Film Flows Driven by Azimuthal Variations in Interfacial Tension

We consider a thin viscous film that lines a rigid cylindrical tube and surrounds a core of in-viscid fluid, and we model the flow that is driven by a prescribed azimuthally varying tension at the core-film interface, with dimensional form σ * m ― a * cos(nθ) (where constants n e ℕ and σ* m , a * ∈ ℝ). Neglecting axial variations, we seek steady two-dimensional solutions with the full symmetries of the evolution equation. For a * = 0 (constant interfacial tension), the fully symmetric steady solution is neutrally stable and there is a continuum of steady solutions, whereas for a* ≠ 0 and n = 2, 3, 4, ..., the fully symmetric steady solution is linearly unstable. For n = 2 and n = 3, we analyse the weakly nonlinear stability of the fully symmetric steady solution, assuming that 0 0 and n = 1, 2, 3,..., the film can evolve towards a steady solution featuring a drained region. We investigate the draining dynamics using matched asymptotic methods.

Wrinkling of Pre-stressed Annular Thin Films under Azimuthal Shearing

The wrinkling instabilities of a pre-tensioned annular thin film undergoing azimuthal shearing are investigated within the framework of the linearized Donnell—von Kármán bifurcation equation for thin plates. The main objective here is to provide a rational understanding of the role played by the presence of finite bending stiffness and to explain the nature of the localized deformation patterns observed in experiments. In order to achieve this, the eigenvalue problem is formulated as a differential equation with variable coefficients depending on a large parameter. The singular perturbation nature of this equation arises from a combination involving both the pre-stress and the geometrical features of the annular domain. The localization mechanism of the corresponding eigenmodes is then unravelled with the help of a WKB analysis motivated by the qualitative behavior of the neutral stability curves. We show that the asymptotic findings are in very good agreement with the results of direct numerical simulations of the original bifurcation equation.

The stability of a pre‐stressed annular thin film in tension

AbstractThe work presented here considers the elastic instabilities experienced by an annular thin filmsubjected to prescribed displacement fields on its two boundaries. It is shown how singular perturbation methods enable an accurate analytical description of the localised wrinkling pattern that sets in near the inner rim of the film. The theoretical results obtained are corroborated by direct numerical simulations of the full problem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Boundary layers and stress concentration in the circular shearing of annular thin films

This work addresses a generalization of Dean's classical problem, which sought to explain how an annular thin elastic plate buckles under uniform shearing forces applied around its edges. We adapt the original setting by assuming that the outer edge is radially stretched while the inner rim undergoes in-plane rotation through some small angle. Boundary-layer methods are used to investigate analytically the deformation pattern which is set up and localized around the inner hole when this angle reaches a well-defined critical wrinkling value. Linear stability theory enables us to identify both the critical load and the preferred number of wrinkles appearing in the deformed configuration. Our asymptotic results are compared with a number of direct numerical simulations.

Direct numerical simulation of supercritical annular electroconvection

We use direct numerical simulation to study electrically driven convection in an annular thin film. The simulation models a laboratory experiment that consists of a weakly conducting, submicron thick liquid crystal film suspended between two concentric electrodes. The film is driven to convect by imposing a sufficiently large voltage across it. The flow is driven by a surface charge density inversion which is unstable to the imposed electrical force. This mechanism is closely analogous to the mass density inversion which is unstable to the buoyancy force in conventional, thermally driven Rayleigh-Bénard convection. The simulation uses a pseudospectral method with Chebyshev polynomials in the radial direction and Fourier modes in the azimuthal direction. The numerical results, which are in good agreement with previous experimental data and theoretical predictions, reveal several insights. The mode competition near a codimension-two point exhibits hysteresis. The primary bifurcation is supercritical for a broad range of fluid and geometrical parameters.