scholarly journals Self-preserving mechanisms in motile oil droplets: a computational model of abiological self-preservation

2021 ◽  
Vol 8 (12) ◽  
Author(s):  
Matthew Egbert
Keyword(s):  
Computational Model ◽  
Empirical Work ◽  
Local Environment ◽  
Active Surface ◽  
Operating Conditions ◽  
Aqueous Environment ◽  
Marangoni Flow ◽  
Oil Droplets ◽  
Spatial Environment ◽  
Behaviour Changes

Recent empirical work has characterized motile oil droplets —small, self-propelled oil droplets whose active surface chemistry moves them through their aqueous environment. Previous work has evaluated in detail the fluid dynamics underlying the motility of these droplets. This paper introduces a new computational model that is used to evaluate the behaviour of these droplets as a form of viability-based adaptive self-preservation , whereby (i) the mechanism of motility causes motion towards the conditions beneficial to that mechanism’s persistence; and (ii) the behaviour automatically adapts to compensate when the motility mechanism’s ideal operating conditions change. The model simulates a motile oil droplet as a disc that moves through a two-dimensional spatial environment containing diffusing chemicals. The concentration of reactants on its surface change by way of chemical reactions, diffusion, Marangoni flow (the equilibriation of surface tension) and exchange with the droplet’s local environment. Droplet motility is a by-product of Marangoni flow, similar to the motion-producing mechanism observed in the lab. We use the model to examine how the droplet’s behaviour changes when its ideal operating conditions vary.

scholarly journals Design of Molecular Water Oxidation Catalysts Stabilized by Ultrathin Inorganic Overlayers—Is Active Site Protection Necessary?

Inorganics ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 105 ◽  
Author(s):  
Laurent Sévery ◽  
Sebastian Siol ◽  
S. Tilley
Keyword(s):  
Water Oxidation ◽  
Atomic Layer ◽  
Deposition Process ◽  
Operating Conditions ◽  
Molecular Water ◽  
Side Reactions ◽  
Aqueous Environment ◽  
Oxidation Catalysts ◽  
Initial Onset ◽  
Anchoring Groups

Anchored molecular catalysts provide a good step towards bridging the gap between homogeneous and heterogeneous catalysis. However, applications in an aqueous environment pose a serious challenge to anchoring groups in terms of stability. Ultrathin overlayers embedding these catalysts on the surface using atomic layer deposition (ALD) are an elegant solution to tackle the anchoring group instability. The propensity of ALD precursors to react with water leads to the question whether molecules containing aqua ligands, such as most water oxidation complexes, can be protected without side reactions and deactivation during the deposition process. We synthesized two iridium and two ruthenium-based water oxidation catalysts, which contained an aqua ligand (Ir–OH2 and Ru–OH2) or a chloride (Ir–Cl and Ru–Cl) that served as a protecting group for the former. Using a ligand exchange reaction on the anchored and partially embedded Ru–Cl, the optimal overlayer thickness was determined to be 1.6 nm. An electrochemical test of the protected catalysts on meso-ITO showed different behaviors for the Ru and the Ir catalysts. The former showed no onset difference between protected and non-protected versions, but limited stability. Ir–Cl displayed excellent stability, whilst the unprotected catalyst Ir–OH2 showed a later initial onset. Self-regeneration of the catalytic activity of Ir–OH2 under operating conditions was observed. We propose chloride ligands as generally applicable protecting groups for catalysts that are to be stabilized on surfaces using ALD.

Design and Analysis of an Intentional Mistuning Experiment Reducing Flutter Susceptibility and Minimizing Forced Response of a Jet Engine Fan

2017 ◽  
Author(s):  
Felix Figaschewsky ◽  
Arnold Kühhorn ◽  
Bernd Beirow ◽  
Jens Nipkau ◽  
Thomas Giersch ◽  
...  
Keyword(s):  
Computational Model ◽  
Paint Layer ◽  
Forced Vibrations ◽  
Forced Response ◽  
Operating Conditions ◽  
Jet Engines ◽  
Jet Engine ◽  
Aspect Ratios ◽  
Engine Order ◽  
Stall Flutter

Recent demands for a reduction of specific fuel consumption of jet engines have been opposed by increasing propulsive efficiency with higher bypass ratios and increased engine sizes. At the same time the challenge for the engine development is to design safe and efficient fan blades of high aspect ratios. Since the fan is the very first rotor stage, it experiences significant distortions in the incoming flow depending on the operating conditions. Flow distortions do not only lead to a performance and stall margin loss but also to remarkable low engine order (LEO) excitation responsible for forced vibrations of fundamental modes. Additionally, fans of jet engines typically suffer from stall flutter, which can be additionally amplified by reflections of acoustic pressure waves at the intake. Stall flutter appears before approaching the stall line on the fan’s characteristic and limits its stable operating range. Despite the fact that this “flutter bite” usually affects only a very narrow speed range, it reduces the overall margin of safe operation significantly. With increasing aspect ratios of ultra-high bypass ratio jet engines the flutter susceptibility will probably increase further and emphasizes the importance of considering aeromechanical analyses early in the design phase of future fans. This paper aims at proving that intentional mistuning is able to remove the flutter bite of modern jet engine fans without raising issues due to heavily increased forced vibrations induced by LEO excitation. Whereas intentional mistuning is an established technology in mitigating flutter, it is also known to amplify the forced response. However, recent investigations considering aeroelastic coupling revealed that under specific circumstances mistuning can also reduce the forced response due to engine order excitation. In order to allow a direct comparison and to limit costs as well as effort at the same time, the intentional mistuning is introduced in a non-destructive way by applying heavy paint to the blades. Its impact on the blade’s natural frequencies is estimated via finite element models with an additional paint layer. In parallel, this procedure is experimentally verified with painted fan blades in the laboratory. A validated SNM (subset of nominal system modes) representation of the fan is used as a computational model to characterize its mistuned vibration behavior. Its validation is done by comparing mistuned mode shape envelopes and frequencies of an experimental modal analysis at rest with those obtained by the updated computational model. In order to find a mistuning pattern minimizing the forced response of mode 1 and 2 at the same time and satisfying stability and imbalance constraints, a multi-objective optimization has been carried out. Finally, the beneficial properties of the optimized mistuning pattern are verified in a rig test of the painted rotor.

Multi-Objective Optimization Model Development to Support Sizing Decisions for a Novel Reciprocating Steam Engine Technology

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
J. M. Hamel ◽  
Devin Allphin ◽  
Joshua Elroy
Keyword(s):  
Computational Model ◽  
Design Optimization ◽  
Kinematic Model ◽  
Operating Conditions ◽  
Steam Engine ◽  
System Model ◽  
System Level ◽  
Multi Objective Optimization ◽  
Multi Objective ◽  
Crank Angle

A system-level computational model of a recently patented and prototyped novel steam engine technology was developed from first principles for the express purpose of performing design optimization studies for the engine's inventors. The developed system model consists of numerous submodels including a flow model of the intake process, a dynamic model of the intake valve response, a pressure model of the engine cylinder, a kinematic model of the engine piston, and an output model that determines engine performance parameters. A crank-angle discretization strategy was employed to capture the performance of engine throughout a full cycle of operation, thus requiring all engine design submodels to be evaluated at each crank angle of interest. To produce a system model with sufficient computational speed to be useful within optimization algorithms, which must exercise the system level model repeatedly, various simplifying assumptions and modeling approximations were utilized. The model was tested by performing a series of multi-objective design optimization case studies using the geometry and operating conditions of the prototype engine as a baseline. The results produced were determined to properly capture the fundamental behavior of the engine as observed in the operation of the prototype and demonstrated that the design of engine technology could be improved over the baseline using the developed computational model. Furthermore, the results of this study demonstrate the applicability of using a multi-objective optimization-driven approach to conduct conceptual design efforts for various engine system technologies.

Computational Evaluation of Low NOx Operating Conditions in Arch-Fired Boilers

1999 ◽  
Vol 121 (4) ◽  
pp. 735-740 ◽  
Author(s):  
N. Fueyo ◽  
V. Gambo´n ◽  
C. Dopazo ◽  
J. F. Gonza´lez
Keyword(s):  
Computational Model ◽  
Field Measurements ◽  
Operating Conditions ◽  
Formation Mechanisms ◽  
Local Concentration ◽  
Nox Formation ◽  
Operating Modes ◽  
Computational Evaluation ◽  
Chemical Conditions ◽  
Coal Boiler

In the present paper, a computational model is used to simulate the aero-dynamic, thermal, and chemical conditions inside an arch-fired coal boiler. The model is based on the Eulerian-Eulerian concept, in which Eulerian conservation equations are solved both for the gas and the particulate phases. A NOx formation and destruction submodel is used to calculate the local concentration of NO. The model is used to simulate a range of operating conditions in an actual, 350 MW, arch-fired boiler, with the aim of reducing, using primary measures, the emissions of NOx. The model results shed some light on the relevant NOx-formation mechanisms under the several operating conditions. Furthermore, they correlate well quantitatively with the available field measurements at the plant, and reproduce satisfactorily the tendencies observed under the different operating modes.

scholarly journals Evaporating pure, binary and ternary droplets: thermal effects and axial symmetry breaking

2017 ◽  
Vol 823 ◽  
pp. 470-497 ◽  
Author(s):  
Christian Diddens ◽  
Huanshu Tan ◽  
Pengyu Lv ◽  
Michel Versluis ◽  
J. G. M. Kuerten ◽  
...  
Keyword(s):  
Thermal Effects ◽  
Pure Water ◽  
Three Dimensional ◽  
Marangoni Flow ◽  
Oil Droplets ◽  
Spontaneous Emulsification ◽  
Micro Particle Image Velocimetry ◽  
Dimensional Finite Element ◽  
Preferential Evaporation ◽  
Three Dimensional Finite Element

The Greek aperitif Ouzo is not only famous for its specific anise-flavoured taste, but also for its ability to turn from a transparent miscible liquid to a milky-white coloured emulsion when water is added. Recently, it has been shown that this so-called Ouzo effect, i.e. the spontaneous emulsification of oil microdroplets, can also be triggered by the preferential evaporation of ethanol in an evaporating sessile Ouzo drop, leading to an amazingly rich drying process with multiple phase transitions (Tan et al., Proc. Natl Acad. Sci. USA, vol. 113 (31), 2016, pp. 8642–8647). Due to the enhanced evaporation near the contact line, the nucleation of oil droplets starts at the rim which results in an oil ring encircling the drop. Furthermore, the oil droplets are advected through the Ouzo drop by a fast solutal Marangoni flow. In this article, we investigate the evaporation of mixture droplets in more detail, by successively increasing the mixture complexity from pure water over a binary water–ethanol mixture to the ternary Ouzo mixture (water, ethanol and anise oil). In particular, axisymmetric and full three-dimensional finite element method simulations have been performed on these droplets to discuss thermal effects and the complicated flow in the droplet driven by an interplay of preferential evaporation, evaporative cooling and solutal and thermal Marangoni flow. By using image analysis techniques and micro-particle-image-velocimetry measurements, we are able to compare the numerically predicted volume evolutions and velocity fields with experimental data. The Ouzo droplet is furthermore investigated by confocal microscopy. It is shown that the oil ring predominantly emerges due to coalescence.

scholarly journals Utilization of Sawdust Waste Biomass as an Eco-Friendly Biosorbent for Bioremediation of Manganese Pollution in Aqueous Environment

2019 ◽  
Vol 2 (3) ◽  
pp. 823-830
Author(s):  
Fatih Deniz
Keyword(s):  
Operating Conditions ◽  
Aqueous Environment ◽  
Order Kinetic ◽  
Waste Biomass ◽  
Equilibrium Studies ◽  
Manganese Removal ◽  
Removal Capacity ◽  
Order Kinetic Model ◽  
Langmuir Isotherm Model ◽  
Pseudo Second Order

In this study, the sawdust waste biomass was used as an eco-friendly biosorbent material for the bioremediation of manganese pollution in aqueous environment. The effects of various environmental variables such as pH, biosorbent amount, metal concentration and contact time on the manganese biosorption were studied in batch operating conditions. The kinetic and equilibrium studies were performed to elucidate the biosorption behavior of biosorbent material. The biosorption capacity of biosorbent was strongly influenced by the operating parameters. The experimental data were more successfully modeled by the pseudo-second-order kinetic model and Langmuir isotherm model compared to other models applied in the study. The maximum manganese removal capacity of biosorbent was found to be 25.655 mg g-1. These findings showed that the sawdust waste biomass can be used as an eco-friendly biosorbent material for the bioremediation of manganese pollution in aqueous environment.

A Numerical and Experimental Study on the Fabrication GaN Films by Chemical Vapor Deposition

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Sun Wong ◽  
Yogesh Jaluria
Keyword(s):  
Chemical Vapor Deposition ◽  
Computational Model ◽  
Vapor Deposition ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Reactor Design ◽  
Film Deposition ◽  
Operating Conditions ◽  
Chamber Pressure ◽  
Organic Chemical

Abstract Computational modeling and simulation are employed to study a rotating susceptor vertical impinging chemical vapor deposition (CVD) reactor to predict GaN film deposition. Many metal-organic chemical vapor deposition reactor manufacturers use prior experience to design and fabricate CVD reactors without a fundamental basis for the process and information on the optimal conditions for the deposition. Through trial and error, they fine tune the gas flow parameters, heater temperatures, chamber pressure, and concentration of species gases for optimal growth. However, expensive raw precursor gas and time are wasted through this method. A computational model is an important step in the CVD reactor design and GaN growth prediction. It can be used to model and optimize the reactor to yield favorable operating conditions. In this paper, a simple geometry consisting of a rotating susceptor and flow guide is considered. The focus is on gallium nitride (GaN) thin films. The study shows how the computational model can benefit reactor design. It also presents comparisons between model prediction results and experimental data from a physical, practical, system. Commercially available software is used, with appropriate modifications, and the results obtained are discussed in detail.

Finite Element Analysis of a CNC Milling Machine Frame

2016 ◽  
Author(s):  
Antonin Max ◽  
Lubos Rehounek ◽  
Tomas Keckstein
Keyword(s):  
Finite Element ◽  
Computational Model ◽  
Operating Conditions ◽  
Cutting Conditions ◽  
Milling Machine ◽  
Linear Motion ◽  
Cnc Milling ◽  
Linear Guide ◽  
Harmonic Response ◽  
Cnc Milling Machine

A computer numerically controlled (CNC) milling center is a machine tool for the production of parts with planar, cylindrical and shaped surfaces. The milling center analyzed here includes an open frame — a structure resembling the shape of the letter C. The main cutting motion is performed by a tool clamped in the spindle. Secondary motion can be linear, rotary or a combination of these. Linear movements in three axes are performed by the tool by means of linear motion components (i.e. motion screws and linear guide rails). Rotary motion is performed only when the workpiece is clamped to the rotary table which is mounted on the mounting plate. The basic demands placed on the structure of a milling center include high static and dynamic stiffness during machining processes. This article is primarily aimed at evaluating the response of the frame of the CNC milling machine to the excitation caused by the fluctuation of cutting forces due to step changes in the number of engaged cutting edges. To ensure optimum machining conditions it is important to set suitable cutting conditions for a frame structure with sufficient stiffness. Unsuitable cutting conditions and low stiffness of the machine frame may lead to dimensional inaccuracies of the workpiece, to decreased quality of the machined surfaces or even to the destruction of the tool cutting edges. The aims of the study include the determination of the static deformation, modal analysis to assess the dynamic properties of the frame, and harmonic response analysis, taking into consideration the amplitudes of the loading forces specified in accordance with the recommended operating conditions of the individual tools. Finite element method (FEM) analyses of the frame were performed using MSC.Marc software. Due to the high structural complexity of the computer aided design (CAD) model, the computational model for the FEM analysis had to be simplified. Only the major structural parts and the connecting parts were meshed in detail, combining both structured and unstructured mesh. Geometrically complicated cast parts with large changes of thickness were meshed with linear tetrahedral elements (tetra4) with full integration. Rotationally symmetrical parts, plates and linear guide rails components were meshed with linear brick elements (hex8) with full integration. The overall number of elements was approximately 1,400,000. Tools, including the clamping head and the spindle, are represented by approximate meshes of brick elements. However, a detailed FEM model of the spindle and the tool would be needed for the analysis of the self-excited oscillations during machining, which is the subject of a large number of scientific publications. Increased attention was paid to the incorporation and set-up of the springs between corresponding pairs of nodes of the meshed linear motion components. As a computational model for modal and harmonic response analyses needs to be strictly linear, only linear elastic material properties and linear springs were defined in the analyses presented here.

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