898 research outputs found

    Computer simulations of evaporation of sessile liquid droplets on solid substrates

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    Present work is focused on the numerical study of evaporation of sessile liquid droplets on top of smooth solid substrates. The process of evaporation of a sessile liquid droplet has lots of different applications both in industry and research area. This process has been under study for many years, and still it is an actual problem, solution of which can give answers on some fundamental and practical questions. Instantaneous distribution of mass and heat fluxes inside and outside of an evaporating sessile droplet is studied in this research using computer simulations. The deduced dependences of instantaneous fluxes are applied for self-consistent calculations of time evolution of evaporating sessile droplets. The proposed theory of evaporating sessile droplets of liquid has been validated against available experimental data, and has shown a good agreement. Evaporation of surfactant solution droplets is studied experimentally. The theory, proposed for two stages of evaporation, fits experimental data well. An additional evaporation stage, specific for surfactant solutions, is observed and described. Mathematical modelling of this stage requires further research on surfactant adsorption and its influence on the value of receding contact angle. Numerical study of the evaporation of microdroplets is conducted in order to evaluate the significance of different evaporation mechanisms (diffusive and kinetic models of evaporation) and different physical phenomena (Kelvin s equation, latent heat of vaporization, thermal Marangoni convection, Stefan flow)

    A CDNO/S3 Study of the p-Quinonemethide-Phenol Interaction

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    The dependence of the electronic structure of p-quinonemethide - phenol and p-quinonemethide - phenolate anion systems on interplane distance and mutual orientation of the reactants was analyzed on the basis of CNDO/S3calculations. The approach of two reactants results in aminor change in the charge transfer electron transition, Its high energy indicates a low probability of electron transfer to be the first stage of the chemical reaction

    Simulations of Jets Driven by Black Hole Rotation

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    The origin of jets emitted from black holes is not well understood, however there are two possible energy sources, the accretion disk or the rotating black hole. Magnetohydrodynamic simulations show a well-defined jet that extracts energy from a black hole. If plasma near the black hole is threaded by large-scale magnetic flux, it will rotate with respect to asymptotic infinity creating large magnetic stresses. These stresses are released as a relativistic jet at the expense of black hole rotational energy. The physics of the jet initiation in the simulations is described by the theory of black hole gravitohydromagnetics.Comment: Science VOL 305., pg. 978 8/13/04. Link to movies is http://geo.phys.spbu.ru/~ego/ Note that movies are 3-7 mb and can take awhile to downloa

    Thermodynamics of Yukawa fluids near the one-component-plasma limit

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    Thermodynamics of weakly screened (near the one-component-plasma limit) Yukawa fluids in two and three dimensions is analyzed in detail. It is shown that the thermal component of the excess internal energy of these fluids, when expressed in terms of the properly normalized coupling strength, exhibits the scaling pertinent to the corresponding one-component-plasma limit (the scalings differ considerably between the two- and three-dimensional situations). This provides us with a simple and accurate practical tool to estimate thermodynamic properties of weakly screened Yukawa fluids. Particular attention is paid to the two-dimensional fluids, for which several important thermodynamic quantities are calculated to illustrate the application of the approach.Comment: Submitted to Phys. Plasma

    Boundary conditions for a one-sided numerical model of evaporative instabilities in sessile drops of ethanol on heated substrates

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    International audienceThe work is focused on obtaining boundary conditions for a one-sided numerical model of thermoconvective instabilities in evaporating pinned sessile droplets of ethanol on heated substrates. In the one-sided model, appropriate boundary conditions for heat and mass transfer equations are required at the droplet surface. Such boundary conditions are obtained in the present work based on a derived semiempirical theoretical formula for the total droplet's evaporation rate, and on a two-parametric nonisothermal approximation of the local evaporation flux. The main purpose of these boundary conditions is to be applied in future three-dimensional (3D) one-sided numerical models in order to save a lot of computational time and resources by solving equations only in the droplet domain. Two parameters, needed for the nonisothermal approximation of the local evaporation flux, are obtained by fitting computational results of a 2D two-sided numerical model. Such model is validated here against parabolic flight experiments and the theoretical value of the total evaporation rate. This study combines theoretical, experimental, and computational approaches in convective evaporation of sessile droplets. The influence of the gravity level on evaporation rate and contributions of different mechanisms of vapor transport (diffusion, Stefan flow, natural convection) are shown. The qualitative difference (in terms of developing thermoconvective instabilities) between steady-state and unsteady numerical approaches is demonstrated

    Evaporation of pinned sessile microdroplets of water on a highly heat-conductive substrate: Computer simulations

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    The aim of the current numerical study is to investigate the influence of individual effects (kinetic effects, latent heat of vaporization, Marangoni convection, Stefan flow, droplet’s surface curvature) on the rate of evaporation of a water droplet placed on a highly heat conductive substrate for different sizes of the droplet (down to submicron sizes). We performed simulations for one particular set of parameters: the ambient relative air humidity is set to 70%, the ambient temperature is 20 ∘C, the contact angle is 90∘, and the substrate material is copper. The Suggested model combines both diffusive and kinetic models of evaporation. The obtained results allow estimation of the characteristic droplet sizes where each of the mentioned above phenomena becomes important or can be neglected

    Influence of contact angle and temperature on evaporation of droplets [Abstract]

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    Influence of contact angle and temperature on evaporation of droplets [Abstract

    Recent Progress with bioSFQ Circuit Family for Neuromorphic Computing

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    Superconductor single flux quantum (SFQ) technology is attractive for neuromorphic computing due to low energy dissipation and high, potentially up to 100 GHz, clock rates. We have recently suggested a new family of bioSFQ circuits (V.K. Semenov et al., IEEE TAS, vol. 32, no. 4, 1400105, 2022) where information is stored as a value of current in a superconducting loop and transferred as a rate of SFQ pulses propagating between the loops. This approach in the simplest case dealing with positive numbers, requires single-line transfer channels. In the more general case of bipolar numbers, it requires dual-rail transfer channels. For this need, a new comparator with dual-rail output has been developed and is presented. This comparator is an essential part of a bipolar multiplier that has also been designed, fabricated, and tested. We discuss strategic advantages of the suggested bioSFQ approach, e.g., an inherently asynchronous character of bioSFQ cells which do not require explicit clock signals. As a result, bioSFQ circuits are free of racing errors and tolerant to occasional collision of propagating SFQ pulses. This tolerance is due to stochastic nature of data signals generated by comparators operating within their gray zone. The circuits were fabricated in the eight-niobium-layer fabrication process SFQ5ee developed for superconductor electronics at MIT Lincoln Laboratory.Comment: 5 pages, 7 figures, 12 references. This paper was presented at Applied Superconductivity Conference, ASC 2022, October 23-28, 2022, Honolulu, Hawai
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