Numerical simulation of heat and mass transfer under the conditions of phase transitions and chemical reaction during ignition of condensed substances by single hot particles

Physical and mathematical models of heat and mass transfer under the conditions of phase transitions and chemical reactions have been developed for the numerical analysis of condensed substances ignition by a single particle (size from 0.5 mm to 5 mm) heated up to high temperature (above 800 K). Liquid, solid and gel fuels were considered as condensed substances. Metal and non-metal particles were used as ignition sources. A heat and mass transfer mathematical model is presented as a system of nonlinear non-stationary differential equations in the private derivatives corresponding to the basic provisions of the general theory of heat transfer in chemical kinetics and free convection. An algorithm for solving differential equations with the corresponding initial and boundary conditions is based on the finite- difference method. The locally one-dimensional method was used to solve difference analogous of differential equations. One-dimensional difference equations were solved using an implicit four-point difference scheme. Nonlinear equations were solved by the iteration method. Mathematical model verification and the assessment of numerical research results reliability was executed by its comparison with experimental results. Also the verification of the law of conservation of energy in the solution area of the ignition problem was performed. Besides, testing of applied numerical methods and the developed silving algorithm on the example of a group of less complex challenges of thermal conduction and thermal convection was held. The minimum parameters of hot particles (temperature, size) and the ignition delay time of condensed substances were determined for local heat sources with different shapes. The influence of thermal conduction, convection and radiative heat transfer mechanisms in the “particle – condensed substance” system was established on the ignition characteristics

Numerical simulation of water and water emulsion droplets evaporation in flames with different temperatures

The models of heat and mass transfer and phase transition for “water droplet – flame” system have been developed using non-stationary nonlinear partial differential equations. The system of differential equations was solved by the finite-difference method. The locally one-dimensional method was used to solve the difference analogous of differential equations. One-dimensional differential equations were solved using an implicit four-point difference scheme. Nonlinear equations were solved by the iteration method. The evaporation rates of water droplets (with sizes from 0.05 mm to 5 mm) in the flame zone (at the temperatures from 500 K to 1200 K) were determined. Theoretical analysis established essentially nonlinear (close to exponential) form of dependence of the water droplet evaporation rate on the temperature of the external gas area and the temperature of a droplet surface. In particular, the water droplet evaporation rate varies from 0.25 to 0.29 kg/(m2s), when the temperature of external gas area is about 1100 K. On the other hand, the water droplet evaporation rate does not exceed 0.01 kg/(m2s) when the temperature of external gas area is about 350 K. Besides, it has been found out that droplets warm up at different rates depending on their initial temperature and velocity. As a result, the integral characteristics of droplet evaporation can increase substantially, when droplets move through the external gas area at the same temperature. We performed a similar investigation or droplet streams with droplet concentration 0.001–0.005 m3 in 1 m3 of gas area (typical parameters for modern spray extinguishing systems)

Individual and synergistic effects of modifications of the carrier medium of carbon-containing slurries on the viscosity and sedimentation stability

The study is devoted to revealing the individual and synergistic effects of modifications of the carrier medium of the coal-water slurries (CWS) based on coking coal and carbon-containing flotation wastes of this coal on the effective viscosity and sedimentation stability. Synthetic and natural wetting agents as well as liquid solvents (alcohol, oil, conventional liquid fuel, methyl ethers) and solid organic compounds exemplified by sawdust are used for this. The relationships between the effective viscosity, water separation ratio, and zeta potential for the CWS with the separate addition of a wetting agent and a solvent is established. The categories of fuel compositions are identified according to the “stability” criterion. The synergistic effect of the additions of a wetting agent and a solvent on the sedimentation stability and effective viscosity is demonstrated. The physicochemical model of interaction between the solid particles and the additives in CWSs is proposed

Remaining life definition of crane metal construction on value of coercive forces

In this work, the condition definition of bridge crane metal construction and prognostication of its remaining life on the basis of nondestructive control method by using coercive forces is presented. Basic approaches and performance stages of the magnetic control for the purpose of metal condition definition and remaining life of its work are considere

Droplet evaporation in water jet at the motion through high temperature gases

Abstract. Heat and mass transfer model for the numerical investigation of the evaporation process of a single droplet in water jet when moving through high temperature gases was developed. The integral characteristics of the process under investigation were calculated. The macroscopic regularities of water droplet evaporation, as elements of jet, in the high temperature gas mixture (as exemplified by combustion products of typical condensed substances) were determined

Numerical Investigation of Water Droplets Shape Influence on Mathematical Modeling Results of Its Evaporation in Motion through a High-Temperature Gas

The numerical investigation of influence of a single water droplet shape on the mathematical modeling results of its evaporation in motion through high-temperature gases (combustion products of a typical condensed substance) has been executed. Values of evaporation time, motion velocity, and distance passed by various droplet shapes (cylinder, sphere, hemisphere, cone, and ellipsoid) in a high-temperature gases medium were analyzed. Conditions have been defined when a droplet surface configuration affects the integrated characteristics of its evaporation, besides temperature and combustion products concentration in a droplet trace, insignificantly. Experimental investigations for the verification of theoretical results have been carried out with using of optical diagnostic methods for two-phase gas-vapor-liquid flows

‎2D Planar Simulation of Collisions between Liquid Droplets and ‎Solid Particles in a Gas

Here we present a 2D planar simulation of the collisions between liquid droplets and solid particles that are most often used in industrial applications. The collisions are modeled using a combination of Volume of Fluid and Level Set methods. We study the impact of the particle-to-droplet size ratio and the shape of solid particles on the collision behavior and interaction regimes. The findings are presented in the form of collision regime maps. The interaction regimes are also distinguished for binary droplet collisions: deposition, separation, and disintegration. We show the impact of density, viscosity, and surface tension on the droplet collision regime maps as well as on the number of secondary fragments. The practical value of the research comes from the newly established differences of collision regimes between droplets and particles of different shapes and sizes

Experimental demonstration of scalable quantum key distribution over a thousand kilometers

Secure communication over long distances is one of the major problems of modern informatics. Classical transmissions are recognized to be vulnerable to quantum computer attacks. Remarkably, the same quantum mechanics that engenders quantum computers offers guaranteed protection against such attacks via quantum key distribution (QKD). Yet, long-distance transmission is problematic since the essential signal decay in optical channels occurs at a distance of about a hundred kilometers. We propose to resolve this problem by a QKD protocol, further referred to as the Terra Quantum QKD protocol (TQ-QKD protocol). In our protocol, we use semiclassical pulses containing enough photons for random bit encoding and exploiting erbium amplifiers to retranslate photon pulses and, at the same time, ensuring that at the chosen pulse intensity only a few photons could go outside the channel even at distances of about a hundred meters. As a result, an eavesdropper will not be able to efficiently utilize the lost part of the signal. The central component of the TQ-QKD protocol is the end-to-end loss control of the fiber-optic communication line since optical losses can in principle be used by the eavesdropper to obtain the transmitted information. However, our control precision is such that if the degree of the leak is below the detectable level, then the leaking states are quantum since they contain only a few photons. Therefore, available to the eavesdropper parts of the bit encoding states representing `0' and `1' are nearly indistinguishable. Our work presents the experimental demonstration of the TQ-QKD protocol allowing quantum key distribution over 1079 kilometers. Further refining the quality of the scheme's components will expand the attainable transmission distances. This paves the way for creating a secure global QKD network in the upcoming years.Comment: 23 pages (main text: 15 pages, supplement: 8 pages), 21 figures (main text: 7 figures, supplement: 14 figures

Оптимизация параметров намагничивающего устройства электромагнитно-акустического преобразователя для контроля легированных сталей

Contactless electromagnetic-acoustic transducers have a set of significant advantages over contact transducers, but at the same time they have significant disadvantages that require the development of effective magnetizing devices. Compared to magnetizing devices that are using permanent magnets, electric current magnetization devices are easily removed from the object of testing and cleaned from contamination by metal particles. Unfortunately, such transducers have significant dimensions and weight.A transducer containing a magnetic circuit magnetized by an electric current coil and two independent electromagnetic inductors located in the gap between the central part of the magnetic circuit and the object of testing has been developed. Inductors are two flat coils, each of them has form like a butterfly. The inductor conductors located in the working area have mutually perpendicular directions; they allow exciting and receiving the transversely polarized acoustic waves without rearranging the transducer. In order to reduce the overall dimensions and mass of the transducer, the mass and dimensional parameters of the magnetizing device were optimized for operating conditions when the magnetization of the object of testing and measurement are performed during the active measurement phase. During the passive measurement phase, which is three times longer than the active phase in time, the magnetizing device cools down. The cyclic mode with alternating active and passive phases made it possible to reduce the weight of the transducer by more than 3 times. In the working area of the transducer with a size of 15×15 mm, with a gap of 1 mm between the magnetic field concentrator and the object of testing, a field with a normal component of 2.4 T is created. The transducer has protection of the magnetization device from overheating, and the cyclic mode of operation allows for continuous performance of up to 30 measurements per minute at an ambient temperature of 20 °C.The developed magnetizing device can be used in solving a number of problems of structuroscopy, thickness measurement, flaw detection by electromagnetic-acoustic methods based on accurate measurement of the propagation time of elastic waves in the object of testing. Бесконтактные электромагнитно-акустические преобразователи обладают набором значительных преимуществ по сравнению с контактными преобразователями, но при этом у них есть существенные недостатки, требующие разработки эффективных намагничивающих устройств. По сравнению с устройствами намагничивания на постоянных магнитах устройства намагничивания электрическим током легко снимаются с объекта контроля и очищаются от загрязнения металлическими частицами. К сожалению, такие преобразователи имеют значительные габариты и массу.Разработан преобразователь, содержащий магнитопровод, намагничиваемый катушкой с электрическим током, и два независимых электромагнитных индуктора, расположенных в зазоре между центральной частью магнитопровода и объектом контроля. Индукторы представляют собой две плоские катушки, каждая из которых выполнена в виде бабочки. Проводники индукторов, расположенные в рабочей области, имеют взаимно перпендикулярные направления; с их помощью можно эффективно возбуждать и регистрировать поперечно поляризованные акустические волны без перестановки преобразователя. С целью уменьшения габаритных размеров и массы преобразователя произведена оптимизация массогабаритных параметров намагничивающего устройства для условий эксплуатации, когда намагничивание объекта контроля и измерения производятся во время активной фазы измерения. Во время пассивной фазы измерения, в три раза превышающей активную фазу по времени, происходит остывание намагничивающего устройства. Циклический режим с чередованием активной и пассивной фаз позволил уменьшить вес преобразователя более чем в 3 раза. В рабочей зоне преобразователя размером 15×15 мм при зазоре в 1 мм между концентратором магнитного поля и объектом контроля создаётся поле с нормальной компонентой в 2,4 Тл.Преобразователь содержит защиту устройства намагничивания от перегрева, а циклический режим работы позволяет обеспечить непрерывную производительность до 30 измерений в минуту при температуре окружающей среды 20 ºС.Разработанное намагничивающее устройство может быть использовано при решении ряда задач структуроскопии, толщинометрии, дефектоскопии электромагнитно-акустическими методами, основанными на точном измерении времени распространения упругих волн в объекте контроля