The paper presents an experimental and computational study of various regimes of firing coal-water fuel in a low-power hot-water boiler that enable both dry and liquid slag removal. The experimental...

A mathematical model developed to describe the interaction of a thermal convective flow with a moving body is presented. The model was implemented within the framework of the SigmaFlow computational software package, which is based on computational fluid dynamics methods. The thermal convective flow is described by the Navier–Stokes equations in the Boussinesq approximation, and the moving body model is implemented using the immersed boundary method. The article presents the results of verification of the proposed mathematical model by solving the following test problems: unsteady laminar flow around the cylinder; natural convection in the channel between two cylinders; developed convective flow in a closed rectangular area with a fixed plate. The results of a numerical study of the plate motion in a thermal convective flow in a closed volume (cuvette) with hot lower and cold upper walls are presented. The calculations showed that the moving plate has an impact on the dynamics of formation of large-scale cells, the local distribution of heat flux density on the lower wall and the integral heat flux. In particular, they revealed a local decrease in the heat flux under the plate, an increase in the number of large vortices in the cuvette and the destruction of the horizontal temperature gradient observed in the case of a fixed plate. In addition, for a fixed plate, the value of heat flux under it depends on its position, and in the case of a moving plate – on the position and direction of its movement. A qualitative comparison of calculations for two different Rayleigh numbers with the experimental data obtained at the Institute of Continuous Medium Mechanics of the Ural Branch of the Russian Academy of Sciences showed that the behavior of the plate is governed by similar regularities. Представлена математическая модель, предназначенная для описания взаимодействия свободно-конвективного потока с подвижным телом. Модель реализована в рамках расчетного программного комплекса SigmaFlow, основанного на методах вычислительной гидродинамики. Свободно-конвективное течение описывается уравнениями Навье–Стокса в приближении Буссинеска, а модель подвижного тела реализована с помощью метода погруженных границ. В статье приведены результаты верификации предложенной математической модели на следующих тестовых задачах: нестационарное ламинарное обтекание цилиндра; естественная конвекция в канале между двумя цилиндрами; развитое конвективное течение в замкнутой прямоугольной области с неподвижной пластиной. Представлены результаты численного исследования движения пластины в свободно-конвективном потоке в замкнутом объеме (кювете) с горячей нижней и холодной верхней стенками. В результате расчетов обнаружено влияние подвижной пластины на динамику формирования крупномасштабных ячеек, на локальное распределение плотности теплового потока на нижней стенке и интегральный тепловой поток. В частности, выявлено локальное уменьшение теплового потока под пластиной, увеличение числа крупных вихрей в кювете и разрушение горизонтального градиента температуры, который наблюдается в случае закрепленной пластины. Кроме этого, для закрепленной пластины величина теплового потока под ней зависит от ее положения, а в случае подвижной пластины – от положения и направления ее движения. Качественное сравнение расчетов для двух разных чисел Релея c экспериментальными данными, полученными в Институте механики сплошных сред УрО РАН, показало, что поведение пластины имеет схожие закономерности.

The effect of the preheating rate of the char particles from Kuznetsk bituminous coal on their specific reaction rate was determined. The experiments were carried out with char samples with mean diameters of 0.15 and 0.35 mm heated to temperatures of 900–1000°C. It was found that the specific surface area of the initial coal, measured by CO₂ adsorption at 273 K, for rapid and slow heat treatments increased more that two times. According to the results of thermogravimetric analysis, it was established that rapid pyrolysis in a muffle furnace led to the production of char whose maximum specific reaction rate was higher than that of the samples after slow pyrolysis.

Calculation studies of the effect of the turbulent flow simulation method on the combustion processes of swirling pulverized coal flow have been performed. A comparative analysis of the results of mathematical modeling with experimental data has shown that the DES and LES methods can correctly resolve the complex vortex structure of a coal torch. It was found that the choice of turbulence simulation method when calculating the combustion of swirling pulverized coal flow has a significant impact on the results of the numerical experiment.

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The work is devoted to application of different-scale models in the simulation of hydrodynamics and heat transfer of large and/or complex systems, which can be considered as a combination of extended and "compact" elements. The model consisting of simultaneously existing three-dimensional and network (one-dimensional) elements is called multiscale. The paper examines the relevance of building such models and considers three main options for their implementation: the spatial and the network parts of the model are calculated separately; spatial and network parts are calculated simultaneously (hydraulically unified model); network elements "penetrate" the spatial part and are connected through the integral characteristics at the tube/channel walls (hydraulically disconnected model). Each proposed method is analyzed in terms of advantages and disadvantages. The paper presents a number of practical examples demonstrating the application of multiscale models.