Range Of Regime Parameters Research Articles

Экспериментальное исследование пульсационных характеристик закрученного потока в модели четырехвихревой топки

Актуальность исследования обусловлена необходимостью вовлечения в топливно-сырьевую базу низкосортных высокозольных углей в связи с ограниченностью запасов высококачественного топлива. Для их эффективного и экологически безопасного использования требуется разработка новых и модернизация имеющихся котельных агрегатов с предварительным физическим и численным моделированием. Целью работы является экспериментальное исследование пульсационных характеристик турбулентного закрученного потока в модели перспективного топочного устройства, использующего четырёхвихревую схему сжигания пылеугольного топлива. Объектом исследования является изотермическая лабораторная модель четырёхвихревой топки, выполненная из оптически прозрачного оргстекла для проведения измерений в рамках современных бесконтактных методов диагностики потоков. Методы: физическое лабораторное моделирование аэродинамики и процессов переноса в четырехвихревой топке; бесконтактное исследование осредненных и пульсационных характеристик в объеме модели топки при различных режимных параметрах; исследование пульсаций давления с использованием конденсаторного микрофона. Результаты. С использованием метода цифровой трассерной визуализации получены распределения осредненных и пульсационных характеристик скорости потока в ряде сечений модели в широком диапазоне режимных параметров. Определено положение зон с высоким значением турбулентных пульсаций и застойных зон, установлены особенности их расположения в зависимости от режимов. С использованием конденсаторного микрофона получены данные о пульсациях давления в локальных областях объема модели. Анализ спектральных характеристик с применением к полученным данным преобразования Фурье показал, что в изучаемой модели отсутствуют нестационарные периодические колебания, связанные с прецессией вихревого ядра потока. Измеренные пульсации давления вызваны акустикой, пульсации скорости носят случайный характер и не связаны с динамикой когерентных структур.

Experimental investigation of hydrodynamics and heat exchange in the ring channel with heat exchangers in the modes of single-phase convection and bubble boiling

The effectiveness of the heat exchange intensifier “rib-twisted wire” is considered in this paper. The main goal is to study the influence of the wire coiling step t on heat transfer and hydraulic resistance for different values Ḣ of the dimensionless height of the edge Ḣ, as well as some results on heat exchange during bubbly boiling in an annular channel.Show:• a brief description and an image of the heat exchange intensifier “rib-twisted wire”;• generalized results of studies of heat exchange and hydraulic resistance in the annular channel in the single-phase convection with different geometric characteristics of the intensifier;• empirical correlations of the generalized experimental results that allow to calculating the coefficient of hydraulic resistance and heat transfer in the range of regime parameters in the single-phase convection that is being studied.• some results of experiments in bubbly boiling regimes and near-critical thermal loads.

Intensification of heat exchange by method of interacting flows

The effectiveness of the heat exchange intensifier “rib-twisted wire” is considered in this paper. The main goal was to study the influence of the wire coiling step t on heat transfer and hydraulic resistance for different values of the dimensionless height of the edge , as well as some results on heat exchange during bubbly boiling in an annular channel.Given:• a brief description and an image of the heat exchange intensifier “rib-twisted wire”;• generalized results of studies of heat exchange and hydraulic resistance in the annular channel in the single-phase convection with different geometric characteristics of the intensifier;• empirical correlations of the generalized experimental results that allow to calculate the coefficient of hydraulic resistance and heat transfer in the range of regime parameters in the single-phase convection that is being studied.• some results of experiments in bubbly boiling regimes and near-critical thermal loads.

Heat transfer at boiling of refrigerants in channels with twisted tape insert

The paper presents the review results of heat transfer at boiling in channels with twisted tape inserts. Various methods and approaches to the research of heat transfer processes at boiling of refrigerants in channels with twisted tape inserts were identified, a significant difference of the influencing factors on the heat transfer depending on the range of regime parameters under study was noted and also the necessity for research in this field was shown.

Hydrodynamics and Heat Transfer in the Case of Combined Flow in a Annular Channel of Small Cross Section

The present work is a continuation of experimental investigations conducted at the Moscow Power Engineering Institute (MPEI) on heat-transfer intensification. Brief descriptions of the working section and structure of intensifiers are given and their basic geometric parameters are enumerated. New systematized experimental data on the coefficients of hydraulic resistance and heat transfer in the regime of single-phase convection are given in an extended range of regime parameters and geometric characteristics of the intensifiers. Considerable increase in the heat-transfer coefficient as a function of the geometric characteristics of the intensifier has been established experimentally. The values of the relative fin height, at which these are the maxima of heat transfer and hydraulic resistance, have been established. Calculated dependences for the coefficient of hydraulic resistance and heat transfer have been obtained.

Study of the heat-transfer crisis on heat-release surfaces of annular channels with swirl and transit flows

The results of the experimental study of the heat-transfer crisis on heat-release surfaces of annular channels with swirl and transit flow are presented. The experiments were carried out using electric heated annular channels with one and (or) two heat-release surfaces. For the organization of transit flow on a convex heat-release surface, four longitudinal ribs were installed uniformly at its perimeter. Swirl flow was realized using a capillary wound tightly (without gaps) on the ribs. The ratio between swirl and transit flows in the annular gap was varied by applying longitudinal ribs of different height. The experiments were carried out using a closed-type circulatory system. The experimental data were obtained in a wide range of regime parameters. Both water heated to the temperature less than the saturation temperature and water-steam mixture were fed at the inlet of the channels. For the measurement of the temperature of the heat-release surfaces, chromel-copel thermocouples were used. It was shown that the presence of swirl flow on a convex heatrelease surface led to a significant decrease in critical heat flows (CHF) compared to a smooth surface. To increase CHF, it was proposed to use the interaction of swirl flows of the heat carrier. The second swirl flow was transit flow, i.e., swirl flow with the step equal to infinity. It was shown that CHF values for a channel with swirl and transit flow in all the studied range of regime parameters was higher than CHF values for both a smooth annular channel and a channel with swirl. The empirical ratios describing the dependence of CHF on convex and concave heat-release surfaces of annular channels with swirl and transit flow on the geometrical characteristics of channels and the regime parameters were obtained. The experiments were carried out at the pressure p = 3.0–16.0 MPa and the mass velocity ρw = 250–3000 kg/(m2s).

Experimental investigation of film boiling on spheres using high-speed video

The experimental investigation of saturated Freon-113 film boiling on spheres with different diameters at atmospheric pressure under conditions of free convection is executed. It was found that with increasing diameter of the sphere and the temperature difference is changing the wave motion of the vapor film with two-dimensional to three-dimensional mode. Also, found that in a range of regime parameters at which observed a three-dimensional interface motion, the destruction method of two-dimensional wave is similar to a series of three or more waves. I.e. was some system memory. When the temperature difference close to critical after the passage of a wave are possible the local contacts of liquid with a heated surface of the sphere. However, these contacts do not lead to degradation of the wave motion of the interface, and the film boiling crisis of saturated Freon-113 occurs smoothly in contrast to the crisis at boiling of saturated and subcooled water.

Characteristics of the Hydrodynamic Coefficient for Flow of a Steam-Water Mixture in a Pebble Bed

Pressure loss for flow of a steam-water mixture in a pebble bed is experimentally investigated (the first stage of the study was described in Avdeev, et al., 2003 [High Temp., 41, pp. 371–383]). The measurements of the care performed within the wide range of regime parameters: pressures of 0.9-15.6MPa, mass-flow rates of 107-770kg∕(m2s) and steam quality of 0–0.49. The experimental data for the pressure loss of single-phase air and water flows were used as reference data. The final results are represented in the form of the ratio of the pressure loss for the steam-water flow to that for the single-phase water flow at identical mass-flow rates.

Investigation of the combustion dynamics of low-volatile fuel particles by measuring “thermometric” and color temperatures

A new technique for studying the combustion dynamics and entrainment of lowvolatile fuel particles is proposed. It is based on simultaneous measurements of “thermometric” and pyrometric (color) temperatures. The technique permits a detailed study of time phases and mass rates of combustion of fuel particles in a wide range of regime parameters.

Heat transfer in hydrocarbon fuel boiling under conditions of natural convection

Data on the heat-transfer coefficient in boiling of five jet fuels, two automotive gasolines, and a diesel fuel are presented over a wide range of regime parameters. The obtained results are described by a unified similarity equation.

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER AND BURNOUT IN CONDITION OF NONUNIFORM MEGAWATT HEAT FLUXES

Burnout is investigated in tubes under nonuniform heating on the perimeter. Data on heat transfer and critical heat flux (qcht) in the case of water were obtained for ranges of mass velocity pw = 200-3000 kg/m2 s, pressure p = 0.1-1 MPa, and inlet water temperature T = 25-98°C. The test section was a horizontal copper tube of 21 mm outer diameter, 8 mm inner diameter with a technically smooth surface and heat transfer-intensifying twisted tape and porous sintered coating. The test section was heated by bombardment with electrons. It is established that a redistribution of heat fluxes and an increase of wall temperature fluctuations occur at burnout. The range of regime parameters to prevent burnout of a heat transfer surface is determined.

Investigation of hydrodynamic and heat and mass transfer processes for crystal growing by the Czochralski method

A mathematical model and numerical method are developed and used to investigate nonstationary flow and heat and mass transfer regimes in a melt appropriate to the conditions of Czochralski crystal growth. A study is made of the separate and combined influence of rotation and thermal, concentration, and thermocapillary convection on the distribution of the temperature and the dopant in the range of regime parameters corresponding to large charging masses of the melt with small value of the kinematic viscosity. Large-scale fluctuations are found to occur when rotation and thermal convection interact. Thermocapillary convection is shown to have an important influence on the resulting motion when it interacts with the thermal and concentration forms of convection. A comparison is made with the results of experimental and theoretical investigations of other authors.

Experimental investigation of horizontal two-phase flow by an electrodiffusion method

The results of an experimental investigation of the local mean and fluctuating friction at the wall of a horizontal tube are presented for the case where a gas-liquid stream flows in the tube with a wide range of regime parameters. The electrodiffusion method is used for measuring the friction. Curves of the tangential stresses along the perimeter of the tube as well as along its length are constructed, permitting an objective determination of certain flow regimes. The experimental results are compared with those of the existing computational methods.