Heat-mass Exchange Processes Research Articles

APPLICATION OF THERMAL ANEMOMETRY FOR TURBULENT FLOW ASSESSMENT

This paper is devoted to a review of the physical principle and effective methodology of thermal anemometry. Its uniqueness lies in the ability to realize a comprehensive high-frequency assessment of the dynamic and thermal state of the turbulent flow. It is worth noting that the American Nobel Prize winner in physics Richard Feynman called turbulence "the most important unsolved problem of classical physics", since there is no direct description of this phenomenon according to classical principles. Therefore, its physical interpretation is still considered one of the six most important mathematical issues of our time. Thus, despite its long history, thermal anemometry remains one of the leading techniques for studying of turbulent flow. Which has a significant impact on hydromechanical and heat-mass exchange processes, particularly in food technology. One of the most common types of thermal anemometry is the Hot-Wire anemometer, where a thin platinum wire is used as a sensor. The principle of operation of the anemometer is to maintain a constant heating of the wire while it is cooled by the surrounding flow of liquid or gas. Thus, the power required to compensate for the thermal state of the sensor wire correlates with the flow rate. The first part of the paper is devoted to the description of the physical principles of thermal anemometry, its advantages and limitations. In particular, special attention is paid to the mathematical interpretation of the heat transfer process between the incremental element of the sensor wire and the surrounding flow. After that, the paper provides a detailed analysis of the design features and practical application of various types of wire sensors. Finally, the last section discusses the calibration methodology and various approaches to the linearization procedure of the obtained calibration curves. Among them, the linearization method based on the Collis-Williams law deserves special attention, since it provides highly accurate interpolation of calibration data and takes into account the temperature compensation of the sensor.

CRITERIA AND CONDITIONS OF THE INTER-CIRCUIT THERMODYNAMIC INSTABILITY OF THE NPP’S MODERNIZED TURBINE SYSTEM

The original method of determining the criteria and conditions of inter-circuit thermodynamic instability in the modernized system "steam turbine - regeneration system with absorption heat pumps" is presented. This was developed through a thermodynamic analysis of the effect of independent fluctuating deviations from equilibrium in both the wet vapor flow at the absorption heat pump inlet and the measured pressure in the absorption heat pump/low pressure mixing heaters. Unlike known approaches to modeling thermodynamic processes, the thermodynamic model of the developed method takes into account the influence of fluctuating deviations from the equilibrium state of thermodynamic parameters, which determine the criteria and conditions of interloop thermodynamic instability. Based on the analysis of the received criteria and conditions, it was established that the main cause of inter-circuit thermodynamic instability in the modernized system "steam turbine unit — a regeneration system with absorption heat pumps" is determined by the incompleteness (inertia) of heat-mass exchange and hydrodynamic processes during fluctuating deviations from the equilibrium state of thermodynamic parameters. Prevention of the conditions for inter-loop thermodynamic instability in the modernized system "steam turbine unit — a regeneration system with absorption heat pumps" can be ensured by installing flow controllers in the wet steam supply circuits from the high-pressure cylinder of the turbine to the absorption heat pumps, and absorption heat pumps in mixing heaters low pressure to maintain a constant pressure in absorption heat pumps and low pressure mixing heaters. It is also necessary to consider that the modernization of the "steam turbine unit — a regeneration system with absorption heat pumps" system can affect the performance and conditions of inter-loop thermodynamic instability of "neighboring" systems. These issues determine the need for further analysis of the validity of the modernization of the "steam turbine unit — a regeneration system with absorption heat pumps" systems.

ТЕПЛООБМІН В ТЕПЛОВІЙ ТРУБІ ЗІ ЗМІННИМИ КУТАМИ НАХИЛУ ТА ВПЛИВУ ВІБРАЦІЙ

The article presents the results of experimental studies of the influence of modeling of external factors, such as vibrations and changes in the gravity vector, on the heat and mass transfer processes inside the heat pipe. Heat pipes are widely used as devices that allow the transfer of significant heat flows to solve various problems in power plants. Equipment using heat pipes can be found in the thermal power complex, metallurgy, aviation and rocket and space technology. Complex heat-mass exchange processes of boiling, evaporation, condensation, movement of the liquid phase in porous or capillary structure stake place inside the heat pipe. Existing methods of calculation and design are often of a recommendatory nature. The complexity of heat pipe work processes prompts scientists in the field of heat and mass transfer to further scientific research. In this work, a series of experimental studies is conducted on the modeling of work processes in the middle of heat pipes, namely the influence of vibrations and the angle of inclination on the intensity of heat exchange. This work is a generalization of experimental data on the study of the influence of vibrations and the angle of inclination on the characteristics of heat pipes.

Autonomous Energy-Efficient Complexes Based on Crude Oil for Working in Arctic Conditions

The work is devoted to solving scientific and technical problems on the development of new generation Russian power equipment. Comprehensive theoretical and experimental studies of the effect of aerodynamic and heat-mass exchange processes on the ignition and combustion of crude oil in the straitened conditions of fire-tube boilers are reviewed and described. Based on the results of the research, design developments were carried out, prototypes of a fire-tube hot-water boiler with a remoted economizer and an automated low-emission burner device were manufactured and successfully tested. The efficiency of the boiler more than 94% and the reduced level of pollutants emissions in the operating load range are confirmed.

Mathematical Modeling of Coal Dust Screening by Means of Sieve Analysis and Coal Dust Combustion Based on New Methods of Piece-Linear Function Approximation

This study focuses on the development of new methodological approaches to dust-preparation and burning of separated particles, including through the use of polyfractional ensembles. Coal dust screening by means of sieve analysis is described in standard methods. However, in order to further use the results obtained during mathematical modeling of particle motion in fuel-air mixture and exothermal reactions of oxidation while burning in a torch, it must be possible to differentiate and integrate continuous functions. The methodology is based on the continuity of particle motion in a mixture with air in the calculation of aerodynamic and heat-mass exchange processes in a torch. The paper employs new scientific approaches to transforming and normalizing a continuously differentiable function described by the Gauss curve. We propose to combine mathematical modeling of such functions with methods of approximation of piece-linear functions developed by Professor S. V. Aliukov. The implementation of such methods helps reduce calculation errors of particle size and deviations thereof from average equivalent diameter and to avoid the Gibbs effect while differentiating. The paper contains analytical calculations based on the proposed method and experimental data. Quantitative and qualitative results of comparing analytical and experimental data are also presented. We provide recommendations on the further use and extension of the range of the results obtained in a computer simulation of fuel production and burning processes in a torch.

HEAT MASS EXCHANGE IN THE BROKEN AND ADVANCE WORKINGS OF DEEP MINES

The intensity and mutual intereffect of heat mass exchange processes in broken and advance workings of deep mines have been investigated. The nomograms determining the dimensionless potentials and temperature of the mass transfer are given.

Thermodynamic assessment of the phenomena of heat and mass transfer for energy-technological systems production of groats concentrates

To assess the thermodynamic excellence of food processing technologies of raw material, it is proposed to use the exergy method based on the second law of thermodynamics. A procedure has been developed for calculating thermal and exergy costs in the moisture-heat treatment of capillary-porous colloidal materials. Thermal and exergy calculations of the production of cooked-dried rice groats were performed. Thermal and exergy analysis of heat and mass transfer processes energy-technological systems (ETS) of various schemes for the production of groats concentrates was carried out. The thermal and exergy estimates of the processes of heat-mass exchange during the moisture-thermal treatment of capillary-porous colloidal materials are obtained using the example of cooked-dried groats. A thermodynamic assessment of the phenomena of heat and mass transfer of ETS for the production of groats concentrates based on the theoretical and experimental studies, which resulted in the development of recommendations on the scientific and practical support for heat and mass transfer processes of moisture- thermal treatment of raw materials. It has been proven that a change in product moisture has a greater effect on exergy than a change in temperature does. It is suggested to use, for an assessment of energy efficiency and a comparative exergy analysis of various ETS for processing raw materials, along with exergy efficiency, specific exergy values characterizing exergy costs per unit of dried finished product, per unit of moisture removal and moisture adsorption

Heat-mass exchange processes dynamics in fires in multi-apartment buildings and its impact on safe people evacuation probability

The urgency of people safe evacuation problem from small and medium storeys typical residential sectional type multi-apartment buildings, which in accordance with current regulatory requirements are not equipped with technical means of fire detection and notification of residents, are not equipped with active smoke ventilation systems and do not have effective structural evacuation solutions is shown. Based on modern software systems, numerical experimental studies were conducted to assess the dynamics impact (intensity rate impact) of heat and mass exchange combustion processes on the people evacuation parameters and the corresponding rate of increase dangerous factors for human viability in fire. The time intervals available to residents for safe and timely evacuation are calculated, depending on the typical residential premises fire load characteristic quantity. Taking into account the results obtained, practical measures aimed at improving the people safety in fires in residential multi-apartment buildings are proposed for implementation.

Heat-mass exchange processes dynamics forecasting in fires in typical multistorey apartment buildings

Heat-mass exchange dynamics forecasting in fires in typical multistorey buildings allows to prove the need and determine organizational and technical solutions parameters aimed to increasing such buildings residents safe evacuation probability, which is an urgent problem according to statistics on the deceased persons number of this population category as a result of fires. On the numerical studies results basis, the characteristic time changes regularities of critically dangerous fire factors for humans are established; the most dangerous factor according to the people safe evacuation possibility from these buildings is the optical smoke concentration level. A method for determining the critical smoke time for safe evacuation has been proposed. It is proposed to equip mass construction 5–9 storey apartment buildings with early fire detection and warning systems.

Calculation of Heat-Bearing Agent’s Steady Flow in Fuel Bundle

This paper introduces the result of studying the heat exchange in the fuel bundle of the nuclear reactor’s fuel magazine. The article considers the fuel bundle of the infinite number of fuel elements, fuel elements are considered in the checkerboard fashion (at the tops of a regular triangle a fuel element is a plain round rod. The inhomogeneity of volume energy release in the rod forms the inhomogeneity of temperature and velocity fields, and pressure. Computational methods for studying hydrodynamics in magazines and cores with rod-shape fuel elements are based on a significant simplification of the problem: using basic (averaged) equations, isobaric section hypothesis, porous body model, etc. This could be explained by the complexity of math description of the three-dimensional fluid flow in the multi-connected area with the transfer coefficient anisotropy, curved boundaries and technical computation difficulties. Thus, calculative studying suggests itself as promising and important. There was developed a method for calculating the heat-mass exchange processes of inter-channel fuel element motions, which allows considering the contribution of natural convection to the heat-mass exchange based on the Navier-Stokes equations and Boussinesq approximation.

Approaches to the Simulation of Thermal Hydraulic Processes in the Oil System Elements of Gas Turbine Engine

Design of the oil-system for gas-turbine engines requires the calculation of the exact fuel consumption and pressure losses in the pipelines, the heat exchange between the oil and the lubrication system elements, critical modes of the flow in the pipelines and local resistances. A development of the model of oil system that will enable the measurement of the flow rate and other parameters at any place inside the oil system, the numerical investigation of the influence of structural improvements taking into account these parameters is a rather promising outlook. A specific feature of the oil system of gas turbine engine is that the oil and air mixture is passing instead of single-phase liquid (oil) actually in each element of it, which affects the behavior of thermohydraulic processes in these elements. This scientific paper gives consideration to the peculiarities of the two-phase flow of oil-gas mixture, heat-mass exchange processes that occur in the oil cavity of the rotor rack of gas turbine engine and prevalent approaches to their analysis. Consideration was also given to specific features of software products available for the numerical simulation of thermal hydraulic processes and the possibility of their use for the development of the model of oil system for the gas turbine engine has been analyzed. This scientific paper showed that the investigations carried out in this field require theoretical approaches to the problem solution, the use of state-of-the-art program packages for numerical experiments and the availability of experimental base.

Chemical engineering systems modeling and efficiency analysis of heat and mass exchange

The object of research is the chemical engineering system and the heat-mass exchange processes taking place in it. In engineering practice, systems are represented by process flow diagrams. The lack of standardization in the graphical representation of engineering systems does not allow creating a general logic for reading the graphic information and then processing it with the software for analyzing the energy efficiency of the chemical engineering system. The rules for creating flowcharts, symbols for devices, and the chemical engineering system representation technique are developed, allowing any engineering system to be transformed into its topological representation. To combine the two branches of different networks and organize the heat and mass exchange processes in the system are elements intended for heat and energy exchange between networks with streams pair interaction. Mathematical models of heat and mass exchange networks for chemical industry have been developed, and energy efficiency and mass transfer efficiency criteria have been introduced. This allows to: construct a software environment that generates a system model based on its topological representation; analyze various options for implementing the process flow diagram for finished products production; synthesize the optimal, energy-saving production option. A numerical experiment was performed using a modeling software developed by the German company NETWORK SOLUTION DEVELOPMENT CO and transferred for testing. The model adequacy to the real engineering system approves the comparison of the model parameters and the parameters of the design regime of the urea production synthesis unit. The error in determining the mass flow rates doesn’t not exceed 2.4 % on branches, and the temperatures values at the nodes are strictly correspond to the technological regulations. Preliminary analysis indicates the possibility of improving the energy efficiency of production due to the integration of heat streams within the production cycle and the structural and parametric optimization of the engineering system.

Экспериментальное исследование тепломассообменных процессов при работе парогенератора ВВЭР в аварийном конденсационном режиме

Экспериментальное исследование тепломассообменных процессов при работе парогенератора ВВЭР в аварийном конденсационном режиме

Numerical investigation of heat and mass transfer processes in the combustion chamber of industrial power plant boiler. Part 1. Flow field, temperature distribution, chemical energy distribution

In the present paper, the furnace chamber of the BKZ-160 boiler of Almaty TPP-3 (Kazakhstan) has been calculated. The thermal characteristics of the process were studied in the form of the distribution of temperature fields and chemical energy, and the aerodynamics of the combustion chamber was also calculated. The type of fuel, its elementary and fractional composition, exerts the greatest influence on the course of heat-mass exchange processes and aerodynamics. The computational experiment was carried out with two models of particle size distribution: a polydisperse fuel flame (the particle diameter varies from 10 to 120 μm) and monodisperse fuel flame (particle size identical and equal to dp = 60 μm). Based on the results of the computational experiments, the main regularities in the distribution of heat fluxes in the combustion chamber volume and flow aerodynamics were obtained. It is shown that the greatest thermal load falls on the central region of the walls of the combustion chamber and the location of the burner devices, which is typical for both mono- and polydisperse fuel flames. The temperature data obtained as a result of the computational experiment showed better convergence with the empirical data obtained directly at TPP-3. Aerodynamics of the flow for the two selected models of particle size distribution has insignificant differences, but how they affect other characteristics of the process is one of the following tasks in view of the authors. It should be noted that the calculation of the polydisperse fuel flame takes much more calculation time.

Simulation of the processes of heat- and the mass transfer in the rooms of public building with the natural ventilation

In the article the mathematical model of the processes of heat exchange and mass exchange in the room of building with the natural ventilation is shown. The verification of mathematical model is performed via the comparison of the results of calculation in ANSYS Fluent with the data of experiment. Experiment was conducted in the room of educational institution. In the experiment were measured the temperature of air, air speed and moisture content in air. A low relative error in the calculation with the use of a mathematical model makes its use for predicting the parameters of microclimate after the introduction of the energy-saving measures possible

Searching for the energy efficient operation modes of absorption refrigeration devices

The work demonstrates advantages of absorption refrigeration devices (ARD), as well as their essential shortcoming – a larger, in comparison to the compression analogs, energy consumption. In this connection, the main directions are examined of increasing energy efficiency of absorption refrigeration devices and the prospect of direction of improving the systems of automatic control is substantiated. It is shown that the only controlling influence on the efficiency of the ARD performance is achieved by the thermal power supplied in the generator-thermosyphon. Based on the analysis of the processes of heat mass exchange and the modes of flow of vapor-liquid water-ammonium mixture in the ARU generator–thermosyphon, the ambiguous influence of numerical values of the height of the lift part of the generator on energy characteristics of a standard ARU is shown. On one hand, this increase in height leads to the increase in hydraulic resistances at the motion of the VLM flow and heat losses, on the other hand, there appears a possibility of increasing the surface of heat mass exchange in the absorber. We run analysis of the effect of ambient temperatures on the ARD and ARU energy efficiency and the conditions of optimal operation. To examine the working modes of real objects, we carried out experimental studies of the modernized one-chamber ARD “Kiev-410” with a low-temperature compartment (LTC) of the Ash-160 type (manufactured by Vasilkovskiy Plant of Refrigerators, Ukraine) We obtained a set of quasi-static performance characteristics of the modernized one-chamber ARD “Kiev-410” with LTC of the Ash-160 type along the channels “thermal power supplied to the ARU generator – temperatures of the surface of the ARU elements in control points” at different conditions of heat removal from the external surface of dephlegmator (nominal, intensive heat removal, thermal insulation along the entire length of dephlegmator). As a result of conducted studies of the real object, we selected 5 types of the working modes of generator: optimal by energy efficiency (IІІ), “waiting” (ІІ), “accelerating” (IV) and two non-working modes (I and V). It was shown that at modes I and V the refrigeration cycle of ARU is not realized. Mode ІІ may be used by designers when working with positional algorithms of control as the “waiting” mode, which ensures the state of “readiness” for the rapid start; mode IV – as the “accelerating” at the start of ARU from non-operating state to the rapid attaining of the working load.

Fundamentals, current state of the development of, and prospects for further improvement of the new-generation thermal-hydraulic computational HYDRA-IBRAE/LM code for simulation of fast reactor systems

The conceptual fundamentals of the development of the new-generation system thermal-hydraulic computational HYDRA-IBRAE/LM code are presented. The code is intended to simulate the thermalhydraulic processes that take place in the loops and the heat-exchange equipment of liquid–metal cooled fast reactor systems under normal operation and anticipated operational occurrences and during accidents. The paper provides a brief overview of Russian and foreign system thermal-hydraulic codes for modeling liquid–metal coolants and gives grounds for the necessity of development of a new-generation HYDRA-IBRAE/LM code. Considering the specific engineering features of the nuclear power plants (NPPs) equipped with the BN-1200 and the BREST-OD-300 reactors, the processes and the phenomena are singled out that require a detailed analysis and development of the models to be correctly described by the system thermal-hydraulic code in question. Information on the functionality of the computational code is provided, viz., the thermalhydraulic two-phase model, the properties of the sodium and the lead coolants, the closing equations for simulation of the heat–mass exchange processes, the models to describe the processes that take place during the steam-generator tube rupture, etc. The article gives a brief overview of the usability of the computational code, including a description of the support documentation and the supply package, as well as possibilities of taking advantages of the modern computer technologies, such as parallel computations. The paper shows the current state of verification and validation of the computational code; it also presents information on the principles of constructing of and populating the verification matrices for the BREST-OD-300 and the BN-1200 reactor systems. The prospects are outlined for further development of the HYDRA-IBRAE/LM code, introduction of new models into it, and enhancement of its usability. It is shown that the program of development and practical application of the code will allow carrying out in the nearest future the computations to analyze the safety of potential NPP projects at a qualitatively higher level.

МАТЕМАТИЧЕСКАЯ МОДЕЛЬ ПРОЦЕССОВ ТЕПЛОМАССОПЕРЕНОСА В ПЛОСКОМ СОЛНЕЧНОМ КОЛЛЕКТОРЕ SUN 1

МАТЕМАТИЧЕСКАЯ МОДЕЛЬ ПРОЦЕССОВ ТЕПЛОМАССОПЕРЕНОСА В ПЛОСКОМ СОЛНЕЧНОМ КОЛЛЕКТОРЕ SUN 1

Analysis of heat losses of underground tunnel for engineering utilities with available methods

Methods for calculation of thermal regime and heat loss parameter for underground tunnel into surrounding sub-soil were developed in first half of XX century, when the study of complex heat-mass exchange processes between underground tunnel, sub-soil and outdoor air is started. In tunnel it need to be provided a specific microclimate parameters, that requires a certain load on environmental control system. At present time there are some methods for calculation of heat loss parameter for underground tunnel. In this paper the analysis of real methods of calculation of heat losses of underground tunnel is accomplished.

Experimental and numerical studies of current load in power supply cables, depending on layout conditions

A laboratory setup that simulates a variety of ways to lay cables in beams is designed and constructed for the experimental determination of current loads in the cables. The conductors of the test cable form a shading coil, which is a current transformer secondary winding. The required value of current in the cables is provided by the laboratory autotransformer. The temperature in the center of the cable beam is measured with a thermocouple. Numerical studies of heat-mass exchange processes in the cables are performed using mathematical models that take into account the natural air convection and heat radiation. The mathematical description of convective processes is considered in the Boussinesq approximation and based on the laws of conservation of energy, mass, and linear momentum. The problem of heat conduction of cables is solved together with the problem of convective heat exchange of the air flow in the cable channel. The resulting system of differential equations, which describes the thermal processes in the liable channel, is supplemented by the appropriate boundary conditions. The problem is numerically solved in the ANSYS simulation software. Four ways to lay cables in the beams, each of which is loaded with five different currents, is considered. The coincidence of the mathematical model to real processes is confirmed by the comparing the experimentally measured temperatures on the surface of the cable in the beam center with the results. The difference between the experimental and numerical data does not exceed 11%. The allowable current loads in the cables in the different layout variants are determined by a mathematical model with using an iterative procedure. It is noted that the allowed current load of the cable lines in many ways depends on the cables disposition in the beams.