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Thermal engineering
Maik Nauka - Interperiodica
Thermal engineering

Maik Nauka - Interperiodica

月刊

0040-6015

Thermal engineering/Journal Thermal engineeringSCIEIESCI
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    Studies of Thermohydraulic Processes to Substantiate the Safety Characteristics of Fast Reactors (Review)

    A. P. SorokinYu. A. KuzinaV. N. Del’novN. A. Denisova...
    439-452页
    查看更多>>摘要：Abstract The article presents the results of current problem-oriented studies of thermal-hydraulic processes to substantiate the characteristics and safety of sodium-cooled fast neutron reactors across a wide range of thermophysical problems, including hydrodynamics and heat exchange in channels and fuel assemblies (FA) of the core, including under conditions of fuel element assemblies’ deformation during the campaign, intravessel circulation and coolant stratification in the tank of a fast neutron reactor with an integral equipment layout in the nominal mode with forced convection and natural convection of the coolant in the emergency cooldown mode, in the intermediate heat exchanger, and in the large-modular steam generator. The data of experimental hydrodynamic studies of flow parts of reactor installations, heat exchangers, and reactors of nuclear power plants are presented. The article analyzes the patterns of hydrodynamic processes occurring in the flow sections of cylindrical collector systems in reactors and heat exchangers identified during experimental studies on an aerodynamic stand and a hydraulic flume. These patterns are registered as scientific discoveries as previously unknown patterns and phenomena related to the atomic, space, metallurgical, and chemical fields of science and technology. The results of the computational studies performed using the version of the channel-by-channel code implementing a two-fluid model of a two-phase flow of liquid metal in the approximation of equal pressures in the vapor and liquid phases reproduce the development of the flow regimes of a two-phase flow, the pulsations of the liquid metal flow obtained in experimental studies, and also demonstrate antiphase pulsations of the flow of a two-phase coolant in a system of parallel fuel assemblies and interchannel instability characterized by a significant increase in the amplitude of the pulsations of the coolant flow in parallel FA.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Coolant Hydrodynamics in a Fuel-Rod Bundle of a Fuel Assembly in the RITM Reactor of the Retrofitted Floating Power Unit

    S. M. DmitirievT. D. DemkinaA. A. DobrovD. V. Doronkov...
    453-461页
    查看更多>>摘要：Abstract Results are presented of the experimental investigation into peculiarities of the coolant flow in a fuel-rod bundle of a fuel assembly in the RITM reactor of the retrofitted floating power unit. The purpose of this study was to experimentally determine hydrodynamic characteristics of the flow in a fuel-rod bundle of a fuel assembly. The experiments were performed in an experimental facility with air as a working fluid using a model of a fragment of a fuel-rod bundle in a fuel assembly on the basis of the hydrodynamic simulation theory. The experimental model included a bundle of fuel-rod simulators, burnable poison rod simulators, spacer grids simulators, a central displacer, and stiffening angles. Invasive methods, such as the pneumometric method and the method of tracer injection, were employed in the study. The flow features were visualized using axial and tangential velocity maps and the tracer distributions. The experiments revealed the axial flow features and the structure of transverse coolant flows. Three zones are identified in the flow structure: in the region of regular cells, at the central displacer, and at the periphery (near the fuel-assembly casing). The flow velocity in them differs by 25–30%. The arrangement of plates in the grids considerably affects the flow structure at a distance greater than L/dh ≈ 10.0. The found flow features should be taken into account in substantiating the thermal reliability of new cassette-type cores using cellular thermohydraulic codes. The procedure of thermohydraulic calculation in cellular thermohydraulic codes should be revised to increase the number of types of calculation cells and to consider the flow maldistribution among the regions in a fuel-rod bundle and the cell types.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Computational and Experimental Study of a Sector Cascade Consisting of Nozzle Vanes of a High-Pressure Gas Turbine

    A. V. GranovskiyI. V. AfanasievV. D. Venediktov
    462-472页
    查看更多>>摘要：Abstract Experimental studies of blading from cooled gas turbines involve difficulties in simulating actual shape and operating conditions of the blades. Therefore, studies of linear turbine blade or vane cascades composed of blades that usually correspond to plane sections of real spatial turbine rows at the hub, at the middle diameter, and at the tip have received wide acceptance. When investigating linear blade cascades, the spatial effects that are crucial for the formation of the overall flow structure in the blade rows cannot be examined. Application of actual spatial turbine rows enables us to determine more reliably the causes and value of energy losses in turbine blade assemblies even under simulated operating conditions used in an experimental facility. Naturally, a study of a complete annular blade row seems most preferable. However, such studies require high costs associated not only with the manufacture of the turbine blading but also with provision of the required flowrate of the working fluid to conduct tests under conditions simulating the real operating conditions of the experimental object. In this case, the study of a sector cascade composed of full-scale cooled nozzle vanes is an acceptable alternative to testing a full-scale complete annular cascade. A sector cascade was tested at the Central Institute of Aviation Motors in a wide range of the reduced adiabatic velocity at the outlet (0.6–1.3) with cooling air ejection through perforation holes on the airfoil and end surfaces as well as through the trailing edge. The tests were performed under isothermal conditions when the temperatures of the working fluid and cooling air were almost the same. The total pressure fields upstream and downstream of the sector cascade were determined in the tests. The numerical study of the spatial structure of the flow and losses was carried out using the 3D NS and ANSYS CFX codes, which solve the 3D Reynolds-averaged Navier–Stokes (RANS) equations using various turbulence models.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Мeasurement of Dry Spot Features during Boiling Using Neural Network Processing of High-Speed Visualization

    A. S. SurtaevP. O. PerminovI. P. MalakhovM. A. Polovnikov...
    473-482页
    查看更多>>摘要：Abstract It is known that dry spots formed under vapor bubbles during the boiling process have a huge impact on both local heat transfer and the development of crisis phenomena. In this study, new experimental information on the evolution of dry spots under vapor bubbles during liquid boiling was obtained using high-speed reflected light imaging, and an algorithm for automatic processing of experimental data based on U-Net convolutional neural networks was developed. It is shown that it is possible using machine learning models and high-precision optical high-speed methods to determine a wide range of characteristics of dry spots during liquid boiling in a short period of time and with high accuracy, including the evolution of the total area and size of dry spots, total number, and the growth rate and lifetimes of dry spots in a wide range of heat fluxes. Based on the analysis of the collected data, it was established that the average total area of dry spots and the nucleation site density during boiling of water increase linearly with increasing heat flux in the studied range. It has been demonstrated that the growth rate of dry spots is constant in the period before the onset of the bubble detachment stage, with the average value of this rate increasing with increasing heat flux. The characteristic maximum size of dry spots turns out to be almost half the capillary length. The results obtained, presented in the article, indicate that there is a huge potential for using artificial intelligence methods, which open up new prospects for studying two-phase systems, modeling heat transfer during boiling, and predicting crisis phenomena associated with uncontrolled growth of dry spots.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Slip-Flow Enhanced Heat Transfer in Microchannel Heat Sink via Carbon Nanotube-Based Nanofluid

    Manoj KumarSheshang Singh ChandelSafwan MondalSumit Sinha-Ray...
    483-498页
    查看更多>>摘要：Abstract Microchannel heat sinks (MCHS) belong to one of the most prominent methods of passive cooling of microelectronics. In this work, a circular microchannel-based MCHS was installed over a microelectronic mimicking heated surface, which was subjected to 50 to 125 kW/m2, and the convective cooling of MCHS was studied using nanofluids of copper (Cu) and carbon nanotube (CNT) [both at 0.05 wt % concentration in de-ionized (DI) water] as coolant, along with DI water. The experimental results suggest that the nanofluid-cooled MCHS, especially the CNT one, outperformed the pure water-cooled system, with significantly higher heat transfer coefficient (HTC), and lower pumping power, rendering the former system more energetically favorable. At a flow rate of 60 ml/min and heat flux of 100 kW/m2, the HTC enhancements in water + CNT and water + Cu were 15.7 and 6.2% more than water, respectively. Due to addition of surfactant in DI water for suspending CNT, an apparent slip flow became prevalent in the microchannel, leading to a significant pressure drop reduction while pumping water + CNT. This observation helped in gauging the total power saving that can be accessed using water + CNT, if one follows periodic heating/cooling between an upper critical temperature and safe temperature range rather than continuous cooling of the electronic surface.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Experimental Study of Hydrodynamics and Heat Transfer in a Loop Thermosyphon for Thermal Control of Power Plants of Electric Aircraft

    L. L. VasilievA. S. ZhuravlyovM. A. Kuz’mich
    499-504页
    查看更多>>摘要：Abstract The heat-transmitting capability, i.e., the ability to transfer heat flux with minimal losses, of thermosyphons and the prospects for using passive systems based on them for heat exchangers of various purposes, such as those for the utilization of heat from renewable energy sources and secondary energy resources (water basins, soil, groundwater, waste water and steam from industrial production, etc.) are considered. In small-scale power engineering, thermosyphons can be used to increase the potential of heat pumps that use heat from alternative sources. Passive heating/cooling systems ensure savings in the electricity required to power electric motors. Thermosyphons are easy to operate, do not require constant maintenance and can be effective intermediate links between heat sources and consumers, and are capable of maintaining a constant temperature of cooled objects. They can be used to organize the removal and transfer of heat outside a high-temperature environment. The design of a loop thermosyphon with a porous evaporator (LTSPE) and a condenser installed horizontally is presented. The article presents the results of experimental studies of a thermosyphon with two working fluids (freon R245fa and water). The temperature distribution and thermal resistances of the evaporator, condenser and thermosyphon as a whole are determined under different thermal loads. The effect of the cooling medium temperature on the heat-transmitting capability of the thermosyphon heated by a constant heat flux is analyzed. With an increase in the cooling medium temperature, the thermal resistance of the thermosyphon monotonically decreases. The studied device has a high heat-transmitting capability (up to 1.5 kW), a short start-up time, and a dynamic attainment of a steady-state mode when the load changes. The developed loop thermosyphons can be recommended for use in energy-saving systems, in particular in solar power engineering (thermal control of PV and PVT panels1); in combination with heat pumps – in trigeneration plants generating electricity, heat and cold; in thermostatic equipment for electric transport, electronic equipment and in other areas
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Characterization and Comparative Analysis of Multi-Layered Thermal Barrier Coatings for High-Temperature Applications

    Y. RenukaA. Anderson
    505-513页
    查看更多>>摘要：Abstract This study investigated multi-layered thermal barrier coatings deposited by atmospheric plasma spraying for improved performance compared to a single-layered Sm2Zr2O7 (SZO) coating. Two novel designs were evaluated: a yttria-stabilized zirconia (YSZ) intermediate layer and a functionally graded coating with variable YSZ/SZO ratios. Vickers microhardness revealed a uniform 22% increase for all coatings after heat treatment. Functionally graded YSZ/SZO coatings displayed a significant 23% reduction in coefficient of friction compared to the YSZ/SZO double layer coating at room temperature. While heat treatment slightly increased wear depth in functionally graded coatings, they emerged as the most promising candidate due to their improved mechanical strength and low coefficient of friction, suggesting their potential for enhanced durability and thermal barrier performance.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc

    Experience Gained from Applying Low Emission Burners in a Coal Fired CHPP Power Generating Boiler for Reducing Nitrogen Oxide Emissions

    A. V. ShtegmanI. A. RyzhiiD. V. SosinA. V. Sokolova...
    514-525页
    查看更多>>摘要：Abstract For the Omsk combined heat and power plant no. 5 (Omsk CHPP-5), which is located in the central part of a large city, there is an acute need to reduce the atmospheric emissions of pollutants. Grade KSN (coking low-caking low-metamorphized) high-ash Ekibastuz coal is the design fuel for this power plant. For reducing the solid fuel fly ash and nitrogen oxide NOx emissions, it was proposed to make a shift for combustion of other coals having a higher heating value and lower ash content. To see whether or not off-design coals can be used, experimental combustion of such coals as grade DR (as-received, jet) Vinogradov coal, grade DR Shubarkol coal, and grade DR Maikubensk coal was carried out; the furnace process mathematical simulation was performed out in the ANSYS Fluent software, and the thermal balance was compiled in the Boiler Designer software. As a result of the studies performed, a conclusion has been drawn that for securing efficient use of off-design fuel, it is necessary to modernize the existing combustion system with installing new low emission vortex burners. Based on the data of a computational study carried out in the ANSYS Fluent software, the design of a new burner was developed. The simulation results have shown that by using the new burners it will be possible to achieve a significantly lower amount of nitrogen oxide emissions produced. After the design documentation had been developed, the new burners were manufactured and installed in BKZ-420-140 boiler No. 7 at the Omsk CHPP-5. The tests of the boiler equipped with the new burners carried out with combustion of design grade KSN Ekibastuz coal have confirmed the effectiveness of the adopted technical solutions: the concentration of nitrogen oxides in the boiler flue gases is a factor 1.7 lower in comparison with the values that were before the boiler refurbishment. A lower level of carbon-in-ash losses and the corresponding increase in the boiler efficiency have been recorded. Preliminary experiments on combusting off-design grade DR Vinogradov coal confirm the possibility of using it on a regular basis jointly with grade KSN Ekibastuz coal provided that the project has been implemented in a full scope.
      原文链接:
    • NETL
    • NSTL
    • Pleiades Publishing Inc