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This article presents an experimental study on the hydrodynamics of coolant flow within the pressure vessel of a small modular reactor (SMR) cooled with water, including areas such as the annular downcomer, bottom chamber, and core-simulating channels that are being developed for use in land-based nuclear power plants. This paper describes the experimental setup and test model, measurement techniques used, experimental conditions under which this research was conducted, and results obtained. This study was conducted at the Nizhny Novgorod State Technical University (NNSTU) using a high-pressure aerodynamic testing facility and a scale model that included structural components similar to those found in loop-type reactors. Experiments were performed with Reynolds numbers (Re) ranging from 20,000 to 50,000 in the annular downcomer space of the test model. Two independent techniques were used to simulate the non-uniform flow field in the pressure vessel: passive impurity injection (adding propane to the airflow) and hot tracer (heating one of the reactor circulation loops). The axial velocity field at the inlet to the reactor core was also investigated. This study provided information about the spatial distribution of a tracer within the coolant flow in the annular downcomer and bottom chamber of the pressure vessel. Data on the distribution of the contrasting admixture are presented in plots. The swirling nature of the coolant flow within the pressurized vessel was analyzed. It was shown that the intensity of mixing within the bottom chamber of the pressure vessel is influenced by the presence of a central vortex. Parameters associated with the mixing of admixtures within the model for the pressure vessel were estimated. Additionally, the possibility for simulating flow with different temperature mixing processes using isothermal models was observed.

The results of an experimental study into the features of the process of coolant flow formation in the inlet section of the fuel assembly (FA) of the core of a RITM-type reactor of a small nuclear power plant (SNPP) are presented. The purpose of the work is to evaluate the influence of different design elements of the inlet section on the formation of coolant flow. To achieve this goal, a series of experiments was completed on a research aerodynamic stand with an air working environment using a large-scale experimental model, including structural elements of the FA inlet section from the throttle orifice to the fuel rod fastening unit to the diffuser, as well as a fragment of the fuel rod bundle between the absorber and spacer grids. The studies were carried out using the pneumometric method and the method of injection of a contrast admixture in several sections along the length of the model. Measurements were made over the entire cross section of the model. Features of the coolant flow are visualized by cartograms of the axial flow velocity of the working medium and the distribution of admixture in the cross section of the model. The research results were used by specialists from the design and calculation departments of OKBM Afrikantov to substantiate engineering solutions when designing new cores of RITM reactors. The results of the experiments were collected into a database and used in the validation of the LOGOS CFD computer program created by employees of the All-Russian Research Institute of Experimental Physics and the Institute for Theoretical and Mathematical Physics of Moscow State University as analogues of foreign computer programs of the same class, which include ANSYS, Star CCM, etc. Experimental data were also used when validating one-dimensional thermal-hydraulic codes used at OKBM Afrikantov in substantiating the thermal reliability of reactor cores. The thermohydraulic code CANAL is also included in this class of computer programs.

The results of experimental studies and a comparative analysis of the coolant hydrodynamics in the outlet section of the fuel cartridge behind heads of different designs are presented. The considered fuel assemblies are designed for installation in the core of a RITM-type reactor of a small ground-based nuclear power plant. The aim of the work was to study the distribution of the axial velocity and flow rate of the coolant at the outlet of the fuel bundle, behind the heads of different designs, and in front of the coolant extraction pipe and in the holes of the upper base plate as well as to determine the areas of the fuel bundle from which the coolant flow is most likely to enter the sampling pipe and, accordingly, to the resistance thermometer installed in this pipe. The experiments were carried out on a research aerodynamic stand with an air working medium on a model of the outlet section of the fuel cartridge, which includes a fragment of the outlet part of the fuel bundle with spacer grids, dummies of two types of heads, an upper support plate, and a coolant extraction pipe. When studying the coolant flow rate in the outlet part of the fuel cartridge, the pneumometric method and the method of contrast impurity injection were used. The measurements were carried out over the entire cross section of the model. The hydrodynamic picture of the coolant flow is represented by cartograms of the distribution of axial velocity, coolant flow rate, and contrast impurities in the cross section of the model. The results of the research were used by specialists from the design and calculation departments of Afrikantov OKBM to justify engineering solutions in the design of new cores of RITM reactors. The results of the experiments were compiled into a database and used in the validation of the LOGOS CFD program developed by the employees of RFNC-VNIIEF and ITMP Moscow State University as analogues to foreign programs of the same class, which include ANSYS, Star CCM+, etc. Experimental data are also used to validate one-dimensional thermal-hydraulic codes used in Afrikantov OKBM when substantiating the thermal reliability of the cores of reactor installations; the thermal-hydraulic code KANAL also belongs to this class of programs.

Fuel rod assemblies with tight lattice bundles are considered promising for increasing the conversion rate and heat transfer in small modular reactors. The main feature of the flow in a tight lattice rod bundle is the formation of quasi-periodic large-scale velocity oscillations in the gap between fuel rods. These oscillations enhance mixing between the subchannels and significantly increase heat transfer between the fuel rods and the coolant. The large-scale oscillations are directly related to the pitch-to-diameter (P/D) ratio of the rod bundle and the Reynolds number. In this study, we experimentally investigate the unsteady flow structure in a gap between a flat wall and three rods with a relative pitch P/D = 1.077 using time-resolved particle image velocimetry (TR-PIV) technique. The obtained TR-PIV velocity vector fields were used to analyze flow characteristics, including two- and three-dimensional mean velocity, velocity fluctuations, and Reynolds stress profiles. We also examined the influence of the Reynolds number on flow oscillations in the gap. The spatial most energy-intensive flow modes were further analyzed using the proper orthogonal decomposition (POD) method. Our results indicate the presence of several traveling waves propagating along the flow. Modulation of flow oscillations in the gap was observed. These findings are consistent with those of other researchers.

This paper presents the results of experimental investigations of the influence of mixing spacer grids with different types of deflectors on the coolant flow in the TVS-Kvadrat fuel assembly of the PWR-type reactor. Investigations were conducted on an aerodynamic stand with the use of a multichannel pneumometric probe. Analysis of the spatial distribution of projections of the absolute flow velocity permitted detailing the coolant flow pattern behind the mixing spacer grid with various types of deflectors of mixing grids. The results obtained in the present paper are used to verify three-dimensional CFD programs, and in applied cell by cell codes they also serve as a database in calculations of thermotechnical reliability of the cores of PWR-type reactors with the TVS-Kvadrat.

When fixed abrasive wire saw is used to cut polysilicon, free SiC abrasives are added into the cutting coolant to form the fixed and free abrasive combined wire sawing process, so as to impact and roll the as-sawn wafer surface to remove the ductile amorphous silicon layer. Then, the as-sawn wafer can be textured by acid etching technology. The movement characteristics of free abrasives in sawing area directly affect their lapping behavior and the morphology generation of as-sawn wafer surface. In this paper, the flow field characteristics of cutting coolant and the movement characteristics of free SiC abrasives in the sawing area were studied, when using an abrasive groups interval distribution diamond wire for sawing. A three-dimensional model of cutting coolant in sawing area was established. Based on FLUENT, the influences of wire speed, feed speed, wire pretensioning force, viscosity of cutting coolant and wire surface structure parameters on the concentration peak position of free SiC abrasives in the cutting coolant along the wire axial direction were analyzed. The results show that the concentration peak of free abrasives will gradually shift to both sides along the circumferential direction of the wire in the sawing area. The deflection angle and width angle of free abrasives concentration peak are only related to the length of the bare wire area, and decrease with the increase of its length. Comprehensively considering the hydrodynamic pressure effect in the bare wire area, reducing the wire speed and tension, and increasing the feed speed and cutting coolant viscosity are conducive to enhance the lapping effect of free SiC abrasives on the as-sawn wafer surface. The change of wire structure parameters has no regular effect on the lapping behavior of free SiC abrasives in the bare wire area.

Conjugate heat transfer analysis plays an important role in the design of heavily cooled gas turbine vane or blade. In this study, the aerodynamic and heat transfer performance of the E3 engine nozzle guide vane is investigated through conjugate heat transfer analysis using ANSYS CFX software. Computational fluid dynamic analysis indicates that the shear stress transport turbulence model gives high accuracy in simulating the vane main-stream aerodynamic performance. However, when the simulated surface temperature of the vane was compared with the cooling test data, in which the vane was 3D-printed, significant deviation of the surface temperature distribution was observed. To understand the sources of these deviations, analyses are conducted considering main-stream and coolant flow parameters, as well as manufacturing discrepancies. The results reveal that the large deviation in the manufactured vane (up to 0.5 mm at the leading edge) alters the direction of the coolant flowing out from the leading-edge film-cooling holes, affects the film coverage along the surface, and in consequence, causes the temperature near the stagnation point increasing by approximately 40 K. Furthermore, variations in coolant inlet pressure, decreasing by 10 kPa, and temperature, increasing by 10 K, result in the vane surface temperature increased by 20 ~ 30 K. When the turbulence intensity of the main-stream increased from 5% to 20%, the vane surface temperature increased by approximately 20 K. Hence when conducting conjugate heat transfer analysis to validate the cooling performance of turbine vane or blade, emphasis should be focused on not only the uncertainties of the aerodynamic parameters but the manufacturing deviations.

This article presents the results of an experimental study on the hydrodynamics of the coolant at the inlet of the fuel assembly in the RITM reactor core. The importance of these studies stems from the significant impact that inlet flow conditions have on the flow structure within a fuel assembly. A significant variation in axial velocity and local flow rates can greatly affect the heat exchange processes within the fuel assembly, potentially compromising the safety of the core operation. The aim of this work was to investigate the effect of different designs of orifice inlet devices and integrated absorber grids on the flow pattern of the coolant in the rod bundle of the fuel assembly. To achieve this goal, experiments were conducted on a scaled model of the inlet section of the fuel assembly, which included all the structural components of the actual fuel assembly, from the orifice inlet device to the second spacer grids. The test model was scaled down by a factor of 5.8 from the original fuel assembly. Two methods were used to study the hydrodynamics: dynamic pressure probe measurements and the tracer injection technique. The studies were conducted in several sections along the length of the test model, covering its entire cross-section. The choice of measurement locations was determined by the design features of the test model. The loss coefficient (K) of the orifice inlet device in fully open and maximally closed positions was experimentally determined. The features of the coolant flow at the inlet of the fuel assembly were visualized using axial velocity plots in cross-sections, as well as concentration distribution plots for the injected tracer. The geometry of the inlet orifice device at the fuel assembly has a significant impact on the pattern of axial flow velocity up to the center of the fuel bundle, between the first and second spacing grids. Two zones of low axial velocity are created at the edges of the fuel element cover, parallel to the mounting plates, at the entrance to the fuel bundle. These unevennesses in the axial speed are evened out before reaching the second grid. The attachment plates of the fuel elements to the diffuser greatly influence the intensity and direction of flow mixing. A comparative analysis of the effectiveness of two types of integrated absorber grids was performed. The experimental results were used to justify design modifications of individual elements of the fuel assembly and to validate the hydraulic performance of new core designs. Additionally, the experimental data can be used to validate CFD codes.

Nowadays, the need for not only technically but also environmentally efficient machining processes is increasing. In this context, the reduction of oil emulsion type coolants used during machining of aeronautical engine components supposes a great challenge. In this paper, a novel approach based on the design, optimization and validation of a nozzle adaptor combining cryogenic technology and minimum quantity lubrication systems is proposed. The proposed work also deals with the aim of obtaining a cost-effective process. Thus, CO 2 flow and velocity was optimized in this line. Theoretically-based analysis were performed and compared with computational fluid dynamics (CFD) simulations and with real experimental tests as well. Once optimizing these key factors, two nozzle adaptors were designed and simulated by CFD. Different geometries were tested looking for the most efficient design. Finally, to obtain a feasible industrial product, the developed nozzle was tested as a CryoMQL demonstrator comparing with other lubricoolant techniques during milling Inconel 718. Results show a successful balance between technical and environmental issues using this technology when milling aeronautical alloys.

The results of experimental studies of the hydrodynamics of a coolant in the outlet section of a cassette fuel assembly of the RITM reactor of a low-power nuclear power plant are presented. The purpose of the work was to study the redistribution of axial velocity and coolant flow rate at the outlet of the fuel rod bundle, behind the fuel assembly cap, near the coolant extraction pipe, and in the holes of the upper support plate. To achieve the goal, experiments were carried out on a research stand with an air working medium on a model of the outlet section of the fuel assembly, including the outlet fragment of the fuel rod bundle, the cap, the upper support plate with the coolant extraction pipe. When conducting research, the pneumometric method and the method of injection of a contrast impurity were used. An area covering the entire cross section of the model was chosen as the study area. The picture of the coolant flow is represented by cartograms of the distribution of axial velocity and coolant flow rate, as well as cartograms of the distribution of the contrast impurity. The experimental results can be used in the design of new active sections of RITM reactors. The resulting experimental base can be used for local validation of CFD programs and onedimensional thermal-hydraulic codes used to substantiate the thermal reliability of cores.