bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seeking missing pieces in learning about single slit diffraction: results from a teacher survey
Authors: Mešić Vanes , Škaljo Edvin , Mitrevski Boce , Nešić Ljubiša , Hatibović Senad , Maličević Mevludin 
Published: March 2021

Abstract
Single slit diffraction is part of many high-school physics curricula throughout the world. In this study, we aimed to investigate whether high-school physics teachers from Bosnia and Herzegovina, Serbia and North Macedonia are adequately prepared to discuss with their students about various aspects of the single slit diffraction pattern, particularly about vertical length of diffraction fringes. To that end we conducted a written survey which included 57 high-school physics teachers. Besides asking teachers about students’ difficulties in learning about single slit diffraction, we also asked them to specify their own difficulties with this topic and required them to solve a conceptual task. Almost every second teacher believed that vertical length of diffraction fringes can be increased by changing shape or width of the slit and only 1 out of 57 teachers managed to correctly answer why diffraction fringes become shorter when we move away from the central maximum. We concluded that physics teacher education programmes should be changed to develop understanding of both, horizontal and vertical aspects of the diffraction pattern. To that end it is useful to provide learning opportunities which encourage combining ray and wave model of light.
Pressure-driven stochastization of flux surfaces in stellarator equilibria: a review of the experimental observations and their analysis
Authors: Reiman Allan H 
Published: March 2021

Abstract
Stellarator vacuum fields are designed to have a dense set of nested flux surfaces, with only small islands and stochastic regions in the interior of the confinement region. As the plasma pressure is increased, pressure driven currents appear, and they can significantly modify the vacuum field. The question arises whether pressure driven currents can cause significant flux surface breakage. Both the Wendelstein 7-AS and large helical device stellarators had dedicated experimental campaigns to study the

β

limit in those devices. This paper reviews the evidence that the flux surfaces in a significant fraction of the plasma volume were stochastized by the pressure-driven currents in the highest

β

experiments. That phenomenon appears to have been the dominant source of pressure-driven flux surface loss in these experiments.
Unsteady effects at designing of modern aircraft jet engines
Authors: Kraev V M , Aslanov A R 
Published: March 2021

Abstract
The operating conditions of advanced aircraft engines powered by cryogenic fuel analyze in the paper. The authors demonstrate cryogenic fuel supply systems must be designed with transients’ processes consideration. These processes based on significant changes in heat exchange and hydrodynamics in unsteady conditions. Unsteady conditions result to dramatic up to 3 times and more growth of heat exchange coefficient and hydraulic resistance. The authors suggested a methods can be used for unsteady processes in cryogenic fuel system calculation.
Radiative and convective heat exchange in technological furnaces of petrochemical industry
Authors: Abdullin A M 
Published: March 2021

Abstract
Complex heat transfer in radiant chambers of technological furnaces of the petrochemical industry is considered. The object of research is a vertically located flat channel, approximately simulating a radiant chamber. The walls of the channel are formed by a refractory lining and a tubular screen with a known temperature. The chamber volume is filled with selectively emitting, absorbing and weakly scattering media of gaseous fuel combustion products. The research method is based on the numerical solution of two-dimensional integro-differential equations of radiation gas dynamics, closed by a two-parameter model of turbulent convection. The influence of the modes of organization of the combustion process, the radiation properties of the combustion products and refractory lining on the distribution of heat fluxes and the characteristics of the total heat transfer are considered.
Integrated researches of topical problems of fast reactors thermal physics
Authors: Sorokin A P , Kuzina Yu A , Alekseev V V , Grabezhnaya V A , Zagorulko Yu I , Kamaev A A , Orlov Yu I 
Published: March 2021

Abstract
The results of actual studies are presented to justify the thermophysical characteristics and safety of fast reactors with sodium and lead coolants. The influence of a stratified coolant flow on the formation of velocity and temperature fields in a fast reactor vessel with a sodium coolant is shown. The development of the degradation of the fuel assembly during the development of a severe accident with the loss of sodium flow rate in a fast reactor, the blockage of the cross sections of the fuel assembly and the release of marker materials beyond it are demonstrated. The expediency of the combined sodium purification system built into the reactor vessel is shown, in which “cold traps” are an indispensable element, and “hot traps” provide accelerated oxygen purification during operation of the NPP in nominal regime. The results of studies of a large-modular sodium-water steam are presented. As applied to a reactor with a lead coolant, the influence of spacer grids on heat transfer in a fuel assembly of the core is shown. On the model of the steam generator of the reactor installation with lead coolant, it was found that the values of the steam temperature at the outlet of both collectors coincide. The temperature of lead at the exit from the lowering section and in the main path of lead is coincides also. The state and prospects of the development of technology for heavy liquid metal coolants are analyzed. The principle possibility of providing the required parameters of a high-temperature fast reactor with a sodium coolant for the production of hydrogen is shown. The problems of further thermophysical research are analyzed.
Analysis of flow-field and heat exchange for a blunted cone at hypersonic speeds
Authors: Drozdov S M , Rtishcheva A S 
Published: March 2021

Abstract
The possibility of decoupled analysis of flow-field and heat transfer for a solid structure was investigated using numerical simulation of conjugate problem on hypersonic flow and heat transfer for a blunted cone made of heat-conducting material. The considered cones had semi vertex angle ϕ≈7 ° and two radii of blunting:

r

1

и

r

2

=

2

3

r

1

. This form is typical for noses of modern hypersonic aircraft. The ANSYS FLUENT software package was used to simulate a laminar flow with developed physicochemical models of nonequilibrium air (a five-component gas mixture was considered: O2; N2; O; N; NO) and S2S built-in model of radiative heat transfer. The accuracy of the decoupled analysis was evaluated as a result of comparison with the solution of the conjugate problem on flow-field and internal heat transfer.
Functional identification of transition processes in elements of the system of air heater-fan-room by the experimental results
Authors: Mansurov R Sh 
Published: March 2021

Abstract
The main energy-saving equipment used in the systems of providing of microclimate (SPM) are recuperative, regenerative heat exchangers and heat pump units (HPU). Of energy-saving technologies of air treatment possible to isolate the bypass of humidification chamber, first and second recycling of air, regulation of the flow rate of intake air depending on the contents of various hazards in the working zone air - heat, moisture, CO2, dust etc. To energy - saving modes of SPM include: normal operating mode; modes of intermittent heating, cooling and ventilation; modes of operation taking into account the assimilative capacity of the air volume and heat-accumulating properties of the enclosing structures of the room.
Combining energy-and resource-saving equipment, air treatment technologies into an integrated complex of technical solutions on a single platform, as well as the use of different modes of operation of the CPM will optimize energy and resource consumption to maintain the specified parameters of the microclimate in the room. Management of a single platform requires the development of an appropriate management system.
The basis for the creation of control systems is the knowledge of the transients occurring in the elements of SPM, and in the external environment. Since the main processes in the elements of SPM are the processes of thermal processing of air, for the construction of mathematical models requires knowledge about the laws of thermodynamic processes in the investigated elements of SPM. Identification in full-scale conditions achieves high accuracy and reliability of the developed mathematical models of transfer functions of elements of SPM. Experimental studies allow us to establish all the characteristics that determine the thermodynamic process in the element under study SPM.
Effect of packing factor and conductivity on heat transfer in reactor core domain with spherical fuel
Authors: Slyusarskiy K V , Larionov K B , Koothan V V 
Published: March 2021

Abstract
The effect of packing factor and conductivity on temperature distributions on the surface of the spherical fuel element in conditions of pebble bed nuclear reactor were studied 0.35by means of numerical simulation using Ansys Fluent. The body centred cubic geometry was applied. The packing factor was varied in range 0.1-0.35 while the conductivity was varied in range 1-100 W/(m K). The maximal and minimal surface temperatures were varied in ranges 695-900 and 680-780 K, respectively. The conductivity at 20 W/(m K) and above was found to had nearly no effect while the packing factor increasing resulted into nearly proportional decreasing of surface temperatures.
Determination of void fraction in a bed of solid particles by the method of flow cutoff
Authors: Tairov E A , Safarov A S 
Published: March 2021

Abstract
The paper presents a new method for determining the void fraction of two-phase flow with a condensable vapor phase. This method relies on the known technique of blocking the flow and allows measuring void fraction in the pore space of solid particle packings. The paper presents the results of experiments with packed beds of steel balls with diameters of 2 mm and 4 mm, 250 mm high. A comparison with some techniques for calculation of void fraction for empty vertical pipes is made.
Separation features of multicomponent gas mixtures at the border of regime change diffusion – concentration gravitational convection
Authors: Kossov V N , Fedorenko O V , Krasikov S A , Kalimov A B 
Published: March 2021

Abstract
The mixing of carbon dioxide dissolved in multicomponent gas mixtures at various pressures was studied. It was found that at a certain pressure the diffusion separation of components is violated and structured flows arise in the system. The pressure regions are fixed at which the conditions of priority transfer of the component with the highest molecular weight in the mixture are realized in the system. To analyze the effect of pressure on the process of changing the diffusion – convection modes, a mathematical model has been proposed that takes into account the kinetic features of multicomponent mixing. It is shown that the change in mass transfer modes is associated with a significant difference in the diffusion abilities of the components.
Numerical research of the influence of the geometric parameters of shadowing fins on the intensity of jet cooling by supercritical carbon dioxide
Authors: Rogalev A N , Kindra V O , Osipov S K , Makhmutov B A , Zonov A S 
Published: March 2021

Abstract
This paper discloses computer simulation results of thermos-hydraulic processes in cooling channels of carbon dioxide turbines used in oxy-fuel power production facilities. Stream cooling systems may be modified by the installation of shadowing ribs on the pressure and suction sides of a hollow blade and this intensifies heat transfer and reduces the cooling agent flow. The heat transfer maximal intensity is obtained at the distance between deflector orifice and shadowing fin of 0.25 orifice diameter. Change of the shadowing fin cross-section shape from oval to circular causes increases of the channel hydraulic resistance for 20–28% and the mean Nusselt number for 8–25%.
A Study of the Short Heat Pipes by the Monotonic Heating Method
Authors: Seryakov AV , Alekseev A P 
Published: March 2021

Abstract
The results of studies using the monotonous heating method in a vacuum adiabatic calorimeter the thermal resistance and heat capacity of short linear heat pipes (HP’s) designed for cooling spacecraft and satellites with strict take-off mass regulation are presented. Experimental results of thermal resistance, obtained at high thermal loads and starts boiling of the working fluid in the HP’s evaporator allow us to determine the evaporator heat capacity by solving the inverse coefficient problem of thermal conductivity equation. This allows us to estimate the thickness of the working fluid layer and the specific heat of evaporation, the heat capacity of the liquid and vapour phase of the boiling two-phase working fluid on the evaporator surface.
Experimental-theoretical approach to calculating the partial density of hydrogen cyanide during fires at energy facilities
Authors: Puzach S V , Boldrushkiev O B , Suleykin E V 
Published: March 2021

Abstract
It is made analysis of toxic effect of hydrogen cyanide on people during fire evacuation at energy facilities premises. The critical value of the partial density of hydrogen cyanide is substantiated. An experimental and theoretical approach is proposed for calculating the partial density of hydrogen cyanide indoor fire. The proposed approach is based on the analytical dependence of the average volumetric partial density of HCN on the change in the volumetric average partial density of oxygen in the premises. The results of experiments on measuring the partial density of HCN in the case of combustion of modern cable products used at energy facilities are presented. The results of experimental and theoretical studies make it possible to determine the time variation of the average volumetric partial density of hydrogen cyanide in a fire in a full-scale premises using the experimental values of the specific coefficients of formation of hydrogen cyanide and oxygen absorption obtained in a small-scale experimental setup, and the change of the volumetric average partial density of oxygen obtained from the solution of the conservation law equation mass of oxygen. It is substantiated that the calculation can also be made without solving the differential equation of the law of conservation of the mass of hydrogen cyanide using only the experimental dependence of the HCN density on the change in O2 density.
Theoretical researches of air permeability during development of cracks in building facilities
Authors: Vorob’eva Y A , Zherlykina M N , Burak E E , Kononova M S , Muravyov AV 
Published: March 2021

Abstract
The article considers a mathematical model of air infiltration through cracks in building envelopes. Air movement for the given flow diagram of a continuous medium is described by the Navier - Stokes equations. As applied to thin layers of the air, assumptions are made that make it possible to compose a system of equations, including equations of dynamics and equations of continuity. The results of assessing the physical deterioration of residential buildings constructed according to standard designs taking into account their number of storeys and wall materials are presented. The influence of various damage to the building on the state of its heat balance is considered. The dependences of reducing thermal protection of building envelopes on the degree of wear in houses made of various materials are revealed. The main recommendations for improving the energy efficiency of buildings are proposed, which allow minimizing heat losses and ensuring comfortable microclimate parameters in the premises.
Particle separation in cyclones of circulating fluidized bed systems
Authors: Ryabov G A , Folomeev O M 
Published: March 2021

Abstract
Circulating fluidized bed (CFB) plants are widely used in energy, petrochemicals, aluminum production (alumina firing), and other industrial sectors. The CFB technology is characterized by relatively high reactor velocity that exceed the transport velocity of medium-sized particles, and the presence of separators (mainly of the cyclone type) with a system for returning trapped particles to the reactor. This ensures a long residence time of the particles in the reaction zone, a high circulation rate, and a stable and relatively low temperature in the reactor. In fact, it is the cyclone capture efficiency that directly determines the multiplicity of circulation and the flow rate of circulating particles and their size characteristics. The report discusses the current state of development and methods for cyclones calculating. Data from our and foreign studies are reviewed and the dependence of the correction on the mass concentration of particles is proposed. A brief description of the test rigs and the results of our own studies of particle separation in cyclones are given. Experimental data on the effect of dust on the capture efficiency are presented in the form of a dependence of the relative entrainment of particles (1-efficiency) on the mass concentration of particles at the entrance to the cyclone. Entrainment is noticeably reduced when the concentration increases, as small particles are attracted by larger ones to the wall of the cyclone.
Application of numerical modelling for determining the optimal position of the suction slot in the steam turbine vane cascade
Authors: Gribin V G , Tishchenko A A , Alekseev R A , Gavrilov I Yu , Popov V V , Tishchenko V A 
Published: March 2021

Abstract
The numerical investigations of liquid film development in the last stages of steam turbines were performed. This data was used to suggest the position of the suction slot used to evacuate the liquid phase from the turbine flow path. The object of study is a periphery 2D section of vanes cascade. The movement of coarse droplets in the blade passage was simulated. Their collision with the blade surfaces results in the appearance of additional sources of mass and momentum for liquid film. The influence of theoretical Mach number on the features of liquid film formation was studied. The distributions of main characteristics, reflecting the formation of the film, have been obtained. They were used to analyse the liquid phase flow along the surfaces and to point out base recommendations about the location of the suction slot.
Evaluation of the dynamical characteristics of fluid flow caused by collapse of a non-spherical near-surface bubble
Authors: Le T C , Melikhov V I , Melikhov O I , Yakush S E 
Published: March 2021

Abstract
The paper is devoted to numerical study of the influence of the initial shape of a vapor bubble on the surface impact of the water jet emerging due to the bubble collapse. This problem is relevant to spreading of high-temperature melt under a layer of subcooled water. The vapor bubbles formed on the melt-water interface, upon complete penetration in water, are condensing rapidly to produce high-velocity water micro-jets directed towards the melt. Impact of these jets causes upward melt splashing. Superposition of these processes forms a dynamic layer where melt is mixed with water; the presence of this premixed layer can be a pre-requisite for steam explosion. In this work, numerical modelling by the boundary element method is performed for the collapse of a bubble of an oblate spheroid. It is shown that the water jets generated in this process possess the impulse comparable to that generated by a collapsing spherical vapour bubble of the same volume. By the numerical simulations and subsequent estimates it is obtained that collapse of non-spherical bubbles near the melt-water interface produces melt splashes of the height of few centimetres, which is sufficient for the occurrence of steam explosions.
A review to the specific problems of nano thermal physics
Authors: Khvesyuk V I , Barinov A A , Liu B , Qiao W 
Published: March 2021

Abstract
The paper is devoted to three current problems that related to thermal transfer in the solid-state nanostructures. The first task is the analysis of interaction of phonons with rough solid boundaries, the presence of which leads to a significant increase in the resistance to heat transfer in nanostructures. This fundamental problem is discussed in a connection to the theoretical formulation of rough interface between solids. The second task is exploring methods to calculate diffusion and heat transfer in solids within the framework of detailed consideration of phonon interaction processes. The development of the computational model that adequately represents the physics of interaction processes and allows to calculate thermal properties that are in a good agreement with experimental data remains open. The third task is to calculate the thermal bound-ary conductance. The problem is solved by considering the processes of scattering and refraction of elastic waves at the interface. For the first time, the dispersion properties of elastic waves are taken into account in the problems of this kind. The result is the applicability of the new model in a much wider temperature range than in the existing models.
An experimental study of heat transfer and pressure drop during flow boiling of R134a and R236fa in a microchannel system
Authors: Shamirzaev A S 
Published: March 2021

Abstract
An experimental study was made of heat transfer and pressure drop during the boiling of R134a and R236fa refrigerants in a system with two slotted microchannels. A copper block with two microchannels 2.05 mm wide, 0.4 mm deep, and 16 mm long was used as an experimental test section. The mass velocity varied from 500 to 2000 kg/m2s, the initial subcooling was from 40 °C to 0 °C. Data analysis showed that, when the flux of R236fa refrigerant becomes saturated, nucleate bubble boiling is absent. In the case of R134a saturated flow boiling, suppression of nucleate bubble boiling was observed with heat flux increasing.
Analytical study of the velocity and pressure of the electrovortex flow in hemispherical bowl in a Stokes approximation
Authors: Malyshev K Yu , Mihailov E A , Teplyakov I O 
Published: March 2021

Abstract
The problem of an electrovortex flow in a hemispherical bowl with an internal electrode is considered. In the framework of the Stokes approximation, analytical expressions for the velocity and pressure fields are obtained. Two types of boundary conditions were used: non-leakage on the entire boundary (with no-slip condition on the free surface and partly slip on the electrodes) and an approximate adhesion condition on the electrodes. The non-leakage condition corresponds to the homogeneous Dirichlet boundary condition for the vector potential and the vorticity on the entire boundary. An approximate adhesion condition is posed using the Thom difference approximation. The analytical expressions for the velocity and pressure fields are written uniformly for both types of boundary conditions.
Maps of hydrodynamic regimes of evaporation and boiling in the thin horizontal liquid layer on the modified surface
Authors: Shvetsov D A , Pavlenko A N , Brester A E , Zhukov V I 
Published: March 2021

Abstract
The paper reports the results of the study of evaporation and boiling regimes of a thin horizontal liquid layer on a modified surface. The formation of various structures was observed at the different heat fluxes, pressures, and heights of the liquid layer. The paper presents maps of the hydrodynamic regimes of evaporation and boiling of thin liquid layers on a modified surface. The regions of existence of various structures observed in the layer are indicated depending on the pressure and heat flux. The results are compared with the calculation dependencies.