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Thermophysics and Aeromechanics
Journal Prestige (SJR): 0.447  Citation Impact (citeScore): 1 Number of Followers: 6  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1531-8699 - ISSN (Online) 0869-8643 Published by Springer-Verlag  [2467 journals]
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- Heat capacity of gadolinium-scandium-gallium and calcium-niobium-gallium
garnets-
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Abstract: Abstract An experimental study of the heat capacity of gadolinium-scandium-gallium and calcium-niobium-gallium garnets widely used in laser technology and microelectronics was carried out by the method of differential scanning calorimetry. New experimental results on the specific isobaric heat capacity in the temperature range of 300–1270 K were obtained; approximation equations and a table of recommended values for scientific and practical use were developed on their basis. The comparison with the known literature data was carried out. The estimated error of the data obtained was 2–4%.
PubDate: 2022-11-01
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- Thermal conductivity of the R-32/R-125 (15/85) mixture in the vapor phase
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Abstract: Abstract The thermal conductivity of the R-32/R-125 (15/85) mixture was investigated in the range of temperatures of 305–411 K and pressures of 0.1–1.8 MPa. Measurements were carried out by the stationary method of coaxial cylinders. The error of the experimental data on thermal conductivity was 1.5–2.5 %, and the measurement errors of temperature and pressure did not exceed 0.05 K and 4 kPa, respectively. A generalizing equation for calculating the thermal conductivity as a function of pressure and temperature was obtained. The thermal conductivity on the dew line and in the ideal gas state was determined.
PubDate: 2022-11-01
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- Structure of the proximal anastomosis flow in stationary mode at moderate
Reynolds numbers-
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Abstract: Abstract Results of an experimental study and direct numerical simulation of the steady flow in a channel branching region modeling the proximal anastomosis of femoral artery are reported. The Reynolds number was Re = 1500, which value corresponded to the maximum blood flow during the period of heart contractions. The ratio of the rates of the liquid flows through the branch and main channel was a varied parameter. Regularities in the development of the flow structure in the main channel and in the branch region are revealed, with much attention having been paid to flow separation regions. The occurrence of secondary flows localized within the separation regions has been established. The ranges of the flow rate ratio at which flow turbulence signs appear in the mixing layer at the interface between these regions are identified.
PubDate: 2022-11-01
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- Numerical simulation of the evolution of localized disturbances generated
by two synchronous separated sources in a supersonic boundary layer-
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Abstract: Abstract The paper presents the results of numerical simulation for the development of localized disturbances emerging from a single source or two synchronous sources of laminar boundary disturbances allocated on the plate with the flow at Mach number M = 2 (variants for different distances between two sources were considered). Simulation was performed using the FlowVision software package at the flow parameters typical of T-325 wind tunnel (ITAM SB RAS). The problem was studied in the range of the linear development of disturbance. The study demonstrates that, depending on the distance between the sources, the generated disturbances might either enhance or decay downstream. The frequency-wave analysis of disturbance structure was performed. Two separated synchronous local sources generate the disturbances with wave spectra: these spectra exhibit nodes and antinodes and their positions depend on the distances between two sources.
PubDate: 2022-11-01
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- Study of thermal efficiency of a wall gas jet blown through the holes in
the transverse trench-
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Abstract: Abstract We present the experimental results on the thermal efficiency in a wall gas jet blown through inclined cylindrical holes along a smooth surface, and when a secondary flow is blown through cylindrical holes into a transverse trench. The thermal efficiency fields of the wall jet were measured using an infrared camera. In the case of blowing into a trench, the experimental data are characterized by an insignificant influence of the injection parameter on the thermal efficiency of the wall jet for all the trenches under study. It has been established that an increase in the trench depth leads to an increase in the thermal efficiency of the wall gas jet. The maximum increase in thermal efficiency is achieved for a trench with relative depth h/d = 0.94. The data of measurements presented are compared with the experimental and numerical results of other authors for the cases of blowing through the holes into a transverse trench.
PubDate: 2022-11-01
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- Experimental study of the flow turbulent structure in a cell of a lattice
matrix-
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Abstract: Abstract The experimental results on the turbulent flow structure in a lattice matrix cell, which is a region between intersecting ribs on the opposite walls of a flat channel, are presented. The angle between the ribs was 2β = 60°, 90° and 120°; the Reynolds number calculated from the average velocity and hydraulic diameter of the channel was varied in the range Re = (1–7)·104. The aerodynamic characteristics of the flow inside a lattice matrix cell placed in a rectangular channel with a cross section of 20×150 mm and a length of 400 mm were measured using a two-component laser Doppler anemometer (LDA). The flow structure was studied in individual cells of 15×15 mm, formed by crossing ribs on the opposite channel walls. The complex three-dimensional structure of the flow in the matrix cells and strong turbulence of the flow in the near-wall regions are shown. The installation of ribs leads to a significant increase in hydraulic losses, especially at large crossing angles.
PubDate: 2022-11-01
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- Plasma ignition of solid fuels at thermal power plants. Part 2. 3D
modeling of the furnace of a pulverized coal boiler-
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Abstract: Abstract This paper presents calculation results on plasma ignition and combustion of coal in the furnace of the PK-39-II boiler at Reftinskaya SDPP. For mathematical modeling of coal combustion in the boiler furnace, a three-dimensional mathematical model Cinar ICE and a software package for physical modeling and calculation of hydrodynamics, heat and mass transfer and combustion of fuels in the volume of furnaces were applied. Calculations were performed for two regimes of pulverized coal combustion: the traditional one and using plasma activation of coal combustion. It is shown that the use of plasma-fuel systems (PFS) allows the optimization of the coal combustion process in the combustion chamber. Three-dimensional modeling of a pulverized coal furnace equipped with a PTS allows one to determine the optimal PTS layout on boilers of thermal power plants.
PubDate: 2022-11-01
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- Chemoconvective mixing in a Y-shaped continuous-flow microchannel
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Abstract: Abstract The continuous-flow microreactors, being designed for small-scale production of pharmaceutical substances, have a moderate volume and ensure steady synthesis for pharmaceutical production while using noninvasive methods for mixing of ingredients. The paper describes experimental and simulation study of the efficiency for natural convection mechanisms for solutions mixing in a Y-type symmetric microreactor. The mixing zone is arranged for the discovery of convection potential. We consider both variants of chemically inert and chemically active systems. A model reaction is represented by a rapid acid-base neutralization reaction. The theoretical model comprises the 3D Navier—Stokes equation and the reactants transport equations (written with account for nonlinear diffusion). Experimental and numerical results have been compared. The dependency for the effective mixing length on the instability type and solvents flow rates was found.
PubDate: 2022-11-01
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- Experimental study of dispersed flows in microchannels for 3D printing of
composite materials-
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Abstract: Abstract The paper studies the segmented flow patterns of immiscible liquids in microchannels with T- and X-junction for 3D printing technologies. The flow visualization results serve to build the flow pattern maps with a distinguished area of stable plug flow. A fair agreement of the maps plotted using the superficial flow velocities is revealed, and the influence of the junction geometry on the boundaries of flow patterns is shown to be insignificant. When using a less viscous carrier phase, the region of a stable plug flow is demonstrated to expand towards higher superficial flow velocities. The separation of microdroplets from the trailing edges of plugs is investigated. It is found that the transition to the separation of microdroplets is described in terms of the capillary number, constructed from the bulk velocity of the phases, and the ratio of phase flow rates. Thus, a range of dimensionless parameters of microchannel devices, suitable for 3D printing of composite materials with specified properties is determined.
PubDate: 2022-11-01
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- Experimental investigation of the flow structure in a single trench dimple
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Abstract: Abstract A technique is described and the results of an experimental study of the aerodynamic structure of turbulent streamlining, velocity fluctuations, and pressure fields on the surface of a single trench dimple located on the wall of a flat rectangular channel are presented. The trench dimple cross section is a cylindrical segment with hemispheres at its edges. The measurements were carried out with a two-component laser-Doppler anemometer at two angles of the dimple inclination relative to the flow direction φ = 0 and 45°. The development of the flow in the direction transverse to the trench, as well as along it, was studied. The fundamental difference between the velocity fields and their fluctuations in a trench located normally and at an angle to the flow is shown.
PubDate: 2022-11-01
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- Study of n-heptane combustion atomized with superheated steam and at
different excess air ratios in the gas generation chamber-
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Abstract: Abstract Combustion of liquid hydrocarbons atomized with a jet of superheated steam is experimentally studied using n-heptane as an example. This is considered as a promising method for efficient and environmentally safe combustion. The study uses a burner with forced air supply to the gas generation chamber. It is a modernized design of an atmospheric burner with natural air inflow, studied by the authors earlier, and it allows obtaining additional information about the effect of changing the excess air ratio inside the device on the process of burning liquid fuel in the presence of superheated steam. New data on the environmental and energy characteristics of the burner under study were obtained based on thermocouple measurements, gas analysis of intermediate flame components, measurements of combustion efficiency and harmful emissions in the final combustion products. They were compared with characteristics of the burner with natural air inflow. It was found that the formation of carbon monoxide during heptane combustion is reduced by 25 %, and the formation of nitrogen oxides is reduced by 15 % with a decrease in the excess air ratio in the combustion chamber from 0.7 to 0.16. At the same time, a burner with natural air inflow is characterized by a higher flame temperature and a shorter flame length. At that, the level of CO and NOx emissions in all regimes corresponds to the European standard EN 267. It was determined that the forced air flow does not have a noticeable effect on the heat generated for the studied regimes, and the calorific value of fuel combustion in all cases is close to the higher calorific value of heptane, which indicates the high efficiency of the combustion method under study.
PubDate: 2022-11-01
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- High-speed visualization of cavities, arising in a slit channel of complex
shape-
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Abstract: Abstract The article presents the results of an experimental study of the cavitation flow around the NACA 0012 series foil in a slit channel with a width of 1.2 mm. The aspect ratio of the streamlined body was 0.02. To identify the main features of the two-phase flow, high-speed visualization was performed using the Photron FASTCAM NOVA S12 camera with a sampling frequency of 20 kHz. The internal structure of cavities was detected. The main frequencies of cavities formation in the flow were determined using digital processing of visualization data. The close location of the channel walls was shown to significantly affect the return flow propagation under the cavity and its separation.
PubDate: 2022-11-01
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- Numerical study of aerodynamics and heat transfer for an advanced design
of pulverized coal fired furnace-
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Abstract: Abstract The paper deals with the numerical study of aerodynamics and heat transfer for a case of a four-vortex furnace chamber designed for jet fire of brown coal from the Eastern-region coalfields. The combustion modeling is achieved by a set of linked submodels: they describe turbulent gas flow, thermal and radiative heat transfer, processes of degradation and burning for coal particles, and NOx generation. Simulation demonstrated that using of these types of brown coal in a specific-design furnace chamber creates a steady four-vortex flow structure that provides a uniform temperature field in the volume and admissible generation of NOx.
PubDate: 2022-11-01
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- Investigation of dielectric liquid FC-72 boiling in a slit microchannel
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Abstract: Abstract Microchannel cooling systems are widespread due to their efficiency. In this work, boiling of dielectric liquid FC-72 in a slit microchannel with a height of 66 µm and a width of 10 mm was studied. Heating was carried out by a thin-film ITO heater in direct contact with the working liquid. The flow regimes at boiling in a wide range of liquid flow rates were investigated. It is shown that boiling regimes in a slit microchannel differ significantly from the flow regimes in circular and rectangular mini- and microchannels. The dependences of heat flux on the temperature head have been plotted. The dependence of the heat transfer coefficient on the heat flux was investigated for different regimes of the two-phase flow.
PubDate: 2022-11-01
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- Water motion near graphene and its electric conductivity
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Abstract: Abstract The paper is the study of electric resistance of a graphene layer washed by a liquid with different flow rate parameters. Experiments demonstrate that if the fabricated composite (graphene upon a PET/EVA polymeric substrate) is submerged into distilled water, the sample resistance increases by 120 %. Meanwhile, the flow of liquid near the graphene layer decreases this gain in the electric conductivity. The effect offers a general design of a flow rate sensor based on the graphene layer taken as a flow-sensitive matrix. The study demonstrates that this design of graphene flow sensor (tested for distilled water) exhibits a linear dependency of the sensor resistance on the flow rate.
PubDate: 2022-11-01
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- Bubble growth in a volatile liquid drop: interface dynamics
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Abstract: Abstract The process of bubble growth inside an intensively evaporating sessile liquid drop on a heated structured black silicon has been studied. Experiments are carried out with volatile fluids FC-72, HFE 7100, ethanol, and water. The schlieren-based method was developed for investigations of the bubble growth inside a liquid droplet. The contact line velocity was measured during the droplet evaporation, including the case of a growing bubble inside the drop. The velocities of the contact line for droplet evaporation with/without bubble were compared. The contact line instability was detected emerging also due to the developed substrate structure. This can lead to an increase of local flows in the microregion and to significant heat transfer enhancement.
PubDate: 2022-11-01
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- On “new methodologies of processing” of results calculated for
rotating detonation engines and of results of force measurements for
ramjet models tested in supersonic test benches-
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Abstract: Abstract It is shown that the “new methodologies of processing and using” of the results calculated for rotating detonation engines, as well as those of recent measurement of forces acting on the rotorless ramjet models in “hot” and “cold” tests in supersonic test benches, which are developed and promoted by S.M. Frolov and V.I. Zvegintsev with their colleagues, are incorrect.
PubDate: 2022-11-01
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- Effects of different processing parameters on laser water jet-machining
silicon-
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Abstract: Abstract Laser water jet processing is a new hybrid method developed on the basis of traditional laser processing technology. It combines high laser processing efficiency with the impact and cooling effects of water jets. Laser water jet processing can effectively process hard and brittle materials such as silicon. In-depth study of the processing technology has important practical significance. For this reason, the controlled variable method is used to study the influence of different processing parameters on groove depth. The research results show that with the increase of current and laser pulse width, the groove depth gradually increases; with the increase of laser repetition frequency and water jet velocity, the groove depth increases first and then decreases. The experiment of laser water jet processing silicon can provide guidance for processing other difficult-to-process materials in the future.
PubDate: 2022-11-01
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- Equation for the viscosity coefficient of liquid, gas, and fluid of inert
gases. Krypton-
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Abstract: Abstract Using the previously established dependence of the excess viscosity on the internal energy density, a simple low-parameter equation was obtained to describe the krypton viscosity coefficient in a wide range of state parameters. It was shown that the proposed low-parameter equation for calculating the viscosity coefficient of liquid and gas allows for reliable extrapolation beyond the limits of the studied area.
PubDate: 2022-11-01
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- Determination of thrust characteristics of air-breathing jet engine
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Abstract: Abstract The traditional approach to measuring the thrust of air-breathing jet engines (ABJEs) was proposed by B.S. Stechkin in 1929. In this approach, the thrust is determined as the difference between the momenta of the gas flows at the engine inlet and outlet. This approach involves some methodological and terminological problems. Based on the critical analysis of available concepts, the present article proposes a new approach to the determination of ABJE thrust in the form of the reduction of the initial drag of the aircraft + ABJE assembly observed when the propulsion system operates with fuel supply and energy release. For the thrust thus obtained, we propose using the term “real thrust”. It is shown that the proposed approach eliminates terminological problems and simplifies the technique for measuring the thrust characteristics of ABJEs. The paper considers various options in applying the proposed approach to the determination of the “real thrust” for different cases of using and modeling ABJEs, including the calculation of flight trajectories of ABJE-powered aircraft.
PubDate: 2022-11-01
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