Radial Temperature Distribution Research Articles

Finite element analysis of radial temperature of transmission conductor in low-temperature environment

Abstract Most existing studies simplify conductors as isothermal cylinders, neglecting their actual structure and the inter-conductor contacts. This is especially problematic in regions like Northeast and Northwest China, where the conductors face harsh working environments due to significant seasonal temperature variations. Additionally, there is a lack of research under extreme low-temperature conditions. Considering these factors, a temperature field in low-temperature environments was established based on the heat conduction equation. A finite element model and a mathematical model for the transmission conductor were developed using the actual structure of the JL/G1A-240/30 type steel-core aluminum stranded conductor as a reference. Constraint conditions were set, and the model was simulated under various environmental conditions using the finite element ANSYS software. This simulation calculated the radial temperature distribution of the conductors in low-temperature environments, along with the combined effects of transmission line current load, air convection cooling, sunlight intensity, and wind speed on the radial temperature distribution. The results indicate that this method can effectively determine the radial temperature values of transmission conductors under different meteorological conditions, which are significantly influenced by environmental temperature and wind speed. This is beneficial for enhancing the operational safety and stability of transmission lines, achieving dynamic capacity expansion, and improving the transmission capacity of the lines.

Resolving nonuniform flow in gas turbines: challenges, progress, and moving forward

Abstract The flow in gas turbines exhibits a highly unsteady, complex and nonuniform manner, which presents two main challenges. Firstly, it introduces instrumentation errors, contributing to uncertainties when calculating one-dimensional performance metrics during rig or engine tests using fixed-location rakes. Secondly, it raises mechanical concerns, including high-cycle fatigue due to blade row interactions in turbomachines and thermal fatigue caused by hot-streaks at the combustor exit. Experimental characterisation of the flow nonuniformity in gas turbines is highly challenging due to the confined space and harsh environment for instrumentation. This paper presents recent efforts to address this issue by resolving the nonuniform flow in gas turbines using spatially under-sampled measurements. The proposed approach utilises discrete probe data and leverages a ‘Fourier-based approximation’ method developed by the author. The technique has undergone preliminary experimental validation involving reconstruction of the total pressure distribution in a multi-stage axial compressor and the total temperature field at the exit of the combustor and high-pressure turbine. Results show that, in the multi-stage axial compressor environment, reconstruction of inter-stage total pressure is achieved using a reduced dataset covering less than 20% of the annulus with reasonably good accuracy. The reconstructed total pressure yields almost identical mean total pressure values at all spanwise locations, with a maximum deviation of less than 0.02%. Additionally, reconstruction of the total temperature distribution at an engine-representative full annulus combustor is achieved using measurements at ten carefully selected circumferential locations. Results show that the reconstructed temperature field successfully captures the primary features associated with combustor exit temperature flow. The reconstructed temperature field yields excellent agreement in the magnitude of radial temperature distribution factor (RTDF) and overall temperature distribution factor (OTDF) predictions to the experiment, with a deviation of less than 0.5% for RTDF and less than 2.5% for OTDF. Lastly, reconstruction of the total temperature distribution at the exit of the GE E3 high-pressure turbine (HPT) is achieved using measurements at eight carefully selected circumferential locations. Results demonstrate remarkable robustness in resolving the temperature profile at the HPT exit with high fidelity, irrespective of the HPT inlet conditions. The initial validation results are promising, demonstrating that the new probe layout scheme and the Fourier-based approximation method enable effective characterisation of flow nonuniformity in gas turbines, thereby providing valuable insights into the complex flow of gas turbine engines.

Kriging surrogate model for optimizing outlet temperature distribution in low-emission combustors without dilution holes

Designing advanced combustors that operate at high temperatures and produce little pollution, especially in the absence of primary and dilution holes, is a difficult task that may bring significant challenges. In this regard, this paper introduces a Kriging surrogate model approach to optimize the outlet temperature distribution of the combustor to achieve such advanced low-pollution combustors. Building upon previous research, this study explores the effects of the swirler blade installation angle on the outlet temperature distribution of the combustor without primary or dilution holes. Traditional methods, such as the control variable method using computational fluid dynamics (CFD) for numerical simulation, are limited in application due to the complex coupling of flow, heat transfer, mass transfer, and combustion processes. In contrast, surrogate models, especially the Kriging model, offer a rapid and efficient alternative to extensive CFD simulations that provide accurate predictions and error estimates for the solution of the problem. In summary, this paper details the process of generating sample points through three-dimensional numerical simulations, develops a Kriging surrogate model through Latin hypercube sampling, and optimizes the model to identify the most uniform outlet temperature distribution achievable by adjusting the installation angle of the swirl blade. The optimal design parameters, which are quickly obtained through the Kriging model, showed a significant reduction in the overall temperature distribution function and the radial temperature distribution function by 21% and 27.14%, respectively.

Simulation of heat stabilizer with a distributed refrigerant supply to the outer surface

To prevent the breaking of buildings in the cryolithozone due to thawing of permafrost soil due to thermal load from these objects, it is necessary to use heat stabilizers. Two-phase passive thermosyphons are widely used among them. To increase the efficiency of such device, a design of a heat stabilizer with a distributed refrigerant supply to the outer surface is proposed. Determining the optimal operating parameters of such device is impossible without a stage of modeling heat and mass transfer. This determines the purpose of the study — the calculation of the temperature distribution in the ground with such heat stabilizer. A calculation is carried out using physico-mathematical model of it with three related tasks: 1) description of the movement of liquid refrigerant through the inner tube of the thermosyphon; 2) calculation of the upward flow of refrigerant in the gap between the outer tube and the segments of the flow separator; 3) calculation of conductive heat transfer in the heat stabilizer-soil system. The modeling is based on the approaches of non-isothermal multiphase mechanics and thermophysics. The temperature profile was calculated in the gap between the flow-separating device consisting of four segments and the heat stabilizer pipe, as well as in the soil at 1 m from the surface of the thermosyphon. The proposed model makes it possible to determine the radial temperature distribution consistent with practical data with an accuracy of 90%. It was found that the use of such separating device can increase the efficiency of reducing soil temperature by 20%.

Analysis of enthalpy and energy conversion efficiency in high-power inductively coupled plasma

The Near-Space Plasma Electromagnetic Science Experimental Research Apparatus is designed for ground-based simulation of plasma sheath and is capable of providing pure, high-enthalpy, and high-density plasma jets. The high enthalpy implies a high plasma state, which can achieve high Mach equivalent simulation in flight conditions. This paper takes this device as the research object and establishes a multi-physics coupling magnetohydrodynamics model to simulate the heat transfer process under high-power conditions. Through numerical simulation, the distribution rules of plasma temperature and enthalpy value under different power states considering the radiation source are obtained. By combining numerical simulation with experimental verification, the simulated enthalpy and energy conversion efficiency results are compared with experimental data, showing good consistency. The study finds that the enthalpy at the center of the jet outlet is higher, increasing from 5.4 MJ/kg to 9.5 MJ/kg when the high-frequency power increases from 150 kW to 426 kW, with an increase of 4.0 MJ/kg. The overall distribution of plasma jet enthalpy exhibits a central peak, gradually decreasing radially from the center to both sides. Meanwhile, during the axial jet injection process, there is a transition in the radial distribution of temperature and enthalpy, shifting from a saddle-shaped distribution at the coil position to an arch-shaped distribution at the nozzle outlet. In this power range, the energy conversion efficiency of the high-frequency power source ranges from 53% to 30%, with both calculated and measured efficiencies decreasing with increasing power. Additionally, the paper discusses the impact of radiation source terms on the distribution of enthalpy in high-power inductive-coupled plasma. In conclusion, the model proposed in this paper can be used to estimate the outlet enthalpy distribution and energy conversion efficiency of the Near-Space Plasma Electromagnetic Science Experimental Research Apparatus, providing data support for the design, control, and application of the device.

Numerical and experimental studies on the thermodynamic characteristics of post-buckling separate plate in the clutch

Considering the influence of the contact and friction for buckling deformation, a comprehensive model is proposed to study the timing-varying thermodynamic characteristics of the clutch. The mathematical model is developed to calculate the contact status of the post-buckling separate plate, which is testified by the finite element method and bench experiments. The post-buckling plate undergoes a five-stage deformation, and the radial contact pressure finally forms ‘M/W′ shape during engagements. With the increasing buckling angle, the plate flattening threshold and pressure decay increase gradually; meanwhile, the radial temperature distribution is sculptured as ‘W′ shape, creating larger thermal stress and thermal bending moment. Thus, the surface morphology is changed by the wear which related to the pressure and thermal distribution.

Surface temperature of a 2 in. Ti target during DC magnetron sputtering

Recently, there has been increasing interest in the use of hot targets to enhance the sputter deposition of materials. However, the actual temperature of the target surface is normally not known. In this work, we directly measured the radial distribution of the surface temperature of a MAK 2 in. Ti water-cooled target using a type K thermocouple during the operation of the sputtering system. Principally, the measurements were made as a function of applied DC power and argon gas pressure. Given the importance of chemical reactions between the gas and the target during reactive sputtering, we have also measured the target temperature as a function of the nitrogen concentration in an argon-nitrogen gas mixture. A few of the reactively sputtered samples were analyzed by x-ray photoelectron spectroscopy.

Development and preliminary verification of a 1D–3D coupled flow and heat transfer model of OTSG

Introduction: A simulation model was developed by coupling a one-dimensional (1D) system code and 3D CFD software, to analyze the three-dimensional (3D) flow and heat transfer characteristics of the once-through steam generator (OTSG).Methods: The shell side of the OTSG was simulated by FLUENT, and the tube side was simulated by the system code LOCUST. Through spatial mapping, the 1D and 3D simulations were coupled along the outer wall of the OTSG's helically coiled tubes.Results and Discussion: This coupling method enabled the acquisition of high-resolution flow and heat transfer characteristics of the OTSG, and the error of heat flux calculation result by the coupled model is within 15%. Through coupling simulation analysis of the prototype OTSG, it was found that the inlet and outlet temperature difference reached as high as 150°C. The unevenness of the radial temperature distribution increased along the flow direction, and the wake swing effect caused by the sweeping flow of the tube bundle at the exit position was evident. The results of this study provide reference and a coupled simulation method for the engineering design and thermal-hydraulic characteristics analysis of OTSG.

Two-dimensional high resolution electron properties of femtosecond laser-induced plasma filament in atmospheric pressure argon

This work reports the measurement of two-dimensional electron properties over a nanosecond scale integration time across a femtosecond laser-induced plasma filament in atmospheric pressure argon. Radial electron properties across the ∼100\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 100$$\\end{document} μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}m diameter filament are obtained at discrete axial locations at 2.5 mm steps by one-dimensional high-resolution laser Thomson scattering with a spatial resolution of 10 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}m. These measurements reveal plasma structural information in the filament. The Thomson spectral lineshapes exhibit clear spectral sidebands with an α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} parameter ∼1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 1$$\\end{document}, enabling the measurement of both electron temperature and density profiles. These measurements yield electron densities on the order of 1022\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{22}$$\\end{document}/m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{3}$$\\end{document} and electron temperatures of ∼2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 2$$\\end{document} eV. Heating from the probe laser due to inverse bremsstrahlung is taken into account to correct the Thomson scattering electron temperature measurements. Under these conditions, electron-neutral collision induced bremsstrahlung becomes the dominant laser-induced plasma heating process associated with the probe laser. The measurements reveal structural features of the filament, including an asymmetrically skewed density structure in the axial direction and reversed radial distributions of electron density and temperature.

Investigation of plasma parameters, distributions, and optical emission for the anti-microbial performance of non-woven fabric under direct current glow discharge

The distribution of electron temperature Te and density Ne for direct current glow plasma discharge was investigated, using a single Langmuir probe, inserted inside the plasma cell. The radial temperature distribution has the same values, except with a small increment variation at the cathode edge, and an axial decrement for the temperature Te distribution profiles from the cathode fall region, passing the abnormal glow region, up to the faraway axial region.The radial distribution of the electron density Ne has its highest value at the cathode, with very intense plasma at the cathode fall region, and more Ne decrement in the abnormal glow region, passing the abnormal glow region up to the faraway axial region. In the axial Ne distribution, an increase in Ne from the cathode fall region reaches maximum values in the abnormal glow region and decreases in the faraway axial region.The optimal plasma surface treatment of non-woven silk fabric (n-WSF) can be achieved by utilizing a high plasma density and low energy of electrons to inactivate viable cells attached to (n-WSF) at very short application times, leading to complete inactivation, where the bacterial inactivation rate increases in the abnormal glow region. Based on analyses of the experimental data of initial and final densities of viable cells using survival curves in the abnormal glow discharge region, a dramatic inhibitory effect of plasma discharge on the residual survival microbe ratio was observed.

Laser Thomson scattering measurements around magnetized model in rarefied argon arcjet plume

To elucidate the role of the Hall effect in magnetohydrodynamic (MHD) aerobraking in rarefied flows,we measured the radial distributions of electron temperature and density in front of a magnetized model in a rarefied argon arcjet wind tunnel using the laser Thomson scattering method. We also developed a water-cooled magnetized model to prevent thermal demagnetization during the measurement. The measured electron densitydistributions were inexcellent agreement with computational fluid dynamics (CFD) predictions. It was also found that the magnetic field had little effect on the electron density distribution around the model. In the case without the magnetic field, the measured electron temperature almost agreed with the CFD prediction. However, the measured electron temperature increase caused by applying themagnetic field was about 1,000 K less than that of the CFD prediction. This discrepancy indicates that the location of an insulating boundary in the plasma is far from the model.

A method to improve the barrier performance of flexible riser internal pressure sheath—Heat transfer experiment and simulation

AbstractA considerable amount of acidic gas penetrates into the annulus between the internal pressure sheath and the outer protective sheath during the service of flexible risers, which will inevitably lead to corrosion of the metal functional layer. Many researchers have modified nanocomposites from the mass transfer perspective to reduce the materials' permeability coefficient. While permeation is an integrated process of heat and mass transfer process, heat distribution directly impacts gas permeation. Herein, the thermal conductivity of flexible riser liner materials is predicted for the first time by a combination of molecular dynamics and experiments, and then the radial temperature distribution under different seawater temperatures and internal fluid temperatures is investigated by finite element analysis. Finally, the effect of temperature distribution on the permeation coefficient was analyzed. The results demonstrate that the thermal conductivity can be predicted by molecular dynamics simulation, and the thermal conductivity of (polyvinylidene difluoride) PVDF/TiO2 decreases, while the thermal conductivity of PVDF/carbon nanotube (CNT) increases compared with pure PVDF. The temperature distribution of the internal pressure sheath material decreases when condensate water is present. As the fluid temperature rises from 30 to 110°C, the maximum increase ratio in the permeability of PVDF/CNT over PVDF increased from 3.6% to 14.8%, and the maximum decrease ratio of PVDF/TiO2 permeability coefficient compared with PVDF is from 1.2% to 4.6%. The results present a new idea to improve the barrier properties of materials by decreasing thermal conductivity.

Estimation of the effective length of microcracks occurring in the water-steam pipeline at cyclic operation mode of NPP steam generator

During operation of water-water reactors including KLT-40 type reactors widely used nowadays on icebreakers and floating power units (FPU), the issue of the duration of safe operation of steam generators is acute. The problem is connected with the formation of microcracks in the steam generator water and steam piping during normal operation at power, through which radioactive nitrogen 16N7 enters the steam piping, the content of which in the steam is just a sign of leakage failure of the steam generator second circuit water and steam piping. This effect, further named "leaks", was considered earlier in a number of works of the authors under conditions of cyclic operation of the steam generator water-steam mode. In the present work the main attention is paid to mathematical and physical analysis of the mechanisms causing the formation of microcracks in the steam pipeline of a steam generator arising in the steam pipeline region in which water and steam pressures are balanced, and their effective length is estimated. Calculations of temperature distribution along the steam-pipe thickness in the steam-water transition region at periodic "slamming" of this region with water are carried out. It is shown that depending on the time period of steam-water oscillations, the radial temperature distribution along the tube thickness shows a significant difference in the distribution at a constant temperature on the outer surface of the tube, and the maximum temperature difference is observed in the area of the inner surface of the tube. The distribution of mechanical stresses arising in the tube metal is characterized by a linear dependence of stresses on temperature, the maximum value of which corresponds to the maximum temperature difference characteristic of the area of the inner surface of the tube. This allows us to state that the formation of cracks starts exactly from the area of the inner surface of the tube of the steam generator in the specified transitional area of the tube.

Transient Tip Clearance Prediction Model Considering Transient Radial Temperature Distribution of Discs in a Gas Turbine Engine

Abstract The tip clearance of turbomachinery components, such as compressor and turbine, significantly impacts the gas turbine engine performance, including the thrust and fuel consumption. Therefore, an appropriate prediction of the turbomachinery tip clearance is indispensable in improving the accuracy of engine performance evaluations. The traditional 1D transient tip clearance prediction model does not consider the radial temperature distribution of the disk (also called disc). However, as the engine performance keeps improving, the radial temperature gradient of the disk also increases. In order to maintain the prediction accuracy within an acceptable range, a generic transient tip clearance prediction model is developed in this paper. Based on the special treatment of the axial and radial convective heat transfer boundary regions of the disk, a 2D transient heat transfer model is established, and the radial temperature of the disk is predicted. At the same time, the interaction effect of the thermal expansion between the two different layers of the shroud is studied to improve the prediction accuracy further. In addition, the centrifugal deformation of the blade and disk with variable-thickness characteristics is considered in the new transient model. Compared with the traditional 1D transient prediction model, the model developed in this paper further improves the predicting accuracy of the transient tip clearance, which is verified by the high-fidelity fluid–solid–thermal coupling method. The prediction model provides a useful tool for evaluating the transient tip clearance. It may also benefit the future design strategy of active clearance control.

Numerical simulations on the effect of swirler installation angle on outlet temperature distribution in gas turbine combustors

The higher demand for temperature rises and low-pollution combustion methods make it more problematic to regulate the outlet temperature distribution (OTD) of advanced gas turbines. The present investigation tackles the significant challenge of achieving uniform outlet temperature distribution in advanced low-emission gas turbine combustors devoid of dilution holes, a concern that directly impacts the service life of turbine blades. Differing from the reliance on dilution holes characteristic of conventional combustor designs, this study aims to control the OTD by adjusting the installation angles of the swirler blades. To this end, a thorough numerical analysis is conducted to assess the impact of swirler blade angles on the temperature distribution within the combustor. The findings reveal that an elevated swirl number drives the flame front and regions of high temperature toward the downstream section of the combustor. This downstream shift exhibits the dual effect of potentially improving heat exchange due to enhanced mixing and substantially reducing the outlet temperature distribution factor (OTDF). Quantitatively, the obtained results demonstrate that by fine-tuning the swirler blade angles, a reduction in the OTDF by approximately 33.6 % and a decrease in the radial temperature distribution factor (RTDF) by about 20.4 % can be achieved. These reductions represent a substantial improvement in controlling the temperature field inside the combustor, which is crucial for minimizing the thermal load on turbine blades. In summary, the research provides valuable insights into the design of gas turbine combustors, highlighting an innovative approach to achieving more uniform temperature distributions at the outlet without the exploitation of dilution holes. The results of this scrutiny contribute to extending turbine blade life and improving the overall performance of gas turbine systems, thereby advancing the development of environmentally friendly combustion technologies.

Research and analysis of the thermal and control characteristics of the plate-type fuel assembly for the supercritical CO2 reactor

Small nuclear reactors can be applied to micro grid power generation, island and space nuclear power systems. The plate-type fuel assembly has a compact design structure, low fuel core temperature, large heat exchange area, and high heat exchange efficiency, which is widely used in small nuclear reactors. To supplement the lack of research in S-CO2 small nuclear reactor, The Brayton cycle reactor system analysis program of S-CO2 plate-type fuel assemblies (BRESA-PFA) is developed, and the reactor control system program is developed to simulate the transient condition in this paper. This article establishes a fuel assembly flow and heat transfer model and a control rod control model using Modelica language, achieving physical and thermal coupling and power control of the reactor. The steady-state operating parameters of the developed program BRESA-PFA were studied, and the flow distribution, coolant and fuel temperature distribution of BRESA-PFA were obtained. The flow distribution conforms to the experimental parameters of CARR, and the fuel assembly radial temperature distribution is high at the center and low at the edge. After verification, the maximum fuel temperature did not exceed the limit value and met the design requirements. Transient characteristic analysis was conducted to study the rod lifting strategy during the startup process, the start-up and rod lifting process of BRESA-PFA is N2-N1-G2-G1, using the logic of step control. Research on reactor control system response under loss of coolant accident, after the accident, the coolant flow suddenly decreased to 65 % of the rated value, and the reactor power also decreased to 65 % FP, G2 and G1 control rods were inserted downwards, the coolant temperature fluctuates by 1 %∼2%. The reactor control system was able to respond quickly, ensuring the stability of coolant temperature, proving the safety and reliability of BRESA-PFA, and providing theoretical reference and scheme support for the research of S-CO2 small nuclear reactors.

Effect of initial generating eddy height on temperature, velocity and air entrainment of fire whirl

In this paper, we present an experimental effort to reveal the effect of the initially generated eddy height on the thermal, velocity, and air entrainment properties of the fire vortex plume. Experiments were performed by a fixed-frame facility with variable channel wall height (h), using propane as the fuel (20 cm in burner exit diameter, 50.0–100.0 kW in heat release rate). Results show that the growth rates of centerline excess temperature and axial velocity tend to increase with h in the continuous flame below h. It is found that the radial distribution of excess temperature is always of hump-type and little affected by h at lower levels, while the radial profile of axial velocity changes from the plateau-type into the hump-type as h is increased. In the upper continuous and intermittent flames, the radial profile of excess temperature evolves from the hump type into the unimodal type, and that of axial velocity develops into the unimodal type from the plateau type as h is increased. The growth rates of excess temperature radius and axial velocity radius with the normalized height decrease with h for the continuous and intermittent flames. The axial position corresponding to the significant increase in the growth rate moves upstream with the increase of the heat release rate (Q˙). Under small h, the tangential velocity within the vortex core decreases with height, suggesting that the rotational strength becomes weakened. It is found that the air entrainment is weak at the flame bottom within the initial generating eddy height, and the entrained air is insufficient for complete combustion. The axial mass flow rate increases obviously as the channel wall disappears. With the increase of h, turbulence suppression is enhanced, and its role in flame elongation becomes more significant. The reduction of flame height is probably attributed to the greater turbulent mixing length under lower initial generating eddy height.

Consequences of variable wall permeability and magnetic field on non-isothermal flow in converging/diverging tubes

The current article is devoted to the development of a theoretical model investigating heat transfer analysis of MHD blood flow through renal tubules. For this purpose, we consider the transport of Newtonian fluid inside a non-uniform tube whose lateral surface is kept at constant temperature. The walls of tube are considered to admit the variable permeation and the flow is actuated by an externally applied magnetic field. The solution of the problem is formulated analytically in terms of axial and radial velocities and temperature distribution under the presumption of lubrication approximation in the inertia free flow field. Implication of Darcy’s law for fluid seepage across the tubular membrane results in an ordinary differential equation having variable coefficients for the unknown pressure, which is successfully computed numerically using RK45 routine. Performance of velocity, pressure and temperature distributions has been investigated for various values of the physical parameters involving in the model. Moreover, flow rate behavior, fluid reabsorption and the leakage flux has been analyzed through graphs and tables. The characteristics of heat transfer in the flow field is also evaluated for various values of Brinkman number. A significant discovery reported in the results of present model reveals that the axial flow exhaustion and radial flow reversal are significantly influenced by the tube converging/diverging parameter and the Hartmann number as well. By employing a strong magnetic field, exhaustion and reversal phenomena in the flow field can be restrained up to a certain limit. Moreover, with an increasing wall permeability, there is a significant exhaustion of axial flow in a divergent tube and a prominent assistance takes place in the radial flow reversal for convergent tube. It is hoped that the present model will bear the potential to study flow in renal tubules and in hemodialyzer.

Transient heat transfer study of small-caliber barrel in continuous fire

In this paper, the barrel of small-caliber automatic rifle is taken as the research object. An experiment was taken on the gun barrel and an infrared thermal imager was used to measure the change of barrel temperature field during the continuous shooting, and the finite difference model of barrel heat transfer was established. The formula of the correction coefficient of heat transfer of gunpowder gas on the inner surface of the body tube was obtained by fitting with the experimental results. The barrel transient heat transfer analysis calculation software with independent intellectual property rights was developed by C++, and the characteristics of temperature field were analyzed. The experimental results show that the temperature of the outer surface of the barrel rises and then falls along the axial direction from the bottom of the barrel to the muzzle, and the rising slope will decrease in the next 30 rounds of continuous firing. The calculation results of the small-caliber barrel with chromium layer show that the temperature of the outer surface of the chromium layer of each shot rises instantaneously and then drops rapidly, in the form of pulse, and the temperature of the steel matrix rises continuously, but it is significantly lower than the peak temperature of the chromium layer, and the presence of the chromium layer provides buffer protection for the barrel matrix material. There is still an influence region in the matrix behind the interface between the chromium layer and the barrel matrix, and the temperature of the steel matrix in this region fluctuates. The thickness of the influence region is determined by analysis. The temperature of the inner surface of the barrel reaches a maximum at the tail of the barrel along the axial axis and then slowly decreases in the direction of the muzzle, the radial temperature distribution of the barrel is steeper at the tail end and the muzzle area is relatively flat. The calculation results of the model in this paper are basically consistent with the experimental results, which provides a rapid calculation model and tool for the thermal design and analysis of the gun barrel.

Transition from MAR to EIR of deuterium plasma detachment in NAGDIS-II

Volumetric plasma recombination in a detached deuterium (D) plasma was experimentally studied in the linear plasma device NAGDIS-II. The radial distributions of the electron temperature (T e ) and the electron density (n e ) were measured by upstream and downstream laser Thomson scattering (LTS) systems and D-atom excited states of the Balmer series (n = 3–7) were measured by optical emission spectroscopy (OES). The results indicated that the electron static pressure, particle flux and heat flux present a two-step reduction with an increasing neutral pressure, suggesting that molecule activated recombination (MAR) and electron–ion recombination (EIR) were activated, respectively. The difference in the distributions of the atomic state population densities was observed to be a feature of the transition from the MAR-dominant phase to the EIR-dominant phase. The transition between the two phases had a distinct boundary at T e ∼0.7 eV, which was considered a transition point between the phases. The ratios of the atomic state population densities showed different features in the two phases, and are expected to be useful in characterizing the phase and degree of plasma detachment.