Values Of Temperature Gradient Research Articles

Study on asymmetric forming and performance strengthening mechanisms of 6061-T6 aluminum alloy joints fabricated by oscillating laser based on keyhole characteristics and molten pool dynamic behaviors

The study intends to unravel the processes behind the particular forming and performance improvement of 6061-T6 aluminum alloy joints by getting a thorough understanding of keyhole features and dynamical characteristics of molten pools during the laser welding with circular oscillation (C-OLW) process. The C-OLW experiments were carried out considering the pivotal parameters, including oscillation frequency (f) and amplitude (A), and their impacts on joint formation, microstructure, and performance were analyzed. Increasing f from 200 Hz to 300 Hz results in a more homogeneous and centered laser energy distribution, reducing weld breadth and the maximum depth. Raising A from 1.2 mm to 1.5 mm concentrated energy along the workpiece surface, increasing weld breadth but decreasing the maximum weld depth. A three-dimensional transient numerical model was established and verified. The simulation results reveal that increasing f considerably improves keyhole stability by virtue of the beam's mixing effect on energy, resulting in a more evenly distributed temperature within the molten pool. The velocity of the beam's motion intensifies, leading to elevated local temperature and subsequently causing an escalation in splattering. When A grows, keyhole stability reduces, as does the intensity of molten pool flow. The major effect of increased frequency is refining the grain size while increasing amplitude primarily promotes the columnar-to-equiaxed transition (CET) process. The extracted results of temperature distribution illustrate that an increase in f leads to an increase in the solidification rate (R), and temperature gradient values (G) are similar or higher along the same isotherm. Therefore, the G/R ratio rises, promoting the formation of finer microstructures. Although increasing A diminishes G, the reduced overall temperature and molten pool volume contribute to the rise in R. Consequently, the G/R ratio declines, fostering equiaxed grain growth, in line with experimental observations. A higher G value on the left side corresponds to finer grain structures, corroborating experimental findings via Electron Backscatter Diffraction (EBSD). The keyhole stability and microstructure characteristics explain why increasing f or A can enhance joint performance. The research reveals that strategically augmenting both oscillation frequency and amplitude enables the achievement of enhanced performance in 6061-T6 aluminum alloy joints.

Analysis of a Rainstorm Process in Nanjing Based on Multi-Source Observational Data and Lagrangian Method

Using multi-source observation data including automatic stations, radar, satellite, new detection equipment, and the Fifth Generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA-5) data, along with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) platform, an analysis was conducted on a rainstorm process that occurred in Nanjing on 15 June 2020, with the aim of providing reference for future urban flood control planning and heavy rainfall forecasting and early warning. The results showed that this rainstorm process was generated under the background of an eastward-moving northeast cold vortex and a southward retreat of the Western Pacific Subtropical High. Intense precipitation occurred near the region of large top brightness temperature (TBB) gradient values or the center of low TBB values on the northern side of the convective cloud cluster. During the heavy precipitation period, the differential propagation phase shift rate (KDP), differential reflectivity factor (ZDR), and zero-lag correlation coefficient (ρHV) detected by the S-band dual-polarization radar all increased significantly. The vertical structure of the wind field detected by the wind profile radar provided a good indication of changes in precipitation intensity, showing a strong correspondence between the timing of maximum precipitation and the intrusion of upper-level cold air. The abrupt increase in the integrated liquid water content observed by the microwave radiometer can serve as an important indicator of the onset of stronger precipitation. During the Meiyu season in Nanjing, convective precipitation was mainly composed of small to medium raindrops with diameters less than 3 mm, with falling velocities of raindrops mainly clustering between 2 and 6 m·s−1. The rainstorm process featured four water vapor transport channels: the mid-latitude westerly channel, the Indian Ocean channel, the South China Sea channel, and the Pacific Ocean channel. During heavy rainfall, the Pacific Ocean water vapor channel was the main channel at the middle and lower levels, while the South China Sea water vapor channel was the main channel at the upper level, both accounting for a trajectory proportion of 34.2%.

Geotermalny przepływ ciepła w Portugalii kontynentalnej

Heat flow density measurements in Portugal were made in boreholes used for mining prospecting. Heat flow density values in the sedimentary basins of the western and southern margins of the country were obtained using data from oil or gas prospecting works. Due to the scarcity of data in the central and northern regions of the country, numerical models based on some characteristics of the region were used to obtain more heat flow values. The total of heat flow values used in this work is 69, with 17 values obtained using numerical models, 36 obtained in boreholes and 16 obtained from oil/gas prospecting wells data. The analysis and location of these data allows to define different regions in the territory and characterize them using average values of heat flow density, temperature gradient and thermal conductivity. Statistical values with all the data in the territory are also presented.

Absorption characteristics of diffracted X-ray radiation in a quartz crystal at an external temperature gradient

In this work the dependence of the anomalous absorption of X-rays on the crystal thickness and temperature gradient value was studied. The refracted and reflected beams intensities, as well as their sum intensities were measured for crystal thicknesses in the range of 0.3–4.5 mm. Significant increase in the sum intensity of the refracted and reflected beams is observed in presence of temperature gradient. It is shown that the anomalous absorption in the crystal in presence of the temperature gradient is decreased and this effect is stronger expressed in thick crystals.

Evolution of cross-sectional shapes of liquid inclusions enclosed in a crystal: Computer simulation and its application for studying interface kinetics

The previously developed model of the cross-sectional stationary shape of a liquid inclusion migrating through a non-uniformly heated crystal has been extended to the case of transient processes caused by changes in the temperature gradient value and/or temperature oscillations. On the basis of computer simulations, the evolution of the cross-sectional shapes of the inclusions with 4 facets in their cross sections has been analyzed for the cases of different mechanisms of interfacial processes. A technique for estimating kinetic coefficients from the geometry of the inclusion shapes established after imposing and removing the temperature gradient has been proposed. The possibility of controlling the velocity and shape of the 4-faceted inclusions by means of temperature oscillations has been demonstrated and discussed.

Macro- and Microstructural Homogeneity of Nickel-Based Superalloy Product Material Obtained by Wire-Feed Electron Beam Additive Manufacturing

This paper investigates the structural homogeneity of samples of articles made of ZhS6U alloy obtained by wire-feed electron beam additive technology. It is found that the formed material is represented by directionally growing dendrites and does not contain any defects. The temperature gradient value and its dependence on the height of the additively formed product are estimated using the change in the primary dendrite arm spacing. On this basis, it is concluded that the temperature gradient values achieved during the additional formation process correspond to the modern methods of directional solidification. The features of the electron-beam additive process that affect the heat removal conditions and cause changes in the temperature gradient are shown. It is found that changes in these conditions do not significantly affect the size and morphology of the intermetallic γ'-phase. It is demonstrated that the mechanical properties of the additively formed product material are superior to those of the original material in the as-cast state.

Reconstruction of Nusselt number in RANS computations with wall function approach

Two novel methods for reconstruction of Nusselt number (Nu) are proposed when the wall function approach is used in the RANS framework for defining wall boundary conditions for high Reynolds number flows. The work is motivated by the observation that the velocity and temperature fields are often well predicted when the wall function formulations are used, while at the same time Nu is not. The reason for discrepancy in predictions of flow fields and temperature, and prediction of Nu, is because Nu estimation is solely dependent on the wall function, while the variables obtained from the transport equations are determined also by the convection and pressure force in the momentum transport. The method based on the correction factor Ψ∗ originates from the simplified analytical wall function approach of Popovac and Hanjalić (2007) and modifies the formulation of so-called wall viscosity. The method based on a wall shape function of exponential type approximates temperature variation in the near-wall region. Once the shape function’s coefficients are calculated using values of temperature in three near-wall consecutive cells, the wall values of temperature or temperature gradient, needed for calculation of Nu, can be determined. The methods are tested for four standard benchmark cases, backward-facing step, impinging jet, differentially heated square cavity, and Rayleigh-Bénard convection. The method based on the correction factor significantly improved Nu predictions for the cases where the velocity field is strongly impacted by pressure force. The method based on the wall shape function improves predictions of Nu in all tested cases, with somewhat less accurate predictions of the maximum value of Nu compared to the correction factor method.

Interdependence of constructive and operation parameters of brake friction units

Problem. Theoretical and experimental studies of the relationship between the braking torques developed by the friction assemblies of various types of brakes and their design and operational parameters made it possible to establish the following: the values of the braking torques developed by the friction assemblies of various types of braking devices and the influence of design parameters on them; changing the gradients of the braking moments for the most loaded friction pairs of the belt-pad brake of the drilling winch; values of local temperature gradients at the beginning and at the end of braking of vehicles and drilling winches to determine the thermal stresses in the metal friction element. Goal. The purpose of the work is to establish the relationship between the braking torques developed by the friction brake assemblies and their design and operational parameters. Methodology. The solution to the tasks is that the design is based on the principle, according to which, if possible, massive elements that interfere with the free expansion of less massive heated areas are excluded. Results. The relationship between the design parameters of various types of brakes and their operational parameters is established. Originality. It was determined that the design and operational parameters of the brakes depend on the density of the heat flow that penetrates the rims of the pulley and the drum, as well as the body of the disc. O. I. Volchenko proposed three theorems to establish the regularities of heating and cooling of isotropic metal friction elements with compliance with the initial and boundary conditions for metal-polymer friction pairs of brakes. Practical value. The use of a new operating parameter, which is the gradient of braking moments developed by friction pairs "brake pulley - friction lining", allows to estimate their values for each friction lining of the brake belt.

Particle pump-out induced by trapped electron mode turbulence in electron cyclotron heated plasmas on XuanLong-50 spherical torus

Particle pump-out effects induced by low-frequency (<200 kHz) density fluctuations were observed in solely electron cyclotron wave (ECW)-heated plasmas on the spherical torus XuanLong-50 (EXL-50) without a central solenoid. The intensity of the relative density fluctuations increases with increasing ECW power and decays when the ECW is turned off while sustaining the plasma current. The electron densities are maintained relatively high and steady when the density fluctuations are completely absent, indicating that the outward transport of electrons is dominated by the particle pump-out effect of the ECW. The density fluctuations are modulated by a supersonic molecular beam injection pulse and the modulation amplitude decreases with increasing electron density at the same ECW injection power and decreasing ECW power at the same electron density, respectively. Analysis revealed that a critical value of electron temperature gradient (ETG) triggers the density fluctuations, and the intensity of the relative density fluctuations is positively correlated with the ETG and approximately inversely proportional to the effective collision frequency. With plasma parameters similar to those of EXL-50 experiments, the HD7 code simulations demonstrate that trapped electron mode (TEM) turbulence can be excited by ETG higher than the critical value observed in the experiment. In addition, the dependence of the mode growth rate (supposed to be proportional to the saturation level of fluctuations in quasi-linear theory) and the measured intensity of the density fluctuations is comparable. The simulated outward particle flux integrated over the poloidal wave number spectrum is significant and proportional to ETG. These observations demonstrate that the density fluctuation is TEM turbulence, which is driven by ETG and induces particle pump-out when the electron density/effective electron collision frequency is low. The potential relevance of this work with the controls of plasma profiles, impurities, helium ash, and heat transport in future reactors of similar low effective collision frequency is also discussed.

Computational simulation of the ore-forming processes associated with the Sanshandao-Haiyu gold belt, Jiaodong Peninsula, eastern China: implications for the duration of ore formation

The Sanshandao-Haiyu gold belt, Jiaodong Peninsula, Eastern China accounts for more than 1,400 t gold resources, which is always recognized as a coupled result of structural deformation, pore-fluid flow, and hydrothermal alteration-mineralization processes. However, the ore-forming processes associated with this gold belt has not been fully understood by the coupled perspective. In this paper, we use computational modeling to study the spatial distribution of dilation (positive volumetric strain) and the mineralization rate, which can predict the mineralization patterns from a chemical perspective, so as to solve the fully coupled problem during ore-forming processes. The model was loaded on the FLAC3D platform to test four scenarios: 1) Syn-compression in the NW-SE direction; 2) syn-compression in the WNW-ESE direction; 3) syn-compression in the NNW-SSE direction, and 4) syn-extension in the NW-SE direction. The simulation results show that only the syn-compressional scenario can produce wide dilation zones with a distribution pattern similar to the known orebodies. The higher dilation zones with the volumetric strain (&amp;gt;0.1%) and the highest pore-fluid flux are closely associated with the fault geometry, particularly for the gentle segments near the steep-flat transition areas. Besides, the dilation zones also occur with very high absolute values of pore-fluid pressure gradient and temperature gradient, indicating significantly perturbed physical-chemical conditions. The receiver operating characteristic (ROC) curves of the mineralization rate show that the area under the curve (AUC = 0.862) of the NW-SE syn-compression model is the highest among these four scenarios, indicating a major paleo compression stress direction of NW-SE during ore-forming period. Furthermore, based on the mineralization rate, we estimated that the mineralization duration of the Sanshandao-Haiyu gold belt would be less than 100,000 years. These simulation results can not only enhance our understanding of the ore-forming processes in the Sanshandao-Haiyu gold belt and Jiaodong Peninsula but also demonstrate that these can be used directly or indirectly for deep mineral exploration.

Semi-empirical model of the spatiotemporal surface temperature distribution on the plain part of Ukraine

The spatial variation of temperature is found to depend linearly on climate continentality, morphology of the relief, the position of the site with respect to seas, in addition to the usual elevation, latitude and longitude predictors. There are other factors that can have an additional significant influence: big bodies of water, terrain attributes relief, atmospheric factors (local circulation), configuration and aspect of coasts and vegetation. Therefore, these multifactorial influences form the climatic field of temperature.&#x0D; In this study, the regional semi—empirical model of the spatiotemporal distribution of the average annual and monthly temperature for the plain part of Ukraine on the basis of the methodology for assessing the influence of height above sea level and geographic coordinates is proposed. Based on the method for determining the altitudinal, latitudinal, and longitudinal gradients of meteorological parameters, we calculated these gradients for annual and monthly air surface temperature for the periods 1961—1990 and 1991—2020.&#x0D; Thus, on the plain part of Ukraine, the annual surface air temperature decreases by an average on 0.60—0.63 °C with a shift of 100 m height above sea level, on 0.51—0.55 °C with a shift of one latitude degree to the north, on 0.067—0.071 °C with a shift of one longitude degree to the east. Also, the variations of these annual mean temperature gradients from year to year over the period 1991—2020 are characteristic.&#x0D; The seasonal variation of gradients has a pronounced non—monotonic character: highest values of altitudinal gradientare typical for July—August (from –0.63 to –0.73 °C per 100 m), and the lowest values — for April—May (from –0.45 to –0.55 °C per 100 m); highest values of latitudinal gradient are typical for August—September (from –0.60 to –0.70 °С per 1 °N), and the lowest values — for April—May (from –0.20 to –0.35 °С per 1° N); the longitudinal gradients have positive values in June—August (0.074—0.128 °C per 1° E), and negative values in November—March (from –0.228 to –0.154 °C per 1° E).&#x0D; We found that the altitudinal and latitudinal gradients of temperature have the most spatiotemporal variability and the longitudinal gradient has the smallest one. Greatest variabilities of temperature gradient values are typical for February—March and July—September, and the least variability — for April—May.&#x0D; The analysis of the dynamics of gradient changes in the period 1991—2020 compared to the period 1961—1991 showed the following: the altitudinal gradientvalues increased by 8—13 %. in January and March—May; the latitudinal gradient values increased by ~30 % in December—February and decreased by ~20 % in May—August.&#x0D; The proposed semi—empirical model contains a coefficient that takes into account influence of additional effects associated with pronounced orographic and other terrain features. This study presents the numerical values of this coefficient for some specific microclimate regions of the plain part of Ukraine.&#x0D; The model estimates of thirty—year monthly mean temperature in Ukraine for the periods 1961—1990 and 1991—2020was calculated. A comparison of the model estimates of of the average annual and monthly temperature for 72 meteostations in Ukraine with their actual values showed a statistically significant correlation (the reliability of the linear approximation is 0.89—0.98). Thus, the presented design of the semi-empirical model makes it possible to quite well restore the annual and monthly temperature on the territory of Ukraine

Thermal Radiation and Chemical Reaction Effects of Unsteady Magnetohydrodynamic Dissipative Squeezing Flow of Casson Nanofluid Over Horizontal Channel

This work investigates the effects of chemical reaction and thermal radiation on the magnetohydrodynamic (MHD) squeezing Casson fluid flow through a porous media under the influence of heat absorption, which is motivated by the application of flow in industrial issues. The flow is generated by the compression of two plates together. The transformation of partial differential equations (PDEs) to ordinary differential equations (ODEs) is accomplished via similarity variables. The numerical analysis was carried out using the shooting method, which involved solving the competent controlling equations with dominant parameters for a thin liquid film. It is necessary to compare the numerical findings with previous research to verify the present solutions. The findings reveal that the velocity and wall shear stress increase as the distance between the two plates becomes closer. The higher values of squeezing number diminish the squeezing force on the fluid flow, which in turn reduces the thermal field. The thinner temperature boundary layer corresponds to the lower values of thermal diffusivity and it shows the higher values of temperature gradient for the increasing values of β. Due to the presence of stronger Lorentz forces the temperature and velocity fields behave like decreasing functions of Hartmann number.

Prediction of Primary Dendrite Arm Spacing of the Inconel 718 Deposition Layer by Laser Cladding Based on a Multi-Scale Simulation.

Primary dendrite arm spacing (PDAS) is a crucial microstructural feature in nickel-based superalloys produced by laser cladding. In order to investigate the effects of process parameters on PDAS, a multi-scale model that integrates a 3D transient heat and mass transfer model with a quantitative phase-field model was proposed to simulate the dendritic growth behavior in the molten pool for laser cladding Inconel 718. The values of temperature gradient (G) and solidification rate (R) at the S/L interface of the molten pool under different process conditions were obtained by multi-scale simulation and used as input for the quantitative phase field model. The influence of process parameters on microstructure morphology in the deposition layer was analyzed. The result shows that the dendrite morphology is in good agreement with the experimental result under varying laser power (P) and scanning velocity (V). PDAS was found to be more sensitive to changes in laser scanning velocity, and as the scanning velocity decreased from 12 mm/s to 4 mm/s, the PDAS increased by 197% when the laser power was 1500 W. Furthermore, smaller PDAS can be achieved by combining higher scanning velocity with lower laser power.

Effects of surface micro-structure of fruits on droplet evaporation process: Peach and apple cases

Droplet evaporation at the fruit surface is a common issue related to the efficiency of pesticide spraying as well as freshness preservation. Many works have been carried out demonstrating the impacts of substrate characteristics on the droplet profile, wettability, and evaporation properties in the field of industrial applications. However, the influences of specific fruit skin on the droplet evaporation rate have been rarely studied. Thus, the present works aim to explore the effects of different surface micro-structures of fruits on the droplet properties experimentally through the 3D video microscope, drop shape analyzer, and infrared camera. Apple and peach have been selected respectively as two examples of waxy and hairy skins, and comparisons have been made focusing on the surface roughness, droplet profile including contact angle, contact area, and contact diameter, evaporation rate, and temperature distribution of droplets with a constant initial volume of 2ul. The results show that the differences in micro-structure for apple and peach surfaces have significant impacts on the droplet evaporation performance. A larger evaporation rate has been found for apple skin with three distinct phases including spreading, pinning, and shrinkage periods. However, the pinning phenomenon tends to be broken for the peach case due to the unique properties of super-hydrophobic surfaces and the existence of fluff. Moreover, lower values of temperature at the top center of a droplet can be always observed during the whole evaporating process with peak values of temperature gradient near the triple-phase region.

Effects of temperature gradient and beam path height from heat source on phase structure and mutual coherence functions of a light beam propagating through convective air turbulence

In this paper, we investigate the effects of different values of temperature gradient (TG) and the distance of a plane wave path from a flat heat source generating an anisotropic and non-Kolmogorov convective air turbulence medium on the phase structure function (PSF) and mutual coherence function (MCF) of the light beam propagating through the medium. The non-Kolmogorov and anisotropic convective air turbulence is created using an electrical heater with a surface size of 50 cm × 100 cm. The heater temperature is changeable from room temperature to 100 °C. The laser beam with a diameter of 20 cm passes through the turbulent medium at different distances from the heater surface. At the end of the path, the wavefront of the light beam is reconstructed using a two-channel moiré wavefront sensor. Then, the PSF and MCF are calculated, and the effects of different TGs and the different beam path heights from the heater are studied. Results show that with increasing the TG and decreasing the beam path distance from the heat source, the turbulence intensity and PSF increase, while the MCF decreases.

Фактологическое обоснование структуры данных ГИС «Паспорт климатической безопасности республики Адыгея»

The study is aimed at determining the optimal data structure of the regional monitoring and forecasting system of climate change and related weather and climate risks for the socio-economic infrastructure of the Republic of Adygea. The basic spatial units of monitoring identified landscape and climatic regions, allocated according to a combination of factors correcting the zonal mode of meteorological processes in the North-West Caucasus under the conditions of the mountain-plain Adygea. With regard to landscape and climatic areas, differences have been identified in both the variation of climatic parameters in the multi-year and annual course, and in the recurrence and severity of hazardous and adverse hydrometeorological processes. Preliminary studies of climate change in Adygea and the results of reanalysis have revealed a steady trend of warming of the climate, especially intensive in the last 20 years (1.2°C/10 years), caused by the increase of temperature in the cold half of the year, at a low temperature change of the warm period. The dramatic increase in air temperature over the past two decades highlights the challenge of current climate change and its impacts. The results proving coherence of the course of parameters of the energetic field of the ground atmosphere (gradient field of temperature) with the course of parameters of intensity of the hydrometeorological phenomenon at the forecasting point have been obtained. It is proposed to use the regional temperature gradient value reflecting the dynamics of the thermal field of the region as a predictor in models of forecasting hydrometeorological phenomena and processes of different advance. Successful long-term forecasting of weather-climatic phenomena will provide the fulfillment of those functions, which are intended “Climate Safety Passport”.

Suction/blowing impact on magneto-hydrodynamic mixed convection flow of Williamson fluid through stretching porous wedge with viscous dissipation and internal heat generation/absorption

This research investigates the suction/blowing influence on mixed convective MHD Williamson fluid flow over-stretching porous wedge where viscous dissipation and internal heat absorption/generation are present. Similarity variables are employed to transform the governing partial differential equations (PDEs) to nonlinear ordinary differential equations (ODEs) which are then solved numerically using the bvp4c package in MATLAB. The boundary layers lateral to the stretching wedge are examined and discussed with the help of diagrams and tables. It is observed that an increase in the non-dimensional parameter, ξ, improves the velocity and temperature, whereas the intensification in the mixed convection parameter λ, porosity (R), and magnetic parameter (M) lowers the temperature profile. The increased values of M cause the velocity to increase at R = 0.2 whereas the decline in the velocity value is noted at R = 2.2. However, the temperature decreases at both the values of R. Increasing heat generation/absorption (Q) leads to an increase in the Nusselt number with the decline in the skin friction coefficient. When Q is raised at R = 1.5, the magnitude of skin friction rises with a decreEase in the temperature gradient. Increasing ξ at R ≷ 1 results in the decline of the skin friction coefficient and an increase in the Nusselt number. At R = 1.5, the quantitative values of (We = 0.1, 0.2, 0.3) temperature gradient decreases but velocity gradient increases but at R = 0.4, |−θ′(0)| enhances, also |f″(0)| upsurges. At quantitative values of (ξ=0.1,0.2,0.3) , |−θ′(0)| increases for both R = 1.5 or 0.4 but |f″(0)| declines at both the values of R. The quantitative values of (Q = 0.1, −1.1 at R = 1.5) decreases |−θ′(0)| but increases |f″(0)|. However, at R = 0.4 we noticed opposite behaviour of both velocity and temperature gradient as detected from Table2. Similarly the effects of quantitative values of (Ec = 0.1, 0.2, 0.3, Pr = 0.3, 0.4, Nr = 0.3, 0.4) on |−θ′(0)| are given in Table 3.

Darcy–Forchheimer MHD radiative flow through a porous space incorporating viscous dissipation, heat source, and chemical reaction effect across an exponentially stretched surface

AbstractThe impacts of viscous dissipation, Brownian motion, and the thermophoresis caused by temperature gradient on the steady two‐dimensional incompressible chemically reactive and radiative flow of traditional fluid through an exponentially stretched sheet embedded in a Darcy porous media are explored by approaching boundary layer analysis. A magnetic field effect is also addressed along the transverse direction of the horizontal stretched sheet. With the implementation of some suitable nondimensional quantities, the regulating nonlinear partial differential equations, which represent the flow geometry, are transformed into coupled nonlinear ordinary differential equations. To acquire the numerical findings from this set of equations, a three‐stage Lobatto IIIa, in‐built MATLAB scheme named, Bvp4c is used. The effects of the dimensionless physical factors on the flow, heat, and concentration profile, as well as on the coefficient of drag force and the rate of thermal and mass transit at the surface, are graphically and numerically depicted. The thermal profile, as well as the magnitude of the coefficient of the drag force and the Sherwood number, is found to be escalated with the Darcy–Forchheimer factor, but the depreciation in the value of temperature gradient at the wall is noticed for the same.

CFD‐based analysis of entropy generation due to mean and fluctuating fields during turbulent natural convection in a square enclosure

AbstractThe current study aims to numerically investigate the entropy generation during the natural convection flow of air in a square cavity. The governing equations for the conservation of mass, momentum, energy, and turbulence are solved using a control volume‐based technique employing the commercial code Fluent. Runs have been performed for both laminar and turbulent flow regimes by varying the Rayleigh number (Ra) from 103 to 1010. On the other hand, various viscous distribution coefficients (ϕ = 10−4, 10−3, and 10−2) and constant Prandtl number (Pr = 0.71) were considered. Given the conflicting perspectives in the literature regarding the entropy generation under turbulent regimes, more research is needed to better understand the impact that the fluctuating flow has on entropy production. The four terms of entropy generation inherent to turbulent natural convection (entropy generation due to dissipation in the mean and the fluctuating velocity fields in addition to the heat flux due to the mean and the fluctuating temperature) are computed in the present work and compared to calculations based on only mean values of temperature and velocity gradients. It was found that taking into account the fluctuating terms of temperatures and velocities augment the total entropy generation by 10.10%, 14.43%, and, 17.70%, up to 32.60%, respectively, for Ra = 5 × 108, Ra = 109, Ra = 1.58 × 109, and Ra = 1010. The gain shows the tendency to increase with the Rayleigh number. Thus, the fluctuating terms cannot be neglected particularly for high Rayleigh numbers. Furthermore, unlike entropy production due to the mean flow field, numerical outcomes reveal that the generated irreversibilities due to fluctuating flow are located around the upper hot and the lower cold corners of the heated walls. In addition, a numerical relationship between the first and the second laws of thermodynamics has been derived. A promising result that emerged from this study has shown that the Nusselt number and therefore the first law of thermodynamics is sufficient to estimate the heat part of entropy generation without the necessity of using the second law.

Relationship between area and wind speed along the edge of the Antarctic polar vortex

The Antarctic polar vortex forms in autumn, intensifies in the winter-spring period and decays in late spring. Inside the vortex in the lower stratosphere, favorable conditions are created for the annual spring ozone depletion. One of the conditions for the formation of the Antarctic ozone hole is the presence of a dynamic barrier along the vortex edge in the winter-spring period, which contributes to a decrease in temperature inside the vortex (necessary for the existence of polar stratospheric clouds) and prevents the penetration of air masses into the vortex. The dynamic barrier exists when the wind speed along the vortex edge in the lower stratosphere is at least 20 m/s. When the vortex area decreases below 10 million km2 , the dynamic barrier usually weakens, preceded by the vortex breakdown. The purpose of this work is to consider the relationship between the vortex area and the wind speed along the vortex edge using the Antarctic polar vortex as an example. To analyze the dynamics of the Antarctic polar vortex, we used a method based on vortex delineation, which makes it possible to calculate the vortex area and wind speed along the vortex edge using geopotential values determined from the maximum values of temperature gradient and wind speed and, thus, characterizing the polar vortex edges. Seasonal variations in the vortex area are mainly determined by the time of the beginning, peak and end of the polar night. In turn, seasonal changes in wind speed along the edge of the Antarctic vortex are additionally determined by the influence of the temperature of the lower subtropical stratosphere. To eliminate the influence of the seasonal variation, polynomial trends were removed from the time series of the parameters considered. We have shown that the relationship between the vortex area and the wind speed along the vortex edge can be traced for area values of less than 25 million km2 and more than 50 million km2 . At small values of the vortex area (&lt; 25 million km2), during its formation and destruction, a positive correlation appears between the vortex area and the wind speed along the vortex edge. At high values of the vortex area (&gt; 50 million km2), a negative correlation can be traced between the parameters studied.