Effects Of Buoyancy Forces Research Articles

Thermodynamic and buoyancy force effects of Cu and TiO2 nanoparticles in engine oil flow over an inclined permeable surface

This study investigates the heat and mass transmission behavior in an unsteady magnetohydrodynamic (MHD) movement of nanofluids over an inclined permeable surface, with applications in enhancing thermal management systems such as automotive cooling and industrial heat exchangers. The model specifically examines the consequence of thermal diffusion (Soret effect) and buoyant forces on Cu and TiO2 nanoparticles dispersed in engine oil. The governing equations, comprising velocity, energy, and concentration equations, are recast into nonlinear ODEs manipulating similitude adaptations. These ODEs are then solved through a standard perturbation method under appropriate boundary conditions. The key findings indicate that enhancing thermal radiation diminishes the velocity and temperature profiles, while raising chemical reaction rates decrease concentration levels. Additionally, higher Soret parameter values are associated with increased velocity and concentration. Quantitatively, TiO2-engine oil nanofluids exhibit a 15% higher velocity compared to Cu-engine oil nanofluids, highlighting the superior performance of TiO2 in dynamic thermal systems. Furthermore, numerical outcomes for the local skin contention, Nusselt numeral, and Sherwood digit are tabulated to illustrate the consequence of material properties. The outcomes of this study are particularly beneficial in optimizing the design of heat exchangers, improving fuel efficiency in automotive engines, and enhancing industrial processes where precise thermal control is critical.

Steady and periodical heat-mass transfer behavior of mixed convection nanofluid with reduced gravity, radiation and activation energy effects

Significance of this study is to explore Arrhenius activation energy, microgravity, chemical reaction and porous medium effects on Darcy nanofluid over a stretching sheet with nonlinear thermal radiations. Purpose of this study is to enhance the lubrication efficiency, excessive heat reduction, surface roughness and tool wear in drilling, milling, grinding and cutting tools of machining procedures. Use of Brownian and thermophoretic nanoparticles in base liquid is very effective to reduce friction in tool-chip and tool-work interfaces, tool life ability and cooling ability through nanofluid minimum quantity lubrication in machining operations. A refined mathematical model is solved using dimensionless variables; oscillatory stokes conditions and primitive variables. The implicit form of finite difference method is applied for numerical results using Gaussian elimination approach. The numerical and physical outputs are secured using Gaussian elimination methodology in FORTRAN tool and TecPlot-360. Graphs are displayed by using numerical data in Tecplot-360 program. Impact of activation energy (AE), solar radiation (Rd), microgravity (RG), porosity (Ω), thermophoresis (NT), chemical reaction (Kr), Prandtl (Pr) and Schmidt factor (Sc) on oscillating frequency of heat and mass transport is depicted. Amplitude in fluid velocity, surface temperature and volume of concentration is enhanced as radiation, microgravity and activation energy increases. It is noted that the increasing amplitude in fluid velocity, temperature and fluid concentration is found with activation energy, radiation and buoyancy force effects. Steady behavior of skin friction and mass transport decreases as Darcy porous medium and reaction rate decreases. Frequency of oscillating skin friction and oscillating heat transfer increases as Schmidt and Prandtl coefficient increases. Fluctuations and amplitude in the frequency of heat and mass transport enhances as thermophoretic nanoparticle enhances.

Combined fluid and ferrofluid buoyancy force, heat absorption and non linear ferro-viscosity effects on ferro- hydrodynamics fluid flow in orthogonal porous surface

Mixed convection incompressible ferro-hydrodynamic (FHD) boundary layer fluid flow on vertical porous curvilinear orthogonal surfaces is examined in our present study in presence of combined fluid and ferro-fluid buoyancy force, nonlinear ferro-viscosity parameter, and heat absorption/generation effects. Design/Methodology/Approach: Types of Prandtl momentum and thermal boundary layer partial differential equations in a curvilinear system are converted into non-dimensional ordinary nonlinear differential equations (ODE) by introducing dimensionless velocities, temperature functions and similarity variable. Missing initial conditions are found by shooting method and solving the system of nonlinear ODEs by Runge-Kutta integration scheme of order six. With the help of MATLAB, the numerical solutions are graphically displayed in the forms of primary velocity profile, secondary velocity profile, and temperature profile. Three types of magnetic nano-ferrofluid are considered such as water-based ferrofluid (Taiho W-40), Hydrocarbon based ferrofluid (EMG-901) and kerosene-based ferrofluid (C1-20B) whose Prandtl numbers are 44.3, 79.3 and 128 respectively shown in Table 1. For kerosene based ferro-fluid, Table 3 presents the coefficient of skin friction and heat flux. Finding: The effects of combined fluid and ferrofluid buoyancy forces, nonlinear ferro-viscosity parameter, suction/injection, and heat absorption/generation parameters on the velocity and temperature profiles are investigated. Our physical interest is to calculate the local shearing stresses and the local heat flux at the surface. Finally, we have made comparisons of the results which are highlighted the validity of our numerical calculations adopted for the presence study.

Hydromagnetic Turbulent Flow in Porous Media Over a Stretching Surface in a Rotating System with Heat

This study investigates the combined effects of magnetic fields, buoyancy forces, porosity, rotation, and Joule’s heating on fluid flow and heat transfer dynamics. The analysis is performed using a numerical approach, with the system oriented along three axes: the z-axis aligned with the plate, the y-axis perpendicular to the plate, and the x-axis orthogonal to the y-z plane. An infinite plate extends along the x and z axes, with a uniform transverse magnetic field applied parallel to the y-axis. By employing the finite difference method in MATLAB, we explore how various dimensionless parameters influence temperature and velocity profiles. Our findings reveal that an increase in the local temperature Grashof number enhances primary velocity while reducing secondary velocity near the fixed end. Temperature profiles show a decrease near the plate, increasing further away. The study also highlights that a higher Joule heating parameter leads to elevated primary velocity and temperature profiles but diminishes secondary velocity. Additionally, increasing rotational parameters is observed to decrease both primary and secondary velocities while augmenting temperature profiles near the plate. These results underscore the significant role that magnetic fields, rotational effects, and Joule heating play in modulating fluid flow and thermal behavior. The insights gained from this study can inform the design and optimization of engineering systems where control of velocity and temperature profiles is critical.

Effect of buoyancy force on buoyancy waterwheel efficiency using numerical flow simulation

In this work, the performance of a buoyant waterwheel to produce hydrokinetic power is investigated through analytical theory and computational fluid dynamics simulation. The impact of the buoyancy wheel is investigated by establishing the performance parameters through the use of a moving mesh approach and a realizable k-ε turbulence model. Transient simulation is required to comprehend the flow of physical processes. Using moving mesh as a transient methodology of the buoyancy waterwheel, numerical flow simulations and theoretical analytical methods are used in this study to assess the effect of buoyant force generated on the performance of the buoyancy wheel. The buoyancy waterwheel that will be put to the test has eight straight blades and a diameter of one meter. The pinwheel force and torque created in the numerical flow simulation (CFD) are 414.96 N and 207.48 Nm, respectively, whereas in the theoretical calculation they are 449.06 N and 224.53 Nm, according to the research findings. It is possible to compute the buoyancy wheel's power output and efficiency mathematically, yielding values of 1619.35 W and 68.07%. The buoyancy wheel's power output and efficiency, as determined by numerical flow simulation, are 1495.95 W and 62.88%, respectively. Based on theoretical and CFD study results, the buoyancy wheel generates a standard deviation of 7.62%. Thus, for the buoyancy wheel, a temporary method that makes advantage of the moving mesh characteristic is advised. This method can also be applied as a future alternative energy source for the Piko hydro turbine

A comprehensive review on the Dynamical behavior of heat and fluid flow mechanism: Thermal performance across different geometries

The prominent novelty of current review is to exhibit the fluctuating and oscillatory convective heat transfer properties along various geometries with magnetic force, variable density, Prandtl number, buoyancy force and magnetic Prandtl number effects. The significance of present work is to illustrate a comprehensive review on transient convective heat transfer. Transient convective heat transfer plays an essential role in various technological and environmental applications, including climate control, structure safety, engines, thermal control, computer heating and cooling, and energy safety. The literature primarily focuses on steady temperature and velocity domains, with few studies exploring time-varying fluid flow in forced, natural, or mixed convective mechanisms with different methods. In current review, justification of results was performed by using oscillating stokes conditions directly in partial differential models. The similarity variables and stream functions are used in literature but in current review, the primitive variable transformation is used with implicit form of finite difference method and Gaussian elimination technique through FORTRAN and Tecplot-360 programming tools. The governing model is reduced into steady, real and imaginary form to explore steady and oscillating convective heat transmission. Transient flows have gained significance due to their ability to achieve large oscillating convective heat transfer rates. Compared with steady movement, oscillating flows exhibit higher velocity variations along the heated surface. Periodic flow produces an improved transient surface heat transmission rate than steady flow. Predicting and controlling transients in thermal exchangers requires a concept of transient forced convection heat transport. Transient convective thermal transmission solutions are important for ensuring the effectiveness and reliability of electrical components, nuclear and thermal power stations, heat-generating engines, steam turbines, condensation systems, catalytic converters, heat shielding for spacecraft, electrical devices, internal combustion engines, air conditioning and refrigerator components, cooling networks for batteries, generators, and transformers. It is found that the frequency of convective heat transport enhances through periodic and oscillating stokes variables. It was depicted that the higher amplitude in convective heat transfer was displayed for each choice of magnetic force parameter around two angles π/4 and π of circular magnetized surface. It was depicted that the maximum transient convective heat transmission was reported along vertical angle π/2 with buoyancy force, Prandtl and magnetic Prandtl values.

Thermal analysis of hybrid nanoliquid contains iron-oxide (Fe3O4) and copper (Cu) nanoparticles in an enclosure

The major aim of this work is to analyze the thermophysical properties of hybrid nanoliquid inside a square lid driven enclosure under the effect of applied magnetic field and mixed convection. The Hybrid nanofluid is considered a suspension of Iron-oxide (Fe3O4) and Copper (Cu) nanoparticles into water. The cavity walls have varying properties such as top adiabatic wall is moving continuously while the lower wall is maintained at a high constant temperature, in addition, the vertical walls are kept at a low fixed temperature. The magnetic field is applied to the right vertical wall in a horizontal direction. Additionally, the effects of buoyancy forces caused by temperature gradients and shear forces caused by continuous lid motion are considered. The mathematical modelling of problem with all assumptions yields the nonlinear partial differential system. First this system is transferred into non-dimensional form and then transformed system is solved by using Galerkin finite element method (GFEM) along with Gaussian elimination method. Results for isotherms, streamlines and average Nusselt number are obtained versus Richardson number (0.1 ≤ Ri ≤ 15), Grashof number (10 ≤ Gr ≤ 10000), Hartmann number (0 ≤ Ha ≤ 100), volume fractions of solid nanoparticles (0.005 ≤ ϕ1 ≤ 0.02) and (0.005 ≤ ϕ2 ≤ 0.02). It is observed that the Richardson number and Grashof number have significant impacts on both flow velocity and temperature. In addition, concentration of hybrid nanoparticles improves the heat transfer performance. The obtained results may be crucial for thermal management in the cooling of electronics, heat exchangers, solar thermal collectors, industrial operations, medical equipment, HVAC systems, food processing, and renewable energy systems.

Predicting the Slowing of Stellar Differential Rotation by Instability-driven Turbulence

Differentially rotating stars and planets transport angular momentum (AM) internally due to turbulence at rates that have long been a challenge to predict reliably. We develop a self-consistent saturation theory, using a statistical closure approximation, for hydrodynamic turbulence driven by the axisymmetric Goldreich–Schubert–Fricke instability at the stellar equator with radial differential rotation. This instability arises when fast thermal diffusion eliminates the stabilizing effects of buoyancy forces in a system where a stabilizing entropy gradient dominates over the destabilizing AM gradient. Our turbulence closure invokes a dominant three-wave coupling between pairs of linearly unstable eigenmodes and a near-zero frequency, viscously damped eigenmode that features latitudinal jets. We derive turbulent transport rates of momentum and heat and provide them in analytic forms. Such formulae, free of tunable model parameters, are tested against direct numerical simulations; the comparison shows good agreement. They improve upon prior quasi-linear or “parasitic saturation” models containing a free parameter. Given model correspondences, we also extend this theory to heat and compositional transport for axisymmetric thermohaline-instability-driven turbulence in certain regimes.

Significance of shape factor on magnetohydrodynamic buoyancy thin film flow of nanofluid over inclined sheet with slip condition: Irreversibility analysis

This work aims to examine the entropy production, heat transport, and dynamics of the unsteady thin film magnetohydrodynamic (MHD) flow of a nanofluid composed of alumina (Al2O3) and water. The fluid flow is seen to pass over an inclined sheet, taking into account the effects of buoyancy force, viscous dissipation, and joule heating. The system of partial differential equations (PDEs) is optimized under the boundary layer assumptions. Appropriate transformations are used to convert the governing partial differential equations (PDEs) and boundary conditions into dimensionless forms. Using MATLAB’s bvp4c code and a local non-similarity technique with up to second-degree truncation, we can obtain the findings of the enhanced model. The effect of multi-shape Al2O3 nanoparticles on flow, heat, and entropy-generating features is also investigated after the calculated results have been successfully aligned with published data. Mixed convection, nanoparticle volume percent, inclination angle, magnetic field intensity, mass suction, Eckert number, and Biot number are only a few of the governing parameters whose effects are graphically shown for selected values. As a result, the local Nusselt number and skin friction coefficient may be calculated. The skin friction and Nusselt number profiles exhibit a decreasing trend as the values of nanoparticle volume fraction ([Formula: see text]) magnetic [Formula: see text] and unsteadiness (A) increase toward mixed convection ([Formula: see text]). On the other hand, Nusselt number profile increases with increasing values of mass suction parameter [Formula: see text] The profiles of entropy generation and Bejan number show an upsurge as the values of the magnetic parameter [Formula: see text] and Brinkman number (Br) increase. Conversely, the entropy generation reduces with an increase in the temperature difference parameter [Formula: see text] and Bejan number increases.

Numerical analysis of thermal improvement in hydrogen‐based host fluids under buoyancy force and EPNM effects: Study for vertical cylinder

AbstractThe nanofluids became much of interest due to their superior heat mechanism over the conventional fluids. The addition of nanoparticles in the host solvent enhances the internal ability of the liquid to store and transmit heat. Therefore, these fluids are widely used in biomedical engineering, detergents, medication, applied thermal engineering, mechanical, and chemical engineering and so forth. Keeping in mind the significance of nanofluids, this study is conducted to investigate the comparative heat transmission in and under the Effective Prandtl Number Model (EPNM) effects over a vertical permeable cylinder. Formulation of the model is carried out over a vertical cylinder about the stagnation point and the heat transport model is achieved after the successful implementation of the cylindrical stream function, nanofluids effective characteristics, and cylindrical similarity equations. The mathematical treatment was done via RK technique and furnished the results. The nanofluids have the capacity to control the fluid motion more effectively than ordinary fluid and combined convection is better where rapid fluid movement is desired. In the existence of EPNM, higher heat transmission is achieved and is prominent for based on their thermophysical values. Further, the skin friction and Nusselt number are optimum for against .

Dynamic behavior of mixed convection heat transfer among horizontal co-axial fixed pipes at varying temperatures: Efficiency of cylindrical heat sink

The aim of the current research is to highlight the time-dependent properties of laminar convective thermal transmission inside a semi-infinite pipe, with an emphasis on flow frequencies that impact inter-fluid momentum and energy. The implicit finite difference approach is used to solve two-dimensional mathematical model composed of nonlinear partial differential equations. The research includes forecasting thermal performance of time-dependent flow in a pipe over several parameter ranges relevant to the flow model. The obtained forecasts were emphasized graphically. The numerical solutions were separated into steady and unsteady components, with the steady component yielding findings that were then used to determine the time dependent surface shearness and energy shearness in the time dependent phase. The stable component of the investigation revealed that raising the buoyancy force parameter and the impact of viscous dissipation significantly improved the flow velocity pattern and heat distributions throughout the flow domain. While the amplitude of time dependent surface shearness varied somewhat across various buoyancy force parameter values, the amplitude of time dependent heat transmission rates varied significantly. This study sheds light on the interaction of several characteristics, such as buoyancy force effects and internal energy loss, on time-dependent thermal energy flow inside a semi-infinite pipe subjected to laminar convective flow. It is worth noting that the amplitude of the time dependent rate of heat transmission shows more noticeable variations with different values of the buoyancy force parameter, in contrast to the minute change in the amplitude of the time dependent surface sheerness.

Thermal analysis of mixed convective peristaltic pumping of nanofluids in the occurrence of an induced magnetic field and variable viscosity

The present study investigates the heat and flow characteristics of mixed convective peristaltic transport of nanofluids containing magnetite γAl2O3 nanomaterials dispersed in conventional liquids, namely, ethylene glycol (C2H6O2) and water (H2O). The research provides a comprehensive analysis, considering various factors such as induced magnetic field, variable viscosity, buoyancy force, viscous dissipation, and porous media effects. The mathematical model is formulated based on a set of governing equations encompassing continuity, temperature, momentum, and induction, which are subsequently transformed into dimensionless form through appropriate scaling. A numerical method is employed to solve the resulting nonlinear differential equations. Results indicate that the velocity profile exhibits substantially higher magnitudes in the case of the γAl2O3-C2H6O2 nanoliquid when compared to the γAl2O3-H2O nanoliquid. Increasing the magnetic Reynolds number leads to a higher magnitude of the axial-induced magnetic field. An observed reduction in system entropy is associated with an increase in the permeability parameter.

Computational analysis of entropy generation minimization and heat transfer enhancement in magnetohydrodynamic oscillatory flow of ferrofluids

Improvements in heat transfer rate and entropy generation minimisation are critical issues in many engineering and industrial applications where efficient heat transfer is essential to achieve optimal performance and lower energy consumption. This study investigates the entropy generation of the mixed convection flow of ferrofluids in the presence of viscous and Joule dissipation. The flow is oscillatory and induced by the sinusoidal oscillations of a flat plate in its plane. Two Newtonian fluids, namely, kerosene oil C12H26C15H32 and methanol CH3OH are considered base fluids containing magnetite Fe3O4 nanoparticles. Governing equations are first modelled by employing the fundamental laws of transport phenomena. Then, using scaling analysis, these equations are transformed into a dimensionless system of partial differential equations. Numerical simulations are performed using the Gear-Generalized Differential Quadrature Method (GGDQM), and the model is validated with special cases from the literature. It has been found through numerical analysis that the convergence of GGDQM can be guaranteed by using only a small number of grid points. The thermal boundary layer of methanol-based nanofluid is thicker than that of kerosene. It has been observed that the skin friction coefficient increases for both categories of nanofluids as the values of the Eckert number, solid volume fraction, and Grashof number increase. The Nusselt number increases as the solid volume fraction increases, while the opposite trend is observed when the values of the Hartman, Eckert, and Grashof numbers rise. With increasing values of the Grashof number, the rise in the velocity of methanol-based nanofluids is higher than that of kerosene oil-based nanofluids. The maximum percentage difference between the velocities is identified to be 22.2177% at Gr=4.0. The temperature of methanol-based nanofluids rises more quickly than that of kerosene oil-based nanofluids with increasing values of the Grashof number. It is determined that the largest percentage difference between the temperatures is 20.5968% at Gr=4.0. When Ec=0, the percentage difference between velocities is 29. 1721 %, while the percentage difference between temperatures is 78.7155%. Compared to methanol-based ferrofluid, the volumetric entropy production is more extensive in kerosene-based ferrofluid. On the other hand, in comparison to a kerosene-based nanofluid, thermal irreversibility predominates in a methanol-based nanofluid. The novelty of this study lies in the computational treatment of coupled partial differential equations (momentum and energy) that incorporate buoyancy force, Joule heating and viscous dissipation effects, complementing the underlying physics and mathematical modelling of the research problem.

Simulation of conjugate convective heat transfer in a vertical channel with thermal conductivity property of the solid blocks under the effect of buoyancy force

Currently, the cooling of electronic circuits is one of the most serious problems due to the exponential growth in demand for ever more powerful computer systems; overheating of these components becomes a serious problem. This article presents a number of computational results obtained by simulating a two-dimensional air flow for cooling occurring in a vertical channel. The area under study contains two square blocks simulating a set of electronic elements that are evenly installed in the vertical direction. The 2-D conjugate model of heat transfers between a solid body and an air flow is used with defined boundary conditions. In particular, the basic partial differential equations are approximated by the finite volume method. To study the impact of different parameters on the resulting heat transfer inside the channel, calculations are made for various parameters: Reynolds number, materials, and geometric parameters.

Numerical Investigation of the Magnetohydrodynamic Mixed Convection inside an Extended Curved Duct in the Presence of a Nanofluid of Different Metallic Oxides Nanoparticles

The numerical work presented in this paper focuses on the influence of the magnetic field and the nanoparticles metallic nature on the hydrodynamic and thermal behavior of a nanofluid flowing in an extended curved duct. It deals with a semi-toroidal curved duct with an expanded circular section. The narrowed part of this duct from which the nanofluid enters with a cold temperature, is considered to be thermally insulated. However, the extended part is kept at a constant hot temperature. The nanoparticles used in the present study respectively are Alumina (Al2O3), copper oxide (CuO) and iron trioxide (Fe3O4). In this study, the effects of inertia, buoyancy and Lorentz forces as well as the metallic nature of the nanoparticles suspended in the pure water have been highlighted on the thermal, hydrodynamic and economic levels. The study is based on the resolution of the classical monophasic equations governing the non-isothermal flow of nanofluids by the use of finite element method, namely: the mass, momentum and energy equations. The obtained results have shown that the buoyancy and inertia forces strongly favor the global heat exchange rate. Moreover, the magnetic force acts negatively on these thermal exchanges. Furthermore, the CuO nanoparticles have demonstrated a better heat transfer rate, approximately 7% higher than that of pure water. Nevertheless, according to the economic needs, we suggest we suggest using alumina nanoparticles, as their transfer rate is comparable to that of CuO nanoparticles. It should be noted, that this study provides important insights for many industrial applications where the curved ducts are strongly presented.

Simulation of hydrogen leakage diffusion behavior in confined space

In this paper, the diffusion characteristics and laws of hydrogen leakage in confined spaces are investigated using a combination of numerical simulations and experiments, and a small-scale cube model (dimensions: 0.47 m×0.33 m × 0.20 m) is used. The effects of leak source location, obstacles, leak hole size and shape on hydrogen diffusion and concentration evolution were investigated. The results show that the top funnel is sprayed vertically downward, the diffusion velocity decreases rapidly under the blocking effect of air and buoyancy force, and the momentum of the airflow is exchanged. During the injection phase, the leaking gas is mainly subjected to strong buoyancy forces and the hydrogen concentration shows a stratification effect. When the injection stops, the concentration difference decreases and eventually the hydrogen concentration reaches a steady state. The obstacle model in turbulence (4.3%) increases the concentration difference by a factor of about three compared to the empty room model (1.7%), which seriously affects the diffusive behavior of hydrogen. The obstacle in laminar flow model (10.4%) has almost the same concentration difference as the empty room model (10.2%). Rectangular leakage holes have a greater initial kinetic energy and diffuse more widely and faster.

Global stability of Bénard–Marangoni convection in an anisotropic porous medium

Surface tension is essential in many industrial applications, especially where the liquid surface is in contact with the environment, such as crystal growth, semiconductor manufacturing, and welding. The present article reports a numerical analysis of convection induced by the combined effects of buoyancy force and surface tension in an infinitely extended horizontal fluid-saturated anisotropic porous layer with high permeability. We assume that the bottom boundary is rigid and the top is exposed to the air. Biot numbers establish general thermal conditions at both ends instead of commonly used adiabatic and isothermal boundary conditions. The anisotropy of the porous structure results in thermal and mechanical anisotropy parameters while examining layer's stability. The Chebyshev Tau technique yields the critical Marangoni number, MaLc and MaEc, representing linear and energy stability boundaries. We compare the constraints obtained from linear and energy analyses and conclude that the energy bounds for the current problem are less than linear bounds, indicating subcritical instabilities may exist. It is also observed that thermal anisotropy and Biot numbers stabilize the system. In contrast, mechanical anisotropy and the Darcy number advance the onset of convection. The existing results of limiting cases of the present problem are recovered with remarkable accuracy.

Numerical investigation of natural circulation loop with supercritical CO2 on the thermal control system of micro spacecrafts

Aiming at the heat dissipation problem under the strict constraints of mass, volume, and power consumption in micro spacecrafts, the feasibility of applying a natural circulation loop (NCL) to the thermal control system is performed for the CubeSats (Cube satellites) of orbiting operations or the micro-rovers of extraterrestrial explorations. A 3-dimensional NCL model under variable gravity conditions corresponding the environment of aerospace is established, and the supercritical CO2 as the coolant. The heat transfer and thermal performance of NCL under gravity range of 10−6 g to 10 g are analyzed numerically, including the Earth orbit, the surface of the Moon and the Mars etc. The calculation results present that the gravity has a great influence on the flow circulation characteristics and thermal performance of the NCL. The applicability of employing NCL on the thermal control system of micro spacecrafts is validated with the gravity no less than 0.05 g. It is worth noting that, by designing the range of temperature from inlet to outlet of the heated tube covering the large specific heat region, the superior thermal performance can be obtained on account of the strong heat-carrying capacity of supercritical fluid, even under the low gravity with a small mass flow rate. Finally, a flow correlation is proposed considering the effect of gravity, flow regime, buoyancy force, and geometric factors, which is suitable on the NCL in the thermal control system of micro spacecrafts, and the R2 is 99.77%.

Tribology-informed analysis of convective energy transfer in ternary hybrid nanofluids on inclined porous surfaces

The study on tribological effects of ternary hybrid nanofluids over an inclined stretching surface highlights the potential of nanocomposites for improving a system's heat and flow transmission capacity. It has potential applications in energy storage and catalytic supports due to its higher thermal and electrical conductivity. This study aims to scrutinize the behavior of natural convective energy transfer in a water-based ternary hybrid nanofluid composed of titanium, silver, and alumina nanoparticles on a vertically inclined porous surface with convective boundary conditions. The effects of nanoparticle shapes, solar radiation, buoyancy force, magnetic field, suction/injection, and heat generation/absorption are also considered. The results are obtained using a MATLAB program called bvp4c. It is seen that the velocity profiles along the x-axis decrease while those along the y-axis increase due to the permeability of the surface. Suction at the surface reduces the fluid velocity along both axes, while injection has the opposite effect. Moreover, as the Prandtl number increases, the heat transfer rate and skin friction coefficients decline for low magnetic numbers. The results of this research could assist in improving heat and flow transmission in eclectic systems and have potential applications in energy storage.

Effect of a Sinusoidal Temperature Profile on Entropy Generation Due to Double-Diffusive Natural Convection in a Square Partly Porous Cavity

Abstract In this paper, entropy generation due to double-diffusive natural convection inside a partly porous enclosure under sinusoidal wall heating is numerically analyzed. The resulting dimensionless coupled partial differential equations are discretized using the finite volume method (FVM), while the pressure–velocity coupling is handled using the SIMPLE algorithm. To ensure the validity of the results obtained from the in-house FORTRAN code, a comparison is made with previous numerical and experimental works. The results of the study indicate that the dimensionless thickness of the porous layer (Δ), the thermal conductivity ratio (Rk), the angle of inclination of the cavity (α), and the buoyancy ratio (N) are critical factors in determining local distribution and global maximum value of entropy generation due to heat transfer and fluid friction. In contrast, their effect on entropy generation induced by concentration is insignificant, except for the buoyancy ratio parameter, where an enhancement of the global maximum of entropy generation is observed by increasing N. Moreover, it is found that Sψ (max) experiences a sharp decline as Δ varies from 0.2 to 0.8, resulting in a reduction of about 67% for the case with N=10 and 83% for the case with N=1. These results highlight the importance of carefully controlling system parameters to minimize energy losses and maximize system efficiency in heat transfer and fluid flow systems.