Effects Of Buoyancy Forces Research Articles

An Experimental Study of Natural Convection Heat Transfer from a Horizontal and Slightly Inclined Plate-Fin Heat Sink

The steady-state natural convection from heat sink fin arrays was studied on horizontal, vertical, and inclined heat sinks. Under natural convection, horizontal and vertical heat sinks with parallel fins were tested by considering radiation heat transfer. The experiments were conducted with power inputs ranging from 60 W to 455 W in order to obtain different temperatures. According to the result, when heat input increases, the heat transfer coefficient increases by 38 %, 40.78 % for horizontal and vertical respectively. For horizontal and vertical cases, new correlations have been presented to calculate the Nusselt number influenced by the Rayleigh number. For the incline case, the effect of buoyancy force was studied by changing the inclination angles at 0, 30, 45, and 60 degrees from vertical position. According to comparisons between vertical and incline cases, Nusselt number and heat transfer coefficient were most improved at 30 degrees by 6 %.

Double-Diffusive Nonlinear Buoyancy Force Significance on Free Convective Chemically Reacting Fluids Flow Past Vertical Riga Surface

In this research, double-diffusive nonlinear buoyancy force effects on free convective chemically reacting fluids flow past a vertical plate in a Riga surface have been addressed numerically. Cattaneo-Christov theories, viscous dissipation, thermal radiation, thermophoresis and the Soret-Dufour mechanism were modelled in this paper. Also, thermal radiative heat flux was considered based on the Rosseland approximation because the fluid is optically thin. The flow equations were represented using partial differential equations (PDEs). These sets of PDEs were transformed into ordinary differential equations by utilizing suitable similarity variables. The transformed flow equations were numerically solved by employing the spectral collocation method. The outcomes show that enhancement in the velocity and temperature are observed due to an increase in Eckert number, thermal radiation and heat generation parameters. An increase in the relaxation heat and mass flux is noticed to have effects on the concentration and temperature gradient due to the presence of Soret-Dufour mechanisms. The present outcomes were compared with previously published works and are found to be in good agreement.

Laser welding of dissimilar materials - simulation driven optimization of process parameters

Laser welding can be used to join dissimilar materials to produce lightweight structures, and electric vehicle battery systems, which are important means of limiting the carbon emissions in the transport industry. Due to the differences in melting temperatures, thermal conductivities, and mutual solubility of dissimilar materials, it is still challenging to create defect-free joints with high mechanical strength, or low contact electrical resistance. In this work, we present a state-of-the-art numerical model of laser welding, developed within the Computational Fluids Dynamics (CFD) paradigm. The multi-physics model simulates melting, flow, and solidification of the alloys and accounts for the laser-material interactions, phase change, temperature and alloy-dependent thermophysical properties, recoil pressure, buoyancy force, and Marangoni effect. The simulation predicts weld penetration depth and width, alloy mixing, as well as the temperature gradient and cooling rate during the solidification that can be further fed into a micro-structure prediction model. The model is coupled with an optimization tool, which iterates over different process parameters to optimize the joint. The methodology is presented for steel to aluminium welding in lap configuration, but it can be used for other materials such as steel-copper, aluminium-copper, or steel-nickel, and in arbitrary geometrical configuration.

Mathematical Model for the Effect of Buoyancy Forces on the Stability of a Fluid Flow

Stability analysis of heat transfer (by Conduction, Convection, and Radiation) has been found for a model of flow between two horizontal plates, one of them is thermally insulated. The stability measure through the neutral curve for this model shows that an increase of the buoyancy represented by Gershoff number (Gr) leads to an increase in stability region, especially for the considerable value of Reynolds number R. The results indicated that the effects of buoyancy forces have significant contribution to the field profiles

Double diffusion and Hall effects on MHD sinusoidal natural convection flow of silver water-based nanofluid from a porous vertical plate

This paper scrutinizes Hall current, Soret and Dufour impacts on natural convective flow of nanofluid attributable to variation in sinusoidal surface temperature over a vertical plate through a porous medium with strong transverse magnetic field applied normally to the flow. In this regard, the silver metal is considered as nanoparticles with water as base fluid. The overlapping multi-domain bivariate spectral local linearization method (OMD-BSLLM) has been utilized to solve the dimensionless governing equations which are attained by means of appropriate transformations. The obtained results are portrayed via graphical and tabular formations to inspect flow fields, shear stresses, heat and mass transmission characteristics for varying thermo-physical parameters. We found that there is an enhancement in the flow fields, shear stresses and heat transportation with the use of silver nanoparticles. Thermal and concentration boundary layer thickness enhance by using porous material, whereas diminish with improvement in Hall effect and ratio of buoyancy forces. The flow characteristics decline with the inclusion of porous medium while elevates with increment in Hall parameter. Moreover, an upgrade in thermal-diffusion correspond to a substantial growth in concentration field along with mass transfer rate. Current analysis can be useful in MHD energy generators, and industrial applications such as heating and cooling procedures owing to the involvement of nanoparticles having superior thermal conductivity features.

Experimental study on flame tilt angles of two unequal fires in a longitudinal ventilated tunnel

In historical tunnel fire accidents causing major casualties and property losses, the special fire phenomenon of multiple fires burning was usually accompanied. Other than the longitudinal ventilation in tunnel, the interaction burning of multiple fires will also make the flame tilt. Flame tilt angle is an important parameter to characterize the magnitude of acting forces on fires and it determines the possibility of ignition and flame spread. Former studies were mainly focused on multiple equal fires with same sizes, very limited attention has been paid on multiple unequal fires. Due to the different air entrainment mechanisms, the proposed correlations for flame tilt angle of multiple equal fires might be unsuitable for the multiple unequal fires. This paper presents an experimental study on flame tilt angles of two unequal square gaseous fires of propane in a 1/10 scale tunnel with longitudinal ventilation. Two square burners with different side lengths were located parallel and along the longitudinal centerline of tunnel. The effects of heat release rate of each burner, the burner edge spacing and the ventilation velocity were explored. Using the image processing method, the flame heights and tilt angles of upstream fire and downstream fire were determined. The results showed that due to the shielding effect of upstream fire acting on the downstream fire, the flame height of downstream fire is larger than the upstream fire, while the flame tilt angle of downstream fire is lower than the upstream fire. In addition, the flame heights of upstream and downstream fires are reduced with increasing the ventilation velocity, while the flame height of downstream fire is weakly affected by the separation distance. As the ventilation velocity increases, both the upstream and downstream flame tilt angles increase first and then maintain unchanged. The separation distance has little influence on the upstream flame tilt angle, while it affects the downstream fire more. Among the impact factors, the longitudinal ventilation plays a leading role of the flame tilt behaviors of two fires in tunnel. Based on the force analysis, it is found that the pressure thrust between two fires is much smaller than the buoyancy force and ventilation force. As a result, different correlations for predicting the flame tilt angles of two unequal fires in tunnel are developed based on the coupling effect of buoyancy force and ventilation force of each fire.

A case study for heat and mass transfer of viscous fluid flow in double layer due to ciliated channel

The present study is a measurement of the thermal and mass transfer of a two-layered flow of viscous fluid induced by cilia motion under the effect of buoyancy forces through a channel. Cilia are mostly of two classes: motile and non-motile cilia for locomotion and sensory processing. Cilia tissue cells are epithelia lining the lungs that sweep away liquids or solids, and organisms that have cilia are protozoans that use them for movements are the examples. The ciliary apparatus is related to cell cycle movement and proliferation, and cilia display an energetic fragment in human and animal development and in ordinary life. The fluid is considered to be incompressible, and layers of fluid do not mix with each other. The fluid flow for mass and thermal transfer is modelled in wave and fixed frame. Solutions for temperature, velocity of fluid, and concentration profile are obtained using a well-known method, namely the Homotopy Perturbation Method (HPM), by the computation software "MATHEMATICA". The behavior of emerging parameters is shown graphically in the results section. Graphical results can be analyzed for the temperature and velocity profile, which are extreme in the inner layer for both fluid and concentration distribution and are highest at the external layers of fluid. It is the first study not examined in the literature.

Inspection of unsteady buoyancy and stagnation point flow incorporated by Ag-TiO2 hybrid nanoparticles towards a spinning disk with Hall effects

The viscous flow across a rotating body is an emblematic phenomenon in many production processes, particularly in systems involving rotating disks. This study discusses the impact of buoyancy force and Hall effects on the time dependent stagnation point flow of Ag-TiO2/water hybrid nanofluid (HNF) flow over a rotating disk together. The Ag-TiO2/water HNF flow is investigated for two cases: assisting and opposing flow. Utilizing the appropriate similarity transformations, the partial differential equations (PDEs) representing the heat transfer problem are altered to ordinary differential equations (ODEs). The governing equations are solved numerically employing the “bvp4c function in MATLAB”. The current results are validated by comparison with the available literature and a very close precision is obtained. The influence of the primary relevant parameters on the properties of flow, and heat transmission rate is depicted graphically. The azimuthal and radial velocities of HNF flow are greater for assisting flow. The thermal profile of Ag-TiO2/water HNF flow is greater for opposing flow. The greater values of the Reynolds number surge the HT rate on the surface. The outcomes of this study will be useful in many fields that utilize applications of rotating disk systems such as rotor-stator systems, power generators, geothermal extraction, computer storage devices, engines in gas turbines, brakes, gears, and flywheels.

Heat Transfer in Cavities: Configurative Systematic Review

This study is a systematic review of research on heat transfer analysis in cavities and aims to provide a comprehensive understanding of flow and heat transfer performance in various kinds of cavities with or without the presence of fins, obstacles, cylinders, and baffles. The study also examines the effects of different forces, such as magnetic force, buoyancy force, and thermophoresis effect on heat transfer in cavities. This study also focuses on different types of fluids, such as air, water, nanofluids, and hybrid nanofluids in cavities. Moreover, this review deals with aspects of flow and heat transfer phenomena for only single-phase flows. It discusses various validation techniques used in numerical studies and the different types and sizes of mesh used by researchers. The study is a comprehensive review of 297 research articles, mostly published since 2000, and covers the current progress in the area of heat transfer analysis in cavities. The literature review in this study shows that cavities with obstacles such as fins and rotating cylinders have a significant impact on enhancing heat transfer. Additionally, it is found that the use of nanofluids and hybrid nanofluids has a greater effect on enhancing heat transfer. Lastly, the study suggests future research directions in the field of heat transfer in cavities. This study’s findings have significant implications for a range of areas, including electronic cooling, energy storage systems, solar thermal technologies, and nuclear reactor systems.

Marangoni-driven nonlinear dynamics of bimolecular frontal systems: a general classification for equal diffusion coefficients.

When bimolecular fronts form in solutions, their dynamics is likely to be affected by chemically driven convection such as buoyancy- and Marangoni-driven flows. It is known that front dynamics in the presence of buoyancy-driven convection can be predicted solely on the basis of the one-dimensional reaction-diffusion concentration profiles but that those predictions fail for Marangoni-driven convection. With a two-dimensional reaction-diffusion-Marangoni convection model, we analyze here convective effects on the time scalings of the front properties, together with the influence of reaction reversibility and of the ratio of initial reactants' concentrations on the front dynamics. The effect of buoyancy forces is here neglected by assuming the reactive system to be in zero-gravity condition and/or the solution density to be spatially homogenous. This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'.

Numerical study on heat transfer characteris tics of supercritical water in straight and helical tubes

The subcritical steam generators in high-temperature gas-cooled reactor pebble-bed modules can be replaced by supercritical steam generators to improve thermal efficiency. The axial and circumferential nonuniform flow and heat transfer characteristics of supercritical water in straight and helical tubes with varying inclinations (0–90°) are simulated to investigate the combined effects of tube structure, flow direction, thermophysical properties, property variations, buoyancy, and centrifugal forces. With heat fluxes of 233–930 kW/m2 and inlet mass fluxes of 225 or 1260 kg/(m2 s) under a working pressure of 24.5 MPa, the friction coefficients, turbulent kinetic energy, secondary flow, temperature, and heat transfer coefficients are studied in the cross section of variable structure tubes. The wall temperature and heat transfer coefficients of four regions are compared in straight and helical tubes; the maximum heat transfer coefficient appeared before the pseudo-critical point. The heat transfer coefficients are the greatest at the bottom of the straight tubes, where fluidity was high, and at the outer of the helical tubes, where the fluid velocity was high under centrifugal force. The secondary flow in the helical tubes causes a nonuniformity in the wall temperature, causing the circumferential maximum wall temperature to move.

Semi-spectral computational algorithm for fractional characterization of time-dependent fluid model with convergence and stability analysis

The current study is carried out to analyze the unsteady MHD flow of fractional-order Oldroyd-B nanofluid and heat transfer via a semi-spectral computational method. The governing model for MHD naturally convective fractional-order Oldroyd-B is expressed in terms of a coupled PDE system. To analyze the numerical solution novel scheme is suggested, where finite difference is used to approximate the temporal derivative whereas spatial variable is approximated via operational matrices which are computed using Chelyshkov polynomials. The proposed scheme transforms the nonlinear system of PDEs into a system of linear algebraic equations. Relevant theorems are presented to support the mathematical justification of the operational matrices-based method whereas stability analysis is being made for the proposed computational algorithm. The impact of involved physical parameters on velocity temperature, skin friction, and Nusselt number profiles are studied numerically. The impact of the magnetic field drops the velocity behavior whilst the effect of buoyancy forces on velocity is the opposite. The radiation pass through the nanofluid transmits the energy to the fluid particles and eventually causes an increase in the temperature of the fluid whereas similar behavior is noticed in heat generation. The substantial effect of the fractional parameter is noted for smaller values.

Effect of Buoyancy Force on an Unsteady Thin Film Flow of Al2O3/Water Nanofluid over an Inclined Stretching Sheet

The present study looks at the heat transfer and the unsteady thin film flow of Al2O3 water nanofluid past an inclined stretching sheet having a buoyancy force effect. The boundary value problem solver (bvp4c) package in Matlab is utilized in solving the converted set of ordinary differential equations (ODEs). The multi-shape Al2O3 nanoparticles’ impact with respect to the flow as well as heat transfer characteristics are studied and visually displayed for certain governing parameter values, which include the mixed convection, inclination angle, magnetic, slip, and Biot number. Thus, the skin friction coefficient and the local Nusselt number are also determined. Here, the platelet shape of Al2O3 nanoparticles possesses a high heat transfer and flow rate based on the outcomes. In addition, increasing the slip and magnetic parameters improves the temperature, whereas increasing the buoyancy and inclination angle parameters has reverse effects. The results also show that increasing the unsteadiness parameter and the magnetic parameter reduces the film thickness.

Buoyancy force and magnetic field effects on laminar vortex breakdown and fluid layers

In this study, the Generalized Integral Transformation Technique (GITT) is used to describe the effect of buoyancy force and magnetic field on the vortex breakdown process generated by the rotation of an electrically conductive fluid. A magnetic field is positioned vertically to stabilize the swirling flow caused by the rotation of the bottom disc of a cylindrical recipient. Three fluids were compared in this study where the range of Richardson number is 0 ≤Ri ≤2.0. When the temperature difference is greater than Ri = 0.1, many layers become visible. These stratified flu id layers act as thermal insulators. In the case of stratification, the increased magnetic field reduces the total number of layers formed in the fluid. The influence of gradient temperature on the distribution of the layers generated is discussed. The limitations between the multilayer structure and the monolayer structure for three fluids are calculated as a function of the flow parameters.

ANALYTIC SOLUTIONS FOR EKMAN BOUNDARY LAYER ON A POROUS PLATE

This study tends to explore a model of Ekman boundary layer on a porous Plate is considered and the governing differential equations are introduced. In this research, the researcher tries to find out steady state solutions for the velocity and temperature distributions are obtained. In this regard, the effect of buoyancy forces on velocity and temperature distributions are studied. The results of this study have indicated that the effects of buoyancy forces have significant contribution to the field of profiles.

Unsteady Falkner-Skan flow of fractional Maxwell fluid towards a stretched wedge with buoyancy effects

The majority of researches for Falkner-Skan flow are dependent on the classical constitutive relations of viscoelastic fluids. Fractional Maxwell fluid model is introduced to depict Falkner-Skan flow innovatively in the paper. Moreover, the momentum equation studying the effects of buoyancy force is established. Analogy to constitutive relevance for fractional Maxwell fluid, fractional derivative is brought in Fourier’s law and Fick’s law. It is worth mentioning that heat source and chemical reaction are discussed. Finite difference method integrated with L1-algorithm is utilized to address the fractional governing equations, whose convergence is verified by constructing an example with accurate solution. Furthermore, the influences of pertinent physical parameters are analyzed diagrammatically. A fascinating phenomenon is discovered that all the velocity profiles initially rise to a maximal value due to the impact of buoyancy force and then decrease to the free flow velocity. Besides, the temperature and concentration distributions first increase slightly while decline significantly, which indicates the thermal relaxation and mass relaxation characteristic of Maxwell fluid.

Hybrid nanofluid mixed convection in a cavity under the impact of the magnetic field by lattice Boltzmann method: Effects of barrier temperature on heat transfer and entropy

The aim of this study is to investigate the effect of barrier temperature on hybrid nanofluid MHD mixed convection via LBM. The shape of the evaluated chamber is trapezoidal, subjected to heat absorption or heat generation. Reducing the share of heat transfer in entropy production up to about 14% is possible by changing the blocking temperature from 1 to zero. By increasing the effect of buoyancy forces, a stronger convection current is formed inside the chamber. When the magnetic field is applied, it reduces the fluid flow speed and temperature gradient. This factor leads to the reduction of convection effects and the weakening of buoyancy forces. So, the stronger the convection, the more obvious this effect. The flow under the influence of heat production results in the lowest mean Nusselt value. The higher heat absorption or heat generation coefficients, lead to a more effective magnetic field application. If the number of Richardson is low, heat absorption or heat generation effects are more obvious. Bejan Number, for the coefficient of heat absorption or heat generation, equals +5 (Q=+5), which is about 10% & 18% higher than Q=0 and Q=-5, respectively.

Effect of Coriolis and buoyancy forces on three-dimensional flow of chemically reactive tangent hyperbolic fluid subject to variable viscosity

Thermophoresis effect has wide range of applications in electro-static precipitators and in biology for calculating single biological macro molecules, such as genomic-length DNA and HIV virus in the micro channels. Current study deal with effects of Coriolis and buoyancy forces on the three-dimensional boundary layer flow of tangent hyperbolic fluid with thermo-migration and haphazard motion of nano-sized particles. Arrhenius kind of chemical reaction is taken along an exponentially stretchable surface. The main focus of current exploration is to execute shear thinning nano-liquid flow past an exponentially rotating stretchable surface under the influence of variable viscosity, mixed convection and activation energy. We are motivated to explore the features of three-dimensional shear thinning model combined under the features of mixed convention, variable viscosity, and activation energy. The mathematical model is designed to generate PDEs and converted them into ODEs by employing fractious transformation. The numerical outcomes are exhibited via graphs by employing Bvp4c numerical technique whereas the values of skin friction coefficient are calculated by monopolizing shooting method. Characteristics of the parameters appearing in modeling like the viscosity parameter, power-law index, local Weissenberg number, mix convection parameter, rotation parameter, Prandtl number and chemical reaction parameter are comprehensively analyzed through graphical behavior. The impact of governing parameters on skin friction, heat and mass transfer rates is illustrated through tables. The detail analysis anticipates that the elevation in Weissenberg number and porosity caused decline in velocity. Further, the temperature behaves doppositely analogous to development Prandtl besides the thermophoresis parameter.

Analysis of nanobiofilm flow of Carreau fluid with the effect of buoyancy forces and activation energy: A numerical approach

In the past few years, many technical strategies, such as molding, condenser heat exchanger, liquefied metal filtration, fusion control and nuclear reactor coolant, that involve hydromagnetic fluxes and thermal intensification in porous media have been observed. This study investigates the Carreau nanofluid of nanobiofilm through stretching/shrinking sheet with a stagnant point flow, nanoparticles and convecting microbes. The orthogonal ([Formula: see text] impinge) coating stagnant point circulation of a medium is considered, although the sheet may be stretched/shrinked as the procedure utilized in industry. The variations in the fluid (dynamic viscosity, thermal conductivity, mass permeability) and microbes are utilized. The similarity transformation factors are used to transform the system of partial differential equations into a nonlinear system of ordinary differential equations. To find the solution of a system of equations, the Runge–Kutta method with shooting technique has been used. The flow rate, temperature and concentration, as well as the heat transfer rate, and the physical quantities have been discussed. The nanoparticle volume fraction increases with the increasing effect of activating energy as well as thermophoresis parameter, but it decreases with the enhancing effect of Lewis number (Le) and Brownian motion parameter (Nb). The graphs and tables display the illustration of the influence of different parameters.

EDL aspect in cilia-regulated bloodstream infused with hybridized nanoparticles via a microtube under a strong field of magnetic attraction

Cilia-regulated micro-scale transit via assorted micro and nanofluidic devices that employ EDL phenomena dictates drugs and physiological constituent delivery. Stirred by these implications, the present mathematical simulation intends to unravel the electric double layer (EDL) aspect in a cilia-attenuated peristaltic transport of viscoelastic ionized blood diffused with hybridized nanoparticles inside a microtube due to its impressive nanomedicine functionalities. A magnetic field extraordinarily durable is usually enforced to the blood transit via a cilia-layered microtube to unfold the electromagnetic (Hall and ion-slip currents) facts. An electric field aligned axially is imputed to the bloodstream. In this modelling, the collective effects of buoyancy force, viscous dissipation, and heat source are also evoked. Gold (Au) and copper (Cu) nanoparticles are selected in the hybridizing process to prepare the requisite hybrid nano-blood. Four unlike geometrical shapes (sphere, brick, cylinder and platelet) of nanoparticles are considered. The Jeffrey fluid model is favoured to emulate the rheological functionality of viscoelastic hybrid nano-blood. The homotopy perturbation method (HPM) is assigned to evaluate the analytical series solution upon simplifying the normalized model equations employing lubrication and Debye-Hückel linearization postulates. The changes in pertinent factors lead to an amendment in hemodynamical attributes, which are elucidated via graphs. The contribution of electro-osmotic force and electromagnetic events (Hall and ion-slip currents) are acknowledged to boost up the bloodstream in the core part of the microtube while impeding it close to the tube wall. The growth in the heat exchange rate for hybrid nano blood (201.5% for Au-Cu/blood) is higher than for nano blood (86.27% for Cu-blood and 148.4% for Au-blood). The captivated boluses expand for Hall and ion-slip, EDL and cilia length factors. This search could benefit the medical domain, such as haematology, haemato-oncology, radiology, pulmonology, electrobiology, etc. • Electric double layer (EDL) aspect in a cilia-attenuated peristaltic transit of viscoelastic blood diffused with hybridized nanoparticles inside a microtube in attendance of stronger magnetic influence is presented. • In this modelling, the cumulative effects of buoyancy force, viscous dissipation, and heat source are also evoked. • The electro-osmotic body force assists the blood flow in the core area of the micro-vessel and resists it in the peripheral region of the micro-vessel. • The augmentation in heat exchange rate for hybridized nanoblood (201.5% for Au-Cu/blood) is greater than nanoblood (86.27% for Cu-blood, and 148.4% for Au-blood). • The captivated boluses notably expanded due to thinner EDL, stronger Hall and ion-slip currents or longer cilia length.