Form Of Streamlines Research Articles

Entropy Generation Analysis and Natural Convection in a Nanofluid-Filled Square Cavity with a Concentric Solid Insert and Different Temperature Distributions

The problem of entropy generation analysis and natural convection in a nanofluid square cavity with a concentric solid insert and different temperature distributions is studied numerically by the finite difference method. An isothermal heater is placed on the bottom wall while isothermal cold sources are distributed along the top and side walls of the square cavity. The remainder of these walls are kept adiabatic. Water-based nanofluids with AlO nanoparticles are chosen for the investigation. The governing dimensionless parameters of this study are the nanoparticles volume fraction (), Rayleigh number , thermal conductivity ratio () and length of the inner solid (). Comparisons with previously experimental and numerical published works verify a very good agreement with the proposed numerical method. Numerical results are presented graphically in the form of streamlines, isotherms and local entropy generation as well as the local and average Nusselt numbers. The obtained results indicate that the thermal conductivity ratio and the inner solid size are excellent control parameters for an optimization of heat transfer and Bejan number within the fully heated and partially cooled square cavity.

Natural convection and entropy generation of a ferrofluid in a square enclosure under the effect of a horizontal periodic magnetic field

The current work is concerned with the study of the impacts of a periodic magnetic field on natural convection and entropy generation of Fe3O4-water nanofluid flowing in a square enclosure. The magnetic field is applied as a sinusoidal function of the y coordinate. The Galerkin finite-element method is employed to numerically solve the model governing partial differential equations. To evaluate the correctness and accuracy of the results, comparisons have been performed between the outcomes of this work and previously published results. The governing dimensionless parameters and their corresponding ranges are the Rayleigh number (Ra = 103–106), Hartmann number which indicates the amplitude of the periodic magnetic field (Ha = 0–50), the period number (λ = 0.1–1.0) and the nanoparticles volume fraction (φ = 0–0.08). The outcomes of the study are presented in the forms of streamlines, isotherms and entropy generation contours as well as the local and average Nusselt numbers. Regardless of Ha and λ values, the average Nusselt number Nuavg and the total entropy generation St associated with the periodic magnetic field are found to be higher than those corresponding to the uniform magnetic field. Additionally, When λ = 0.25 and Ra = 106, for Ha < 10, using the Fe3O4 nanoparticles enhances the total entropy generation St, however, when Ha > 10, the effect of the existence of the nanoparticles on St would be inverse.

Numerical simulation of double diffusive mixed convective nanofluid flow and entropy generation in a square porous enclosure

In the present work, the numerical analysis of a double diffusive mixed convective alumina-water nanofluid flow in a square porous lid driven cavity is investigated to determine the influence of different physical parameters on the heat transfer and entropy generation. The upper wall of the enclosure is moving to the right while all the other walls are at rest. The flow is generated due to the motion of the top wall and the buoyancy forces that are produced due to the difference in temperature. A monolithic Galerkin finite element approach together with geometric multigrid technique has been adopted to solve governing equations for various governing parameters. Analysis has been shown in the form of streamlines, isotherms and isoconcentration, tables and plots. The influence of various physical parameters on the flow, in specific ranges such as the Richardson number (0.01⩽Ri⩽5), Darcy number (0.00001⩽Da⩽0.01), porosity parameter (0.2⩽∊⩽0.8), Lewis number (0.1⩽Le⩽7), buoyancy ratio parameter (-2⩽Br⩽2), heat generation/absorption parameter (-0.4⩽q⩽0.4), chemical reaction parameter (0⩽Kr⩽0.04) as well as the nanoparticles volume fraction (0⩽ϕ⩽0.04) are investigated and findings are very closely comparable to the previous analysis for the special cases in the literature.

Numerical Study on Mixed Convection in Ventilated Cavities with Different Aspect Ratios

An unsteady numerical investigation on mixed convection in a two dimensional open ended cavity with different aspect ratios is carried out. In this investigation, uniform temperature is set to the left and the right sides of the cavity while the other surfaces are adiabatic. The simulation is performed for a wide range of Reynolds numbers (Re = 100–1000) and Richardson numbers (Ri = 0.132–6.5 × 102), and various cavity aspect ratios (L/D = 0.5–4.0) and H/D = 0.1. Governing equations are solved using a cell centered finite volume code, a SIMPLE numerical projection scheme and a 2nd order accuracy. Results are presented in the form of streamlines, isothermal lines, and velocity profiles in the channel. The conclusion is that the enhancement of heat transfer rate is generated principally by the increasing Re and the assisting configuration is thermally more efficient when compared to the opposing one.

Natural convection in an inclined porous triangular enclosure with various thermal boundary conditions

The aim of the study is to analyse the effect of two different thermal boundary conditions on natural convection in a porous triangular enclosure. Sinusoidal and linearly varying temperature profiles on the left wall are considered. The top wall of the enclosure is kept to be adiabatic. The Darcy model is adopted in this study and the governing equations are solved using the finite difference method for various values of inclination angle and Darcy-Rayleigh number. The results are presented in the form of streamlines, isotherms, and Nusselt numbers. The heat transfer rates are calculated and compared between two thermal boundary conditions. The heat transfer is more enhanced in the case of sinusoidal wall temperature than linearly varying wall temperature.

Main trends in intensification of rotor-screw processing of parts

The ways of productivity increase in details finishing-strengthening processing executed in rotor-screw technological systems are presented. It is shown that the use of rotor-screw machines makes it possible to combine the parts machining using a vibrating field with a large amplitude of oscillations and their transportation in a streamlined form of production organization. Two main directions of rotor-helical processing stimulation are identified: on the basis of structural changes in the screw rotor, as the main working element of the rotor-screw machine and by equipping the screw rotor with activation elements of the process. The classification of screw rotors is presented, which allows purposeful search for the most effective designs of screw rotors and the mechanism is revealed of their influence on the process of parts finishing-hardening processing. Dependence is established for determining the longitudinal movement speed of the parts being processed in the screw rotor. The constructive-technological scheme of the rotor-screw machine is proposed, which allows increase of the productivity of the process and simplification of the design of machines for their implementation, by dismembering the complex screw propulsion of the load mass, which takes place in the screw rotors, into relatively simple in kinematic sense motions. The technological possibilities of rotor-screw processing application for finishing-strengthening operations are presented.

Conjugate natural convection of Al2O3–water nanofluid in a square cavity with a concentric solid insert using Buongiorno’s two-phase model

The problem of conjugate natural convection of Al2O3–water nanofluid in a square cavity with concentric solid insert and isothermal corner boundaries using non-homogenous Buongiorno’s two-phase model is studied numerically by the finite difference method. An isothermal heater is placed on the left bottom corner of the square cavity while the right top corner is maintained at a constant cold temperature. The remainder parts of the walls are kept adiabatic. Water-based nanofluids with Al2O3 nanoparticles are chosen for the investigation. The governing parameters of this study are the nanoparticle volume fraction (0 ≤ ϕ ≤ 0.04), the Rayleigh number (102 ≤ Ra ≤ 106), thermal conductivity of the solid block (kw=0.28, 0.76, 1.95, 7 and 16) (epoxy: 0.28, brickwork: 0.76, granite: 1.95, solid rock: 7, stainless steel: 16) and dimensionless solid block thickness (0.1 ≤ D ≤ 0.7). Comparisons with previously experimental and numerical published works verify good agreement with the proposed method. Numerical results are presented graphically in the form of streamlines, isotherms and nanoparticles volume fraction as well as the average Nusselt number and fluid flow rate. The results show that the thermal conductivity ratio and solid block size are very good control parameters for an optimization of heat transfer inside the partially heated and cooled cavity.

Interaction of a trailing vortex with an oscillating wing

A technique of particle image velocimetry is employed to characterize the flow structure of a trailing vortex incident upon the tip region of an oscillating wing (plate). The amplitude and velocity of the wing are nearly two orders of magnitude smaller than the wing chord and free stream velocity, respectively. Depending upon the outboard displacement of the incident vortex relative to the wing tip, distinctive patterns of upwash, downwash, and shed vorticity are observed. These patterns are a strong function of the phase of the wing motion during its oscillation cycle. At a given phase, the wing oscillation induces upwash that is reinforced by the upwash of the incident vortex, giving a maximum net upwash. Conversely, when these two origins of upwash counteract, rather than reinforce, one another during the oscillation cycle, the net upwash attains minimum value. Analogous interpretations hold for regions of maximum and minimum net downwash located outboard of the regions of upwash. The magnitude and scale of the vorticity shed from the tip of the wing are directly correlated with the net upwash, which takes different forms related to the outboard displacement of the incident vortex. As the location of the incident vortex is displaced towards the wing tip, both the maximum upwash and the maximum vorticity of the tip vortex initially increase and then decrease. For the limiting case where the incident vortex impinges directly upon the tip of the wing, there is no tip vortex or induced region of upwash. Furthermore, at small values of vortex displacement from the wing tip, the position of the incident vortex varies significantly from its nominal position during the oscillation cycle. All of the foregoing features are interpreted in conjunction with the flow topology in the form of streamlines and critical points, superposed on patterns of vorticity. It is shown that despite the small amplitude of the wing motion, the flow topology is fundamentally different at maximum positive and negative values of the velocity of the wing tip, that is, they are not symmetric.

Heat transfer enhancement of mixed convection in an inclined porous cavity using Cu-water nanofluid

In this paper, mixed convection of Cu-nanofluid in an inclined fluid-saturated porous cavity is numerically analyzed by considering three different cases depending on the direction of moving wall(s). The equations of nanofluid-saturated porous medium can be derived by the Darcy-Brinkman-Forchheimer model and are solved using the SIMPLE algorithm. The effect of various non-dimensional parameter such as the Richardson number, Darcy number, inclination angle, solid volume fraction and three different cases are carefully analyzed. The obtained results are presented in the form of streamlines, isotherms, mid-height velocity profiles and average Nusselt number. It is found that the flow and heat transfer play a significant role with the direction of the moving wall(s).

Earthquake-induced deformations on ice-stream landforms in Kuusamo, eastern Finnish Lapland

Kuusamo in eastern Finnish Lapland is characterized by ice-streamlined landforms as well as clusters of historical and recent earthquakes (Mw<4). Since recent earthquakes are often found to be located on the traces of postglacial faults (PGFs) within the Fennoscandian shield we postulate that some part of the ice-stream landforms have been deformed by the past earthquakes in Kuusamo. Airborne LiDAR (Light Detection And Ranging) DEMs (digital elevation models) revealed significant numbers of postglacial deformations, such as liquefaction deformations, rotational landslides, earth flows as well as kettle holes (craters), on the fluted surfaces within the Kuusamo ice-stream fan. We found these deformations to be a common feature on the Archean granitoid gneisses and within a 20km wide and NW-SE oriented corridor between the major intrusives, the Iivaara nepheline syenite and the Näränkävaara gabbro. Of the paleolandslides, liquefaction morphologies were generally developed on the distal slopes (1.3–2.8%; 0.75–1.6°) of the streamlined forms. Sedimentary anisotropy, obtained with azimuthal electrical conductivity (σa; skin depth down to 3–6m), of the deformed flutes significantly deviated from the non-deformed (clean) ones. The fields of the Pulju moraine, a subglacial landform, formed a grounding zone for the ice-streaming SW of the paleolandslide cluster. We therefore propose that both subglacial and postglacial earthquake-induced landforms are present in Kuusamo. No PGFs could be verified in the Kuusamo area, yet gravity, airborne magnetic, and LiDAR morphological lineaments suggest that the old Paleoproterozoic structures have been reactivated as strike-slip faults, due to the lithospheric plate stresses and glacio-isostatic adjustment (GIA).

Hydromagneto quadratic natural convection on a lid driven square cavity with isothermal and non-isothermal bottom wall

PurposeThis paper aims to focus on linear and non-linear convection in a lid-driven square cavity with isothermal and non-isothermal bottom surface.Design/methodology/approachIt is assumed that the top moving wall is adiabatic and the bottom wall is heated in two modes, and the rest of the walls are maintained at uniform cold temperature. The coupled governing non-linear partial differential equations are solved numerically with MAC algorithm for conducting a parametric study with uniform and non-uniform temperature bottom wall.FindingsThe numerical results are depicted in the form of streamlines, temperature contours and variation of local Nusselt number. The local Nusselt number at the bottom wall of the cavity increases in presence of non-linear temperature parameter as compared with linear temperature parameter and heat transfer reduces with increasing of Ha for uniform and non-uniform heating of bottom wall.Research limitations/implicationsThe numerical investigation is conducted for unsteady, two-dimensional natural convective flow in a square cavity. An extension of the present study with the effect of inclination of cavity, wavy walls and triangular cavity will be the interest of future work.Originality/valueThis work studies the effect of magnetic field in the presence of linear convection and non-linear convection. This study might be useful to cooling of electronic components, alloy casting, crystal growth and fusion reactors, etc.

A three‐dimensional CFD and experimental study to optimize naturally air‐cooled electronic equipment enclosure: Effects of inlet height, heat source position, and buoyancy on mean rise in temperature

AbstractThe major reason behind failure of electronic components is the rise in temperature. To optimize design of naturally cooled electronic equipment enclosure, a detailed experimental study and a computational fluid dynamics (CFD) analysis were performed. Commercially available software, ANSYS Fluent, was used for CFD analysis. The three‐dimensional form of Navier–Stokes equations was used to solve the problem computationally. Aluminium enclosure having dimensions of 40 cm × 40 cm × 21 cm and thermal conductivity of 210 W/m·K were manufactured for experimentation in this research study. Electronic components were modelled as constant heat flux body during experimentation and CFD analysis. Effect of heat source vertical and horizontal position, inlet height, and buoyancy effect on mean rise in temperature inside the aluminium enclosure was studied. Mean temperature inside the casing was increased by increasing either heat source height or inlet height. At the end, computational results were compared with experimental results in order to check the validity of results. Computational results were highly in accordance with experimental results, because maximum percentage difference between experimental and CFD results was less than 6%. On the basis of results obtained from experiments and simulations, the best configuration of heat source and inlet was proposed, which will provide optimum thermal performance. Numerical results of velocity and temperature inside the enclosure were plotted in the form of streamlines and isotherms. This study can be used as a fundamental step prior to designing electronic equipment enclosure.

Study on the Influence of the Convoy Rolling over Aerodynamic Resistance

The aim of the study is to investigate how the aerodynamic resistance is influenced by the convoy rolling and to see how much this is possible by varying the distance between trucks. Then to see how the gains correlate with the position occupied by the truck in the convoy. The study starts from current research on the premises of running in convoy. Aerodynamic analysis was performed using software finite element of Computational Fluid Dynamics (CFD) type, where it was modeled the convoy rolling of a variable number of trucks. The number of trucks and the distance between them was varied in the model in order to acquire an understanding of the flow field around the trucks and how the distance between them can improve the aerodynamic parameters. The results are presented in the form of streamlines of the air, which indicates the air volume travel speed and direction and of the pressure distribution on the surface of the body. The most significant drop in pressure on the front surface was obtained for the second truck of the convoy, whereas for the following ones the reduction was less important. The participation in a convoy of more than two trucks is justified by the reduction of the whirls that appear and by the uniform air flow. The main advantage of running in convoy mode is to decrease aerodynamic resistance, with beneficial consequences on economic and ecological parameters. Continuing work from here on, it could be analyzed the impact of changing the distance between trucks on the aerodynamic coefficient. The results of CFD simulations need to be verified with experimental data, such as wind-tunnel test, to ensure reliability of the results.

Numerical investigation of heat transfer and pressure drop of heat transfer oil in smooth and micro-finned tubes

The laminar, non-isothermal flow of the heat transfer oil in horizontal smooth and micro-finned tubes with different fin heights and helical angles are investigated numerically for the constant wall temperature boundary condition. Simulations have been performed for the Reynolds number ranging from 100 to 1000, the fin height varying from 0.2 to 0.5 mm, and the fin helix angle between 5 and 45°. The results are presented in the form of streamlines, temperature contours, relative Nusselt number, and friction factor. The numerical procedure is validated by comparing the simulation results for the flow and heat transfer of the oil through the micro-finned and smooth tubes with the corresponding experimental results from the literature. The comparisons demonstrate good agreements between the simulation and the experimental results for both the smooth and micro-finned tubes. The results indicate maximum heat transfer enhancement of 44 percent and friction factor increase of 69 percent for the flow of heat transfer oil through the micro-finned tubes in comparison with heat transfer and friction factor of the fluid flow through the corresponding smooth tube at the Reynolds number of 103.

Convection in a sinusoidally heated square enclosure utilizing [formula omitted] nanofluid with heat generating solid body

In this study, natural convection flow in a square enclosure filled with Ag−water nanofluid and with a heat conducting solid square body are carried out numerically. A two-dimensional solution for steady laminar incompressible flow is obtained by using the finite volume method based on the control volume approach. The study goes further to investigate the effect of the various thermal boundary conditions on the fluid flow and heat transfer inside the enclosure. The area of the solid body is changed at the centerline of the enclosure. Effect of area ratio of solid-enclosure, the thermal conductivity ratio of solid-fluid, solid volume fraction and temperature difference ratio of solid-fluid are studied. The flow and heat transfer characteristics are expressed in the form of streamlines and isotherms, respectively.

Finite amplitude cellular convection under the influence of a vertical magnetic field

At the onset of stationary convection, the effect of a vertical magnetic field on the heat transfer of Rayleigh-Benard convection for an electrically conducting fluid is studied. The nonlinear governing equations describing the motion, temperature and magnetic fields are expanded as the sequence of non-homogeneous linear equations, which depend on the solutions of the linear stability problem. Infinite number of steady state with finite amplitude solutions are obtained for the stress-free boundary conditions. The perturbation method proposed by Kuo (1961) is used for the first time to highlight the heat transfer features of magnetoconvection. An explicit expression at the onset of convection in terms of parameters of the system is obtained. The dependence of heat transfer rate on Rayleigh number (R), Chandrasekhar number, thermal and magnetic Prandtl numbers is extensively examined until sixth order using an expansion of R as proposed by Kuo (1961). The results show that the magnetic field dampens the heat flow for stationary convection, i.e., the onset of convection shifts to higher values of R as the vertical magnetic field increases. Under the uniform magnetic field, heat flow gets enhanced as the thermal Prandtl number increases, whereas heat flow diminishes for the increase in magnetic Prandtl number. The results of flow field and heat transfer characteristics are depicted in the form of streamlines and isotherms, respectively. The presence of magnetic field changes the flow structure of streamlines from unicellular to multicellular patterns. This is due to the magnetic susceptibility of colder fluid flow towards the magnetic field. The flow field is analyzed with respect to the topological invariant relation. To trace the path of convective heat transport, the concept of Heatfunction has been employed. This methodology explains the comprehensive interpretation of energy distribution in terms of heatlines.

Numerical simulation of magnetic convection ferrofluid flow in a permanent magnet–inserted cavity

The magnetic convection heat transfer in an obstructed two-dimensional square cavity is investigated numerically. The walls of the cavity are heated with different constant temperatures at two sides, and isolated at two other sides. The cavity is filled with a high Prandtl number ferrofluid. The convective force is induced by a magnetic field gradient of a thermally insulated square permanent magnet located at the center of the cavity. The results are presented in the forms of streamlines, isotherms, and Nusselt number for various values of magnetic Rayleigh numbers and permanent magnet size. Two major circulations are generated in the cavity, clockwise flow in the upper half and counterclockwise in the lower half. In addition, strong circulations are observed around the edges of the permanent magnet surface. The strength of the circulations increase monotonically with the magnetic Rayleigh number. The circulations also increase with the permanent magnet size, but eventually, are suppressed for larger sizes. It is found that there is an optimum size for the permanent magnet due to the contrary effects of the increase in magnetic force and the increase in flow resistance by increasing the size. By increasing the magnetic Rayleigh number or isothermal walls temperature ratio, the heat transfer rate increases.

Numerical simulation of MHD mixed convection in a nanofluid filled non-darcy porous enclosure

This paper examines numerically the thermal and flow field characteristics of the mixed convection flow in a rectangular lid-driven porous enclosure filled with Cu-water nanofluid subjected to the influence of an inclined uniform magnetic field. The enclosure has sinusoidal heating vertical walls, thermally insulated horizontal walls and a heated moving lid at the centre of the enclosure move at a uniform velocity. The non-linear governing equations and boundary conditions are discretized using finite volume approach with power law scheme and solved numerically by SIMPLE algorithm for the pressure-velocity coupling together with under relaxation technique. Numerical study has been carried out for different values of Richardson number (0.01 ≤ Ri ≤ 100), Darcy number (10−3 ≤ Da ≤ 10−5), Hartmann number (0 ≤ Ha ≤ 100), orientation of magnetic field (0° ≤γ ≤ 90°), solid volume fraction (0.0 ≤ φ ≤ 0.1) and described in the form of streamlines, isotherms, average Nusselt number and velocity graphs. Based on the obtained results, it is found that Hartmann number and the orientation of the magnetic field have adverse impact on convection, hence dominated conduction mode occurs. Moreover, it leads to the reduction of overall heat transfer rate.

Numerical investigation for heat transfer enhancement using nanofluids over ribbed confined one-end closed flat-plate

Impinging jet is one of various methods of cooling with the ability to achieve high heat transfer rates and improve average surface’s Nusselt number. This method has vast industrial applications including integrated use in solar collectors, gas turbine cooling, refrigeration, air conditioning and electronics cooling. A numerical study is conducted to study the effects of using nanofluids on impinging slot jet over a flat plate with a ribbed surface. The main objective of the study was to investigate the possibility of improving the overall heat transfer rate by focusing on the improvements in the local and average surface Nusselt number values. Several parameters effects are studied including Solid Volume Fraction, Richardson number and Reynolds number. These results indicated a marked improvement in average Nusselt number with the increase in the solid volume fraction. Also, there is an amended value when the buoyancy effect is dominant over the whole domain. The results are shown in the form of streamlines, isotherms and Nusselt numbers contra other variables. The current work was simulated using a FORTRAN CFD Code, which discretizes the non-dimensional forms of the governing equations utilizing the finite volume method and solving the consequent algebraic equations using Gauss-Seidel method Utilizing TDMA.

Numerical simulation of MHD mixed convection in alumina–water nanofluid filled square porous cavity using KKL model: Effects of non-linear thermal radiation and inclined magnetic field

This study examines the influence of non-linear thermal radiation and inclined magnetic field on mixed convection in a square porous cavity. Here, the cavity is saturated with alumina–water nanofluid. Darcy-Brinkman-Forchheimer-extended model has been adopted to formulate governing differential equations. After transforming equations to dimensionless form, these are solved by utilizing weighted residual Galerkin finite element method. Latest Koo-Kleinstreuer-Lee (KKL) model is employed for the evaluation of effective thermal conductivity and dynamic viscosity of nanofluid. Effect of pertinent parameters in specific ranges such as Richardson number (0.01 ≤ Ri ≤ 100), radiation parameter (0 ≤ Rd ≤ 5), temperature ratio parameter (1.1 ≤ Nr ≤ 1.4), inclined magnetic field parameter (0°≤ γ ≤ 90°), Darcy number (10−6 ≤ Da ≤ 10−3), porosity parameter (0.2 ≤ ϵ ≤ 0.8) and volume fraction of solid particles (0 ≤ ϕ ≤ 0.04) has been studied and presented in the form of streamlines, isotherms and plots. Moreover, kinetic energy and average temperature have also been taken into account for better understanding the flow philosophy. It is found that radiation parameter, temperature ratio parameter, Darcy number and porosity parameter augment heat transfer, kinetic energy and average temperature while inclined magnetic field parameter in selected aforementioned range declines heat transfer due to hot bottom wall.