Steady Incompressible Laminar Flow Research Articles

Comparative Study on Thermal Transmission Aspects of Nano and Ferrofluid in Enclosures Holding Heat-Generating Body

The heat-transmission characteristics of Co ferrofluid and SiO2−water nanofluid are compared numerically inside enclosures including a heat-generating body. Using the finite-volume method, a steady laminar incompressible flow in two dimensions is solved. The numerical study is conducted to determine the impacts of the solid volume fraction (φ=0.02,0.1 and 0.2), the temperature-difference ratio (ΔT*=0,4 and 20), and the Rayleigh number (Ra=105,106 and 107) on both SiO2−water nanofluid and Co ferrofluid, respectively. In consideration of isothermal and streamlines contours, the aspects of temperature transmission and fluid flow are addressed. It is shown that there is no remarkable difference in the convection rate for both the fluids while increasing the Rayleigh number and temperature difference ratio.

Theoretical drag analyses of laminar channel and pipe flows with wall roughness

In this paper, an exact expression for the drag coefficient of a streamwise-periodic steady incompressible laminar channel and pipe flow with micro- or macro-scale wall roughness is derived, whereby the drag coefficient is decomposed into contributions from different components of the velocity gradient tensor in the flow field. It is shown through our theoretical analysis that drag reduction cannot be achieved by adding micro- or macro-scale spanwise-periodic/-symmetry wall roughness structures to the smooth inner walls of streamwise-periodic steady incompressible laminar channel/pipe flows while maintaining the same volumetric flow rate. It is also shown that wall roughness produces a higher drag due to two factors: (a) wall roughness induces other non-zero velocity gradient terms apart from the wall-normal/radial gradient of streamwise velocity that exists in a smooth channel/pipe flow; (b) the profile of streamwise velocity in the wall-normal/radial direction deviates from the parabolic profile that produces the minimum kinetic energy loss for a given volumetric flow rate. Finally, numerical simulations of laminar channel flow with longitudinal and transverse bars are conducted, and the numerical results confirm the theoretical finding.

Mass-based hybrid nanofluid model for entropy generation analysis of flow upon a convectively-warmed moving wedge

In this research, the steady incompressible laminar two-dimensional hybrid nanofluid flow upon a convectively-warmed moving wedge with radiative transition has been studied numerically. The nanoparticles are the magnetite (Fe3O4) and the graphene oxide (GO), in two research parts of spherical and non-spherical (brick, cylinder, platelet, and disk) shapes, suspended in the pure water as base fluid. Three main geometries of the well-known Falkner-Skan problem including: (i) the flat plat (named Blasius flow), (ii) the wedge, and (iii) the vertical plate (named Hiemenz stagnation flow) have been considered to present a comprehensive development of this significant problem. The applied methodology is according to the single-phase Tiwari-Das hybrid nanofluid model considering the masses of nanoparticles and base fluid instead the volume concentration of first and second nanoparticles. For the first time, the mentioned mass-based method will be utilized in combination with the entropy generation analysis. The governing dimensional PDEs are varied to a system of non-dimensional ODEs with the use of similarity transformation technique which is then solved numerically through Runge–Kutta–Fehlberg method coupled with a conventional shooting procedure. The effect of the governing parameters on the hybrid nanofluid velocity, the temperature distribution, the skin friction coefficient, the Nusselt number, the entropy generation, and the Bejan number has been investigated and interpreted through the tabular and graphical results. A reliable treatment of the mass-based method for the hybrid nanofluid flow, the heat transfer and especially the entropy analysis is the substantial achievement of the present research; although, the detailed results have been presented and discussed in the article's body. Certainly, new modeling and approaches for the hybrid nanofluid can be dramatically beneficial in the various industries in which the cooling technologies are vital

Effects of an external constant pressure gradient on a steady incompressible laminar flow through a semi-porous annular pipe

Abstract In this paper, we examine a steady laminar flow for an incompressible fluid located in a semi porous annular pipe and subjected to a favorable constant pressure gradient applied between the two borders of the pipe. The inner wall is impermeable and the fluid is sucked or injected at the outer wall at constant and uniform velocity, orthogonally to the wall. The problem under study depends on three parameters: the pipe gap ratio, the dimensionless external pressure gradient, and the Reynolds number defined from the sum of the suction or injection velocity and the maximum Hagen–Poiseuille velocity. The conservation of mass induces the zero-divergence velocity field which allows replacing the steady-flow Navier–Stokes equations with a single equation satisfied by the stream function and called the vorticity equation. Assuming the similarity-solution hypothesis, the problem under consideration is reduced to a fourth-order nonlinear ordinary differential equation with two boundary conditions at each wall. The numerical shooting technique including the Runge–Kutta algorithm and the Newton–Raphson optimization method is applied to obtain the solution for the steady flow. For various values of the dimensionless external pressure gradient, the profiles of the velocity components are found and investigations on the wall shear stress for both walls are performed. The results obtained are discussed and physical understandings for the problem studied are derived.

Finite element analysis on the hydrothermal pattern of radiative natural convective nanofluid flow inside a square enclosure having nonuniform heated walls

AbstractThe present article enlightens us on the hydrothermal pattern of a steady incompressible laminar natural convective nanofluid flow inside a heated square chamber. The square enclosure is filled with water‐based spherical‐shaped ferrous (Fe3O4) nanoparticles. Magnetic effect and thermal radiation are presumed within the flow. The left‐sided vertical wall and one bottom wall of the chamber are nonuniformly and uniformly heated, while the remaining right‐sided vertical wall is isothermally cooled at a constant temperature and the upper wall is insulated. A detailed analysis is conducted to exhibit that how nonuniform and uniform heated walls influence flow within the square chamber. The leading dimensional equations are made into a dimensionless form using apposite similarity variables and the Galerkin finite element technique is executed to solve those equations. The grid independence test and a parallel comparison with existing literature are presented to verify the validity of the outcomes. The streamlines, isotherms, temperature, velocities, and average Nusselt number are depicted through several graphs for several parametric values of Rayleigh number, Hartmann number, thermal radiation, and nanoparticle volume fraction. The outcomes showed that increasing nanoparticle concentration and Rayleigh number lead to improve the Nusselt number, while heat transport is reduced for Hartmann number and radiation parameter. The uniformly heated walls convey better heat transport as compared to nonuniformly heated walls.

Assessment of Performance of Tesla Turbine in Water Distribution Systems for Energy Harvesting

Abstract This article composes a systematic design methodology to obtain optimal parameters of the Tesla turbine, which is applicable in water distribution systems, faced with the need to supply power for wireless sensors and other components used in smart water networks and the challenges associated with the feasibility of Tesla turbine in a small scale. The optimal geometric model is sought by using a theoretical model relating turbine physical properties and flow conditions to power output by solving Navier–Stokes equations for steady laminar incompressible flow between adjacent disks. The model shows that the proposed design with dimensions and flow conditions relevant to water pipe networks can achieve a power output of 1.55 mW using a 2.5-cm diameter turbine given a pressure difference of 140 Pa. At 70 Pa using a 1-cm diameter turbine, a power output of 0.17 mW can be obtained. This study shows a great potential in application of Tesla turbine for energy harvesting in water distribution systems.

Computation of Second-order Design Sensitivities for Steady State Incompressible Laminar Flows Using the Extended Complex Variables Method

In the current paper, the general procedure of the first and second-order sensitivity analysis is presented using the extended complex variables method (ECVM). In the traditional complex variables method, only the imaginary step is used for sensitivity analysis. However, in the ECVM, both of the real and imaginary parts are employed to improve the efficiency of the method. To show this, the ECVM is applied to the steady state incompressible laminar flow around a cylinder. The governing Navier-Stokes equations are solved by the finite element method and then the ECVM is employed. The results are validated through comparing with those of obtained by an analytical as well as the finite difference methods and the convergence rate is investigated. It is illustrated that the first-order sensitivity analysis is not influenced by the change of the step length for both of the traditional and extended complex variables methods. However, it is shown that unlike the traditional complex variables method, the ECVM is less dependent on the step size for calculating the second-order sensitivity. This can be considered as an enhancement in the efficiency of this method. Hence, the ECVM is suggested as an appropriate technique for calculating simultaneously the first and second-order sensitivities with high accuracy as well as low computational cost. The proposed method is applicable to a wide range of problems having simple or complex parameters.

Finite element analysis of couple stress micropolar nanofluid flow by non‐Fourier's law heat flux model past stretching surface

AbstractNumerical analysis has been done to investigate magnetohydrodynamics nonlinear convective flow of couple stress micropolar nanofluid with Catteneo‐Christov heat flux model past stretching surface with the effects of heat generation/absorption term, chemical reaction rate, first‐order slip, and convective boundary conditions. The coupled highly nonlinear differential equation governing the steady incompressible laminar flow has been solved by a powerful numerical technique called finite element method. The impacts of diverse parameters on linear velocity, angular velocity (microrotation), temperature, concentration profile, local skin friction coefficient, local wall couple stress, local Nusselt number, and Sherwood number are presented in graphical and tabular form. The result pointed out that the enhancement in material parameter β increases the velocity of the fluid while the couple stress parameter K has quite opposite effect. Heat and mass transfer rate of the fluid are enhanced by increasing material parameter while couple stress parameter shows the opposite influence. Moreover, heat and mass transfer rate are higher with the Catteneo‐Christov heat flux model than Fourier's law of heat conduction. The accuracy of the present method has been confirmed by comparing with previously published works.

Enhancing drug delivery to human trachea through oral airway using magnetophoretic steering of microsphere carriers composed of aggregated superparamagnetic nanoparticles and nanomedicine: A numerical study

Magnetic drug targeting (MDT) is a drug delivery method which implements a high gradient magnetic field in order to enhance the deposition of drugs, containing magnetic materials, in a target area. In this study, we investigated drug delivery to the anterior side of human trachea by means of the MDT method. The drug delivery process was studied numerically in a realistic model of human airway and the drug deposition due to the presence of magnetic field was analyzed. The human airway model used, consists of nasal cavity, oral cavity, pharynx, larynx and trachea. A steady incompressible laminar flow regime was considered for modeling the inhalation of air into the respiratory tract. Microsphere drug particles were injected orally into the airway model. The particles were assumed to have a core-shell structure with aggregated superparamagnetic magnetite nanoparticles in the core and nanomedicine stored in the shell. A permanent magnet with a stationary magnetic field was placed near the trachea in order to enhance the particle deposition in this region. Also, a human mannequin model was employed for determining the exact location of the magnet with respect to the airway. Simulations were performed for various airflow rates, particle sizes and drug compositions in the presence and absence of the magnetic field. In addition, two different air breathing conditions were examined. Furthermore, the effects of magnetic source strength, magnetic source placement angle and gravity, as well as volume packing fraction of the aggregate core, on the drug deposition were explored. The simulation results showed marked improvement in the drug deposition in the presence of magnetic field. Finally, the appropriate conditions for the efficient application of MDT were evaluated. It was shown that the optimal drug delivery results were obtained for low airflow rates (~ 5 l/min), midsize particle diameters (~ 8 µm) and high fractions of magnetic material in the particle composition (75% volume fraction). For the optimum particle diameter, the oral inhalation was shown to lead to a more successful drug delivery relative to the oronasal inhalation. Also, increasing the strength of the magnetic source, placing the magnetic source with an angle of 0° and having the patient lie on his/her back had positive impact on the MDT outcome. Moreover, increasing the volume packing fraction improved the efficieny of drug delivery for low and moderate particle sizes (≤ 8 µm).

Local field synergy analysis of conjugate heat transfer for different plane fin configurations

The aim of the present study is to achieve conjugate heat transfer enhancement in a finned heat exchanger by only modifying the isotherms distribution in the fins. A three-dimensional numerical study of a flat plate and its geometric variants is therefore carried out for a steady incompressible laminar flow. The results are analyzed by carrying out an extensive analysis of the local field synergy which shows the effect of local velocity and local temperature gradient vectors on the heat transfer process. Depending upon the magnitudes of the field synergy parameters, in general, it is found that the local heat transfer coefficient is in accordance with the field synergy principle for the regions in the thermal boundary layer very close to the heated surface. Gain in thermal performance is obtained due to orientation of the velocity and the temperature gradient vectors in the same direction near the upstream fin modification as well as due to the enhancement of the modulus of the inner product of velocity and temperature gradient. For one of the tested configurations, the results show an increase of 7% of PEC associated with about 14.4% less aluminum material used.

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.

Influence of mixed convection in an exponentially decreasing external flow velocity

This article explores the influence of mixed convection in a steady incompressible laminar boundary layer flow for an exponentially decreasing free stream velocity in presence of surface mass transfer and heat source or sink. The nonlinear partial differential equations governing the flow and thermal fields are expressed in dimensionless form with the help of suitable non-similar transformations. The mathematical complexities in obtaining non-similar solutions at the leading edge of the streamwise coordinate as well as non-similarity variable ξ have overcome by using the implicit finite difference scheme in conjunction with Quasi-linearization technique by choosing an appropriate finer step sizes along the streamwise direction. The effects of various dimensionless physical parameters on velocity and thermal fields are analysed.

Performance Analysis of a Multiple Micro-Jet Impingements Cooling Model

The present study investigates the thermal performance of a multiple micro-jet impingements model for electronics cooling. The fluid flow and heat transport characteristics were investigated for steady incompressible laminar flow by solving three-dimensional (3D) Navier-Stokes equations. Several parallel and staggered micro-jet configurations (ie. inline 2 Å~ 2, 3 Å~ 3 and 4 Å~ 4 jets, and staggered five-jet and 13-jet arrays with the jet diameter to the channel height ratios from 0.25–0.5) were analyzed at various flow rates for the maximum temperature rise, pressure drop, heat-transfer coefficient, thermal resistance, and pumping power characteristics. The parametric investigation was carried out based on the number of jets and the jet diameters at various mass flow rates and jet Reynolds numbers. Temperature uniformity and coefficient of performance were evaluated to find out the trade-off among the various designs investigated in the present study. The maximum temperature rise and the pressure drop decreased with an increase in the number of jets except in the case of staggered five-jet array. A higher temperature uniformity was observed at higher flow rates with a decrease in the coefficient of performance. The performance parameters, such as thermal resistance and pumping power, showed a conflicting nature with respect to design variables (viz. jet diameter to stand-off ratio and interjet spacing or number of jets) at various Reynolds numbers within the laminar regime.

Double-Layer Microchannel Heat Sinks With Transverse-Flow Configurations

The performances of various transverse-flow double-layer microchannel heat sink configurations were evaluated compared to those of parallel-flow heat sink configurations via conjugate heat transfer analysis. For the analysis, three-dimensional Navier–Stokes and energy equations for steady incompressible laminar flow were solved using a finite-volume solver. Water with temperature-dependent thermophysical properties was used as a coolant. The thermal resistances were evaluated for various flow configurations of both cross-channel and parallel-channel designs with identical geometric parameters and total flow rate. Changes in the microchannel flow direction lead to remarkable changes in thermal resistance and temperature uniformity. A transverse-flow configuration exhibited the best overall performance among the tested flow configurations in terms of the thermal resistance, temperature uniformity, and pressure drop.

Microcooling system with impinging jets and a stalactite structure

ABSTRACTA novel structure for a microcooling system with an impinging jet array was proposed to enhance heat transfer and reduce the pressure drop. Conjugated heat transfer in the proposed impinging jet array cooling systems, with and without effusion holes, was analyzed to evaluate their heat transfer performance and pressure drop using the three-dimensional Navier–Stokes equations for steady incompressible laminar flow. Grid dependency tests were performed for not only the size, but also the distribution of the grid system. The numerical result was validated using the experimental data. The area-averaged Nusselt number and the maximum temperature on the target surface were selected as the performance parameters for heat transfer. The proposed structure showed remarkable improvement in both the heat transfer performance and pressure drop, but natural effusion from the system did not improve the performance.

Three dimensional simulation of the arc inside an insulator-arrester with a multichamber system

Based on the thermo-physical properties of plasma air, the temperature and flow fields of an insulator–arrester with a multi-chamber system are investigated using three-dimensional computational fluid dynamics. The plasma flow is assumed to be steady incompressible laminar flow and in local thermodynamic equilibrium. The results obtained show that the arc inside the chamber bends downwards, indicating that the Lorentz force induced is directed away from the exit and pushes plasma air down. The outlet also provides passage for plasma flow both in and out of the chamber.

Steady MHD Boundary-layer Slip Flow and Heat Transfer of Nanofluid over a Convectively Heated of a Non-linear Permeable Sheet

The present study investigates the theoretical analysis on steady viscous incompressible MHD laminar boundary-layer flow and heat transfer of an electrically conducting nanofluid over a convectively heated nonlinear permeable sheet with partial slip using homotopy analysis method. The present model used for the nanofluid incorporates the combined effects of magnetic field, partial slip, Biot number, suction/injection, non-linear parameter, Brownian motion, and thermophoresis. We use local similarities variable, the governing equations which are nonlinear partial differential equations was transformed into a system couple of nonlinear ordinary differential equation, which are solved semi-analytical by using homotopy analysis method. Graphically results obtained for the velocity, temperature, and nanoparticle concentration profiles are displayed for various values of the existing parameters controlling the fluid flow: Slip parameter ζ, Magnetic field M, Biot number Bi, suction/injection parameter s, Brownian motion parameter Nb, and thermophoresis parameter Nt. It was found that the Biot number increase the dimensionless temperature profile. Numerical results obtained are compared with the previous published results found on literatures are in good agreement and are discussed quantitatively.

Optimization of a staggered jet-convex dimple array cooling system

Analysis and optimization of a staggered jet-convex dimple array cooling system were performed. A steady incompressible laminar flow and heat transfer in the cooling system were analyzed using three-dimensional Navier–Stokes equations. For the optimization, two design variables, namely the ratio of the height of the dimple to the diameter of the jet and the ratio of the diameter of the dimple to the diameter of the jet, were selected. In addition, thermal resistance was selected as the objective function to evaluate cooling performance. A preliminary parametric study of the objective function was conducted using the design variables, and then, a surrogate modeling of the objective function was performed using the Kriging model. In the optimal design, a lower thermal resistance was achieved with higher pressure drop compared with the reference design. Furthermore, comparative flow analyses for the optimal and reference designs were also performed.

Evaluation of cooling performance of impinging jet array over various dimpled surfaces

Various configurations of an impinging jet–dimple array cooling system were evaluated in terms of their heat transfer and pressure drop performances. The steady incompressible laminar flow and heat transfer in the cooling system were analyzed using three-dimensional Navier–Stokes equations. The obtained numerical results were validated by a comparison with experimental data for the local Nusselt number distribution. The area-averaged Nusselt number on the projected area and the pressure drop through the system were selected as the performance parameters. Among the four tested configurations—inline concave, staggered concave, inline convex, and staggered convex—the staggered convex impinging jet–dimple array showed the best heat transfer performance whereas the staggered-concave configuration showed the lowest pressure drop. A parametric study with two geometric variables, i.e., the height of dimple and the diameter of dimple, was also conducted for the staggered-convex impinging jet–dimple array. As a result, the best heat transfer and pressure drop performances were achieved when the ratio of the height of dimple to the diameter of jet was 0.8. And, the increase in the ratio of the diameter of dimple to the diameter of jet yielded monotonous increase in the heat transfer performance.

HEAT TRANSFER AND PRESSURE DROP PREDICTION IN AN IN-LINE FLAT TUBE BUNDLE BY RADIAL BASIS FUNCTION NETWORK

This paper aims to predict the heat transfer and pressure drop for an in-line flat tubes configuration in a cross-flow using an artificial neural network. The numerical study of a two-dimensional steady state and incompressible laminar flow for an in-line flat tube configuration in a cross-flow is also considered in this study. The Reynolds number varies from 10 to 320. Heat transfer coefficient and pressure drop results are presented for tube configurations at three transverse pitches of 2.5, 3.0, and 4.5 with two longitudinal pitches of 3.0 and 6.0. The predicted results for the average Nusselt number and dimensionless pressure show good agreement with previous work. The accuracy between the actual values and the neural network approach model results was obtained with a mean absolute relative error less than 4.1%, 4.8%, and 3.8% for the average Nusselt number, dimensionless pressure drop and average friction factor, respectively.