Isothermal Cylinder Research Articles

Melting heat transfer of power-law non-Newtonian phase change nano-enhanced n-octadecane-mesoporous silica (MPSiO2)

The heat transfer removal from heated elements in different engineering devices is the main challenge for each engineer in various fields. This problem can be solved using an effective heat-transfer agent or by increasing the heat transfer surface. The present work is devoted to an opportunity to use the phase change material with nanoparticles for an intensification of heat removal within a gap between two coaxial vertical isothermal cylinders. The analysis was performed numerically using the Galerkin finite element approach in the case of the non-Newtonian nature of the nano-enhanced PCM. The power-law was used for the description of the non-Newtonian behavior of the considered material. For the solution to the Stefan problem, a deformed mesh method, based on the Arbitrary Lagrangian–Eulerian (ALE), was used. The developed computational code was validated using the numerical and experimental data of other authors. The effects of the nanoparticles volume fraction, aspect ratio and Fourier number on the melting process were investigated. It has been revealed that the inclusion of nanoparticles within the phase change material leads to both less intensive melting of the material and a reduction of the average Nusselt number.

Flow and Heat Transfer Characteristics of Cylindrical Structures with Corner Radius Variation: Tandem, SIDE-BY-SIDE, and Flow-Induced Vibration

This study investigates the effects of corner radius variation on thermohydraulic parameters around two equal isothermal square cylinders in tandem and side-by-side arrangements. In particular, a two-dimensional numerical study of unsteady laminar-forced convective heat transfer was conducted for a Reynolds number of 100. The Prandtl number was held constant at 0.71. The ratio of cylinder diameter over corner radius was varied from 0.0 to 0.5 with an increment of 0.1. The thermohydraulic parameters such as Strouhal number, drag coefficient, lift coefficient, and Nusselt number were discussed for various spacing ratios. In side-by-side arrangement, the Nusselt number increased for all corner radii with increasing distance between cylinders. However in tandem arrangement, as distance increased from the wake length of upstream circular cylinders, heat transfer was improved for both bodies. Moreover, the mean Nusselt number for the upstream cylinder approached a single cylinder value, while mean Nusselt number for the downstream cylinder was lower than that of a single cylinder. Furthermore, the flow induced vibration was coupled, which enhanced the heat transfer of a single square cylinder.

Numerical study of laminar and turbulent natural convection from a stack of solid horizontal cylinders

Natural convection from a stack of isothermal solid horizontal cylinders has been investigated numerically in a three dimensional computational domain. Simulations were conducted in both laminar and turbulent flow regimes of Rayleigh number (Ra) spanning in the range (104≤Ra≤108) and (1010≤Ra≤1013), respectively. In the present study, the length to diameter ratio of the cylinders has been varied in the range 0.5–20. Three different stack arrangements were considered for the numerical simulations by arranging three, six and ten number of cylinders in a triangular manner. The present computational study is able to appraise very interesting thermo-buoyant plume structures around the stack of cylinders. The average Nusselt number (Nu) shows a positive dependence on Ra for all L/D. The average Nu for a stack of three-cylinders is marginally higher than that of six-cylinders followed by ten-cylinders. Furthermore, at a particular Ra, Nu is significantly higher for short cylinders (low L/D) and decreases with increase in L/D up to 10 or 15 and remain constant for long cylinders. In addition, the present numerical results are also compared with the stack of hollow cylinders. A new Nusselt number correlation has been developed for different stacks as a function of Ra and L/D, which would be useful to industrial practitioners and academic researchers.

Hydrodynamic forces and heat transfer of nanofluid forced convection flow around a rotating cylinder using finite element method: The impact of nanoparticles

A computational approach is utilized to study the nanofluid forced convection flow around a rotating circular cylinder in a horizontal channel. Different types of nanoparticles in the base fluid are considered and investigated such as Silica (SiO2), Copper (Cu) and Alumina (Al2O3). Average Nusselt number (Nuavg) are compared for various conditions of the cylinder, namely adiabatic and isothermal cylinders respectively for two locations of cylinder. A dimensionless system of partial differential equations over a complex computational domain is discretized by applying the higher order stable finite element method. The discretized nonlinear system of algebraic equations is linearized using the Newton method. A geometric multigrid method is implemented for the computation of linearized subproblems in each nonlinear sweep. Impact of the pertinent parameters is investigated such as the Reynolds number (10 ≤ Re ≤ 200), angular velocity (−75 ≤ Ω ≤ 75) and the nanoparticles volume fraction (0.0 ≤ ϕ ≤ 0.04). Numerical results are demonstrated in the form of isotherms, streamlines and suitable graphs for various quantities of interest. It is inferred that the clockwise rotation of the cylinder makes the fluid move over the cylinder while the fluid moves below the cylinder in the anticlockwise case. Moreover, an increase in the nanoparticles volume fraction enhances the average Nusselt number and decreases both of the lift and drag coefficients.

Computational unsteady flow analysis for third‐grade fluid from an isothermal vertical cylinder through a Darcian porous medium

AbstractThe present study describes a mathematical model for free‐convective laminar incompressible boundary layer flow of a third‐grade fluid of the Reiner‐Rivlin differential type, external to an evenly heated semi‐infinite vertical cylinder through a two‐dimensional porous medium. Assuming a homogenous‐isotropic porous medium, simulation of bulk drag effects at low Reynolds number is conducted with the Darcy model. The resulting partial differential equation boundary value problem is normalized using suitable transformation variables. The highly nonlinear time‐dependent coupled conservation equations along with boundary conditions are resolved computationally with an optimized Crank‐Nicolson finite difference code. Validation with previous studies is included. The heat transport and skin‐friction coefficients are computed for different values of emerging nondimensional parameters. Furthermore, steady‐state and transient fluid flow variables are shown graphically. An enhanced fluid velocity is observed for increased Darcy number and the reverse trend is computed for higher values of third‐grade viscoelastic parameter. Also, the rate of heat transfer is observed to increase with greater Darcy number and a reduction in third‐grade viscoelastic parameter. A key observation which is drawn from the present study is that for third‐grade fluid the flow variables deviate significantly from a hot cylindrical wall as compared with a Newtonian fluid. The study is relevant to thermal polymer coating applications in aerospace materials processing.

L1495 revisited: a ppmap view of a star-forming filament

ABSTRACT We have analysed the Herschel and SCUBA-2 dust continuum observations of the main filament in the Taurus L1495 star-forming region, using the Bayesian fitting procedure ppmap. (i) If we construct an average profile along the whole length of the filament, it has FWHM $\simeq 0.087\pm 0.003\, {\rm pc};\,\,$ but the closeness to previous estimates is coincidental. (ii) If we analyse small local sections of the filament, the column-density profile approximates well to the form predicted for hydrostatic equilibrium of an isothermal cylinder. (iii) The ability of ppmap to distinguish dust emitting at different temperatures, and thereby to discriminate between the warm outer layers of the filament and the cold inner layers near the spine, leads to a significant reduction in the surface-density, $\varSigma$, and hence in the line-density, μ. If we adopt the canonical value for the critical line-density at a gas-kinetic temperature of $10\, {\rm K}$, $\mu _{{\rm CRIT}}\simeq 16\, {\rm M_{\odot }\, pc^{-1}}$, the filament is on average trans-critical, with ${\bar{\mu }}\sim \mu _{{\rm CRIT}};\,\,$ local sections where μ > μCRIT tend to lie close to prestellar cores. (iv) The ability of ppmap to distinguish different types of dust, i.e. dust characterized by different values of the emissivity index, β, reveals that the dust in the filament has a lower emissivity index, β ≲ 1.5, than the dust outside the filament, β ≳ 1.7, implying that the physical conditions in the filament have effected a change in the properties of the dust.

Gyrotactic Microorganism Effects on Mixed Convective Nanofluid Flow Past a Vertical Cylinder

The transient mixed convection boundary layer analysis of incompressible flow over an isothermal vertical cylinder is embedded in a saturated porous medium in the vicinity for Gyrotactic microorganism effects. The mathematical model used for the bioconvective nanofluid incorporates the effects of Brownian motion, thermophoresis, and gyrotactic microorganisms. Moreover, the resulting governing nonsimilarity equations are changed into partial differential equations and solved numerically. The results are explained graphically for various physical parameters. It is determined that bioconvection parameter boosts the heat transfer rates and the thickness of the motile microorganism reduces the mass transfer rates. Expanding bioconvection Lewis number leads to decrease in heat transfer rates and the density of the motile microorganism, whereas the mass transfer rates decelerate the flow field. The investigation is pertinent to the nanobiopolymer manufacturing processes.

Buoyancy-assisted flow of yield stress fluids past a cylinder: Effect of shape and channel confinement

• Fluid yield-stress suppresses flow field in severely confined flows. • Confinement of cylinder can lead to augmentation in heat transfer rate . • Shape of the cylinder significantly affects the momentum and thermal transport in channel confined flow. • Strong aiding buoyancy causes flow reversal at the walls at low Reynolds numbers . The aiding-buoyancy mixed convection heat transfer in Bingham plastic fluids from an isothermal cylinder of elliptical and circular shape in a vertical adiabatic channel is numerically investigated. For a fixed shape of the elliptical cylinder E = 2 (ratio of major to minor axes), the effect of confinement is studied for three values of blockage ratio, B , defined as the ratio of the channel width to the circumference of the cylinder/π, as 6.5, 2.17 and 1.3. In order to delineate the role of cross-section of the cylinder, results are also presented here for a circular cylinder of the same heat transfer area as the elliptical cylinder. The results presented herein span the range of conditions as: Bingham number, 0 ≤ Bn ≤ 100, Reynolds number, 1 ≤ Re ≤ 40, and Prandtl number, 1 ≤ Pr ≤ 100 over the range of Richardson number Ri = 0 (pure forced convection) to Ri = 10. Extensive results on drag coefficient, local and surface averaged values of the Nusselt number and yield surfaces are presented herein to elucidate the combined effects of buoyancy, blockage ratio and fluid yield stress. The morphology of the yield surfaces shows that the unyielded plug regions formed upstream and downstream of the cylinder grow faster at low Reynolds numbers with the increasing yield stress effects under the weak buoyancy forces, i.e., small values of Grashof or Richardson number. The heat transfer enhancement is observed with the increasing channel-confinement due to the sharpening of the temperature gradients near the surface of the cylinder. The average Nusselt number shows a positive dependence on the Reynolds number, Prandtl number and Richardson number irrespective of the shape of the cylinder or the type of fluid. By employing the modified definitions of the dimensionless parameters (based on the two choices of the overall effective fluid velocity), predictive correlations have been established for estimating the value of the average Nusselt number in a new application.

Experimental Study of Mixed Convection from Horizontal ‎Isothermal Elliptic Cylinders at Different Aspect Ratios

ABSTRACTMixed convective heat transfer from horizontal isothermal elliptic cylinder is experimentally studied. Three elliptic test cylinders with same perimeter and length are studied giving axis ratio (AR) equal 1, 0.709 and 0.496. The corresponding Gr for the three test sections is 9.8 × 105, 1.5 × 106, and 2.1 × 106, and Re varies from 111 to 1306. Consequently, the corresponding Ri is in range of 1 to 102. The angle of attack (ψ) is changed from 0° (assisting flow) to 180° (opposing flow) with an interval of 30°. New empirical correlation is obtained for the Nuavg as a function of the AR, Ri, and ψ. The experimental results are presented in the form of the average Nusselt number around the elliptic cylinder. It has been concluded that as the axis ratio decreases the averageNusselt number increases, in addition, increasing the angle of attack from 0° to 180° decreases the averageNusselt number considerably. New empirical correlations are obtained for the average Nusselt number as a function of the Richardson number and the attack angle.

Simplified correlations for free convection from a horizontal isothermal cylinder

Heat transfer by buoyancy-driven convection from a heated horizontal cylinder is present in many situations. Applications occur in nuclear reactor safety, solar energy systems, computer cooling, and many heat exchangers. A number of experimental and numerical studies exist for such flow situations and often provide correlating equations to calculate the heat transfer. The existing studies, most of which are for the case where Prandtl number is approximately 0.7, show a considerable variation in their average Nusselt number predictions. Some studies have addressed the variation in Prandtl number with reasonably accurate and consistent correlations but these are often complex and cumbersome to use. To address these issues, the current paper proposes simplified sets of correlating equations using results from prior numerical and experimental studies.

Transient Analysis of Third-Grade Viscoelastic Nanofluid Flow External to a Heated Cylinder with Buoyancy Effects

Nanotechnology is rapidly embracing numerous areas of manufacturing and process engineering. New types of nanomaterials are being exploited to improve, for example, coating integrity, anti-corrosion characteristics and other features of fabricated components. Motivated by these developments, in the current study a mathematical model is developed for unsteady free-convective laminar flow of third-grade viscoelastic fluid (doped with nanoparticles) from a semi-infinite vertical isothermal cylinder, as a model of thermal coating flow of a pipe geometry. Non-Newtonian behavior is simulated with the thermodynamically robust third-grade Reiner–Rivlin model which accurately represents polymer fluids. Nanoscale effects are analyzed with the Buongiorno two-component nanofluid model. The governing equations comprise a set of highly coupled, nonlinear, multi-degree partial differential equations featuring viscoelastic and nanofluid parameters. An implicit Crank–Nicolson numerical scheme is implemented to solve the emerging nonlinear problem with appropriate initial and boundary conditions. Detailed graphical plots for velocity, temperature and nanoparticle volume fraction are presented for a range of different parameters (i.e., third-grade fluid parameter, Brownian motion parameter, thermophoretic parameter, buoyancy ratio parameter, Lewis number). Additionally, distributions of the heat transfer coefficient, skin friction and Sherwood number at the cylinder surface are visualized. Furthermore, streamlines, isotherms and nanoparticle volume fraction contour plots are included for variation of the third-grade parameter. Contour plots for the third-grade nanofluid flow are found to deviate significantly from those corresponding to Newtonian nanofluids. Validation of the numerical solutions with earlier studies is also included.

Passive Natural Convection Augmentation from Horizontal Cylinder Using a Novel Shroud–Chimney Configuration

A novel method to passively improve natural convection from a horizontal isothermal cylinder is proposed and numerically analyzed. The improvement is achieved by using a cylinder configured with semicircular shrouds and expended chimney. The numerical simulations indicate that adding the shroud–chimney configuration (SCC) to the cylinder promotes the convection heat transfer (up to 12%). New parameters describing the physics of the convection activities are introduced. The parameters are demonstrated to correlate well with the enhancement in the heat transfer coefficient when the SCC is used. Three correlations are proposed to optimize the design of SCC, and to evaluate the corresponding enhancement in the heat transfer. The proposed method is inexpensive, simple, and compact compared with other available configurations (e.g., using extended surfaces or confining long vertical walls). This makes the technology more practical for industrial applications.

MHD mixed convection and entropy generation in a lid-driven cavity with rotating cylinders filled by a nanofluid using two phase mixture model

Abstract In this study, mixed convection and entropy generation in a square cavity containing nanofluid subjected to magnetic field has been studied. A two-phase model (mixture) was used to simulate Newtonian fluid flow and heat transfer in a cavity with rotating cylinders. The Richardson and Hartman numbers ranges are 1 ≤ Ri ≤ 100 and 0 ≤ Ha ≤ 30 respectively. The laminar, two-dimensional (2D), steady and Newtonian flows are assumptions that are considered in this study. The angle of cavity (θ) and dimensionless angular velocity of cylinders (Ω) ranges are 0° ≤ θ ≤ 90° and −3 ≤ Ω ≤ −1 respectively. The effect of insulation and isothermal (T = Tc) cylinders on the flow field and heat transfer has been investigated. The distribution of nanoparticles inside the cavity for different Hartman numbers and Richardson numbers also is investigated. In addition, the effect of the presence of the cylinder on the cavity in stationary and rotating states on the flow field and the increase of the heat transfer rate has been studied. Average and local Nusselt number in terms of Hartman numbers, volume fractions, angles of cavity, isothermal (and adiabatic of cylinders) and angular velocity of cylinders were obtained. The effect of the magnetic field intensity on total entropy generation has been investigated. It’s found that by reducing Hartmann number, reducing Richardson number and increasing volume fraction, heat transfer will increase. The presence of the cylinder and its angular velocity also improve the heat transfer. In addition, isothermal cylinders will have a great effect on increasing heat transfer.

Non-Similar Comutational Solutions for Double-Diffusive MHD Transport Phenomena for Non-Newtnian Nanofluid From a Horizontal Circular Cylinder

Abstract This article aims to study theoretically the combined magneto hydrodynamic flows of casson viscoplastic nanofluid from a horizontal isothermal circular cylinder in non-Darcy porous medium. The impacts of Brownian motion and thermophoresis are consolidated and studied. The governing partial differential equations are converted into nonlinear ordinary differential equations using suitable non-similarity transformation and are solved numerically using Keller-Box finite difference technique. The numerical method is validated with previous published work and the results are found to be in excellent agreement. Numerical results for velocity, temperature, concentration along with skin friction coefficient, heat and mass transfer rate are discussed for various values of physical parameters. It is observed that velocity, heat and mass transfer rate are increased with increasing casson fluid parameter whereas temperature, concentration and skin friction are decreased. Velocity is reduced with increasing Forchheimer parameter whereas temperature and nano-particle concentration are both enhanced. An increase in magnetic parameter is seen to increase temperature and concentration whereas velocity, skin friction heat and mass transfer rate are decreased. The present model finds applications in electric-conductive nano-materials of potential use in aviation and different enterprises, energy systems and thermal enhancement of industrial flow processes.

Karakteristik aliran laminar melewati profil persegi berdasarkan komputasi dengan skema central difference dan hybrid difference

The characteristics of two computational schemes, central difference scheme and the hybrid difference scheme, which using identical computing parameters is investigated. The test case employed is isothermal rectangular cylinder laminar cooling to represent two dimensional incompressible transient flow. Simulation results on the first one shows a relatively higher temperature distribution with an energy diffusion contour pattern more intense. Whereas with hybrid difference, temperature are lower in average. Moreover, temperature contour is more stable. Simulation with hybrid difference indicates more converget results based on criterion of flow pattern and accuracy ratio.

Hybrid lattice Boltzmann/Taguchi optimization approach for magnetohydrodynamic nanofluid natural convection in a hemisphere cavity

In the present work, heat transfer optimization for natural convection with MHD flow in the hemisphere enclosure embedded with a vertical isothermal cylinder is investigated using Taguchi method. The simulations were planned based on Taguchi's L25 orthogonal array with each trial performed under different magnetic field, heat source aspect ratio and particle volume fraction of nanofluid. The thermal lattice Boltzmann based on D3Q19 methods was purposed to simulate the flow and thermal fields. Signal-to-noise ratios analyses were carried out in order to determine the effects of process parameters and optimal factor settings. The present results provide a good approximation for choosing effective parameters of designing the thermal system.

Mixed Convection of Hybrid Nanofluids in an Annulus

In this study, mixed convection in an annulus formed by two horizontal isothermal cylinder surfaces and filled with hybrid nanofluids was examined with Galerkin weighted residual finite element method. The outer cylinder is rotating and inner cylinder is stationary. Influence of Rayleigh number, angular rotational speed of the outer cylinder, eccentricity of the inner cylinder, solid volume fractions of different nanoparticles (alumina, copper, hybrid particles between 0 and 0.02) on the fluid flow and heat transfer characteristics were analyzed. It was observed that average heat transfer enhances with Rayleigh number, solid volume fractions of nanoparticles and eccentricity ratio and reduces as the angular rotational speed of the outer cylinder increases. Adding nanoparticles was found to be advantageous for lower values of Rayleigh number and higher values of angular rotational speed. At the highest volume fraction of Cu nanoparticles, average Nusselt number increases by 31.75 % when the inner cylinder center moves in +y direction. Nanofluid with hybrid nanoparticles gives heat transfer rates which are higher than that of with alumina and lower than that of with copper nanoparticles for the same volume fraction.

Numerical investigation of flow and combined natural-forced convection from an isothermal square cylinder in cross flow

Unsteady flow and heat transfer from a horizontal isothermal square cylinder is studied numerically using a three-dimensional computational model to investigate the influence of buoyancy on the forced flow and heat transfer characteristics. The numerical model is based on a horizontal square cylinder subjected to laminar fluid flow in an unconfined channel. The governing equations in 3D form are solved using a fractional step method based on the finite difference discretization in addition to a Crank–Nicholson scheme employed to the convective and the viscous terms. Two working fluids–air (Pr = 0.7) and water (Pr = 7)–are considered, and the flow and heat transfer simulations were carried out for the Reynolds and Richardson numbers in the intervals 55 ≤ Re ≤ 250 and 0 ≤ Ri ≤ 2, respectively. The flow characteristics such as time-averaged drag/lift, rms drag/rms lift coefficients as well as Strouhal number were computed. The heat transfer from the cylinder is assessed by mean Nusselt number (and rms Nusselt number) over the total heated cylinder walls. As the buoyancy increases, the mass and the velocity of the fluid flowing underneath the cylinder increases. The fluid is injected into the near wake region with an upward motion which significantly alters the flow field in the downstream as well as upstream regions. The effects of Reynolds, Richardson and Prandtl numbers on the flow field and temperature distributions are discussed in detail. It is shown that the flow and heat transfer characteristics are influenced more for air than water. To fill the void in the literature, useful empirical correlations of practical importance are derived for pure forced and pure natural as well as mixed convection. The mixed convection correlations, in terms of the ratio of pure forced convection, are also developed, and their implications are discussed.

Mixed convection heat transfer from a triangular cylinder subjected to upward cross flow

Unsteady laminar mixed (forced and free) convection heat transfer and fluid flow over long horizontal equilateral triangular cylinder subjected to upward cross flow are investigated numerically. The computation model is a two-dimensional unconfined rectangular domain with an aspect ratio of 1.4. A second order upwind scheme was used for differencing of the convection terms, and SIMPLE algorithm was adopted. The working fluids are air (Pr = 0.7) and water (Pr = 7). The equilateral isothermal triangular cylinder is placed in a uniform stream. The effect of buoyancy is incorporated into the Navier-Stokes (NS) equations using the Boussinesq approximation. This study is a case of “assisting flow” where the buoyancy-induced flow and fluid motions have the same upward direction. The basic dimensionless simulation variables, Reynolds and Richardson numbers, are varied in the range 10 ≤ Re ≤ 200 and 0 ≤ Ri ≤ 10. The flow characteristics such as the mean drag, mean rms lift coefficients and the Strouhal number are computed for each simulation. The flow patterns and isotherms are generated to interpret and understand the underlying physical mechanism. The cylinder surface mean Nusselt number was computed for mixed as well as for forced and free convection conditions. The computational data were used to develop the several Nusselt number correlations for forced, free and mixed convection flow.

A numerical study on the fluid flow and heat transfer from a horizontal circular cylinder under mixed convection

In this paper, mixed convection effects on the flow and heat transfer characteristics of a horizontal circular cylinder exposed to a laminar, incompressible, and vertical stream were numerically investigated. The vortex shedding elimination is one of the approaches for reducing the undesirable vibrations of bodies. In this regard, in the current study, using the buoyancy-aided flow, a situation was provided to eliminate the vortex shedding of the cylinder with the lowest possible drag coefficient. To reduce the thermal energy consumption and prevent the increase in the drag coefficient due to the buoyancy effect, a part of the cylinder surface was assumed to have a constant temperature, and the other part was insulated. The effect of the Grashof number and isothermal surface on the flow pattern, drag coefficient, and Nusselt number was studied at a constant Reynolds number of 200 and a Prandtl number of 0.71. To simulate the fluid flow and heat transfer numerically, the unsteady Navier-Stokes equations were solved using a finite-volume pressure–velocity coupling method with the second-order accuracy in time and space. In order to validate the present solver, some results were compared with numerical and experimental results and a good agreement was obtained. The results obtained from this study showed that for a fully isothermal cylinder, a critical value for the Grashof number existed. Consequently, for the larger values, the vortex shedding was stopped. Furthermore, by investigating the flow patterns around the cylinder, a new mode of periodic instability in a flow field was observed for a range of the Grashof numbers and isothermal surfaces. The flow in this new mode oscillated with the very low frequency. Finally, it was revealed that the use of a Grashof number of 2 × 104 and isothermal surface angle of 60° led to the elimination of the vortex shedding with lowest drag coefficient and energy consumption.