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Showing papers in "Numerical Heat Transfer Part A-applications in 2016"


Journal ArticleDOI
TL;DR: In this article, the effect of a variable spatial magnetic field on ferro-nanofluid flow and heat transfer in a double-sided lid-driven enclosure with a sinusoidal hot wall is investigated.
Abstract: In this work, the effect of a variable spatial magnetic field on ferro-nanofluid flow and heat transfer in a double-sided lid-driven enclosure with a sinusoidal hot wall is investigated. The working fluid is a mixture of iron oxide (Fe3O4) nanoparticles and water and is referred to as a ferro-nanofluid. The control volume-based finite element method (CVFEM) is used to solve the governing equations in the stream function–vorticity formulation. In deriving the governing equations for this investigation, the effect of both ferro-hydrodynamics and magneto-hydrodynamics is taken into account. The numerical calculations are performed for different governing parameters namely; the Reynolds number, nanoparticle volume fraction, magnetic number (arising from Ferrohydrodynamics (FHD) consideration), and the Hartmann number (arising from Magnetohydrodynamics (MHD) consideration). The results show that an enhancement in heat transfer has a direct relationship with the Reynolds number and the Hartmann number, ...

227 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the electric field on nanofluid viscosity is taken into account and the numerical results show that the voltage used can change the flow shape.
Abstract: Natural convection heat transfer of a nanofluid in the presence of an electric field is investigated. The control volume finite element method (CVFEM) is utilized to simulate this problem. A Fe3O4–ethylene glycol nanofluid is used as the working fluid. The effect of the electric field on nanofluid viscosity is taken into account. Numerical investigation is conducted for several values of Rayleigh number, nanoparticle volume fraction, and the voltage supplied. The numerical results show that the voltage used can change the flow shape. The Coulomb force causes the isotherms to become denser near the bottom wall. Heat transfer rises with increase in the voltage supplied and Rayleigh number. The effect of electric field on heat transfer is more pronounced at low Rayleigh numbers due to the predomination of the conduction mechanism.

181 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the natural convection in an annulus between two confocal elliptic cylinders filled with a Cu-Al2O3/water hybrid nanofluid.
Abstract: In the present paper, natural convection in an annulus between two confocal elliptic cylinders filled with a Cu-Al2O3/water hybrid nanofluid is investigated numerically. The inner cylinder is heated at a constant surface temperature while the outer wall is isothermally cooled. The basic equations are formulated in elliptic coordinates and developed in terms of the vorticity-stream function formulation using the dimensionless form for 2D, laminar and incompressible flow under steady-state condition. The governing equations are discretized using the finite volume method and solved by an in-house FORTRAN code. Numerical simulations are performed for various volume fractions of nanoparticles (0 ≤ ϕ ≤ 0.12) and Rayleigh numbers (103 ≤ Ra ≤ 3 × 105). The eccentricity of the inner and outer ellipses and the angle of orientation are fixed at e1 = 0.9, e2 = 0.6 and γ = 0° respectively. It is found that employing a Cu-Al2O3/water hybrid nanofluid is more efficient in heat transfer rate compared to the simil...

125 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of Rayleigh number (between 103 and 106), angular rotational speed of the cylinder (between 0 and 6,000), Darcy number, cylinder sizes (between R ǫ = 0.1 and Rǫ= 0.3), and three different vertical locations of the cylindrical shape on the fluid flow and heat transfer characteristics are numerically investigated.
Abstract: In this study, mixed convection in a cavity that has a fluid and superposed porous medium with an adiabatic rotating cylinder is numerically investigated. The bottom horizontal wall is heated and the top horizontal wall is cooled while the remaining walls are assumed to be adiabatic. An adiabatic rotating cylinder is inserted inside the cavity. The governing equations are solved by the Galerkin weighted residual finite element method. The effects of Rayleigh number (between 103 and 106), angular rotational speed of the cylinder (between 0 and 6,000), Darcy number (between 10−5 and 10−2), cylinder sizes (between R = 0.1 and R = 0.3) and three different vertical locations of the cylinder on the fluid flow and heat transfers characteristics are numerically investigated. It is observed that the cylinder size has a profound effect on the local and averaged heat transfer. The local and averaged heat transfers generally increase and the convection is more effective in the upper half of the cavity as the ...

71 citations


Journal ArticleDOI
TL;DR: A numerical simulation of magneto-hydrodynamic mixed convection flow and heat transfer of Cu-water nanofluid in a square cavity filled with a Darcian porous medium with a partial slip is numerically investigated in this paper.
Abstract: A numerical simulation of magneto-hydrodynamic mixed convection flow and heat transfer of Cu–water nanofluid in a square cavity filled with a Darcian porous medium with a partial slip is numerically investigated. The left and right walls of the cavity are moving up with a constant speed in vertical direction, and the partial slip effect is considered along these walls. The top and bottom walls of the cavity are assumed to be adiabatic. The right vertical wall of the cavity is assumed to be kept at a lower temperature, while the left vertical wall is kept at a higher temperature. The developed equations of the mathematical model are nondimensionalized and then solved numerically subject to appropriate boundary conditions by the finite-volume method. A parametric study is performed and a set of graphical results is presented and discussed to demonstrate interesting features of the solution.

64 citations


Journal ArticleDOI
TL;DR: In this paper, a water-cooled smooth micro-channel heat sink, a series of rectangular-shaped flow obstructions are designed into a heat sink and then the corresponding laminar flow and heat transfer have been analyzed numerically by computational fluid dynamics.
Abstract: It is recognized that cooling methods incorporating micro-channel heat sinks with high capacities of heat removal are necessary for cooling of electronic devices. In this paper, based on a water-cooled smooth micro-channel heat sink, a series of rectangular-shaped flow obstructions are designed into a heat sink, and then the corresponding laminar flow and heat transfer have been analyzed numerically by computational fluid dynamics. Five different configurations of the flow obstructions are considered by adjusting the length of the flow obstructions. The influence of the length of the flow obstructions on heat transfer, pressure drop, and thermal resistance is also observed and compared to that of the traditional smooth micro-channel heat sink without flow obstructions. The overall resistance versus inlet Reynolds number and pumping power are also compared for whole micro-channel heat sinks (including smooth micro-channel heat sink). The results show that the capacity of heat removal of micro-chann...

57 citations


Journal ArticleDOI
TL;DR: In this paper, an inclined thin local thermal non-equilibrium porous fin and saturated by a nanofluid was used for convection flow and heat transfer in an enclosure.
Abstract: There is growing interest in application of inclined fins to a cavity wall. As such, this paper focuses on the numerical investigation of laminar free convection flow and heat transfer in an enclosure with an inclined thin local thermal non-equilibrium porous fin and saturated by a nanofluid. The porous medium is assumed to be isotropic and homogenous, the cavity walls are assumed to be impermeable to the nanoparticles, and there is a no-slip boundary condition on the enclosure boundaries. The vertical walls are isothermal and the horizontal ones are adiabatic. Moreover, the influence of indispensable parameters regarding heat and mass transfer, such as Rayleigh number, Darcy number, Prandtl number, porosity, thermophoresis and Brownian parameters, fin length, fin position, and the fin angle on the average Nusselt number, are taken into account. Generally, it is found that the average Nusselt number is an increasing function of Ra, Pr, Da, and porosity (e). Furthermore, increasing either fin posit...

44 citations


Journal ArticleDOI
Wei Liu1, Mingang Jin1, Chun Chen1, Ruoyu You1, Qingyan Chen1 
TL;DR: In this article, the authors implemented fast fluid dynamics (FFD) in Open Field Operation and Manipulation and used a local searching method that made the FFD solver applicable to unstructured meshes.
Abstract: This study implemented fast fluid dynamics (FFD) in Open Field Operation and Manipulation and used a local searching method that made the FFD solver applicable to unstructured meshes. Because the split scheme used in FFD is not conservative, this investigation developed a combined scheme that used a split scheme for the continuity and momentum equations and an iterative scheme for scalar equations. The combined scheme ensures conservation of the scalars. This investigation used two two-dimensional cases and one three-dimensional case, with the experimental data, to test the FFD solver. The predicted results were similar with different types of mesh and numerical scheme and agreed in general with the experimental data.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of time t, Hartmann number Ha, wall amplitude a, and solid volume fraction ϕ on the fluid flow and heat transfer were studied in a symmetrical wavy trapezoidal enclosure with viscous and Joule dissipation effects.
Abstract: This article examines the unsteady magnetohydrodynamic free convection flows of Al2O3 (alumina)-water and single-walled carbon nanotube (SWCNT)-water nanofluids within a symmetrical wavy trapezoidal enclosure with viscous and Joule dissipation effects. The governing equations and the corresponding initial and boundary conditions are nondimensionalized and the resulting initial boundary value problem is solved using the mixed finite-element method with polynomial pressure projection stabilization. Streamline and isotherm plots are used to represent the numerical results for the velocity and temperature, respectively. The effects of time t, Hartmann number Ha, wall amplitude a, and solid volume fraction ϕ on the fluid flow and heat transfer are studied.

43 citations


Journal ArticleDOI
TL;DR: In this article, a finite volume-based three-dimensional numerical simulation on natural convection and entropy generation in a cubical cavity filled with a nanofluid of aluminum oxide-water is presented by vorticity-vector potential formalism.
Abstract: A finite volume-based three-dimensional numerical simulation on natural convection and entropy generation in a cubical cavity filled with a nanofluid of aluminum oxide–water is presented by vorticity–vector potential formalism. The blocks are adiabatic and the vertical walls are differentially heated unidirectionally. The variables considered are Ra, volumetric fraction of aluminum oxide particles, and block size. The results for fluid flow with a single-phase model are elucidated with iso-surfaces of temperature, Nusselt number, and Bejan number. The local entropy generated was due to friction surges when the volumetric fraction of nanoparticles was increased. The average Nusselt number rose with the increase in Ra and volumetric fraction of solid particles and declined with the increase in block size.

43 citations


Journal ArticleDOI
TL;DR: In this paper, heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 0.25, 1, and 4mm) at saturation temperatures Tsat = 310, 320, and 330 K are investigated numerically.
Abstract: Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 0.25, 1, and 4 mm) at saturation temperatures Tsat = 310, 320, and 330 K are investigated numerically. Liquid–vapor interfaces and stream traces are also presented to provide a better understanding of the effect of saturation temperature on the condensation process inside micro tubes. The results indicate that local heat transfer coefficients and pressure drop gradients increase with increasing mass flux and vapor quality and with decreasing tube diameter and saturation temperature. Liquid film thickness also increases with increasing saturation temperature because of the lower surface tension at a higher saturation temperature. When gravity dominates the condensation process, a vortex with its core lying at the bottom of the tube is found in the vapor phase region. For annular flow regime at dh = 0.25 mm, the vortex disappears, and stream traces point from the symmetry plan to the liquid–vapor ...

Journal ArticleDOI
TL;DR: In this paper, the influence of the contact angle on the flow field developed inside a nanofluid droplet consisting of a mixture of water and carbon nanotubes (CNT) is investigated.
Abstract: The heat transfer characteristics of liquid droplets are influenced by the hydrophobicity of the surfaces. Fluid properties and surface energy play important roles in heat transfer assessment. In the present study, the influence of the contact angle on the flow field developed inside a nanofluid droplet consisting of a mixture of water and carbon nanotubes (CNT) is investigated. Flow field and heat transfer characteristics are simulated numerically in line with the experimental conditions. It is found that the flow velocity predicted numerically is in good agreement with the experimental data. Nusselt and Bond numbers increase at large contact angles and Marangoni force dominates over buoyancy force.

Journal ArticleDOI
TL;DR: In this paper, the effects of the inclination angle on convection heat transfer and entropy generation characteristics in a two-dimensional square enclosure saturated with water were analyzed numerically and quantitatively.
Abstract: In this paper, we analyze numerically the effects of the inclination angle on natural convection heat transfer and entropy generation characteristics in a two-dimensional square enclosure saturated...

Journal ArticleDOI
TL;DR: In this paper, the numerical performance and accuracy of models when applied in the simulation of blade pin fin arrays are compared to the experimental data from the literature, including mean velocity components, Reynolds stress tensor components, and surface Nusselt number distributions.
Abstract: The current study focuses on numerical investigation of narrow passage flows with pin fin arrays. Six different turbulence models, including linear eddy viscosity models, an explicit algebraic Reynolds stress model, and a V2f model, are explored as they are utilized with k-e and k-ω platforms. The main objective of the work is to study numerical performance and accuracy of models when applied in the simulation of blade pin fin arrays. The main objective is comparison of the numerical accuracy of models, when applied for the simulation of complex flows within narrow passages. Numerical results obtained with the different models are compared to the experimental data from the literature. As such, comparisons are performed of different flow field quantities, including mean velocity components, Reynolds stress tensor components, and surface Nusselt number distributions.

Journal ArticleDOI
TL;DR: In this paper, the roles of Brownian motion of nanoparticles and induced micro-convection in base fluid in enhancing the thermal conductivity of nanofluids were investigated using molecular dynamic simulation.
Abstract: Nanofluids are suspensions of nanoparticles into convectional heat transfer fluid to enhance the thermal conductivity of its base fluid. The roles of Brownian motion of nanoparticles and induced micro-convection in base fluid in enhancing the thermal conductivity of nanofluids were investigated using molecular dynamic (MD) simulation. The roles were determined by studying the effect of particle size on thermal conductivity and diffusion coefficient. Results show that the Brownian motion and induced micro-convection have insignificant effects on enhancing the thermal conductivity. The hydrodynamic effect is restricted by an amorphous-like interfacial fluid structure in the vicinity of the nanoparticle due to its higher specific area.

Journal ArticleDOI
TL;DR: In this article, the authors compared the prediction of two types of Computational Fluid Dynamics (CFD) models to investigate the turbulent forced convection of the Cu-water nanofluid in a tube with a constant heat flux on the tube wall.
Abstract: This study compares the prediction of two types of Computational Fluid Dynamics (CFD) models to investigate the turbulent forced convection of the Cu-water nanofluid in a tube with a constant heat flux on the tube wall. One of the CFD models is based on a single-phase (or homogeneous) model and the other is the Eulerian–Eulerian (two-fluid) two-phase model. The Reynolds number is between 10,000 and 25,000, whereas the volume fraction of the Cu particles is in the range of 0–1.5%. The results from the CFD models are compared with the results from experimental investigations in the literature. Both the single-phase and two-phase models overpredict the Nusselt number in most of the cases investigated. Unexpectedly, the two-phase model was found to be relatively less accurate than the single-phase model. The present study suggests a correction of the two-phase model in terms of selecting an appropriate effective conductivity of the solidus phase and this has resulted in a significant improvement in th...

Journal ArticleDOI
Guodong Xia1, Y.T. Jia1, Y.F. Li1, D.D. Ma1, Bo Cai1 
TL;DR: In this paper, the optimal structure size of a microchannel heat sink with arc-shaped grooves and ribs according to the actual demand is analyzed by combining the multi-objective evolutionary algorithm (MOEA) with computational fluid dynamics (CFD).
Abstract: In order to obtain the optimal structure size of a microchannel heat sink (MCHS) with arc-shaped grooves and ribs according to the actual demand, multiple parameters that influence the performance of the microchannel are analyzed by combining the multi-objective evolutionary algorithm (MOEA) with computational fluid dynamics (CFD). The design variables include the relative groove height, relative rib height and relative rib width, and the two objective functions are to minimize the total thermal resistance and pumping power in constant volume flow rate. The influences of the design variables on the two objective functions are analyzed by CFD firstly. The results show that each design variable has a different impact on the two functions. The competitive relationship between the two objective functions is depicted in plots of the Pareto front obtained by MOEA. Pareto sensitivity analysis is carried out to find that the relative rib height has the most significant impact on the two objective functions.

Journal ArticleDOI
TL;DR: In this article, numerical simulations are conducted to investigate the effects of dimple positions on the endwall heat transfer and friction factor in a pin fin wedge duct, and it is found that the dimple position in line with the pin fin provides the best heat transfer enhancement, with low friction factor penalty.
Abstract: In this study, numerical simulations are conducted to investigate the effects of dimple positions on the endwall heat transfer and friction factor in a pin fin wedge duct. The dimple diameter is the same as the pin fin diameter, while the ratio between dimple depth and dimple diameter is 0.2. Three different dimple positions are investigated (i.e., directly upstream of the pin fins, in a staggered manner relative to the pin fins, or in line with the pin fins. The Reynolds number ranges from 10,000 to 50,000. Results for endwall Nusselt number, friction factor, and flow structure are included. For convenience of comparison, the pin fin wedge duct without dimples is studied as baseline. It is found that dimples can effectively enhance endwall heat transfer. Among the tested parameters, the dimple position in line with the pin fins provides the best heat transfer enhancement, with low friction factor penalty. However, the various dimple positions have distinct effects on the friction factor depending...

Journal ArticleDOI
TL;DR: In this article, the wall-adaptive features offered by two subgrid-scale (SGS) turbulence models: walladapting local eddy viscosity (WALE) and Vreman against the Smagorinsky model were investigated.
Abstract: Numerical assessment was performed to investigate the wall-adaptive features offered by two subgrid-scale (SGS) turbulence models: Wall-Adapting Local Eddy Viscosity (WALE) and Vreman against the Smagorinsky model. The gas temperature and velocity field predictions were enhanced using WALE over Smagorinsky, especially at the flaming and near-wall regions since WALE considers both strain and rotation rates of the turbulent structure and the turbulent viscosity approaches zero at the wall. Conversely, the simulation results by Vreman were under-predicted against the experimental data. The WALE model could notably enhance the simulation accuracy for large-scale compartment fires due to significant improvements of the flow diffusivity modeling.

Journal ArticleDOI
TL;DR: In this paper, the effects of magnetic field on flow and heat transfer during a two-dimensional convection melting of solid gallium in a rectangular cavity are investigated. And the results show that the magnetic field with an inclination angle has a significant impact on the flow transfer in the melting process.
Abstract: A numerical study is presented for two-dimensional convection melting of solid gallium in a rectangular cavity. The bottom wall of the cavity is uniformly heated and a uniform magnetic field is applied separately in both horizontal and vertical directions. The lattice Boltzmann (LB) method considering the magnetic field force is employed to solve the governing equations. The effects of magnetic field on flow and heat transfer during melting are presented and discussed at Rayleigh number Ra = 1 × 105 and Hartmann number Ha = 0, 15, and 30. The results show that the magnetic field with an inclination angle has a significant impact on the flow and heat transfer in the melting process. For a small Hartmann number, similar melting characteristics are observed for both horizontally applied and vertically applied magnetic fields. For a high value of Hartmann number, it is found that in the earlier stage of melting process, the flow retardation effect caused by the horizontally applied magnetic field is l...

Journal ArticleDOI
TL;DR: In this paper, a numerical analysis on flow configurations and heat transfer characteristics of turbulent forced convection in spirally corrugated tubes is presented, which shows that spiral corrugation tube induced vortex flows which helped to increase heat transfer due to enhanced fluid mixing.
Abstract: This paper presents a numerical analysis on flow configurations and heat transfer characteristics of turbulent forced convection in spirally corrugated tubes. The influences of corrugation depth (DR = 0.02–0.16), pitch ratio (PR = 0.10–1.00), and Reynolds number (Re = 5,000–20,000) on flow structure and heat transfer characteristics are described. Comparisons between the full length and periodic domains are also reported. The results show that spirally corrugated tubes induced vortex flows which helped to increase heat transfer due to enhanced fluid mixing. The maximum thermal enhancement factor of 1.16 was obtained by using the spirally corrugated tube with DR = 0.06, PR = 0.25 at Re = 5,000.

Journal ArticleDOI
TL;DR: In this paper, the effect of the moving wall's direction on mixed convective flow and heat transfer in an inclined lid-driven square cavity was investigated, and the results were presented graphically in the form of streamlines, isotherms, velocity profiles, and Nusselt numbers.
Abstract: The aim of the present study is to investigate the effect of the moving wall’s direction on mixed convective flow and heat transfer in an inclined lid-driven square cavity. Sinusoidal heating is applied on the left wall while the right wall is cooled at a constant temperature. The bottom and top walls are taken to be adiabatic. The results are presented graphically in the form of streamlines, isotherms, velocity profiles, and Nusselt numbers to understand the influence of the different directions of the moving wall, Richardson number, and cavity inclination. It is observed that the flow field and temperature distribution in the cavity are affected by the moving wall’s direction. It is also observed that the heat transfer is more pronounced at low Richardson number when the wall is moving to the left.

Journal ArticleDOI
TL;DR: In this paper, a Nusselt number correlation able to describe the convective heat-transfer characteristics of supercritical flow exhibiting deterioration and with negligible buoyancy effects is obtained using data from numerical simulations.
Abstract: Methane heat-transfer deterioration can occur in the regenerative cooling channels of future liquid-oxygen/liquid-methane rocket engines with chamber pressures higher than about 50 bar. Aiming to improve the prediction capabilities for the design of such systems, in the present study, a Nusselt number correlation able to describe the convective heat-transfer characteristics of supercritical flow exhibiting deterioration and with negligible buoyancy effects is obtained using data from numerical simulations. The adopted numerical solver of the Navier–Stokes equations is first validated against the experimental data of near-critical hydrogen in heated tubes and then used to collect heat-transfer data of supercritical methane in a heated tube for different levels of pressure, temperature, and mass flux.

Journal ArticleDOI
TL;DR: In this paper, numerical analysis of the pool boiling heat transfer on isothermal elliptical tubes with different aspect ratios at saturated condition is presented, and the departure time of the first bubble, its time-dependent and averaged velocities, and heat fluxes are obtained.
Abstract: In this paper, numerical analysis of the pool boiling heat transfer on isothermal elliptical tubes with different aspect ratios at saturated condition is presented. Bubbles’ tip velocities and positions, interfacial topological changes as well as convection heat fluxes of five different cases are presented for wide ranges of wall temperatures. Both time-averaged and dynamic behaviors of flow physics and heat transfer are investigated. The departure time of the first bubble, its time-dependent and averaged velocities, and heat fluxes are obtained. Finally, a novel correlation is presented for the Nusselt number that accounts for the elliptical tubes’ diameter and aspect ratio.

Journal ArticleDOI
TL;DR: In this article, a fully transient model of the direct-chill casting process is used to predict the macrosegregation development of aluminum alloy 7050, and the predicted radial composition distributions are fit to Weibull probability density functions at each axial location.
Abstract: A fully transient model of the direct-chill casting process is used to predict the macrosegregation development of aluminum alloy 7050. The ingot diameter, casting speed, superheat, secondary cooling, and thickness of pure Al at startup are varied. Predicted radial composition distributions are fit to Weibull probability density functions at each axial location, and the normalized standard deviation describes the macrosegregation level and the time when the process reaches steady state. The sump depth, steady-state height, and macrosegregation level were most affected by changes in casting speed and ingot diameter. The pure Al dilutes the alloy and delays compositional steady state.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the evolution of turbulent rectangular submerged free jets with a two-dimensional approach by using the large eddy simulations (LES) at several Reynolds numbers.
Abstract: The evolution of turbulent rectangular submerged free jets has been investigated numerically with a two-dimensional (2D) approach by the present authors and, by using the large eddy simulations (LES) at several Reynolds numbers. The average numerical results confirmed the presence of the undisturbed region of flow (URF) located between the slot exit and the beginning of the potential core region (PCR) previously observed experimentally at the University of Rome “Tor Vergata” by Gori and coworkers. The 2D study of the present authors carried out under the conditions previously investigated in the literature, showed that the URF has a self-similar behavior, and proposed a new law for the evolution of the momentum. The present paper extends the LES to three-dimensional (3D) rectangular submerged free jets, in the range from Re = 5,000 to Re = 40,000, showing that the self-similar behavior of URF is also present in the 3D numerical simulations, as well as in the PCR and in the fully developed region (...

Journal ArticleDOI
TL;DR: In this paper, a modified Monte Carlo (MMC) method coupled with the time shift and superposition (TSS) principle is proposed to solve the transient radiative transfer (TRT) in a two-dimensional scattering medium with graded refractive index distribution.
Abstract: Transient radiative transfer (TRT) in a two-dimensional scattering medium with graded refractive index distribution subjected to a collimated short-pulse irradiation is solved by a modified Monte Carlo (MMC) method coupled with the time shift and superposition (TSS) principle. The boundaries are considered as Fresnel surfaces, the refractive index at the boundary mismatches with that of the surroundings, making the reflectivity at the boundary change with the incident directions. The incident pulse consists of two parts when it hits the boundary: bundles directly reflected by the outside boundary and bundles refracted into the medium. The accuracy of the present algorithm is confirmed first. Numerical results show that by using the TSS principle, the computational efficiency is greatly improved. Afterward, the TRT in the media with different graded refractive index distributions is investigated. The time-resolved reflectance and transmittance at different locations are given. Several trends on the...

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the efficiency of nanofluids (ratio of thermal conductivity and viscosity enhancement) with the effects of particle size and temperature using molecular dynamic (MD) simulation.
Abstract: Nanofluids are conventional heat transfer fluids with suspended nanoparticles to enhance their thermal conductivity. However, enhancement of thermal conductivity is coupled with increased viscosity. This study investigates the efficiency of nanofluids (ratio of thermal conductivity and viscosity enhancement) with the effects of particle size and temperature using molecular dynamic (MD) simulation. The efficiency of nanofluids is improved by increasing particle size and temperature. The thermal conductivity enhancement increases with increasing particle size, but is independent of temperature; the viscosity enhancement decreases with increasing particle size and temperature. Particle size variation is therefore shown to be more effective than temperature control.

Journal ArticleDOI
TL;DR: A continuous thermal model of the human body based on the finite-element technique is described and implemented, for the first time, in the context of a patient-warming situation during or following a medical operation.
Abstract: Numerical simulation methods have been applied to calculations of heat transfer within living tissue. Traditionally, those methods have been node-based when applied to a whole-body analysis. With the increased capacity of modern computational hardware and software, it is now possible to routinely solve a continuous thermal model of the human body based on the finite-element technique. Such a continuous thermal model is, for the first time, described and implemented. The model specifies material properties for the various body regions (head, torso, arms, hands, legs, feet) based on the tissue types and distribution found in those zones. Important thermal processes such as metabolism, blood perfusion, and respiration are also included. The computational scheme also allows for the implementation of sweating, shivering, vasoconstriction/vasodilation, and changes to the thermal environment. The model is solved in the context of a patient-warming situation during or following a medical operation. In the...

Journal ArticleDOI
TL;DR: In this paper, the effects of the ratio of jet spacing to swirl chamber radius and Reynolds numbers on swirl cooling performance were investigated with numerical simulation and a Nusselt number correlation on these parameters was suggested.
Abstract: In this paper, flow and heat transfer of a swirl chamber that models an internal cooling passage for a gas turbine airfoil leading edge is studied with numerical simulation. The geometry consists of a circular pipe, and rectangular section inlets that lead inlet flow to impinge tangentially on the circular pipe. The effects of the ratio of jet spacing to swirl chamber radius and Reynolds numbers on swirl cooling performance are investigated. The results indicate how the pressure loss and globally averaged Nusselt number on the swirl chamber wall increase with increases of Reynolds number and the ratio of jet spacing to swirl chamber radius. A Nusselt number correlation on these parameters is suggested. Also shown is how Nusselt numbers on the swirl chamber surface increase with the ratio of jet spacing to swirl chamber radius.