Heat Transfer Of Al2O3-water Nanofluid Research Articles

Investigation on magnetic force and buoyancy force on flow and heat transfer of Al2O3-water nanofluid at various temperature-dependent thermophysical models by a novel PLBM

A novel preconditioned lattice Boltzmann method (PLBM) is applied to investigate the thermo-hydrodynamic characteristics of Al2O3-water nanofluid with various temperature-dependent thermophysical properties and slip boundary conditions in a microchannel. Also, the effects of a magnetic field force, buoyancy force, and volume fraction of nanoparticles are analyzed, respectively. The theoretical level confirms that the convergence performance of the PLBM is greatly improved at large Reynolds numbers compared to the original LBM. Numerical results show that the Koo & Kleinstreuer model has the largest average shear stress and average Nusselt number. Among all the physical models considered, these two values are approximately 1.05 times and 1.2 times of the values by the Maxwell & Brinkmann model, respectively. Once the magnetic field is considered, the average shear stress is increased twice and the average Nusselt number increases by about 10% and further by about 20% at higher buoyancy forces. The growth of these two values gradually slows down when the volume fraction of nanoparticles exceeds 2%. The heat transfer process makes the largest contribution to entropy generation when the magnetic field force is not considered. Accordingly, it will dominate the irreversible loss due to the strong shear stress once the magnetic field force is involved in the heat transfer process.

Research on the characteristics of fluid flow and heat transfer of Al2O3-water nanofluid in an L-shaped chaotic channel

PurposeThis paper aims to investigate the effects of different volume fractions of Al2O3-water nanofluid on flow and heat transfer under chaotic convection conditions in an L-shaped channel, comparing the difference of numerical simulation results between single-phase and Eulerian–Lagrangian models.Design/methodology/approachThe correctness and accuracy of the two calculation models were verified by comparing with the experimental values in literature. An experimental model of the L-shaped channel was processed, and the laser Doppler velocimeter was used to measure the velocities of special positions in the channel. The simulated values were compared with the experimental results, and the correctness and accuracy of the simulation method were verified.FindingsThe calculated results using the two models are basically consistent. Under the condition of Reynolds number is 500, when the volume fractions of nanofluid range from 1% to 4%, the heat transfer coefficients simulated by single-phase model are 1.49%–25.80% higher than that of pure water, and simulated by Eulerian–Lagrangian model are 3.19%–27.48% higher than that of pure water. Meanwhile, the friction coefficients are barely affected. Besides, there are obvious secondary flow caused by lateral oscillations on the cross sections, and the appearance of secondary flow makes the temperature distributions uniform on the cross section and takes more heat away, thus the heat transfer performance is enhanced.Originality/valueThe originality of this work is to reveal the differences between single-phase and two-phase numerical simulations under different flow states. The combination of chaotic convection and nanofluid indicates the direction for further improving the heat transfer threshold.

Two-phase modeling of low-Reynolds turbulent heat convection of Al2O3-water nanofluid in a 2-D helically corrugated channel

Low-Re-number turbulent flow and convective heat transfer of Al2O3-water nanofluid inside a helically corrugated channel (HCC) were examined numerically. The helically corrugated channel (HCC) was studied for the first time by analogy to a helically corrugated tube. The Reynolds number (based on the nanofluid properties) varies between 5000 and 10000. The nanoparticles volume fraction ranges from 0.1% to 5%. Also, the nanoparticle sizes of 20 nm, 40 nm, and 60 nm were considered. The two-phase mixture model was utilized in the simulations. The numerical results were compared with the experimental data. It was illustrated that a previously established correlation for the effective viscosity could be erroneous in certain circumstances. Hence, that model was amended carefully, and a correlation for nanoparticles with the mean diameter of 20 nm was presented. It was argued that the 20 nm nanoparticles slightly decrease the thickness of the velocity boundary layer. Besides, it was shown that there is a critical particle size above that the heat transfer decreases. Based on the present study, the recirculation region in the corrugation cavity has a significant impact on the turbulent mixing for Re ≥ 10000. Among the tested cases, the maximum ratio of Nusselt number was 1.413 for the particle size of 20 nm and the volume fraction of 5%, while the corresponding pressure drop ratio was 7.122.

Numerical analysis for thermal\u2013hydraulic characteristics and the laminar two-phase nanofluid flow inside a tube equipped with helically twisted tapes as swirl and turbulence promoters

In this study, the numerical simulation of heat transfer of Al2O3-water nanofluid in a pipe equipped with helically twisted tapes is investigated. The volume fraction of nanoparticles in this study is equal to 0, 1, 2, and 3%, and a two-phase mixture method has been used to simulate the nanofluids. The flow regime is laminar in the present study, and Reynolds numbers are Re = 250, 500, 750, and 1000. The helical twisted tapes are in three different types, single, double, and triple. The same heat flux 5000Wm-2 is applied to the walls. The simulation results showed that increasing the Re increases the Nusselt number and decreasing the friction factor. Nusselt number in case 1 and volume fraction of nanoparticles 0% for Re = 250, 500, 750 and 1000 are equal to 95.8, 57.11, 56.13 and 22.15, respectively. The average friction factor is equal to 0.18, 0.09, 0.07, and 0.05. The presence of helical twisted tapes increases the {text{Nu}}_{ave}. The friction factor due to secondary flows and increases the contact of the fluid and the solid surface, so that the Nusselt number in volume fraction of nanoparticles 0%, Re = 250 for case 1, case 2, case 3, and case 4 are 95.8, 46.10, 58.11, and 51.12, respectively, and the friction factor are 18.0, 29.0, 0.38 and 0.48, respectively.

Numerical Study of Turbulent Flows and Convective Heat Transfer of Al2O3-Water Nanofluids In A Circular Tube

The convective heat transfer of Al2O3-water nanofluids through a circular tube with a constant heat flux boundary condition is studied numerically. Turbulent flow conditions are considered with a Reynolds number ranging from 3500 to 20000. The numerical method used is based on the single-phase model. Four volume concentrations of Al2O3-water nanoparticles (0.1, 0.5, 1, and 2%) are used with a diameter of nanoparticle of 40 nm. A considerable increase in Nusselt number, axial velocity, and turbulent kinetic energy was found with increasing Reynolds number and volume fractions. However, the pressure losses were also increased with the raise of Re and nanoparticles concentration.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

Abstract A mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of Ri = 1.0 \mathrm{Ri}=1.0 , the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

Numerical study on convective heat transfer of nanofluid in a minichannel heat sink with micro-encapsulated PCM-cooled ceiling

In this work, the convective heat transfer of Al2O3-water nanofluid in a three-dimensional minichannel heat sink is exaimed numerically. The finite volume method (FOV) is applied to discrete the governing equations, and the LINE SOR and TDMA algorithms are used for solving the equations. The FORTRAN program has been developed for the numerical calculation. Ceiling of the minichannel is covered with the micro-encapsulated phase change material. The N-eicosane with the melting temperature of 34.7 °C and the latent heat of 24,300 J/kg is considered as the phase change material. The purpose of placing this material on the ceiling of the minichannel is to cool the working fluid by absorbing the heat from the fluid during melting. All simulations are performed for three values of solid volume fractions of nanoparticles including 0%, 2%, and 10%, two outer surface temperatures of ceiling including 28 °C and 30 °C, and the Reynolds number in the range of 500–2000. The effects of different parameters including the usage of the phase change material, the solid volume fractions of nanoparticles, the outer surface temperature of ceiling, and the Reynolds number on the thermal field, heat flux, melting rate of micro-encapsulated phase change material, and thermal resistance in the mini-channel heat sink are studied. The results reveal that the thermal resistance decreases about 10.88% by using the nanoparticles with solid volume fraction of 10% at Rebf = 500 and Tcw,0 = 28 °C for the case of bare celling. The heat flux received by the ceiling in heating section decreases by using the micro-encapsulated phase change material(MEPCM). In addition, the MEPCM melts faster at lower values of the Reynolds number.

Effect of Phase Shift on Mixed Convection in a Rectangular Vented Cavity filled with a Nanofluid and Submitted to Periodic Heating

The characteristic of flow and heat transfer of Al2O3-water nanofluids flowing through a horizontal ventilated cavity is investigated numerically. The bottom wall is subjected to a sinusoidal hot temperature profile, whereas the other boundaries are assumed to be thermally insulated. In fact, the flow comes forcedly into the system from the bottom of the left vertical wall and leaves it from the top of the right one by suction. The simulations focus on the effects of different key parameters, such as Reynolds number (200 ≤ Re ≤ 5000), nanoparticle’s concentration (0 ≤ ϕ ≤ 0.05) and phase deviation of the sinusoidal heating (γ equal 0 or π), on the flow and thermal patterns and heat transfer performances. The obtained results show that the presence of nanoparticles increases the heat transfer and the mean temperature within the cavity. In addition, the phase shift of the heating temperature may lead to periodic solutions for weaker values of Re and contributes to an increase or a decrease of heat transfer depending on the value of ϕ and the convection regime.

Effects of two-phase nanofluid model and localized heat source/sink on natural convection in a square cavity with a solid circular cylinder

In the present study, natural convection heat transfer of Al2O3-water nanofluid inside a square cavity with a solid circular cylinder is investigated numerically. For numerical computations, the finite element method is used by taking into consideration Buongiorno’s two-phase model. Parts of the vertical surfaces of cavity are kept at constant temperature (left wall Th and right wall Tc) while the other walls (horizontal walls and the remaining of the vertical walls) are taken as adiabatic. The effects of some pertinent parameters such as the Rayleigh number (103≤Ra≤106), nanoparticle volume fraction (0≤ϕ≤0.04), thermal conductivity of the solid cylinder (kw=0.28, 0.76, 1.95, 7 and 16), radius of solid cylinder (0.1≤R≤0.4), heat source/sink length (0.2≤D≤0.8), and the heat source/sink position (0.2≤B≤0.8) on the fluid flow and heat transfer characteristics are investigated. The obtained numerical results are depicted graphically and discussed in detail from the point of view of the streamlines, isotherms, nanoparticle volume fractions and the local and average Nusselt number Nu. It is indicated that the heat transfer is enhanced with an increase in the nanoparticle volume fraction for all studied Rayleigh numbers. Furthermore, the thermal conductivity, solid circular cylinder size, D and B parameters are the key factors to control and optimize the heat transfer inside the cavity that is partially heated and cooled. The proposed method is found to be in good agreement between previously published experimental and numerical results.

Analysis of fully developed flow and heat transfer through n-sided polygonal ducts with round corners using the Galerkin weighted residual method

The Galerkin weighted residuals method is extended solve the laminar, fully developed flow and heat transfer of Al2O3-water nanofluid inside polygonal ducts with round corners for the constant heat flux and uniform wall temperature boundary conditions. Using the method, semi-analytical, closed-form solutions are obtained for the friction coefficient and the Nusselt number in terms of the radius of the round corners for the triangular, rectangular, hexagonal, and octagonal ducts. The effects of varying the radius of the round corners and the volume fraction of the nanoparticles on the friction coefficient and the Nusselt number are analyzed. The results show that the friction factor and the average Nusselt number increase with increasing the radius of the round corners. The study indicates that the Galerkin weighted residuals method is an accurate and efficient technique to obtain closed-form solutions for the flow and temperature fields in ducts with complex cross sectional shapes.

Investigation of nanofluid entropy generation in a heat exchanger with helical twisted tapes

In this research, entropy generation and forced convection heat transfer of Al2O3-water nanofluid in a heat exchanger equipped with helical twisted tape is investigated via Finite volume method. Influences of height ratio (BR), pitch ratio(PR) and Reynolds number (Re) on nanofluid entropy generation are reported. Suitable formula for entropy generation is provided. Results reveal that thermal entropy generation decreases with rise of BR and Re. Frictional entropy generation augments with rise of height ratio.

Numerical approach of Al2O3-water nanofluid in photovoltaic cooling system using mixture multiphase model

This article aims to numerically analyze the cooling system of photovoltaic device using mixture multiphase model. Aluminum oxide (Al2O3)-water nanofluids at various concentration of 0, 0.5, 1 and 2 vol.% were used as cooling fluid for photovoltaic module. The constant and uniform heat flux of 800 W/m2 was applied on photovoltaic (PV) module and the various cooling fluids flowed under PV module at Reynold number of 200 and 500. The temperature distribution and local heat transfer coefficient of cooling fluid were observed. The results show that increasing concentration of Al2O3 nanoparticle enhances the local heat transfer coefficient and decreases the temperature of PV cell. The significant enhancement of convection heat transfer of Al2O3-water nanofluid occur at entrance region. The operating temperature of PV cell can be decreased till 303 K for 2 vol.% Al2O3-water nanofluid at Reynold number of 500.

MHD slip flow and heat transfer of Al2O3-water nanofluid over a horizontal shrinking cylinder using Buongiorno’s model: Effect of nanolayer and nanoparticle diameter

This paper considers the study of electrically conducting alumina-water nanofluid flow induced by horizontal shrinking cylinder under the effect of velocity and thermal slip at the surface. The Buongiorno’s non-homogenous model is implemented which accounted with the nanolayer based effective thermal conductivity and Nielsen’s effective viscosity model. The governing transport model for nanofluid has been transformed into a set of nonlinear similarity equations and solved with a shooting technique using MATLAB ode solver and ‘fsolve’ command. The behavior of skin friction, velocity, Nusselt number and temperature are investigated numerically. The increasing trends of Nusselt number as well as skin friction are noticed as nanoparticle concentration increases at the outer surface of the boundary layer. Nusselt number is found to be decreasing nonlinearly with nanoparticle diameter ranging from 5nm to 60nm. Two branches of solution are also captured in some fixed range of involving parameter, namely mass transfer (suction), curvature and shrinking parameters. The physical existence of these branches is also discussed.

The effects of nanoparticle aggregation on the convection heat transfer investigated by a combined NDDM and DPM method

ABSTRACTIn this study, convective heat transfer of Al2O3-water nanofluids (NFs) of various concentrations under laminar flow in a horizontal circular tube with and without considering particle aggregation was numerically investigated by a combined nanoparticle diameter distribution model (NDDM) with the Discrete Phase Model (DPM). Heat transfer coefficient (h), temperature distribution in axial and radial direction, and pressure drop (ΔP) were studied. It turns out that beside a slight pressure drop, heat transfer near the wall will significantly deteriorate when particle aggregation occurs. With an increase in Re numbers, the effects of particle aggregation on the heat transfer performance of the fluid will decrease.

Thermally developing flow of Al2O3-water nanofluid through regular N-sided polygonal ducts: A semi-analytic weighted residuals approach

A semi-analytical approach is proposed to solve the hydrodynamically fully developed and thermally developing flow and heat transfer of Al2O3-water nanofluid through N-sided polygonal ducts. Using the Galerkin weighted residuals method, closed-form solutions for the flow and temperature fields in various polygonal ducts for the constant wall temperature and uniform wall heat flux boundary conditions are obtained. Variations of the Nusselt number along the axial direction for different duct geometries and different volume fraction of the nanoparticles are presented. Comparisons of the results for special cases with the existing results from the literature indicate that the employed method is quite accurate. The results show that the heat transfer enhances with increasing the nanoparticles volume fraction.

Numerical Computations on Laminar Flow Forced Convective Heat Transfer of Al2O3-Water Nanofluids in a Tube

Numerical Computations on Laminar Flow Forced Convective Heat Transfer of Al2O3-Water Nanofluids in a Tube

On the reliable estimation of heat transfer coefficients for nanofluids in a microchannel

Nanofluids (base fluid and nanoparticles) can enhance the heat transfer coefficient h in comparison to the base fluid. This open the door for the design of efficient cooling system for microelectronics component for instance. Since theoretical Nusselt number correlations for microchannels are not available, the direct method using an energy balance has to be applied to determine h. However, for low nanoparticle concentrations the absolute numbers are small and hard to measure. Therefore, the study examines the laminar convective heat transfer of Al2O3-water nanofluids in a square microchannel with a cross section of 0.5 × 0.5 mm2 and a length of 30 mm under constant wall temperature. The Al2O3 nanoparticles have a diameter size distribution of 30-60 nm. A sensitivity analysis with error propagation was done to reduce the error for a reliable heat transfer coefficient estimation. An enhancement of heat transfer coefficient with increasing nanoparticles volume concentration was confirmed. A maximum enhancement of 6.9% and 21% were realized for 0.6% Al2O3-water and 1% Al2O3-water nanofluids.

Simulation of Flow and Heat Transfer of Nanofluid in an Eccentric Annulus with Multicomponent Lattice Boltzmann Method

In the present study, Lattice Boltzmann method is employed to investigate a two dimensional mixed convection heat transfer of Al2O3-water nanofluid in a horizontal annulus between a cold outer cylinder and the hot, rotating inner cylinder. To do so, the double lattice Boltzmann equation is utilized for the base fluid and the nanoparticles to describe the dynamic as well as the thermal behavior of nanofluid. Moreover, different forces such as Brownian, drag and gravity acting on the nanoparticles are taken into consideration. Calculations have been performed for Rayleigh number ranging from 103 to 2×104, Reynolds number from 5 to 120, vertical and horizontal eccentricity from -0.75 to 0.75 with volume fraction of nanoparticles from 0 to 0.1. The current computational results reveal that by adding nanoparticles, the mean Nusselt number for Ra 104, it decreases. Also, with Re>80, the mean Nusselt number increases with increasing Reynolds number; although for low Reynolds number this rising trend is not observed. Besides, when the inner cylinder moves vertically upward from the center, the addition of nanoparticles increases Nusselt number relative to the base fluid.

Model and comparative study for rotating flow of nanofluids due to convectively heated exponentially stretching sheet

In this work we address the rotating flow of nanofluids induced by an exponentially stretching sheet. Five different types of nanoparticles namely Silver-Ag, Copper-Cu, Copper oxide-CuO, Titanium oxide-TiO2 and Aluminum oxide-Al2O3 are considered. Convective boundary conditions are implemented to inspect the thermal boundary layer. The arising differential system is treated through a numerical approach. Analysis is based on two different models for effective thermal conductivity of nanofluids. The results reveal that the effects of parameters appear to be qualitatively similar in both the considered models. We found that thermal boundary layer thickness increases and heat transfer rate decreases upon increasing the angular velocity of the rotating fluid. The results indicate that convective heat transfer of Al2O3-water nanofluid is superior to the other used nanoparticles.

Benchmark results for natural and mixed convection heat transfer in a cavity

Purpose – The purpose of this paper is to numerically investigate steady, laminar natural and mixed convection heat transfer in a two-dimensional cavity by using a finite volume method with a fourth-order approximation of convective terms, with and without the presence of nanoparticles. Highly accurate benchmark results are also provided. Design/methodology/approach – A finite volume method on a non-uniform staggered grid is used for the solution of two-dimensional momentum and energy conservation equations. Diffusion terms, in the momentum and energy equations, are approximated using second-order central differences, whereas a non-uniform four-point fourth-order interpolation (FPFOI) scheme is developed for the convective terms. Coupled mass and momentum conservation equations are solved iteratively using a semi-implicit method for pressure-linked equation method. Findings – For the case of natural convection problem at high-Rayleigh numbers, grid density must be sufficiently high in order to obtain grid-independent results and capture reality of the physics. Heat transfer enhancement for natural convection is observed up to a certain value of the nanoparticle volume fraction. After that value, heat transfer deterioration is found with increasing nanoparticle volume fraction. Originality/value – Developed a non-uniform FPFOI scheme. Highly accurate benchmark results for the heat transfer of Al2O3-water nanofluid in a cavity are provided.