Alumina-water Nanofluid Research Articles

Heatline visualization of natural convection in a thick walled open cavity filled with a nanofluid

Natural convection of an alumina-water nanofluid in a partially open rectangular cavity with a left heat-conducting solid wall of finite thickness and conductivity has been studied numerically. Governing equations formulated in dimensionless stream function and vorticity variables on the basis of a single-phase nanofluid model with corresponding boundary conditions have been solved by finite difference method. Analysis of the influence of Rayleigh number (Ra=103–106), thermal conductivity ratio (1⩽K⩽20), solid wall thickness (0.1⩽δ⩽0.3) and nanoparticles volume fraction (0⩽ϕ⩽0.05) on streamlines, heatlines and isotherms as well as average Nusselt number at solid-fluid interface and fluid flow rate has been carried out. It has been revealed that for the considered models for an effective thermal conductivity ratio and dynamic viscosity an increase in the nanoparticles volume fraction leads to the heat transfer reduction and decrease of the fluid flow rate.

Analytical Technique for Estimating the Termophysical Properties of Hybrid Nanofluids

Over the past years, the development of functional heat transfer fluids by compounding different substances or different phases of matter (solid, liquid, or gas) has raised increasing interest in view of their potential applications in technologies. In particular, the nanofluids in which the solid particles (<100 nm or smaller) are incorporated as the dispersed phase in the suspensions, are currently focus of great attention because of their perspective potentials as high-performance heat transfer fluids. The potential advantage of utilizing the nanofluid lies mainly in its drastic increase in the thermal conductivity. This paper presents a study of the thermophysical characteristics of some nanofluids and their hybrids. General correlations for the effective thermal conductivity and viscosity of nanofluids are used for this analysis. Regarding the importance of thermophysical properties of water based drilling fluids, the effects of insertion of two oxides in an alumina-water nanofluid on the thermal conductivity, viscosity and density of distilled water were investigated. According to the results, viscosity and density of the nanofluids increased with the concentration. At high concentrations, the least increase in the viscosity of distilled water by adding the nanomaterials is related to H2 (8.2% increase at 1.0 wt.%). As the results show, increase in the density of distilled water by adding the nanomaterials is insignificant, that in the worst case it did not exceed 0.9%. The least increase in the density of base fluid at high concentrations was for H1.

Thermal and hydrodynamic characteristics of water-based suspensions of Al2O3 nanoparticles in a novel minichannel heat sink

Abstract In this study, the effect of using nanofluids on heat transfer and fluid flow characteristics in triangular shaped minichannel heat sink is numerically investigated. The minichannel heat sink performance using alumina-water (Al2O3-H2O) nanofluid as a coolant with different volume fractions is examined. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using finite volume method (FVM). The heat sink performance is evaluated in terms of Nusselt number, friction factor, thermal resistance and pumping power. The results indicate that, using of nanofluid instead of pure fluid as a coolant leads to enhanced heat transfer performance by increasing the amount of heat dissipated. Also, the results reveal that when the volume fraction of nanoparticles is increased under the extreme heat flux, both the heat transfer coefficient and friction factor are increased while the thermal resistance of the heat sink is decreased. Furthermore, only a slight increase in the pressure drop across the minichannel heat sink is found compared with the pure water-cooled heat sink.

Effect of variable thermal conductivity models on the combined convection heat transfer in a square enclosure filled with a water–alumina nanofluid

In this numerical study, the effects of variable thermal conductivity models on the combined convection heat transfer in a two-dimensional lid-driven square enclosure are investigated. The fluid in the square enclosure is a water-based nanofluid containing alumina nanoparticles. The top and bottom horizontal walls are insulated, while the vertical walls are kept at different constant temperatures. Five different thermal conductivity models are used to evaluate the effects of various parameters, such as the nanofluid bulk temperature, nanoparticle size, nanoparticle volume fraction, Brownian motion, interfacial layer thickness, etc. The governing stream–vorticity equations are solved by using a second-order central finite difference scheme coupled with the conservation of mass and energy. It is found that higher heat transfer is predicted when the effects of the nanoparticle size and bulk temperature of the nanofluid are taken into account.

Effect of Variable Thermal Conductivity Models on the Combined Convection Heat Transfer in a Square Enclosure Filled with a Water-Alumina Nanofluid

Effect of Variable Thermal Conductivity Models on the Combined Convection Heat Transfer in a Square Enclosure Filled with a Water-Alumina Nanofluid

Nanofluids as the circuit fluids of the geothermal borehole heat exchangers

Application of the CuO water and Al2O3 water nanofluids as the working fluids of a geothermal borehole heat exchanger is investigated using numerical simulation. For this purpose, the Reynolds Averaged Navier-Stokes (RANS) equations with SST k-ω turbulence model are numerically solved to model the flow. Physical properties of the nanofluids are obtained using the available correlations. To show the validity of the simulations, the results for pure water are compared with available data in the literature. Results show that there is a specific diameter ratio at which the total water flow pressure loss in the heat exchanger is minimum. The results also show that the CuO-water nanofluid gives higher extracted heat than the alumina-water nanofluid but at the penalty of higher pressure losses and pumping powers.

Thermally “<italic>Smart</italic>” Characteristics of Nanofluids in Parallel Microchannel Systems to Mitigate Hot Spots in MEMS

Mitigation of “hot spots” in microelectromechanical systems (MEMS) employing in situ microchannel systems requires a comprehensive picture of the maldistribution of the working fluid and uniformity of cooling within the same. In this paper, detailed simulations employing parallel microchannel systems with specialized manifold-channel configurations, i.e., U, I, and Z, have been performed. Eulerian–Lagrangian discrete phase model (DPM) and effective property model with water and alumina–water nanofluid as working fluids have been employed. The distributions of the dispersed particulate phase and continuous phase have been observed to be, in general, different from the flow distribution, and this has been found to be strongly dependent on the flow configuration. Accordingly, detailed discussions on the mechanisms governing such particle distribution patterns have been proposed. Particle maldistribution has been conclusively shown to be influenced by various migration and diffusive phenomena, such as Stokesian drag, Brownian motion, thermophoretic drift, and so on. To understand the uniformity of cooling within the device, which is of importance in real-time scenario, an appropriate figure of merit has been proposed. It has been observed that uniformity of cooling improved using nanofluid as working fluid as well as enhanced relative cooling in hot zones, providing evidence of the “smart” nature of such dispersions. To further quantify this smart effect, real-time mimicking hot-spot scenarios have been computationally probed with nanofluid as the coolant. A silicon-based microchip emitting nonuniform heat flux (gathered from real-time monitoring of an Intel Core i7–4770 3.40-GHz quad-core processor) under various processor load conditions has been studied, and the evidence of enhanced cooling of hot spots has been obtained from DPM analysis. This paper sheds insight on-the behavior of nonhomogeneous dispersions in complex flow domains and the caliber of nanofluids in cooling MEMS more uniformly and “smarter” than base fluids.

Mixed convection in a rotating eccentric annulus containing nanofluid using bi-orthogonal grid types: A finite volume simulation

In this paper, the steady state and laminar mixed convection of nanofluid in horizontal eccentric annulus with rotating inner cylinder has been investigated numerically. The inner and outer cylinders are considered at constant temperature Ti and To respectively, where Ti>To. The annular space is filled with Alumina-water nanofluid. The nonlinear governing equations and the associated boundary conditions in the polar coordinate are solved numerically using the finite volume method and SIMPLER algorithm. In order to perform the numerical simulations, a code has been written to model the problem using bipolar orthogonal co-ordinates as well as non-orthogonal co-ordinates grid types. It is worth mentioning that in non-orthogonal co-ordinates grid types the code is able to model the problem with or without the effects of non-orthogonality. Due to the inconsiderable non-orthogonality of the grid, difference between the results of three schemes is <3%. Considering the computational cost, the code developed for non-orthogonal co-ordinates grid types without effects of non-orthogonality has been used for this study. The effects of the eccentricity and the nanoparticle volume fraction on the heat transfer inside the annuli have been investigated. According to the results, the average Nusselt number increases by increasing the downward eccentricity of the inner cylinder. Furthermore, the maximum average Nusselt number occurs for an optimal nanoparticle volume fraction.

Second Law Analysis of Nanofluid Flow within a Circular Minichannel Considering Nanoparticle Migration

In the current research, entropy generation for the water–alumina nanofluid flow is studied in a circular minichannel for the laminar regime under constant wall heat flux in order to evaluate irreversibilities arising from friction and heat transfer. To this end, simulations are carried out considering the particle migration effects. Due to particle migration, the nanoparticles incorporate non-uniform distribution at the cross-section of the pipe, such that the concentration is larger at central areas. The concentration non-uniformity increases by augmenting the mean concentration, particle size, and Reynolds number. The rates of entropy generation are evaluated both locally and globally (integrated). The obtained results show that particle migration changes the thermal and frictional entropy generation rates significantly, particularly at high Reynolds numbers, large concentrations, and coarser particles. Hence, this phenomenon should be considered in examinations related to energy in the field of nanofluids.

A new correlation for convective heat transfer coefficient of water–alumina nanofluid in a square array subchannel under PWR condition

The computational fluid dynamic (CFD) simulation is performed to determine on the thermo- and hydrodynamic performance of the water–alumina (Al2O3) nanofluid in a square array subchannel featuring pitch-to-diameter ratios of 1.25 and 1.35. Two fundamental aspects of thermal hydraulics, viz. heat transfer and pressure drop, are assessed under typical pressurized water reactor (PWR) conditions at various flow rates (3×105⩽Re⩽6×105) using pure water and differing concentrations of water–alumina nanofluid (0.5–3.0vol.%) as coolant. Numerical results are compared against predictions made by conventional single-phase convective heat transfer and pressure loss correlations for fully developed turbulent flow. It is observed that addition of tiny nanoparticles in PWR coolant can give rise to the convective heat transfer coefficient at the expense of larger pressure drop. Nevertheless, a modified correlation as a function of nanoparticle volume fraction is proposed to estimate nanofluid Nusselt number more precisely in square array subchannel.

Investigation of alumina nanofluid stability using experimental and modified population balance methods

In this paper, the stability of alumina-water nanofluid is studied both theoretically and experimentally. The theoretical study is accomplished using the two-phase Eulerian-Eulerian method and the population balance model. The model considers interactions between nanoclusters and their fractal structures to predict size distribution, average size, and settling rate of nanoclusters for different temperatures, fractal structures, and spatial concentrations. The experimental study is accomplished using the dynamic light scattering (DLS) method. Experiments are also performed to validate modeling results. It is found that increased concentration and temperature of the nanofluid lead to increasing aggregation and settling rate of nanoclusters. The results also show that the reducing fractal dimension at certain concentrations of primary nanoparticles leads to an increasing rate of nanocluster aggregation. Generally, the findings of the study indicate that the population balance model can be successfully employed to investigate the stability of alumina-water nanofluid when the interactions between the nanoparticles and the fractal structures of nanoclusters are duly considered.

Design optimisation of a nanofluid injection system for LOCA events in a nuclear power plant

The safety issues inside a Nuclear Power Plant (NPP) are encompassing their capacity to ensure the heat sink, meaning the capacity of the systems to release the heat from the rector to the environment. The nanofluids having good heat transfer properties, are recommended to be used in such applications. The paper is solving the following scenario: considering the Safety Injection tank and the Nanofluid injection Tank, and considering the Nanofluid injection Tank filled with a 10% alumina-water nanofluid, how can we select the best design of the connecting point between the pipes of the SIT and the Nanofluid Tank and the pressures inside of any of these tanks in order to have the biggest density of nanoparticles leaving the tanks toward the cold leg. In conclusion the biggest influence over the rate of disposal of the nanofluid inside ECCS is that of the pressure inside the SIT followed in order by the injection pipe diameter and the pressure inside the nanofluid tank. The optimum balance of these three design parameters may be reached following the procedure shown in this paper.

Numerical investigation of water-alumina nanofluid natural convection heat transfer and entropy generation in a baffled L-shaped cavity

This article presents a numerical study of natural convection heat transfer and entropy generation of water-alumina nanofluid in baffled L-shaped cavity. The left vertical and bottom walls are placed in hot and constant Th temperature and the middle horizontal and right vertical walls are in cold and constant Tc temperature. The other walls are insulated. The baffle's temperature is Tc and their existence in cavity has a lot of impacts on flow behavior and it could disrupt flow order. The governing equations are solved numerically with Finite Volume Method using the SIMPLER algorithm simultaneously. The convection heat transfer results show: AR (aspect ratio) increasing enhances heat transfer. With dimensional ratio increasing, nanofluid has a greater impact on Nusselt growing. By baffle length increasing nanofluid has less impact on cooling cavity, as a result heat transfer raises. The entropy generation of mentioned parameters are also investigated and discussed. Finally, with studding the ε=Sm/Num (named thermal performance) the best AR and baffle length are introduced.

Buoyancy induced model for the flow of 36 nm alumina-water nanofluid along upper horizontal surface of a paraboloid of revolution with variable thermal conductivity and viscosity

The motion of nanofluid (water and 36nm alumina nanoparticles) along upper horizontal surface of a paraboloid of revolution in the presence of nonlinear thermal radiation, Lorentz force and space dependent internal heat source within thin boundary layer is investigated theoretically. It is assumed that buoyancy induces the flow over this kind of surface which is neither a horizontal/vertical nor cone/wedge, hence suitable buoyancy model for this case of fluid flow is presented. The viscosity and thermal conductivity are assumed to vary with volume fraction and suitable models for the case 0%≤ϕ≤0.8% are adopted. The transformed governing equations are solved numerically using Runge-Kutta fourth order along with shooting technique (RK4SM). Good agreement is obtained between the solutions of RK4SM and MATLAB bvp5c for limiting case. The influence of pertinent parameters are illustrated graphically and discussed. It is found that temperature and velocity functions are maximum at higher values of internal space dependent heat source. Local heat transfer rate is maximum at smaller values of internal space dependent heat source.

Effects of nanoparticles migration on heat transfer enhancement at film condensation of nanofluids over a vertical cylinder

The change in concentration and direction of nanoparticle migration can control the thermophysical properties of nanofluids. This dynamic is useful since it is able to improve the cooling performance by tuning the flow and heat transfer rate. In the current study, a theoretical investigation on the impact of nanoparticle migration on heat transfer enhancement of nanofluids condensate film over a vertical cylinder has been conducted. The Brownian motion and thermophoretic diffusivity have been considered by using the modified Buongiorno model which can take into account the effect of nanoparticle slip velocity. The results have been obtained for different parameters, including the Brownian motion to thermophoretic diffusivities NBT, the saturation nanoparticle volume fraction ϕsat, and the normal temperature difference γ=(Tsat-Tw)/Tw. It is shown that nanoparticle migration has significant impact on the flow and thermal fields and considerably affects the heat transfer rate. Furthermore, heat transfer enhancement in film condensation is strongly depended on the thermophysical properties of nanoparticles such that alumina-water nanofluid exhibits higher cooling performance than titania-water.

Forced convective transport of alumina–water nanofluid in micro-channels subject to constant heat flux

A modified Buongiorno model of nanofluids was established with full considerations of scaling effects and four driving mechanisms of nanoparticles migration in micro-channels. In order to reveal nanoparticles migration, heat transfer and pressure drop characteristics of alumina–water nanofluid in hydrodynamically and thermally fully developed region of micro-channels, the proposed governing equations were solved by means of the Runge-Kutta-Gill method. The obtained results demonstrated that the viscous dissipation term exhibits adverse influence on heat transfer performance for heating and cooling cases. Moreover, it has been found that the increase of the amount of slip velocity and temperature jump at the wall not only enhances heat transfer, but also decreases pressure drop, indicating promising application prospects of nanofluids in micro-channels. Eventually, four driving mechanisms of nanoparticles migration are discussed. The results clearly indicated that Brownian diffusion and thermophoresis are more important than shear-induced diffusion and viscosity gradient-induced diffusion.

MHD mixed convection and entropy generation of water–alumina nanofluid flow in a double lid driven cavity with discrete heating

In the present study, entropy generation due to mixed convection in a partially heated square double lid driven cavity filled with Al2O3–water nanofluid under the influence of inclined magnetic field is numerically investigated. At the lower wall of the cavity two heat sources are fixed, with the condition that the remaining part of the bottom wall is kept insulated. Top wall and vertically moving walls are maintained at constant cold temperature. Buoyant force is responsible for the flow along with the two moving vertical walls. Governing equations are discretized in space using LBB-stable finite element pair Q2/P1disc which lead to 3rd and 2nd order accuracy in the L2-norm for the velocity/temperature and pressure, respectively and the fully implicit Crank–Nicolson scheme of 2nd order accuracy is utilized for the temporal discretization. The discretized systems of nonlinear equations are treated by using the Newton method and the associated linear subproblems are solved by means of Guassian elimination method. Numerical results are presented and analyzed by means of streamlines, isotherms, tables and some useful plots. Impacts of emerging parameters on the flow, in specific ranges such as Reynolds number (1≤Re≤100), Richardson number (1≤Ri≤50), Hartman number (0≤Ha≤100), solid volume fraction (0≤ϕ≤0.2) as well as the angles of inclined magnetic field (0°≤γ≤90°) are investigated and the findings are exactly of the same order as that of the previously performed analysis. Calculation of average Nusselt number, entropy generation due to heat transfer, fluid friction and magnetic field, total entropy generation, Bejan number and kinetic energy are the main focus of our study.

Bioconvection in MHD nanofluid flow with nonlinear thermal radiation and quartic autocatalysis chemical reaction past an upper surface of a paraboloid of revolution

In this paper, the effects of magnetic field, nonlinear thermal radiation and homogeneous-heterogeneous quartic autocatalysis chemical reaction on an electrically conducting (36 nm) alumina-water nanofluid containing gyrotactic-microorganism over an upper horizontal surface of a paraboloid of revolution is presented. The case of unequal diffusion coefficients of reactant A (bulk-fluid) and reactant B (catalyst at the surface) in the presence of bioconvection is presented. In this article, a new buoyancy induced model for nanofluid flow along an upper horizontal surface of a paraboloid of revolution is introduced. The viscosity and thermal conductivity are assumed to vary with volume fraction and suitable models for the case 0% ≤ ϕ ≤ 0.8% are adopted. The transformed governing equations are solved numerically using Runge-Kutta fourth order along with shooting technique (RK4SM). Good agreement is obtained between the solutions of RK4SM and MATLAB bvp5c for a limiting case. The influence of pertinent parameters are illustrated graphically and discussed. It is found that at any values of magnetic field parameter, the local skin friction coefficient is larger at high values of thickness parameter while local heat transfer rate is smaller at high values of temperature parameter.

Numerical modeling of convective heat transfer of thermally developing nanofluid flows in a horizontal microtube

In this study, forced convection heat transfer of alumina-water nanofluid (1–3 vol%) flows was investigated inside a microtube for Reynolds numbers ranging from 500 to 2000 using the Eulerian multiphase model. In the Eulerian model, the Brownian motion, thermophoresis effect and particle-particle interactions were taken into account. The single phase (homogeneous) model was also congruently implemented to compare with the implemented two-phase (suspended particle) model. In the single phase model, four sets of the most used correlations (viscosity, conductivity) were utilized to study the effect of different correlations on convective heat transfer. Convective heat transfer in a microtube with a length of 12 cm and inner and outer diameters of 500 and 700 μm, respectively, was modeled with relevant boundary conditions. The inlet temperature was set as 293 K, the atmospheric pressure was maintained at the outlet, and constant heat flux ranging from 25 to 300 kW/m2 was imposed on the channel walls. Having validated the model, the effects of volume fraction on heat transfer and flow characteristics were discussed in detail. The velocity and temperature profiles of two phase model were obtained. The results of numerical modeling indicated that adding nanoparticles to the base fluid significantly changed velocity profiles and enhanced heat transfer. While the addition of 3 vol% alumina nanoparticle to the base fluid at Reynolds number of 2000 led to an enhancement in convective heat transfer up to 50%, the single phase model resulted in an enhancement of about 15%. It was observed that the homogeneous (single-phase) model underestimated thermal and hydrodynamic results of nanofluid flows.

Numerical investigation on using of nanofluid in a water-cooled photovoltaic thermal system

Photovoltaic thermal collector or PV/T is a new hybrid technology that produces heat and electricity simultaneously. The objective of the current study is to evaluate the effects of utilizing nanofluid on the performance of PV/T system. The considered coolant fluids in the simulation are pure water, Ag-water nanofluid and Alumina-water nanofluid. The proposed model includes a water riser tube and an absorber plate to consider the conduction and convection heat transfer mechanisms. The numerical results were obtained using the computational fluid dynamics (CFD) by employing conjugate heat transfer. The effects of the nanoparticle volumetric concentration and inlet fluid velocity on the efficiency and heat transfer enhancement were simulated. In this paper, the Second Law analysis of a water-cooled PVT is also represented, based on results of simulations. The results show that the efficiencies (the first and second laws of thermodynamics) and heat transfer coefficient increase by increasing the nanoparticle volume fraction. The maximum increase percentage of heat transfer coefficient versus volume fraction for alumina-water and Ag-water nanofluid are 12% and 43%, respectively. Increasing the inlet fluid velocity improves the heat transfer performance of PV/T system. Increasing the heat transfer coefficient with respect to the inlet fluid velocity for alumina-water nanofluid at φ=5% was in the range of 8–10%, in comparison to pure water. While this value for Ag-water nanofluid at the same volumetric fraction is significantly greater than alumina-water, which varies from 28 to 45%. For the purpose of validating the results of the presented method, a comparison study was carried out with the experimental results in the literature. The comparison shows an appropriate agreement with the results of the literature.