Alumina-water Nanofluid Research Articles

Measurement of Local Convective Heat Transfer Coefficient of Alumina-Water Nanofluids in a Double Tube Heat Exchanger

Heat transfer coefficient and thermal efficiency of γ-Al2O3/water nanofluids flowing through a double tube heat exchanger were experimentally investigated. The nanoparticles were well dispersed in distilled water at 0.05–0.15 %vol. A large number of experiments were performed at different fluid flow rates under turbulent flow regime (18,000<Re<40,000) and various nanofluid inlet temperatures ranging from 45 °C to 65 °C. The heat transfer coefficients were measured along the length of the heat exchanger. Results showed that the local heat transfer coefficients have an asymptotic behavior. Furthermore, the addition of these small amounts of nanoparticles to the base fluid augmented the heat transfer up to 16% at the best conditions. In the end, the thermal performance factor was calculated to find the optimum condition at which the nanofluid was used. It was shown that the thermal performance factor of this nanofluid could reach to 1.11. This value was obtained at the nanoparticle concentration of 0.15 vol.% and Reynolds number 18000

Comprehensive simulation of nanofluid flow and heat transfer in straight ribbed microtube using single-phase and two-phase models for choosing the best conditions

In this paper, the hydrodynamics and heat transfer parameters of nanofluids are investigated using CFD analysis. Laminar convective heat transfer of alumina–water nanofluids with 0, 1%, and 2% volume fraction in a straight microtube heat sink under constant wall heat flux condition is studied. This work is performed in two parts. In the first part, the single-phase and two-phase approaches have been used for modeling heat transfer of pure water and alumina–water nanofluids in a straight microtube. The results of simulation are compared with the experimental data. The results showed that CFD predictions via a two-phase model show better agreement with the experimental measurements. For nanofluid with 1% concentration, the average relative error between the experimental data and CFD result based on a two-phase model is 5.85%, while for nanofluid with 2% concentration that is 2.54%. In the second part of this work, the effects of ribs through the microtube are investigated. The effect of the geometry on the Nusselt number and friction factor in the microtube is studied. We found that spiral pitch increment increases the thermal performance by an average of 19.8%. Finally, the best performance is obtained for the ribs height 1 mm and the pitch 1.5 mm.

Heat Transfer Enhancement by Sinusoidal Motion of a Water-Based Nanofluid

The oscillatory flows are often utilized in order to augment heat transfer rates in various industrial processes. It is also a well-known fact that nanofluids provide significant enhancement in heat transfer at certain conditions. In this research, heat transfer in an oscillatory pipe flow of both water and water–alumina nanofluid was studied experimentally under low frequency regime laminar flow conditions. The experimental apparatus consists of a capillary tube bundle connecting two reservoirs, which are placed at the top and the bottom ends of the capillary tube bundle. The upper reservoir is filled with the hot fluid while the lower reservoir and the capillary tube bundle are filled with the cold fluid. The oscillatory flow in the tube bundle is driven by the periodic vibrations of a surface mounted on the bottom end of the cold reservoir. The effects of the frequency and the maximum displacement amplitude of the vibrations on thermal convection were quantified based on the measured temperature and acceleration data. It is found that the instantaneous heat transfer rate between de-ionized (DI) water (or the nanofluid)-filled reservoirs is proportional to the exciter displacement. Significantly reduced maximum heat transfer rates and effective thermal diffusivities are obtained for larger capillary tubes. The nanofluid utilized oscillation control heat transport tubes achieve high heat transfer rates. However, heat transfer effectiveness of such systems is relatively lower compared to DI water filled tubes.

An experimental investigation of pool boiling characteristics of alumina-water nanofluid over micro-/nanostructured surfaces

Experiments were conducted to investigate the nucleate pool boiling heat transfer of pure water and alumina/water nanofluids on different micro- and nanostructured surfaces prepared via the thermal spray coating method. Results indicate that nanofluids boiling on all the test surfaces led to critical heat flux (CHF) values greater than that obtained for the base fluid (i.e., water). Higher roughness value, however, led to higher CHF values in boiling over the surfaces. Another finding of this study indicated that CHF values obtained with boiling on Cu-coated micro- and nanosurfaces were identical although the heat transfer coefficient (HTC) values obtained for boiling on the micro-structure surface were higher than those obtained for a nanostructured surface with almost the same roughness. A series of consecutive nanofluid boiling cycles were also performed on the aluminum-coated nanostructured surface. The CHF value obtained for water boiling on the surface undergoing repeated nanofluid boiling cycles was by 27% higher than that obtained for a clean surface although the relevant HTC values were nearly identical.

Rayleigh-Bénard Convection for Nanofluids for More Realistic Boundary Conditions (Rigid-Free and Rigid-Rigid) Using Darcy Model

In this article, Rayleigh-Bénard convection for nanofluids for more realistic boundary conditions (rigid-free and rigid-rigid) under the influence of the magnetic field is investigated. Presence of nanoparticles in base fluid has introduced one additional conservation equation of nanoparticles that incorporates the effect of thermophoretic forces and Brownian motion and the inclusion of magnetic field has introduced Lorentz’s force term in the momentum equation along with Maxwell’s equations. The solution of the Eigen value problem is found in terms of Rayleigh number by implementing the technique of normal modes and weighted residual Galerkin approximation. It is found that the stationary as well as oscillatory motions come into existence and heat transfer takes place through oscillatory motions. The critical Rayleigh number for alumina water nanofluid has an appreciable increase in its value with the rise in Chandrasekhar number and it increases moderately as we move from rigid-free to both rigid boundaries. The effect of different nanofluid parameters on the onset of thermal convection for two types of boundaries is investigated.

Effects of Viscosity Variations on Buoyancy-Driven Flow from a Horizontal Circular Cylinder Immersed in Al2O3-Water Nanofluid

The buoyancy-driven boundary-layer flow from a heated horizontal circular cylinder immersed in a water-based alumina (Al2O3) nanofluid is investigated using variable properties for nanofluid viscosity. Two different viscosity models are utilized to evaluate heat transfer enhancement from a cylinder. Exact analytic solutions of the problem are attained employing a novel powerful technique is known as the Optimal Homotopy Analysis Method (OHAM). The accuracy and reliability of the results are verified by comparing them with experimental results in the literature. It is found that the characteristics of flow and temperature distributions are significantly influenced by the volume fraction of alumina nanoparticles, as well as nanofluid viscosity models. Enhancing the volume fraction of nanoparticles, the surface shear stress and the local Nusselt number both increase in the middle regions of the cylinder. The results also indicated that with increasing the nanoparticles volume fraction, isotherms become less dense and the absolute values of the stream-function decrease within the domain. Based on the results of the parametric study, two correlations (based on two different effective viscosity models) are proposed for the average Nusselt number of the alumina-water nanofluid in terms of volume fraction of the nanoparticles and the Rayleigh number which can be used as benchmarks for future investigations. However, uncertainties of viscosity models showed different manners on heat transfer coefficient versus nanoparticles volume fraction.

Stability, thermophysical properties and performance assessment of alumina–water nanofluid with emphasis on ultrasonication and storage period

Owing to the improvements in thermophysical properties, nanofluids are considered advantageous over pure fluids in heat transfer applications. However, these improvements may be regarded as meaningful for applications provided that optimum dispersion of nanoparticles is ensured throughout the process, which mostly depend on preparation technique. In this study, alumina (Al2O3)–water nanofluids of 0.5 vol% were prepared using ultrasonication (up to 5 h) and stored at stationary condition until 30 days. We have evaluated stability as temporal volume fraction by measuring density. Further, thermal conductivity and viscosity were measured, and heat transfer performance was analyzed for the case of fully developed laminar flow inside a tube. All the measurements were conducted at 25 °C temperature. Results revealed that longer ultrasonication reduces sedimentation of nanoparticles and hence, increases stability of nanofluids. Thermal conductivity increased, while viscosity decreased with increasing sonication time. Moreover, these thermophysical properties decreased with storage periods. It was observed, until 30 days of storage that ultrasonication process for different durations induced significant changes in viscosity, although those in thermal conductivity was not as pronounced. All the prepared samples were determined beneficial as heat transfer fluids over water, even after 30 days from preparation.

Experimental investigation of convection heat transfer in the transition flow regime of aluminium oxide-water nanofluids in a rectangular channel

The growing demand for energy worldwide requires that attention be given to designing and operating heat exchangers and thermal devices to utilise and save thermal energy. There is a need to find new heat transport fluids with better heat transfer properties to increase convective heat transfer, and nanofluids have been shown to be good alternatives to conventional heat transport fluids. Although extensive research has been done on the properties of nanofluids in recent decades, there is still a lack of research on convection heat transfer involving nanofluids, particularly in the transitional flow regime. This study investigated the convective heat transfer of a one-step prepared alumina-water nanofluid. A uniformly heated rectangular channel was experimentally investigated. Nanofluids with volume concentrations of 0.3, 0.5, and 1% were used, and a Reynolds number range of 200–7000 was considered, which included laminar and turbulent flows, as well as the transition regime from laminar to turbulent flow. The temperatures and pressure drops were measured to evaluate the heat transfer coefficients, Nusselt numbers, and pressure drop coefficients. The results showed enhancements of the heat transfer coefficients for the nanofluids used. The 1.0% nanofluid showed the maximum enhancements, with values of 54% in the transition flow regime and 11% in the turbulent regime. The convective heat transfer efficiency in the transition flow regime was observed to be better than those in the turbulent and laminar flow regimes.

Study of heat and mass transfer control inside channel partially filled with a porous medium using nanofluids

The steady mixed convection of heat and mass transfer inside and outside a porous vertical wall is numerically studied. The porous wall, placed in a vertical channel, contains a solid phase, a nanofluid phase (Water-Al2O3 or Water-Cu) and gas phase. The effect of several physical quantities such as nanoparticle volume fraction, ambient temperature and initial nanofluid saturation on heat and mass transfer were investigated. Results reveal that the temperature of porous medium is decreased considerably with nanoparticle volume fraction. It has been also found that the heat and mass transfer are dramatically reduced using Water-Alumina nanofluid when compared with pure water.

Natural convection of Al2O3/H2O nanofluid in a cavity with a heat-generating element. Heatline visualization

Cooling of electronic devices is a very important topic. The present paper deals with numerical simulation of natural convection cooling of heat-conducting and heat-generating source using an alumina-water nanofluid under the effect of cold vertical walls. Governing equations formulated in dimensionless stream function, vorticity and temperature variables have been solved by the finite difference method. The effects of nanoparticles concentration, heat source location, internal heat generation flux and heat source material on fluid flow and heat transfer have been studied. It has been found that an addition of nanoparticles can intensify the cooling process when the heat is located near the vertical cold wall.

Modeling of Nanofluid-Fluid Two-Phase Flow and Heat Transfer

This paper presents a model for two-phase nanofluid-fluid flow and heat transfer. The nonuniform nanoparticles are transported using Buongiorno model by convection, Brownian diffusion and thermophoresis. This is the first attempt to employ Buongiorno model for two-phase nanofluid-fluid flow. The moving interface between the nanofluid and the immiscible fluid is captured using the level-set method. The model is first verified and then demonstrated for coupled flow and heat transfer in (1) a water–alumina nanofluid-filled cavity with a rising silicone oil drop and (2) stratified flow of water–alumina nanofluid, pure water and silicone oil in a channel.

Numerical investigation of heat transfer by an impinging jet using alumina–water nanofluid

This article reports numerical investigations of turbulent flow field and heat transfer performance of water-alumina nanofluid jet impingement. The jet impinges over a flat, circular heated surface from a circular pipe of diameter . The influence of jet Reynolds number (1,200 ≤ ≤ 40,000), jet-outlet-to-target wall distance (2 ≤ ≤ 12.8), and particle volumetric concentration (0 ≤ φ ≤ 10%) on the fluid flow and heat transfer are examined. The results of fluid flow and heat transfer are compared with the published experimental data. It is found that the heat transfer increases with increasing values of the particle volumetric concentration while the flow field and turbulent kinetic energy distribution remain unchanged with the inclusion of nanoparticles. About 28% enhancement in stagnation Nusselt number is observed at low values of nanoparticle volumetric concentration (φ = 0.1%) and in the Reynolds number range of 29,000–40,000. For jet-outlet-to-target wall spacing values used in the current study, the local Nusselt number distributions vary according to Nu ∝ . Numerical simulations are performed using Reynolds-averaged Navier–Stokes method with the shear stress transport k-ω model in commercial CFD code ANSYS-CFX.

Natural convection of an alumina-water nanofluid inside an inclined wavy-walled cavity with a non-uniform heating using Tiwari and Das’ nanofluid model

The present study is devoted to numerical analysis of natural convective heat transfer and fluid flow of alumina-water nanofluid in an inclined wavy-walled cavity under the effect of non-uniform heating. A single-phase nanofluid model with experimental correlations for the nanofluid viscosity and thermal conductivity has been included in the mathematical model. The considered governing equations formulated in dimensionless stream function, vorticity, and temperature have been solved by the finite difference method. The cavity inclination angle and irregular walls (wavy and undulation numbers) are very good control parameters for the heat transfer and fluid flow. Nowadays, optimal parameters are necessary for the heat transfer enhancement in different practical applications. The effects of the involved parameters on the streamlines and isotherms as well as on the average Nusselt number and nanofluid flow rate have been analyzed. It has been found that the heat transfer rate and fluid flow rate are non-monotonic functions of the cavity inclination angle and undulation number.

The influence of thermal radiation on unsteady free convection in inclined enclosures filled by a nanofluid with sinusoidal boundary conditions

PurposeThe purpose of this study is a numerical analysis of transient natural convection in an inclined square cavity filled with an alumina-water nanofluid under the effects of sinusoidal wall temperature and thermal radiation by using a single-phase nanofluid model with empirical correlations for effective viscosity and thermal conductivity.Design/methodology/approachThe domain of interest includes the nanofluid-filled cavity with a sinusoidal temperature distribution along the left vertical wall. Horizontal walls are supposed to be adiabatic, while right vertical wall is kept at constant low temperature. Temperature of left wall varies sinusoidally along y-coordinate. It is assumed in the analysis that the thermophysical properties of the fluid are independent of temperature and the flow is laminar. The governing equations have been discretized using the finite difference method with the uniform grid. Simulations have been carried out for different values of the Rayleigh number, cavity inclination angle, nanoparticles volume fraction and radiation parameter.FindingsIt has been found that a growth of radiation parameter leads to the heat transfer enhancement and convective flow intensification. At the same time, an inclusion of nanoparticles illustrates a reduction in the average Nusselt number and fluid flow rate.Originality/valueThe originality of this work is to analyze unsteady natural convection in a square cavity filled with a water-based nanofluid in the presence of a sinusoidal temperature distribution along one wall. The results would benefit scientists and engineers to become familiar with the analysis of convective heat and mass transfer in nanofluids and the way to predict the properties of nanofluid convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

Tuning the water-alumina nanofluids impedance and dielectric relaxation by the diffuse coplanar dielectric barrier discharge

Nanofluids are nowadays representing an exciting tool with significant impact and tremendous potential in several industrial applications. In the present paper, we focus our attention on the tunability of the electrical and dielectric properties of alumina nanoparticle-based nanofluids achieved by preliminary modifying the particle surface charging by a diffuse coplanar dielectric barrier discharge plasma treatment. We produced a parametric study on the tuning of the plasma-treatedalumina-based nanofluid electrical response as a function of the selected discharge feeding gases.

Impacts of moving wall and heat-generating element on heat transfer and entropy generation of Al2O3/H2O nanofluid

Development of various electronic devices demands to create effective cooling complexes. The present paper deals with computational analysis of mixed convection cooling of heat-conducting and heat-generating element located inside an alumina–water nanofluid enclosure with upper moving wall. Usage of upper moving wall, nanofluid and cooling vertical walls allows to create the effective cooling process. Analysis has been performed numerically using the Oberbeck–Boussinesq equations. The effects of nanoparticles concentration, heat source location and upper wall velocity on flow structures, heat exchange and entropy generation have been investigated. It has been ascertained that effective cooling of the heated element occurs for high Reynolds number and central position of the heat-generating element.

Natural Convection Flow of Nanofluids in Squeeze Film with an Exponential Curvature

A theoretical study of the laminar squeeze flow of copper water and alumina water nanofluids between a flat circular stationary disk and a curved circular moving disk is carried out using energy integral method. The squeeze film behaviour is examined analytically and the effects of inertia and curvature on the squeeze film pressure, load carrying capacity of the fluid and temperature are analysed. Further, the problem is solved numerically for a sinusoidal motion of the upper curved disk taking an exponential form of the gap width. It is found that the copper water nanofluid is better than alumina water nanofluid for better heat transfer rates. While high inertia forces strongly influence the squeeze film behaviour, low inertia forces are favourable for temperature distribution. Further, concave nature of the upper disk gives better squeeze film characteristics than convex disk. However, convex disk is better than concave disk as far as the temperature distribution is concerned.

Effects of gravity and variable thermal properties on nanofluid convective heat transfer using connected and unconnected walls

In this paper, heat transfer characteristics of natural convection in an enclosure are investigated by considering variable thermal properties. The heated enclosure with an aspect ratio of unity is full of an alumina-water nanofluid. To analyze the effect of different thermal properties on the flow and temperature distributions, many comparisons are conducted for various cases at various Rayleigh numbers and volume fractions of nanoparticles (1–9.5%). The effect of low-gravity conditions on natural convection is investigated by using the gravity values of 0.25 g (2.45 m/s2), 0.5 g (4.9 m/s2), 0.75 g (7.35 m/s2) and 1.0 g (0.98 m/s2). It was found that larger temperature gradients near the heated and cold walls can be obtained by increasing the Rayleigh number. By increasing the value of gravity, the flow velocity increased along the y direction. This indicated that gravity has great influence on enhancement of heat transfer. The investigation of the volume fraction of nanoparticles shows that the variation of the Nusselt number for high volume fraction presented a more flat profile than for low volume fraction. The Nusselt number decreased with an increase of the volume fraction. Results for cases with connected and unconnected heated walls are presented. The results showed that heat transfer for the case with the nanoparticle volume fraction of 1% at 1.0 g increased by 89.9% using an unconnected heated wall compared to the connected heated wall.

Convective–radiative heat transfer in a cavity filled with a nanofluid under the effect of a nonuniformly heated plate

PurposeThe purpose of this study is to examine the radiation effect on the natural convective heat transfer of an alumina–water nanofluid in a square cavity in the presence of centered nonuniformly heated plate.Design/methodology/approachThe square cavity filled with alumina–water nanofluid has a nonuniformly heated plate placed horizontally or vertically at its center. The plate is heated isothermally with linearly varying temperature. The vertical walls are cooled isothermally with a constant temperature, while the horizontal walls are insulated. The governing equations have been discretized using finite volume method on a uniformly staggered grid system. Simulations were carried out for different values of the heated plate nonuniformity parameter (λ = –1, 0 and 1), the nanoparticles solid volume fraction (Φ = 0.01 − 0.04) and the radiation parameter (Rd = 0 – 2) at the Rayleigh number of Ra = 1e+07.FindingsIt is found that the total heat transfer rate is enhanced with an increase in the radiation parameter for both the horizontal and vertical plates. The role of nanoparticles addition to the base fluid can have dual effects on the heat transfer rate by augmenting and dampening for the absence of radiation while it dampens the heat transfer rate for the presence of radiation.Originality/valueThe originality of this work is to analyze steady natural convection in a square cavity filled with a water-based nanofluid in the presence of centered nonuniformly heated plate. The results would benefit scientists and engineers to become familiar with the analysis of convective heat and mass transfer in nanofluids, and the way to predict the properties of nanofluid convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

Natural convection of Al2O3/H2O nanofluid in an open inclined cavity with a heat-generating element

Free convection of alumina-water nanofluid in a tilted open cavity with a heat-generating solid element has been studied. The considered topic allows understanding an opportunity of nanofluids for cooling of the heat-generating elements in open cavities. Upper border is supposed to be open where nanofluid penetrates into the cavity. Simulation has been performed using the Oberbeck–Boussinesq equations formulated in non-dimensional stream function, vorticity and temperature. Finite difference method of the second order accuracy has been applied. The effects of cavity inclination angle (0≤γ≤π/2), heater location (0.1≤δ≤0.7, where δ is the dimensionless distance between the heater and left wall) and nanoparticles volume fraction (0≤ϕ≤0.04) have been analyzed. It has been found that the considered parameters allow minimizing average heater temperature. The cavity inclination angle of π/3 characterizes the heat transfer enhancement (average Nusselt number has the maximum value), while the heater average temperature has the minimum value. At the same time, a proximity of the heater to the cavity wall characterizes non-essential cooling of the heat-generating element. The most effective cooling of the heat-generating element occurs for central heater location with cavity inclination angle of π/3. The considered alumina-water nanoparticles do not allow to intensify the cooling process for the heater element.