Water-based Al2O3 Nanofluids Research Articles

Thermal properties and rheological behavior of water based Al2O3 nanofluid as a heat transfer fluid

An experimental investigation and theoretical study of thermal conductivity and viscosity of Al2O3/water nanofluids are presented in this article. Various suspensions containing Al2O3 nanoparticles were tested in concentration ranging from 3% to 50% in mass and temperature ranging from 293K to 323K. The results reveal that both the thermal conductivity and viscosity of nanofluids increase with temperature and particle concentration accordingly while the increase in viscosity is much higher than the increase in thermal conductivity. The thermal conductivity and viscosity enhancement are in the range of 1.1–87% and 18.1–300%, respectively. Moreover, the results indicate that the thermal conductivity increases nonlinearly with concentration, but, linearly with the increase in temperature. In addition, the experimental results are compared with some existing correlations from literature and some modifications are suggested. Finally, the average heat transfer coefficient at different basis of comparisons including equal Reynolds number, fluid velocity and pumping power is studied based on the experimental thermal conductivity and viscosity in fully developed laminar and turbulent flow regimes. It is found that equal Reynolds number as a basis of comparison is highly misleading and equal pumping power can be used to study the advantage of using nanofluid instead of the base fluid.

Measurement and Correlation of the Viscosity of Water-Based Al2O3 and TiO2 Nanofluids in High Temperatures and Comparisons with Literature Reports

In this article, the viscosity of two common nanofluids including Al2O3/water and TiO2/water is measured at high temperatures, and high concentrations of the nanofluids. The range of temperature is 15–60°C where the volume fraction of nanoparticles varies from 1 to 8%. Next, comparisons have been done with the most well-known theoretical and experimental reports in the literature. Finally, using the experimental data, a helpful correlation is presented.

The water based Al2O3 nanofluid flow and heat transfer in tangential microtube heat sink with multiple inlets

Micro thermal systems are convenient cooling devices for high heat flux applications. Besides, the nanofluids are used to improve the cooling capabilities. The suspended nanoparticles in the base fluid increase the thermal conductivity, fluid viscosity and fluid density but decrease the effective heat capacity. To analyze the suitability of using the nanofluids for cooling applications, the numerical simulations are made for nanofluid heat transfer and fluid flow in micro-heat sink with straight microtubes and multiple tangential inlet jets. The configurations with five inlet jets is considered and numerical simulations are based on a finite volume method. The Al2O3 water based nanofluid was used in simulations. The heat flux spread through the bottom surface of the heat sink was q=50W/cm2. Re from 15 to 100 was considered to simulate the laminar fluid flow. The analysis is based on thermal and hydrodynamic results obtained for nanofluid and compared with results obtained for water. The results are analyzed on a fixed pumping power, Re or mass flow rate basis. It is observed that the conclusions are strongly dependent on the analysis constraint. Moreover the surface temperature difference is not very much improved by using the nanofluid.

A time variant investigation on optical properties of water based Al2O3 nanofluid

Optical properties of nanofluids are vital for calculating performance of a Direct Absorption Solar Collector (DASC). Characteristics of nanofluids are not constant; they vary with time and growth of nanoparticles. For current investigation, nanofluids were prepared to obtain considerable stability. Stability ratio of our nanofluids was 100 times larger than the threshold limit. Here, we have investigated aggregation process and its effect on optical characteristics of the nanofluids using Transmission Electron Microscopy (TEM) imaging, Dynamic Light Scattering (DLS) approach and UV–visible spectroscopy. Steps of aggregation are broadly described with TEM images. Our results indicate that extinction coefficients of the nanofluids reduce rapidly with time within visible to near IR region. Quasi Crystalline (QC) and Rayleigh Approaches were used to compare the experimental behavior of optical properties of nanofluids. It was found that both of these approaches are weak to predict the optical behavior, especially at UV region and scattering of light is found responsible for high extinction with the experimental results. More experimental effort is still required to get an appropriate explanation.

Pressure Drop and Performance Characteristics of Water-Based Al2O3 and CuO Nanofluids in a Triangular Duct

An experimental study is performed to determine the pressure drop and performance characteristics of Al2O3/water and CuO/water nanofluids in a triangular duct under constant heat flux where the flow is laminar. The effects of adding nanoparticles to the base fluid on the pressure drop and friction factor are investigated at different Reynolds numbers. The results show that at a specified Reynolds number, using the nanofluids can lead to an increase in the pressure drop by 35%. It is also found that with increases in the Reynolds number, the rate of increase in the friction factor with the volume fraction of nanoparticles is reduced. Finally, the performance characteristics of the two nanofluids are investigated using the data of pressure drop and convective heat transfer coefficient. The results show that the use of Al2O3/water nanofluid with volume fractions of 1.5% and 2% is not helpful in the triangular duct. It is also concluded that at the same volume fraction of nanoparticles, using Al2O3 nanoparticles is more beneficial than CuO nanoparticles based on the performance index.

Uncertainties in modeling thermal conductivity of laminar forced convection heat transfer with water alumina nanofluids

At this stage of nanofluids development, their thermal conductivity it is not yet known precisely and the judgment of their true potential is difficult. This fact was illustrated by analyzing their heat transfer performance for laminar fully developed forced convection in a tube with two zones: one adiabatic and one with uniform wall heat flux. Forced convective of a nanofluid that consists of water and Al2O3 in horizontal tubes has been studied numerically. Three different models from the literature are used to express the thermal conductivity in terms of particle loading and they led to different qualitative and quantitative results in a classical problem of replacement of a simple fluid (water) by a nanofluid in a given situation. In particular, the heat transfer coefficient of water-based Al2O3 nanofluids is increased by 3.4–27.8% under fixed Reynolds number compared with that of pure water. Also, the enhancement of heat transfer coefficient is larger than that of the effective thermal conductivity at the same volume concentration. Moreover, the effect of uncertainties in modeling nanofluids properties was noticed.

Shelf stability of nanofluids and its effect on thermal conductivity and viscosity

This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes’ law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.

Study of viscosity and specific heat capacity characteristics of water-based Al2O3 nanofluids at low particle concentrations

In this paper, the specific heat capacity and viscosity properties of water-based nanofluids containing alumina nanoparticles of 47 nm average particle diameter at low concentrations are studied. Nanofluids were prepared with deionised water as base fluid at room temperature by adding nanoparticles at low volume concentration in the range of 0.01%–1% to measure viscosity. The effect of temperature on viscosity of the nanofluid was determined based on the experiments conducted in the temperature range of 25°C to 45°C. The results indicate a nonlinear increase of viscosity with particle concentration due to aggregation of particles. The estimated specific heat capacity of the nanofluid decreased with increase of particle concentration due to increase in thermal diffusivity. Generalised regression equations for estimating the viscosity and specific heat capacity of nanofluids for a particular range of particle concentration, particle diameter and temperature are established.

The effect of real viscosity on the heat transfer of water based Al2O3 nanofluids in a two-sided lid-driven differentially heated rectangular cavity

The heat transfer and fluid flow behavior of water based Al2O3 nanofluids are numerically investigated inside a two-sided lid-driven differentially heated rectangular cavity. Physical properties which have major effects on the heat transfer of nanofluids such as viscosity and thermal conductivity are experimentally investigated and correlated and subsequently used as input data in the numerical simulation. Transport equations are numerically solved with finite volume approach using SIMPLEC algorithm. It was found that not only the thermal conductivity but also the viscosity of nanofluids has a key role in the heat transfer of nanofluids. The results show that at low Reynolds number, increasing the volume fraction of nanoparticles increases the viscosity and has a deteriorating effect on the heat transfer of nanofluids. At high Reynolds number, the increase in the viscosity is compensated by force convection and the increase in the volume fraction of nanoparticles which results in an increase in heat transfer is in coincidence with experimental results.

Inverse geometric optimization for geometry of nanofluid-cooled microchannel heat sink

An inverse geometric optimization for nanofluid-cooled microchannel heat sink (MCHS) considering effects of temperature-dependent thermophyiscal properties for the water-based Al2O3 nanofluid with 1% particle volume fraction was performed under a constant pumping power constraint. A three-dimensional fluid-solid conjugated MCHS model combining the simplified-conjugate-gradient-method was used as the optimization tool. The channel number, N, the channel aspect ratio, α, and the width ratio of channel to pitch, β, affect the cooling performance of MCHS, and were all incorporated in the present, three-parameter optimization study. Increase in viscosity of the nanofluid did not always lead to enhanced MCHS performance under fixed pumping power constraint, contradicting to the results for pure water. The optimal MCHS design is closely related to the assigned pumping power: increase in the pumping power enhances cooling performance; however, in high pumping power regime the performance enhancement is not as effective as in low pumping power regime. At pumping power of 0.05 W and a uniform heat flux of qw = 100 W cm−2, the optimal design for the nanofluid-cooled MCHS presented N = 51, α = 5.69 and β = 0.62, yielding the optimal thermal resistance of RT = 0.1059 K W−1.

Influence of particle size and shape on turbulent heat transfer characteristics and pressure losses in water-based nanofluids

We carry out extensive experimental studies of turbulent convective heat transfer of several water-based Al2O3, SiO2, and MgO nanofluids with a nanoparticle volume fraction up to 4%. The experimental setup consists of an annular tube, where sub-atmospheric condensing steam is used to establish a constant wall temperature boundary condition, with nanofluid forced through the inner tube. To unravel the influence of particle shape and size to heat transfer we also present a detailed characterization of the nanofluids using Dynamic Light Scattering and Transmission Electron Microscopy techniques in situ. In agreement with previous studies, we find that the average convective heat transfer coefficients of nanofluids are typically enhanced by up to 40% when compared to the base fluid on the basis of constant Reynolds number in the turbulent regime, where Re=3000–10,000. However, the increase of the dynamic viscosity of nanofluids leads to significant pressure losses as compared to the base fluids. To account for this, the convective heat transfer efficiency η is determined by comparing the enhanced heat transfer performance to the increased pumping power requirement. When this has been properly taken into account, only the SiO2 based nanofluid with smooth spherical particles (of average size 6.5±1.8nm) shows noticeable improvement in heat transfer with a particle volume fraction of 0.5–2%. Increasing the nanoparticle volume fraction beyond 2% enhances the heat transfer coefficient but at the same time lowers heat transfer efficiency η due to pressure losses, which result from the increased fluid density and viscosity. Through our nanoparticle size and shape analysis we find that in general small, spherical and smooth particles (less than 10nm in size) are best in enhancing heat transfer and keeping the increase of pressure losses moderate. Our results show that the nanoscale properties of the particle phase must be carefully considered in heat transfer experiments.

Heat Transfer Enhancement with Al2O3 Nanofluids and Twisted Tapes in a Pipe for Solar Thermal Applications

Solar thermal energy is currently used for low temperature heating applications using flat plate collectors. The absorbed solar energy is transferred to the working fluid flowing in the pipe. The performance of the system is influenced by heat transfer from tube to working fluid, with minimum convective losses, which has to be considered as one of the primary design factor. In tube and channel flows, to enhance the rate of heat transfer to the working fluid, passive augmentation techniques such as twisted tapes and swirl generators are used in the fluid flow path. In this paper, convective heat transfer analysis for a horizontal circular pipe with fluid in mixed laminar flow range is performed using experimental simulation under constant heat flux boundary condition. The variation of heat transfer coefficient and pressure drop in the pipe flow for water and water based Al2O3 nanofluids at different volume concentrations and twisted tapes are studied. The dependence of particle concentration and Reynolds number for enhancement in heat transfer and increase in the pumping power due to pressure drop is analysed in the range of parameters considered.

Application of Nano Cutting Fluid under Minimum Quantity Lubrication (MQL) Technique to Improve Grinding of Ti – 6Al – 4V Alloy

Minimum Quantity Lubrication (MQL) technique obtained a significant attention in machining processes to reduce environmental loads caused by usage of conventional cutting fluids. Recently nanofluids are finding an extensive application in the field of mechanical engineering because of their superior lubrication and heat dissipation characteristics. This paper investigates the use of a nanofluid under MQL mode to improve grinding characteristics of Ti-6Al-4V alloy. Taguchi’s experimental design technique has been used in the present investigation and a second order model has been established to predict grinding forces and surface roughness. Different concentrations of water based Al2O3 nanofluids were applied in the grinding operation through MQL setup developed in house and the results have been compared with those of conventional coolant and pure water. Experimental results showed that grinding forces reduced significantly when nano cutting fluid was used even at low concentration of the nano particles and surface finish has been found to improve with higher concentration of the nano particles. Keywords—MQL, Nanofluid, Taguchi method, Ti-6Al-4V.

Investigation of grinding characteristic using nanofluid minimum quantity lubrication

Conventional grinding fluid is widely used in grinding process, which results in high consumption and impacting the environment. The promising alternative to conventional dry and fluid coolant application is minimum quantity lubrication (MQL). It is known that the cooling and lubrication performance of the grinding fluid is the key technical area for the success application of MQL grinding process. In this study, Water based Al2O3 nanofluid was applied to grinding process with MQL approach for its excellent convection heat transfer and thermal conductivity properties. The grinding characteristics of hardened AISI 52100 steel were investigated and compared with those of wet, dry and pure water MQL grinding. Experimental results show that water based Al2O3 nanofluid MQL grinding can significantly reduce the grinding temperature, decrease the grinding forces, improve the ground surface morphology and reduce the surface roughness in comparison to pure water MQL grinding. Furthermore, the cooling and lubricating mechanism for nanofluid MQL grinding was discussed in detail.

Experimental investigation of laminar convective heat transfer and pressure drop of water-based Al2O3 nanofluids in fully developed flow regime

This article presents the heat transfer coefficient and friction factor of the nanofluids flowing in a horizontal tube under laminar flow conditions, experimentally. The experiments have been done on fully developed region under the constant wall temperature condition. Al2O3 nanoparticles with diameters of 40nm dispersed in distilled water with volume concentrations of 0.1–2vol.% were used as the test fluid. All physical properties of the Al2O3–water nanofluids needed to calculate the pressure drop and the convective heat transfer coefficient have been measured. The results show that the heat transfer coefficient of nanofluid is higher than that of the base fluid and increased with increasing the Reynolds number and particle concentrations. The heat transfer coefficient increases by approximately 32% in the fully developed region at 2vol.% nanofluid. The measured pressure loss for the nanofluids was in general much higher than for pure water. The experimental results illustrate that the single phase correlation with nanofluids properties could not predict heat transfer coefficient enhancement of nanofluids fairly.

Natural convection heat transfer inside vertical circular enclosure filled with water-based Al2O3 nanofluids

Experimental investigation on natural convection heat transfer has been carried out inside vertical circular enclosures filled with Al2O3 nanofluid with different concentrations; 0.0%, 0.85% (0.21%), 1.98 (0.51%) and 2.95% (0.75%) by mass (volume). Two enclosures are used with 0.20 m inside diameter and with two different aspect ratios. The bottom surface of the enclosure is heated using a constant heat flux flexible heater while the upper surface is cooled by an ambient air stream. Various uniform heat fluxes have been used to generate the natural convection heat transfer data. The average Nusselt number is obtained and correlated with the modified Rayleigh number at each concentration ratio of the nanofluid. The average Nusselt number is obtained for each enclosure and correlated with the modified Rayleigh number using the concentration ratio as a parameter. The results show that the heat transfer coefficient increases as the concentration increases up to a specific value of the concentration and then it decreases as the concentration continues to increase compared to the basic fluid of pure water. Furthermore, a general correlation is obtained using the volume fraction and the aspect ratio as parameters.

Investigations on electrical conductivity of stabilized water based Al2O3 nanofluids

The electrical conductivity is an important property of nanofluids that has not been widely studied. To study both the effects of temperature and concentration, the electrical conductivity of water-based Al2O3 nanofluids with 12 nm diameter particles is measured. Conventional models, such as the Maxwell model and Bruggemann correlation, were considered for comparison and disagreement were noticed. Experimental results showed the Al2O3 nanofluids increased their electrical conductivity with increasing volume fraction as compared to that of the base fluid, as well as with temperature increasing. A stronger influence on volume fraction was noticed. Electrical conductivity measurements for these nanofluids indicate an enormous enhancement (390.11 %) at 60 °C for a volume fraction of 4 %in distilled water. Furthermore, at higher volume fractions, the electrical conductivity enhancement begins to level off, which is attributed to ion condensation effects in the high-surface charge regime. A 3D statistical analysis was also considered to obtain an empirical correlation.

Friction and Wear Characteristics of Water-Based ZnO and Al2O3 Nanofluids

In recent years, nanofluids have been an active area of research due to their enhanced thermal conductivity over base fluids. However, the tribological properties of nanofluids have not been thoroughly studied. In this research, friction and wear characteristics of water-based nanofluids was carried out. Commercially available water-based nanofluids with 50% ZnO and 50% Al2O3 nanoparticle concentration were used as the lubricant. The 50% concentration nanofluids were diluted using deionized water and an ultrasonic bath into different volume concentrations. The effects of nanoparticle type, particle concentration, and surface roughness of the specimen on the friction and wear characteristics were investigated. The friction and wear tests were performed using a UMT-2 Micro-Tribometer with a ball-on-disk configuration. The surface roughness and wear volume were measured using a WYKO 3D optical surface profiler, and chemical characterization analysis was done using a PHI 5000 VersaProbe X-ray photoelectron spectroscope (XPS). It was found that nanoparticles have a great effect on the friction and wear characteristics of lubricants.

Stabilizer effect on CHF and boiling heat transfer coefficient of alumina/water nanofluids

We measured the critical heat flux (CHF) and boiling heat transfer coefficient (BHTC) of water-based Al2O3 (alumina) nanofluids. To elucidate the stabilizer effect on CHF and BHTC of alumina/water nanofluids, a polyvinyl alcohol (PVA) was used as a stabilizer. The plate copper heater (10×10mm2) is used as the boiling surface and the concentration of alumina nanoparticle varies 0–0.1vol.%. The results show that the BHTC of the nanofluids becomes lower than that of the base fluid as the concentration of nanoparticles increases while CHF of it becomes higher. It is found that the increase of CHF is directly proportional to the effective boiling surface area and the reduction of BHTC is mainly attributed to the blocking of the active nucleation cavity and the increase of the conduction resistance by the nanoparticle deposition on the boiling surface.

Flow Characteristics of Nanofluids According to Nanoparticles Shape

In this paper, flow characteristics of water-based Al2O3 nanofluids according to nanoparticles shape are experimentally investigated in fully developed laminar flow regime. Al2O3 nanofluids of 0.3 Vol. % with sphere-, rod-, blade-, platelet-and brick-shaped nanoparticles are manufactured by the two-step method. Nanoparticles shape dispersed in base fluid are also checked using TEM image. Zeta potential and sedimentation are measured to examine suspension and dispersion characteristics of Al2O3 nanofluids with nanoparticles of various shapes. Based on the experimental results, it is found that the pressure drop of Al2O3 nanofluids strongly depends on the shape of nanoparticles at the fixed volume fraction of 0.3%. We experimentally show that the pressure drop characteristics of Al2O3 nanofluids can be explained by both the surface area per unit mass and the size of nanoparticles which are related with the shape of nanoparticles.