Al2O3-water Nanofluid Research Articles

Thermofluidic characteristic of a nanofluid-cooled oblique fin heat sink: An experimental and numerical investigation

This paper presents an experimental and numerical investigation on the thermofluidic performance of 0.5–2.0 % of the volumetric concentration of Al2O3-water nanofluids through oblique fin heat sink microchannel (OFHS MC) in the Reynolds number range 100–300. In comparison, experiments were also performed using a straight channel heat sink microchannel (SCHS MC) of the same hydraulic diameter as the oblique fin channel. The fluid flow is simulated using the RNG k-ε model in both periodic and full domain numerical analysis. The phenomenological behaviour of the nanofluid flow is further studied using numerical results. The oblique fin microchannel encouraged the secondary flow, thus enhanced the macroscopic mixing. Boundary layer disruption and vortices generation in the secondary channel is the critical phenomena of improved heat transfer. A substantial improvement of heat transfer coefficient is achieved for nanofluid and oblique fin heat sink combinations compared to the straight channel heat sink. The heat transfer coefficient is increased at increasing nanofluid concentrations for any given Reynolds number and channel configuration. The enhancement of about 55 % in the heat transfer coefficient with a 2 % volumetric concentration of nanofluid is achieved at Re = 300 in an oblique fin heat sink. The heat transfer enhancement is always significant than the pressure penalty. The oblique fin heat sink improves the average junction temperature considerably compared to the straight channel heat sink. The inclusion of nanofluid can reduce the experimental junction temperature by up to 6 °C. Therefore, the combined advantage of the oblique fin heat sink with nanofluid is anticipated as one of the potential alternatives for electronics cooling.

Experimental investigation into spray cooling heat transfer performance of Al2O3-water nanofluid with different subcooling degrees

This study investigated the spray cooling heat transfer performance of Al2O3-water nanofluid given four different subcooling degrees (0 °C, 10 °C, 20 °C, and 30 °C). The results showed that the subcooled nanofluids were ranked in order of a reducing spray cooling heat transfer performance as follows: 20 °C, 10 °C, 0 °C, and 30 °C. On average, the heat transfer coefficient obtained using the nanofluid with 20 °C subcooling was around 8.3%, 8.6%, and 15.6% higher than that obtained with 10 °C, 0 °C, and 30 °C subcooling, respectively. However, the heat transfer performance decreased with an increasing spray operating time. The scanning electron microscopy observations showed that the reduction in the heat transfer coefficient was the result of a gradual increase in the thickness of the nano-adsorption layer on the heated surface as the spray operating time increased.

Turbulent forced convection and entropy analysis of a nanofluid through a 3D 90° elbow using a two‐phase approach

AbstractIn a scenario characterized by a secondary flow called Dean's vortices, thermal and flow behavior analysis is examined. Forced convection of an Al2O3–water nanofluid through a three‐dimensional (3D) 90° elbow was analyzed numerically using a multiphase mixture model. Turbulence is taken into account by using the shear‐stress transportk–ωmodel. Also, entropy production is presented to obtain the optimized conditions. Simulation parameters consist of different Reynolds numbers (10,000100,000), nanoparticle volume fraction , nanoparticle diameter . The findings reveal that the increase in the and theRealong with a smallerdpdiscourages the appearance of Dean vortices in the flow. The pressure drop increases with the increase in the volume fraction and the decrease in the nanoparticles' diameter. The highestNuMis observed at for . Significant heat transfer rates are observed near the outer wall. The minimum total entropy production is obtained atRe = 100,000 for and .

Spreading-splashing transition of nanofluid droplets on a smooth flat surface

HypothesisEven a small fraction of nanoparticles in fluids affects the splashing behavior of a droplet upon impact on a smooth surface. ExperimentsNanofluid drop impact onto a smooth sapphire substrate is experimentally investigated over wide ranges of Reynolds (102<Re<104) and Weber (50<We<500) numbers for three nanofluid mass concentrations (0.01%, 0.1%, 1%) using high-speed photography. Nanofluids are prepared by diluting a commercial Al2O3-water nanofluid in aqueous glycerol solutions without dispersants. In total, 30 samples are prepared and 1799 data points are acquired. Every sample is experimentally characterized prior to droplet impact measurements in terms of stability, density, viscosity, and surface tension to demonstrate the observed outcomes on the We-Re maps. Each droplet impact condition is repeated at least 3 times to ensure good repeatability. FindingsThe non-monotonic behavior of the spreading-to-splashing transition remains the same for nanofluids. However, nanofluids influence this boundary by promoting splashing at low Reynolds numbers. We explain this behavior by increased lamella spreading speed and lift during the lamella spreading stage. Finally, we develop an empirical correlation which describes the splashing threshold dependency on nanoparticle concentration for the first time.

Numerical Study on the Fluid Flow and Heat Transfer Characteristics of Al2O3-Water Nanofluids in Microchannels of Different Aspect Ratio.

The study of the influence of the nanoparticle volume fraction and aspect ratio of microchannels on the fluid flow and heat transfer characteristics of nanofluids in microchannels is important in the optimal design of heat dissipation systems with high heat flux. In this work, the computational fluid dynamics method was adopted to simulate the flow and heat transfer characteristics of two types of water-Al2O3 nanofluids with two different volume fractions and five types of microchannel heat sinks with different aspect ratios. Results showed that increasing the nanoparticle volume fraction reduced the average temperature of the heat transfer interface and thereby improved the heat transfer capacity of the nanofluids. Meanwhile, the increase of the nanoparticle volume fraction led to a considerable increase in the pumping power of the system. Increasing the aspect ratio of the microchannel effectively improved the heat transfer capacity of the heat sink. Moreover, increasing the aspect ratio effectively reduced the average temperature of the heating surface of the heat sink without significantly increasing the flow resistance loss. When the aspect ratio exceeded 30, the heat transfer coefficient did not increase with the increase of the aspect ratio. The results of this work may offer guiding significance for the optimal design of high heat flux microchannel heat sinks.

MHD double-diffusive mixed convection and entropy generation of nanofluid in a trapezoidal cavity

Double diffusive, Magnetohydrodynamics (MHD), mixed convection flow of Al2O3-water nanofluid inside a trapezoidal enclosure with discrete heat and mass source at the bottom wall of the cavity has been discussed numerically. Together with these entropy generations due to fluid friction, heat transfer, mass transfer and magnetic field are discussed. The upper wall of the cavity is considered to move with a fixed velocity U0 towards positive X-direction. Different inclination angles and different aspect ratios are considered in the present study. Second and fourth order finite difference approximations are used to solve the governing equations by using biconjugate gradient stabilized method (BiCGStab). It is observed that, entropy generation mostly depends on heat transfer and lower values of Richardson number (Ri=0.01) reduces the entropy generation. The highest quantitative value of |Sθ|max is 21,664 for Ri=100,Re=100andϕ=450 and lowest quantative value of |Sθ|max is 5,824 for Ri=0.01,Re=1000andϕ=600 throughout the present study. Also the highest quantitative values of average Nusselt and Sherwood numbers are 0.2597 and 0.4208 for Ri=10,Re=100andϕ=45∘. The main objective of our present study is to minimize entropy generations due to combined effects of fluid flow, heat transfer, mass transfer and the effect of magnetic field so that the loss of energy can be reduced. This study observed that mixed convection flow, low magnetic field and low aspect ratio cavity of rectangular shape is always preferable to reduce total entropy generation and the middle part of the lower wall of the cavity is highly acceptable for heat and mass source for sprinkle of heat and mass throughout the whole of the cavity.

Nucleate pool boiling heat transfer above laser machining heating surfaces with different micro-cavity geometric shape for water-aluminum oxide nanofluid

ABSTRACT The present paper reports the experimental investigation of nucleate pool boiling heat transfer above heating surface with the creation of new geometric micro-cavities. Cylindrical, cubic, and pentagonal micro-cavities created on heating surface were studied. Micro-cavity surfaces were fabricated using a fiber laser machine. The heat transfer coefficient (HTC) of the heating surfaces were estimated experimentally by using pure water and water–Al2O3 nanofluid. The results showed that by creating geometrical micro-cavity on the heating surface, a maximum improvement of 83%–123.4% was obtained when using pure water. At a concentration of 0.005 vol.% nanofluid, the HTC increased by 95.2%–140.5% for different micro-cavities.

Numerical study of fluid flow and heat transfer for flow of Cu-Al2O3-water hybrid nanofluid in a microchannel heat sink

The use of micro-electronic devices in many applications such as aerospace, telecommunications, micro-electronics, robotics is drastically increasing and they need efficient cooling system. Micro-channel heat sinks (MCHS) are getting significant importance due to their very high surface to volume ratio and high heat dissipation rate. The hybrid nanofluids playing a vital role as cooling fluids in various thermal transportation applications due to their extraordinary heat transport characteristics. A numerical study is taken up for laminar flow of hybrid nanofluid as a heat transport medium in a rectangular MCHS to realize thermal and hydrodynamic behaviour in forced convection. The influence of Reynolds number (Re) and volume concentration of nanoparticles in Cu-Al2O3/water hybrid nanofluid on MCHS performance is investigated in the present paper. The correlations presented in the literature are used to calculate the properties of hybrid nanofluids. For various mixture ratios of 25–75%, 50–50% and 75–25% hybrid nanofluids the heat transport rate and pressure drop are calculated at different Reynolds numbers and compared with mono nanofluids of Cu-water (H2O) and Al2O3-water. An enhancement in heat transfer rate is observed with raise in volume fraction and marginal increase in pressure drop is observed for hybrid nanofluids over mono nanofluids of Cu-water and Al2O3-water. The results indicate an increase of 13.2% and 23.07% in Nusselt number for Cu-Al2O3/water hybrid nanofluid compared with Cu/water and Al2O3/water mono nanofluids respectively at 2.5% volume fraction. It is found from the numerical results that the pumping power requirement is less for hybrid Cu-Al2O3/water nanofluid compared to Cu/water nanofluids and an increase of 430 Pa compared to pure water. The data existing for Al2O3-water nanofluid in the literature is used to validate the present model.

Control of the free convective heat transfer using a U-shaped obstacle in an Al2O3-water nanofluid filled cubic cavity

This paper deals with the study of free convection in a 3D enclosure filled with Al2O3-nanofluid and equipped with a U-shaped obstacle. The used U-shaped obstacle is considered perfectly conductive. The effect of the dimension and the orientation of the obstacle is investigated. In addition, the parameters governing the problem are varied as Rayleigh number (103 to 106), and nanoparticles volume fraction (0 to 7.5%). Results are depicted in terms of flow structures, temperature fields, and Nusselt number. Results show that the obstacle dimension and orientation can control the flow and optimize the heat transfer and the addition of nanoparticles enhances significantly Nusselt number.

Numerical investigation on natural convection of Al2O3/water nanofluid with variable properties in an annular enclosure under magnetic field

Numerical investigation of the natural convection of Al2O3-water nanofluid is carried out in a differentially heated vertical annulus under a uniform magnetic field. An in-house Fortran code has been developed to solve the system of equations governing the magneto-hydrodynamic flow. Computations are carried out for different Rayleigh numbers (104 ≤ Ra ≤ 106), nanoparticle diameter (dp = 13 and 47 nm), nanoparticle volume fraction (0 ≤ φ ≤ 0.09), radius ratio (2 ≤ λ ≤ 10), and different Hartmann numbers (0 ≤ Ha ≤ 100). According to the simulation data, nanoparticle size is crucial for evaluating nanofluid properties, such as viscosity and thermal conductivity. The computational results reveal that, for nanoparticles with a diameter dp = 47 nm, the average Nusselt number Nu¯i on the inner cylinder wall decreases as the nanofluid volume fraction increases. This decrease in Nu¯i number is observed up to a volume fraction φ = 0.05, after which it increases again. For the full range of volumetric fractions, it is shown that increasing Ra number causes Nu¯i to increase, while increasing Ha number and increasing the magnetic field causes Nu¯i to decrease. Furthermore, as the Ha number increases, the heat transfer enhancement ratio En increases mainly when the magnetic field is oriented radially. Finally, new correlations of Nu¯i versus Ra, φ, Ha, and λ are derived for the axial and radial magnetic fields cases.

Two-and-three-dimensional analysis of Joule and viscous heating effects on MHD nanofluid forced convection in microchannels

This paper aims to study viscous heating, Joule heating and their simultaneous impacts on Al2O3-water nanofluid laminar flow and thermal characteristics in the presence of a magnetic field inside microchannels. The flow field and heat transfer are modeled two- and three-dimensionally by employing the finite volume method. To investigate the influence of viscosity variation with temperature on viscous heating, a temperature-dependent viscosity correlation specifically presented for Al2O3-water is employed. Predicted results indicate that viscosity changes due to temperature changes are negligible and although viscous heating can be reasonably ignored in the absence of the magnetic field, it must be taken into account when the magnetic field is applied. At the Hartmann number of 20, near microchannel walls, the velocity gradient rises up to 165% where the viscous dissipation significantly increases the temperature. In addition, when the magnetic field is applied, the 2D model underestimates the temperature compared to the 3D model where the effects of maximum velocity and velocity gradient on the energy equation and heat dissipation exist. The temperature profiles demonstrate that at the Hartmann number of 20, the effects of Joule heating or viscous heating increase the maximum dimensionless temperature by a factor of about 2.5 and by the rise of the Hartmann number, the dimensionless temperature increases and the effects of Joule and viscous heating become more significant. All in all, it is concluded that the heat generated by viscous and Joule heating can remarkably decrease the cooling performance of microchannels in the presence of magnetic fields.

Optimization of fins arrangements for the square light emitting diode (LED) cooling through nanofluid-filled microchannel

In current paper, a finned micro-channel is designed for the cooling application in Light Emitting Diode (LED), numerically using Galerkin weighted residual Finite Element Method (GFEM). Selected materials for LED-chip is GaN, Die from Si, Die-attach is made by Au-20Sn, substrate is copper and heat sink material is considered to be Al. To make a convection heat transfer for cooling process, Al2O3-water nanofluid is used as the cooling fluid flow through the micro-channel and tried to maximize the heat transfer efficiency by optimized geometry. For this aim, there geometry variables from the microchannel were selected and minimum possible geometry cases (11 cases) were proposed by Central composite design (CCD) and variables were optimized by the Response Surface Method (RSM). As a main result, parameter B, i.e. fin length had the most effect on the Nusselt number and Al2O3 nanoparticles with φ = 0.05 stated greatest heat transfer value. Also, different designs of fins arrangements, caused up to 6.5% increase in the nanofluid temperature which enhanced the LED cooling process.

Dual solutions of bioconvection hybrid nanofluid flow due to gyrotactic microorganisms towards a vertical plate

The impact of gyrotactic microorganisms in the mixed convection stagnation point flow of Cu-Al2O3/water hybrid nanofluid towards an immovable plate is numerically examined. The boundary layer equation coupled with the energy, nanoparticle volume fraction and conservation equations for microorganisms are simplified into a set of ordinary differential equations by adopting similarity transformation. The validation results are in a good agreement with previous studies approximately by 0% difference relative error. The results imply that the dual solutions only exist in the opposing flow up to a critical value/turning point. Beyond this turning point, the solutions are unavailable which reflects the separation of flow. The hybrid nanofluid is essential in delaying the separation process where the results show that λc,hnf=−3.5804>λc,Cu=−3.3903>λc,Al=−3.2016. Moreover, the advantage of this hybrid Cu-Al2O3/water nanofluid is in the augmentation of heat and mass transfer rates including the density of microorganisms which is higher than the Cu- and Al2O3-water nanofluids.

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.

Improvement of Heat Pipe Solar Collector Thermal Efficiency Using Al2O3/Water and TiO2/Water Nanofluids

Heat pipe solar collectors (HPSCs) are heat exchangers that carry heat based on the phase change of the heat pipe working fluid. It is aimed to increase the operating temperature range of solar collectors by changing the phase of the working fluid in the heat pipe at low temperature. For this reason, it has become widespread to use nanofluids obtained by mixing nanosized metal oxides with the base fluid in certain proportions in order to increase both the thermal conductivity of the heat pipe working fluids and to increase the specific heat closures. The main purpose of this study, which was conducted to evaluate the performance of HPSCs, is to increase performance, and an experimental study has been conducted in this direction. For this purpose, an HPSC designed and manufactured was used. Al2O3-water and TiO2-water nanofluids containing 2% nanoparticles were used in order to increase performance in the study. HPSC used in the study consists of 8 heat pipes with a length of 100 cm. The experiments were carried out for pure water and nanofluids, and their efficiency and strength were compared. The highest value of instantaneous efficiency was calculated as 48% when pure water was used as the working fluid, 58% for Al2O3-water nanofluid, and 64% for TiO2-water nanofluid. The instantaneous power obtained using pure water was determined as 135.66 W, 167.96 W for Al2O3-water nanofluid, and 184.03 W for TiO2-water nanofluid. The improvement in efficiency was determined as 20.8% for Al2O3-water nanofluid and 33.3% for TiO2-water nanofluid. Improvement in powers was found to be 23.8% for Al2O3-water nanofluid and 35.6% for TiO2-water nanofluid.

Investigating the thermal efficiency and pressure drop of a nanofluid within a micro heat sink with a new circular design used to cool electronic equipment

The present study numerically simulates a new circular micro heat sink (HS) used to cool electronic equipment (i.e., CPU). The HS contained Al2O3-water nanofluid (NF) at the concentration of 0–1%. The HS had a diameter and a thickness of 7.6 and 0.5 mm, respectively. It included two separate inlets with a 6 mm-diameter middle section subjected to a fixed heat flux of 100 W/cm2. NF flows were employed to cool the HS at the Reynolds numbers of 500–1500. The FVM-based SIMPLE algorithm was developed to obtain the entropy generation, thermal efficiency, and pressure drop. The results revealed that a rise in Re number and NF concentration enhanced Nu and head loss, while reduced the maximum and average temperatures of the electronic device. The best figure of merit (FOM) of the HS was found to be 1.12. A raise in the fluid velocity and NF concentration increased the pumping power but reduced thermal resistance.

Effect of the wavy tank wall on the characteristics of mechanical agitation in the presence of a Al2O3-water nanofluid

The enhancement of the heat transfer in the stirred tank is a much-desired objective for accelerating certain physical and chemical parameters in the industrial field. From this basis, an attempt is made in this paper to investigate the effect of the wavy wall of a stirred tank on the hydrodynamic, thermal, and energetic behavior of an Al2O3-Water nanofluid. The stirred tank has a flat bottom, and it is equipped with an anchor stirrer. A hot temperature has been imposed on the tank wall, and the agitator has been assumed adiabatic, where the nanofluid has a cold temperature at the initial instant. The laminar flow was governed by the equations that describe the forced convection, and it was solved by the finite element method. The numerical simulation results showed a considerable acceleration in the heat transfer inside the stirred tank by increasing the amplitude of the wavy wall and increasing the nanoparticle concentration. However, there has been a remarkable increase in the stirring power number. This contribution aims to increase thermal efficiency, especially in the chemical and petrochemical fields, to obtain a better yield of certain chemical reactions and mass transfer depending on the heat.

Numerical study on the flow and heat transfer of water-based Al2O3 forced pulsating nanofluids based on self-excited oscillation chamber structure

In this study, the flow and heat transfer characteristics of the forced pulsating Al2O3-water nanofluid were numerically studied. The pulsating excitation of the nanofluid is provided by the Helmhertz self-excited oscillating cavity. The large eddy simulation method is used to solve the equation, and the local Nusselt number and heat transfer performance index are used to analyze the heat transfer characteristics of the nanofluid in the self-excited oscillation heat exchange tube. In addition, the effect of different downstream tube diameters on heat transfer enhancement is discussed. The research results show that the existence of the countercurrent vortex can increase the disturbance of the near-wall fluid, thereby improving the mixing degree of the near-wall fluid and the central mainstream. As the countercurrent vortex migrates downstream, pulse enhanced heat transfer is realized. Furthermore, it was also found that when the downstream tube diameter d2 = 1.8d1, the periodic effect of the local Nusselt number of the wall is the best and the heat transfer performance index has the most stable pulsation effect within a pulsation cycle. But when d2 = 2.0d1, the change curve of heat transfer performance index in a pulsating period is the highest, the maximum value is 3.95.

Experimental investigation of Al2O3-water nanofluid as a secondary fluid in a refrigeration system

In the present study, a new technique of utilizing nanofluid as a secondary fluid in a secondary loop of refrigeration system is examined. This secondary loop serves for providing cooling in specific applications such as walk-in coolers and freezers. The secondary loop is obtained across the evaporator section wherein the refrigerant R134a extracted heat from the nanofluid. The evaporator here is classified as shell and coil heat exchanger where nanofluid flowed in the shell side and refrigerant flowed in the coil. A compressor, expansion valve and water cooled condenser are the major integral parts of the system. Experiments were conducted for various volume concentrations of Al2O3 nanofluid (0-15%), mass flow rates (40-80 g/s) and nanofluid inlet temperatures (30-40 °C). The modified system exhibited superior performance when Al2O3 nanofluid was employed in the secondary loop as compared to base fluid (distilled water) while operating at the same mass flow rate and inlet temperature. A maximum COP of 6.5 was achieved for nanofluid inlet temperature 40 C at mass flow rate 80 g/s and volume concentration 15%. The enhancement in refrigeration effect and coefficient of performance is attributed to micro conduction effect due to the rise in thermal conductivity of nanofluid as compared to distilled water.

Optimization of nanofluid heat transfer in a microchannel heat sink with multiple synthetic jets based on CFD-DPM and MLA

This study uses a combination of computational fluid dynamics consisting of the discrete phase model (CFD-DPM) coupled with support vector regression-particle swarm optimization (SVR-PSO) techniques to maximize the cooling performance of Al2O3water nanofluids in a microchannel heat sink (MCHS) with multiple synthetic jets (SJs). First, a CFD parametric study is carried out to understand the effect of influential parameters, including orifice spacing, particle volume fraction, orifice height, diaphragm length, phase actuation of jets, frequency and amplitude of oscillating diaphragms. A hybrid SVR-PSO algorithm is then adopted to predict the optimum values of the influential parameters for the maximum homogeneous heat transfer. The results predicted by the machine learning algorithm (MLA) are also compared to CFD findings. 0.15% and 3.5% deviations are found between predicted and actual values for the minimum average temperature and temperature uniformity, respectively. The parametric study reveals that heat transfer increases when the two jets are placed apart from each other. Based on the parametric study, the average temperature drops by 4.3 K as the membrane length increases from 0.95 mm to 1.96 mm. The highest heat transfer is obtained at a particle volume fraction of 5% in both jet arrangements. It is found that increasing the amplitude and frequency of the membranes results in better cooling performance. The results also confirm that larger orifice heights allow the creation of longer and stronger flows in the orifices that propagate the furthest in the microchannel. Overall, in-phase jet configurations show more uniform and lower temperatures (e.g., better heat transfer) at higher particle concentrations compared to the 180° out-of-phase jet arrangements.