Experimental investigation on the thermo-physical properties of Al2O3 nanoparticles suspended in car radiator coolant

Nanofluid is a new type of heat transfer fluid with superior thermal performance characteristics, which is very promising for thermal engineering applications. This paper presents new findings on the thermal conductivity, viscosity, density, and specific heat of Al₂O₃ nanoparticles dispersed into water and ethylene glycol based coolant used in car radiator. The nanofluids were prepared by the two-step method by using an ultrasonic homogenizer with no surfactants. Thermal conductivity, viscosity, density, and specific heat have been measured at different volume concentrations (i.e. 0 to 1 vol.%) of nanoparticles and various temperature ranges (i.e. from 10 °C to 50 °C). It was found that thermal conductivity, viscosity, and density of the nanofluid increased with the increase of volume concentrations. However, specific heat of nanofluid was found to be decreased with the increase of nanoparticle volume concentrations. Moreover, by increasing the temperature, thermal conductivity and specific heat were observed to be intensified, while the viscosity and density were decreased.     

Thermal conductivity of ethylene glycol and water mixture based Fe3O4 nanofluid

Thermal conductivity of ethylene glycol and water mixture based Fe₃O₄ nanofluid has been investigated experimentally. Magnetic Fe₃O₄ nanoparticles were synthesized by chemical co-precipitation method and the nanofluids were prepared by dispersing nanoparticles into different base fluids like 20:80%, 40:60% and 60:40% by weight of the ethylene glycol and water mixture. Experiments were conducted in the temperature range from 20 °C to 60 °C and in the volume concentration range from 0.2% to 2.0%. Results indicate that the thermal conductivity increases with the increase of particle concentration and temperature. The thermal conductivity is enhanced by 46% at 2.0 vol.% of nanoparticles dispersed in 20:80% ethylene glycol and water mixture compared to other base fluids. The theoretical Hamilton–Crosser model failed to predict the thermal conductivity of the nanofluid with the effect of temperature. A new correlation is developed for the estimation of thermal conductivity of nanofluids based on the experimental data.     

Experimental investigation and development of new correlation for thermal conductivity and viscosity of BioGlycol/water based SiO2 nanofluids

Nanofluids are a new class of engineered heat transfer fluids which exhibit superior thermophysical properties and have potential applications in numerous important fields. In this study, nanofluids have been prepared by dispersing SiO₂ nanoparticles in different base fluids such as 20:80% and 30:70% by volume of BioGlycol (BG)/water (W) mixtures. Thermal conductivity and viscosity experiments have been conducted in temperatures between 30 °C and 80 °C and in volume concentrations between 0.5% and 2.0%. Results show that thermal conductivity of nanofluids increases with increase of volume concentrations and temperatures. Similarly, viscosity of nanofluid increases with increase of volume concentrations but decreases with increase of temperatures. The maximum thermal conductivity enhancement among all the nanofluids was observed for 20:80% BG/W nanofluid about 7.2% in the volume concentration of 2.0% at a temperature of 70 °C. Correspondingly among all the nanofluids maximum viscosity enhancement was observed for 30:70% BG/W nanofluid about 1.38-times in the volume concentration of 2.0% at a temperature of 70 °C. The classical models and semi-empirical correlations failed to predict the thermal conductivity and viscosity of nanofluids with effect of volume concentration and temperatures. Therefore, nonlinear correlations have been proposed with 3% maximum deviation for the estimation of thermal conductivity and viscosity of nanofluids.     

Nanofluid convective heat transfer in a parallel-disk system

Inherently low thermal conductivities of basic fluids form a primary limitation in high-performance cooling which is an essential requirement for numerous thermal systems and micro-devices. Nanofluids, i.e., dilute suspensions of, say, metal-oxide nanoparticles in a liquid, are a new type of coolants with better heat transfer performances than their pure base fluids alone. Using a new, experimentally validated model for the thermal conductivity of nanofluids, numerical simulations have been executed for alumina-water nanofluid flow with heat transfer between parallel disks. The results indicate that, indeed, nanofluids are promising new coolants when compared to pure water. Specifically, smoother mixture flow fields and temperature distributions can be achieved. More importantly, given a realistic thermal load, the Nusselt number increases with higher nanoparticle volume fraction, smaller nanoparticle diameter, reduced disk-spacing, and, of course, larger inlet Reynolds number, expressed in a novel form as Nu = Nu(Re and Br). Fully-developed flow can be assumed after a critical radial distance, expressed in a correlation R_crit = fct(Re), has been reached and hence analytic solutions provide good approximations. Nanofluids reduce the system’s total entropy generation rate while hardly increasing the required pumping power for any given Re_in. Specifically, minimization of total entropy generation allows for operational and geometric system-optimization in terms of S_gen = fct (Re and δ).     

Transport properties of ultra-low concentration CuO–water nanofluids containing non-spherical nanoparticles

CuO–water nanofluids were prepared from non-spherical CuO nanoparticles by dispersing them in water through the aid of ultrasonication along with the use of Tiron as dispersant. Thermal conductivity enhancements of 13% and 44% have been obtained with 0.016 vol% CuO–water nanofluids at 28 °C and 55 °C respectively, which could be attributed to the high aspect ratio and Brownian motion of nanoparticles. Correlations have been developed to predict the influence of temperature (28–55 °C) and nanoparticles volume concentration (<0.016 vol%) on relative viscosity and thermal conductivity ratio. The results indicate the potential of this nanofluid for thermal management applications.     

Experimental thermal conductivity of ethylene glycol and water mixture based low volume concentration of Al2O3 and CuO nanofluids

Thermal conductivity of ethylene glycol and water mixture based Al₂O₃ and CuO nanofluids has been estimated experimentally at different volume concentrations and temperatures. The base fluid is a mixture of 50:50% (by weight) of ethylene glycol and water (EG/W). The particle concentration up to 0.8% and temperature range from 15 °C–50 °C were considered. Both the nanofluids are exhibiting higher thermal conductivity compared to base fluid. Under same volume concentration and temperature, CuO nanofluid thermal conductivity is more compared to Al₂O₃ nanofluid. A new correlation was developed based on the experimental data for the estimation of thermal conductivity of both the nanofluids.     

Cooling performance investigation of electronics cooling system using Al2O3–H2O nanofluid

In this study, the cooling performance of Al₂O₃–H₂O nanofluid was experimentally investigated as a much better developed alternative for the conventional coolant. For this purpose the nanofluid was passed through the custom-made copper minichannel heat sink which is normally attached with the electronic heat source. The thermal performance of the Al₂O₃–H₂O nanofluid was evaluated at different volume fraction of the nanoparticle as well as at different volume flow rate of the nanofluid. The volume fraction of the nanoparticle varied from 0.05 vol.% to 0.2 vol.% whereas the volume flow rate was increased from 0.50 L/min to 1.25 L/min. The experimental results showed that the nanofluid successfully has minimized the heat sink temperature compared to the conventional coolant. It was noticed also that the thermal entropy generation rate was reduced via using nanofluid instead of the normal water. Among the other functions of the nanofluid are to increase the frictional entropy generation rate and to drop the pressure which are insignificant compared to the normal coolant. Given the improved performance of the nanofluid, especially for high heat transportation capacity and low thermal entropy generation rate, it could be used as a better alternative coolant for the electronic cooling system instead of conventional pure water.     

The effect of alumina/water nanofluid particle size on thermal conductivity

This study examines the effect of particle size, temperature, and weight fraction on the thermal conductivity ratio of alumina(Al₂O₃)/water nanofluids. A Al₂O₃/water nanofluid produced by the direct synthesis method served as the experimental sample, and nanoparticles, each of a different nominal diameter (20, 50, and 100 nm), were dispersed into four different concentrations (0.5, 1.0, 1.5, and 2.0 wt%). This experiment measured the thermal conductivity of nanofluids with different particle sizes, weight fractions, and working temperatures (10, 30, 50 °C). The results showed a correlation between high thermal conductivity ratios and enhanced sensitivity, and small nanoparticle size and higher temperature. This research utilized experimental data to construct a new empirical equation, taking the nanoparticle size, temperature, and lower weight fraction of the nanofluid into consideration. Comparing the regression results with the experimental values, the margin of error was within ?3.5% to +2.7%. The proposed empirical equation showed reasonably good agreement with our experimental results.     

Performance investigation of an automotive car radiator operated with nanofluid-based coolants (nanofluid as a coolant in a radiator)

Water and ethylene glycol as conventional coolants have been widely used in an automotive car radiator for many years. These heat transfer fluids offer low thermal conductivity. With the advancement of nanotechnology, the new generation of heat transfer fluids called, “nanofluids” have been developed and researchers found that these fluids offer higher thermal conductivity compared to that of conventional coolants. This study focused on the application of ethylene glycol based copper nanofluids in an automotive cooling system. Relevant input data, nanofluid properties and empirical correlations were obtained from literatures to investigate the heat transfer enhancement of an automotive car radiator operated with nanofluid-based coolants. It was observed that, overall heat transfer coefficient and heat transfer rate in engine cooling system increased with the usage of nanofluids (with ethylene glycol the basefluid) compared to ethylene glycol (i.e. basefluid) alone. It is observed that, about 3.8% of heat transfer enhancement could be achieved with the addition of 2% copper particles in a basefluid at the Reynolds number of 6000 and 5000 for air and coolant respectively. In addition, the reduction of air frontal area was estimated.     

An experimental study on the heat transfer performance and pressure drop of TiO2-water nanofluids flowing under a turbulent flow regime

Nanofluid is a new class of heat transfer fluids engineered by dispersing metallic or non-metallic nanoparticles with a typical size of less than 100 nm in the conventional heat transfer fluids. Their use remarkably augments the heat transfer potential of the base liquids. This article presents the heat transfer coefficient and friction factor of the TiO₂-water nanofluids flowing in a horizontal double tube counter-flow heat exchanger under turbulent flow conditions, experimentally. TiO₂ nanoparticles with diameters of 21 nm dispersed in water with volume concentrations of 0.2–2 vol.% are used as the test fluid. The results show that the heat transfer coefficient of nanofluid is higher than that of the base liquid and increased with increasing the Reynolds number and particle concentrations. The heat transfer coefficient of nanofluids was approximately 26% greater than that of pure vol.%, and the results also show that the heat transfer coefficient of the nanofluids at a volume concentration of 2.0 vol.% was approximately 14% lower than that of base fluids for given conditions. For the pressure drop, the results show that the pressure drop of nanofluids was slightly higher than the base fluid and increases with increasing the volume concentrations. Finally, the new correlations were proposed for predicting the Nusselt number and friction factor of the nanofluids, especially.     

Rheology and thermal conductivity of non-porous silica (SiO2) in viscous glycerol and ethylene glycol based nanofluids

Nanofluids are advanced fluids with novel properties useful for diverse applications in heat transfer. This article reports the experimental determination of thermal conductivity and viscosity for silica (SiO₂) nanofluids in ethylene glycol (EG) and glycerol (G) as base fluids. A two-step method was applied to disperse the nanoparticles in the base fluids for the particle volume concentration of 0.5–2.0%. The dispersion stability of the nanofluids was evaluated by zeta potential analysis. All the measurements were performed in the temperature interval from 30 °C to 80 °C. It was found that the thermal conductivity increases with temperature. The SiO₂-EG showed higher conductivity enhancement than SiO₂-G nanofluids. Rheological analyses confirm Newtonian behavior for silica nanofluids within shear rate range of 20–100 s^− 1. Viscosity decreases with an increase in operating temperature. The SiO₂-EG demonstrated very weak temperature dependence compared to the SiO₂-G nanofluids. Based on these measured properties, the criterion for heat transfer performance was determined. Furthermore, equations have been proposed with accuracy within ± 10% deviations to predict the thermal conductivity and dynamic viscosity of EG and G-based SiO₂ nanofluids.     

Experimental investigation and model development for thermal conductivity of α-Al2O3-glycerol nanofluids

In order to investigate the effect of nanoparticle volume fraction, nanoparticle size and temperature on the thermal conductivity of glycerol based alumina (α-Al₂O₃) nanofluids, a set of experiments were carried out for temperature ranging from 20 °C to 45 °C. The nanofluids contained α-Al₂O₃ nanoparticles of three different sizes (31 nm, 55 nm and 134 nm) were prepared by two-step method at volume fractions ranging from 0.5% to 4%. The experimental results show that α-Al₂O₃-glycerol nanofluids have substantially higher thermal conductivity than the base fluid and the maximum enhancement of the relative thermal conductivity was 19.5% for the case of 31 nm at 4% volume fraction. The data analyses indicated that the volume fraction and size of the nanoparticles have significant effects on the thermal conductivity ratio (TCR) of Al₂O₃-glycerol nanofluids, while the temperature has almost no significant effect on the data for range of this study. At room temperature, the effective thermal conductivity remains almost constant for 50 h at 4% volume fractions. The comparison of the obtained experimental data and predictions from some existing theoretical and empirical models reveals that the thermal conductivity ratio and its trend could not be accurately explained by the models in open literature. Consequently, a new empirical correlation based on the experimental data has been developed in this study.     

Effect of nanofluids on reflood heat transfer in a long vertical tube

Experiments were conducted to investigate the effect of nanofluids on reflood heat transfer in a hot vertical tube. The nanofluids, which are produced by dispersing nano-sized particles in traditional base fluids such as water, ethylene glycol, and engine oil, are expected to have a reasonable potential to enhance a heat transfer. 0.1 volume fraction (%) Al₂O₃/water nanofluid was prepared by two-step method and 0.1 volume fraction (%) carbon nano colloid (CNC) was prepared by the process self-dispersing by carboxyl formed particle surface. Transmission electron microscopy (TEM) images are acquired to characterize the shape and size of Al₂O₃ and graphite nanoparticles. The dispersion behavior of nanofluids was investigated with zeta potential values. And then, the reflood tests have been performed using water and nanofluids. We have observed a more enhanced cooling performance in the case of the nanofluid reflood. Consequently, the cooling performance is enhanced more than 13 s and 20 s for Al₂O₃/water nanofluid and CNC.     

Thermal performance of multi-walled carbon nanotubes (MWCNTs) in aqueous suspensions with surfactants SDBS and SDS

The surfactants of sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) are used in multi-walled carbon nanotubes (MWCNT) aqueous solution respectively due to the hydrophobic nature of MWCNT. Thermal conductivities of nanofluid solutions are measured via the LAMBDA measuring system by transient hot wire method and compared as function of dispersing two different surfactants. MWCNT (hereinafter sometime referred to as CNTs) nanofluid gets a good dispersion and long time stability with both surfactants within 3/1 relative ratio mixture. However, the thermal conductivity of nanofluid decreases with increasing the concentration of both surfactants, and CNT nanofluid with SDBS exhibits better thermal conductivity than that with SDS dispersant. Finally the proper mixture ratio of CNT nanofluid with SDBS and pH value is examined and results show that 0.5 wt.% CNT nanofluids with 0.25 wt.% SDBS, at pH ≈ 9.0 condition display the best thermal performance which increases by 2.8% totally on thermal conductivity compared with that of base fluid distilled water (DW).     

Experimental investigation of the thermal transport properties of graphene oxide/Co3O4 hybrid nanofluids

The in-situ growth and chemical co-precipitation method was used for the synthesis of uniform dispersion of Co₃O₄ nanoparticles on the graphene oxide (GO) nanosheet. The reductions of aqueous cobalt chloride in the presence of GO with sodium borohydrate result in the formation of hybrid GO/Co₃O₄ nanoparticles. The synthesized GO/Co₃O₄ nanoparticles were characterized using X-ray power diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The hybrid nanofluids were prepared by dispersing synthesized GO/Co₃O₄ nanoparticles in water, ethylene glycol, and ethylene glycol/water mixtures. The properties such as thermal conductivity and viscosity were estimated experimentally at different volume concentrations and temperatures. The thermal conductivity enhancement of water-based nanofluid is 19.14% and ethylene glycol-based nanofluid is 11.85% at 0.2% volume concentration and at a temperature of 60 °C respectively compared to their respective base fluids. Similarly, the viscosity enhancement of water-based nanofluid is 1.70-times and ethylene glycol-based nanofluid is 1.42-times at 0.2% volume concentration and at a temperature of 60 °C respectively. The obtained thermal conductivity and viscosity data is compared with the literature values.     

Impact analysis of natural convection on thermal conductivity measurements of nanofluids using the transient hot-wire method

Significant deviations between published results have been reported measuring the effective thermal conductivity of nanofluids with the transient hot-wire method (THWM). This may be attributed to a poor selection of the temperature data range, which should meet the following conditions. The start time should be chosen after the conductive heat flux delay time, while the end time should be selected before a crossover point when natural convection becomes significant. Considering an EG-based 1.06 vol.% ZnO nanofluid, the thermal conductivity was measured to increase by 5.4% over that of the base fluid.     

Simulation of heat transfer enhancement in nanofluids using dissipative particle dynamics

The current paper applied dissipative particle dynamics (DPD) approach to investigate heat transfer within nanofluids. The DPD approach was applied to study natural convection in a differential heated enclosure by considering the viscosity and the thermal conductivity of the nanofluid to be dual function of temperature and volume fraction of nanoparticles. Experimental data for viscosity and thermal conductivity are incorporated in the current DPD model to mimic energy transport within nanofluids. This incorporation is done through the modification of the dissipative weighting function that appears in the dissipative force vector and the dissipative heat flux. For the entire range of Rayleigh number considered in this study, it was found that the DPD results show a deterioration in heat transfer in the enclosure due to the presence of nanoparticles for φ > 4%. However, some slight enhancement is shown to take place for small volume fraction of nanoparticles, φ ≤ 4%. The DPD results experienced some degree of compressibility at high values of Rayleigh number Ra ≥ 10⁵.     

Investigation of thermal conductivity and viscosity of Fe3O4 nanofluid for heat transfer applications

Experimental investigations and theoretical determination of effective thermal conductivity and viscosity of magnetic Fe₃O₄/water nanofluid are reported in this paper. The nanofluid was prepared by synthesizing Fe₃O₄ nanoparticles using the chemical precipitation method, and then dispersed in distilled water using a sonicator. Both experiments were conducted in the volume concentration range 0.0% to 2.0% and the temperature range 20 °C to 60 °C. The thermal conductivity and viscosity of the nanofluid were increased with an increase in the particle volume concentration. Viscosity enhancement was greater compared to thermal conductivity enhancement under at same volume concentration and temperature. Theoretical equations were developed to predict thermal conductivity and viscosity of nanofluids without resorting to the well established Maxwell and Einstein models, respectively. The proposed equations show reasonably good agreement with the experimental results.     

Thermo-physical properties of water based SiC nanofluids for heat transfer applications

The aim of current paper consists in the fabrication, characterization and preparation of water based on SiC nanofluids and the experimental investigation of their thermo-physical properties. Thermal conductivity, viscosity and surface tension of SiC/water nanofluids were measured for two two weight concentrations of nanoparticles 0.5 and 1.0 wt% respectively, within the range 20 °C to 50 °C. Concerning the thermal-properties of studied nanofluids, the experimental results show that the thermal conductivity increases with the increasing both of the weight concentration of the nanoparticles and temperature. Also, the dynamic viscosity of the SiC/water nanofluids increases with increasing nanoparticles concentration and decreases with the increasing temperature. Furthermore, the surface tension of studied nanofluids increases with the increase of the weight concentrations of the nanoparticles, but the results show that at a concentration of the nanoparticles of 0.5 wt%, the surface tension was lower than the surface tension of the water, while at 1.0 wt% nanoparticles, the surface tension of the nanofluids was close to the surface tension of the water. Measurements were compared with experimental data available in literature and theoretical models. Finally, SiC/water nanofluids were used as working fluid inside of the two-phase closed thermosyphon in order to study of the heat transfer from point of view both of operating temperature and the nanoparticles concentration.     

Heat transfer and entropy generation for laminar forced convection flow of graphene nanoplatelets nanofluids in a horizontal tube

The results are reported of an investigation of the heat transfer characteristics and entropy generation for a graphene nanoplatelets (GNP) nanofluid with specific surface area of 750 m²/g under laminar forced convection conditions inside a circular stainless steel tube subjected to constant wall heat flux. The analysis considers constant velocity flow and a concentration range from 0.025 wt.% to 0.1 wt.%. The impact of the dispersed nanoparticles concentration on thermal properties, convective heat transfer coefficient, thermal performance factor and entropy generation is investigated. An enhancement in thermal conductivity for GNP of between 12% and 28% is observed relative to the case without nanoparticles. The convective heat transfer coefficient for the GNP nanofluid is found to be up to 15% higher than for the base fluid. The heat transfer rate and thermal performance for 0.1 wt.% of GNP nanofluid is found to increase by a factor of up to 1.15. For constant velocity flow, frictional entropy generation increases and thermal entropy generation decreases with increasing nanoparticle concentration. But, the total entropy generation tends to decrease when nanoparticles are added at constant velocity and to decrease when velocity rises. Finally, it is demonstrated that a GNP nanofluid with a concentration between 0.075 wt.% and 0.1 wt.% is more energy efficient than for other concentrations. It appears that GNP nanofluids can function as working fluids in heat transfer applications and provide good alternatives to conventional working fluids in the thermal fluid systems.