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.     

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.     

Experimental studies on thermal conductivity of blends of ethylene glycol-water-based TiO2 nanofluids

A set of three nanofluids of different blends were prepared with ethylene glycol–water and TiO₂ nanoparticles and are characterized for thermal conductivity as a function of temperature and volume concentration of nanoparticles. The measurements were taken in the temperature range from 30 °C to 70 °C, which happens to be most widely used range of temperature for many cooling applications in heat transfer equipment. Nanofluids were prepared by dispersing the nanoparticles in base fluids such as (1) water, (2) ethylene glycol plus water in the ratio of 40%:60% and 3) ethylene glycol plus water in the ratio of 50%:50% by weight. Based on the experimental results, it is observed that the thermal conductivity of TiO₂ nanofluids, considered in the present investigation, increases with increase in percentage of volume concentration of TiO₂ and also with temperature. Current experimental investigation presents valuable data on the measured thermal conductivity of TiO₂ nanofluids for very low volume concentrations from 0.2% to 1.0% of nanoparticles in the temperature range of 30 °C–70 °C.     

Experimental study on the thermo-physical properties of car engine coolant (water/ethylene glycol mixture type) based SiC nanofluids

The engine coolant (water/ethylene glycol mixture type) becomes one of the most commonly used commercial fluids in cooling system of automobiles. However, the heat transfer coefficient of this kind of engine coolant is limited. The rapid developments of nanotechnology have led to emerging of a relatively new class of fluids called nanofluids, which could offer the enhanced thermal conductivity (TC) compared with the conventional coolants. The present study reports the new findings on the thermal conductivity and viscosity of car engine coolants based silicon carbide (SiC) nanofluids. The homogeneous and stable nanofluids with volume fraction up to 0.5 vol.% were prepared by the two-step method with the addition of surfactant (oleic acid). It was found that the thermal conductivity of nanofluids increased with the volume fraction and temperature (10–50 °C), and the highest thermal conductivity enhancement was found to be 53.81% for 0.5 vol.% nanofluid at 50 °C. In addition, the overall effectiveness of the current nanofluids (0.2 vol.%) was found to be ~ 1.6, which indicated that the car engine coolant-based SiC nanofluid prepared in this paper was better compared to the car engine coolant used as base liquid in this study.     

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.     

Unconfined laminar nanofluid flow and heat transfer around a square cylinder

The momentum and forced convection heat transfer for a laminar and steady free stream flow of nanofluids past an isolated square cylinder have been studied numerically. Different nanofluids consisting of Al₂O₃ and CuO with base fluids of water and a 60:40 (by mass) ethylene glycol and water mixture were selected to evaluate their superiority over conventional fluids. Recent correlations for the thermal conductivity and viscosity of nanofluids, which are functions of particle volumetric concentration as well as temperature, have been employed in this paper. The simulations have been conducted for Pe = 25, 50, 100 and 200, with nanoparticle diameters of 30 and 100 nm and particle volumetric concentrations ranging from 0% to 4%. The results of heat transfer characteristics of nanofluid flow over a square cylinder showed marked improvement comparing with the base fluids. This improvement is more evident in flows with higher Peclet numbers and higher particle volume concentration, while the particle diameter imposes an adverse effect on the heat transfer characteristics. In addition, it was shown that for any given particle diameter there is an optimum value of particle concentration that results in the highest heat transfer coefficient.     

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.     

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 Cu/TiO2–water/EG hybrid nanofluid: Experimental data and modeling using artificial neural network and correlation

In the present paper, the thermal conductivity of hybrid nanofluids is experimentally investigated. The studied nanofluid was produced using a two-step method by dispersing Cu and TiO₂ nanoparticles with average diameter of 70 and 40 nm in a binary mixture of water/EG (60:40). The properties of this nanofluid were measured in various solid concentrations (0.1, 0.2, 0.4, 0.8, 1, 1.5, and 2%) and temperatures ranging from 30 to 60 °C. Next, two new correlations for predicting the thermal conductivity of studied hybrid nanofluids, in terms of solid concentration and temperature, are proposed that use an artificial neural network (ANN) and are based on experimental data. The results indicate that these two new models have great ability to predict thermal conductivity and show excellent agreement with the experimental results.     

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 study of Fe2O3/water and Fe2O3/ethylene glycol nanofluid heat transfer enhancement in a shell and tube heat exchanger

Heat transfer characteristics of Fe₂O₃/water and Fe₂O₃/EG nanofluids were measured in a shell and tube heat exchanger under laminar to turbulent flow condition. In the shell and tube heat exchanger, water and ethylene glycol-based Fe₂O₃ nanofluids with 0.02%, 0.04%, 0.06% and 0.08% volume fractions were used as working fluids for different flow rates of nanofluids. The effects of Reynold's number, volume concentration of suspended nanoparticles and different base fluids on the heat transfer characteristics were investigated. Based on the results, adding nanoparticles to the base fluid causes a significant enhancement of the heat transfer characteristics and thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. In this paper, the effect of Fe₂O₃ nanoparticles on the thermal conductivity of base fluids like ethylene glycol and water was studied. The thermal conductivity measurement was made for different concentrations and temperatures. As the concentration of the nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed that there was an improvement in the thermal conductivity of the base fluid as the temperature increased. The measurements also showed that the pressure drop of nanofluid was higher than that of the base fluid in a turbulent flow regime. However, there was no significant increase in pressure drop at laminar flow.     

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.     

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 investigation of the thermophysical properties of AL2O3-nanofluid and its effect on a flat plate solar collector

Experimental investigations have been carried out for obtaining the thermophysical properties of 60:40 (by mass) ethylene glycol/water mixture and water based alumina nanofluids. The effect of density and viscosity on the pumping power for flat plate solar collector has been investigated as well. Nanofluids of 0.05–0.1%v/v concentrations were prepared and characterized. Water based alumina nanofluids were found more preferable against sedimentation and aggregation than ethylene glycol/water mixture based nanofluids. The measured thermal conductivities of both types of the nanofluids increased almost linearly with concentration and are consistent in their overall trend with previous works done at lower concentrations by different researchers. In contrast to thermal conductivity, viscosity measurements showed that the viscosity of the Al₂O₃–water nanofluids exponentially decreases with increasing temperature. Furthermore, the measured viscosities of the Al₂O₃–water nanofluids showed a non-linear relation with concentration even in the low volume concentration except 0.05%v/v at below 40 °C. On the other hand, Al₂O₃–EG/water mixture exhibited Newtonian behavior. Existence of a critical temperature was observed beyond which the particle suspension properties altered drastically, which in turn triggered a hysteresis phenomenon. The hysteresis phenomenon on viscosity measurement, which is believed to be the first observed for EG/water-based nanofluids, has raised serious concerns regarding the use of nanofluids for heat transfer enhancement purposes. Results suggest that nanofluids can be used as a working medium with a negligible effect of enhanced viscosity and/or density. Results also show that the pressure drop and pumping power of the nanofluid flows are very close to that of the base liquid for low volume concentration.     

Synthesis,characterization, and thermal property measurement of nano-Al95Zn05 dispersed nanofluid prepared by a two-step process

Nanofluids are stable suspension of nanometer sized particles and exhibit extremely attractive thermal properties that make them a potential candidate for application in heat transfer devices ranging from microelectronic gadgets to thermal power plants. In the present study, we have synthesized Al-5wt%Zn nanoparticles by mechanical alloying, characterized these nanoparticles using X-ray diffraction and scanning and transmission electron microscopy. Subsequently, these nanoparticles are dispersed to the tune of 0.01–0.10 vol% in ethylene glycol (base fluid) following a careful mixing protocol. Thermal conductivity of the nanofluids and base fluid has been measured using the transient hot-wire method. It is observed that thermal conductivity of the nanofluids strongly depend on the concentration, particle size, fluid temperature and stability of dispersed nanoparticles in the base fluid. A maximum of 16% enhancement in thermal conductivity has been recorded at a nanoparticle loading of 0.10 vol%. Unlike data reported in some articles, thermal conductivity ratio of Al-5wt%Zn dispersed ethylene glycol based nanofluids is observed to decrease with the increase in crystallite/grain size of the particles.     

An experimental study on the thermal conductivity and dynamic viscosity of TiO2-SiO2 nanofluids in water: Ethylene glycol mixture

The hybrid nanofluid has been thriving among researchers due to its potential to improve heat transfer performance. Therefore, various studies on heat transfer properties need to be carried out to provide a better understanding on hybrid nanofluid performance. In this paper, the experimental work is focused on the thermal conductivity and dynamic viscosity of TiO₂-SiO₂ nanofluids in a mixture of water and ethylene glycol (EG) with volume ratio of 60:40. The stable suspension of TiO₂-SiO₂ prepared at volume concentrations of 0.5 to 3.0%. The measurements of thermal conductivity and dynamic viscosity were performed at a temperature range of 30 to 80 °C by using KD2 Pro Thermal Properties Analyser and Brookfield LVDV III Ultra Rheometer, respectively. The thermal conductivity of TiO₂-SiO₂ nanofluids was improved by increasing the volume concentration and temperature with 22.8% maximum enhancement. Besides, the viscosity of TiO₂-SiO₂ nanofluids showed evidence of being influenced by nanofluid concentration and temperature. Additionally, the TiO₂-SiO₂ nanofluids behaved as a Newtonian fluid for volume concentration up to 3.0%. The properties enhancement ratio suggested that TiO₂-SiO₂ nanofluids will aid in heat transfer for concentrations of more than 1.5% and within the range of the temperature studied. A new correlation for thermal conductivity and dynamic viscosity of TiO₂-SiO₂ nanofluids were developed and found to be precise.     

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.     

ReD-dependence of dynamic thermal conductivities of nanofluids

The dynamic thermal conductivity of nanofluids is examined under fully developed laminar flow conditions (440 < Re_D < 818) in a circular tube (1.753-mm ID) subjected to a uniform heat flux. The experiment has been conducted using nanofluids containing Al₂O₃ nanoparticles of 45-nm nominal diameter dispersed in DI water at two volume concentrations of 2% and 4%. At the small Reynolds numbers, the measured dynamic thermal conductivity is lower by as much as 16% in comparison with the corresponding static thermal conductivity at Re_D = 0. The dynamic thermal conductivity gradually increases with increasing Re_D, but never exceeds the static conductivity level up to the highest tested Reynolds number of 818. The hot wall-to-fluid temperature gradient drives thermophoretic depletion of nanoparticles from the wall to the tube center. The lower dynamic thermal conductivity at the small Reynolds number is believed to be attributed to the reduced effective conduction near the wall where the nanoparticle concentration is relatively lower than in the core of the tube. In contrast, examination of the heat transfer between the suspended nanoparticles and the surrounding water molecules shows that the nanoparticle thermophoretic velocities increase with increasing Reynolds number. The increased thermophoretic velocities inside the nanofluid tend to compensate for the aforementioned reduced thermal conductivity near the wall, and this is conjectured to account for the recovery of the dynamic thermal conductivity to the static level at the higher Reynolds number.     

Experimental investigation on the thermal efficiency and performance characteristics of a flat plate solar collector using SiO2/EG–water nanofluids

Application of nanofluids in thermal energy devices such as solar collectors is developing day by day. This paper reports the results of experiments on a flat plate solar collector where the working fluid is SiO₂/ethylene glycol (EG)–water nanofluid with volume fractions up to 1%. The thermal efficiency and performance characteristics of solar collector are obtained for mass flow rates between 0.018 and 0.045 kg/s. The curve characteristics of solar collector indicate that the effects of particle loading on the thermal efficiency enhancement are more pronounced at higher values of heat loss parameter. The results of this work elucidate the potential of SiO₂ nanoparticles to improve the efficiency of solar collectors despite its low thermal conductivity compared to other usual nanoparticles.     

Investigation of thermal conductivity and viscosity of Al2O3/water–ethylene glycol mixture nanocoolant for cooling channel of hot-press forming die application

Hot-press forming process is widely used to produce lightweight chassis in automotive industries. The hot-press forming process currently uses water as coolant to quench boron steels in a closed die with a cooling channel. However, to enhance performance of hot-press forming die, the fluid with better thermal properties will be used instead of normal water. This study dispersed Al₂O₃ nanoparticles with an average diameter of 13 nm in three volume percentages base ratios of water (W) to ethylene glycol (EG) (i.e. 60:40, 50:50, and 40:60) by two-step preparation. The two main parameters in cooling rate performance are thermal conductivity and viscosity. The nanocoolant of Al₂O₃/water–ethylene glycol mixture is prepared for the volume concentration range of 0.2 to 1.0%. The thermal conductivity and viscosity are then measured at temperature range of 15 to 55 °C. The highest enhancement of thermal conductivity was observed to be 10% higher than base fluid for 1.0% volume concentration at 55 °C in 60:40 (W/EG). However, the highest enhancement of viscosity was measured to be 39% for 1.0% volume concentration in 40:60 (W/EG) at 25 °C. The convective heat transfer coefficient of 1.0% concentration in 60:40 (W:EG) at 25 °C is enhanced by 25.4% better than that of 50:50 and 40:60 (W:EG) base fluid. Therefore, this study recommends the use of Al₂O₃ in 60:40 (W:EG) mixture with volume concentration of less than 1.0% for application in cooling channel of hot-press forming die. Nanocoolant as cooling agent with higher heat transfer coefficient compared to the base fluid can reduce the cycle time and increase the productivity of hot-press forming process.