Ethylene Glycol-based Nanofluids Research Articles

Effective thermal conductivity and rheological characteristics of ethylene glycol-based nanofluids with single-walled carbon nanohorn inclusions

ABSTRACTIn this study, we report the effective thermal conductivity and rheological behavior of ethylene glycol with single-walled carbon nanohorn inclusions. The thermal conductivity and viscosity was found to increase with respect to nanohorn loading. Maximum thermal conductivity enhancement of ∼11% at a nanohorn loading of 1.5 vol% was obtained in this study. The viscosity of nanofluids increase with respect to nanohorn loading and decreases with respect to shear rate which indicates the non-Newtonian shear thinning behavior at higher nanohorn loading. Finally, the effectiveness of nanofluids was calculated for laminar and turbulent regions to predict the heat transfer performance and favorability of these nanofluids. The present nanofluids are favorable upto 0.1 vol% in the laminar region. However, these nanofluids are not favorable for turbulent region and loadings beyond 0.1 vol% due to higher viscosity enhancement.

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.

Preparation and rheological behavior of ethylene glycol-based TiO2 nanofluids

In this work, the ethylene glycol-based TiO2 (EG/TiO2) nanofluids were prepared by dispersing TiO2 nanoparticles into the base fluid of EG via ultrasonication. The rheological behavior of EG/TiO2 nanofluids over 25–45°C and particle weight concentration of 0–35wt% were investigated. It was found that the steady state shear viscosity of the nanofluids was remarkably enhanced compared with the base fluid of EG. Moreover, the nanofluids showed a characteristic shear thinning behavior particularly at particle concentrations in excess of ∼5wt%. Significantly, a Newtonian-pseudoplastic transition with a critical exponent of 3.2 was firstly observed as particle concentration increased, suggesting that the nanofluids had entered into the semi-diluted regime and some TiO2 nanoparticles were assembled into agglomerations. In addition, the results of shear viscosity curves and thixotropic loops at different temperature demonstrated that temperature had a remarkable influence on the nonlinear rheological behavior of the concentrated nanofluids. Therefore, the present study could shed light on the processing and application of TiO2-related nanofluids and nanocomposites.

Heat transfer enhancement in natural convection in micropolar nanofluids

In this work an analysis of momentum, angular momentum and heat transfer during unsteady natural convection in micropolar nanofluids is presented. Selected nanofluids treated as single phase fluids, contain small particles. In particular, two ethylene glycol-based nanofluids were analyzed. The volume fraction of these solutions was 6%, 3.5% and 0.6%. The first ethylene glycol solution contained Al 2 O 3 nanoparticles ( d = 38.4 nm), and the second ethylene glycol solution contained Cu nanoparticles ( d = 10 nm).

Experimental data on the dependence of the viscosity of water- and ethylene glycol-based nanofluids on the size and material of particles

The viscosities of all nanofluids considered are shown to be dependent on the size of nanoparticles. It has been established that the greater the nanofluid viscosity, the smaller the size of particles. The measurements carried out in this study make it possible for the first time to fix experimentally the fact of the dependence of the viscosity of nanofluids on the particle material.

Evidence of viscoplastic behavior of exfoliated graphite nanofluids.

The rheological behavior of ethylene glycol-based nanofluids containing exfoliated graphite nanoplatelets has been carried out using a cone-plate Physica MCR rheometer. Initial experiments based on flow curves were carried out, the flow curves were based on the controlled shear stress model, these tests show that the studied nanofluids present non-Newtonian shear thinning behavior with yield stress. Furthermore, linear viscoelastic experiments were conducted in order to determine the viscoelastic behavior: using strain sweep and frequency sweep tests the storage and loss modulus were determined. The fractal dimension (Df) was estimated from the suspension static yield-stress and volume fraction (ϕ) dependence, and was determined to be Df = 2.36, a value consistent with a process of aggregation of RLCA type (reaction limited cluster aggregation). This value is unusual if compared with other nanofluids, and can be regarded as a result of the bidimensionality of the suspended nanoplatelets. Finally, creep-recovery tests and mechanical models confirm the viscoplastic nature of our nanofluids, a feature never shown so far for this type of systems, increasing the solid-like character in the range of concentrations studied if compared with other nanofluids reported in the literature. This is a result of the combination of a remarkable internal structure and strong interactions, which evidence an unexpected behaviour sharing many solid-like features.

Development of CuO–ethylene glycol nanofluids for efficient energy management: Assessment of potential for energy recovery

Ethylene glycol (EG) plays an important role as coolant in sub-artic and artic regions owing to its low freezing point. However one of the limitations of ethylene glycol for energy management is its low thermal conductivity, which can be improved by addition of nanoparticles. In the present work, cupric oxide nanoparticles have been synthesized followed by dispersion in ethylene glycol through extended probe ultrasonication without addition of chemical dispersing agent. Temperature dependency of thermal conductivity of 1vol% CuO–ethylene glycol nanofluid exhibited a minimum at a critical temperature corresponding to lower thickness of interfacial layers and negligible Brownian motion. The influence of liquid layering on thermal conductivity was predominant at temperatures below critical temperature leading to higher thermal conductivity at lower temperature. Brownian motion-induced microconvection resulted in thermal conductivity increase with temperature above the critical temperature. About 14.1% enhancement in thermal conductivity was obtained at 50°C for 1vol% CuO–ethylene glycol nanofluid. The viscosity of CuO–ethylene glycol nanofluid was lower than the viscosity of ethylene glycol at temperatures below 50°C and 120°C for 1vol% and 0.5vol% CuO–ethylene glycol nanofluids. Our data reveal that the CuO–ethylene glycol nanofluids are better coolants than ethylene glycol for transient cooling under constant heat flux conditions with 11.8% enhancement in heat transfer rate for 1vol% CuO–ethylene glycol nanofluid. Hence the use of ethylene glycol-based nanofluids is a promising approach for energy management.

Stability and enhanced thermal conductivity of ethylene glycol-based SiC nanofluids

Nanofluid is one of the most popular fluids in recent scientific community, which exhibits more attractive heat transfer properties than the traditional thermal fluids. Nanofluids are fabricated by dispersing nanostructured solid particles in a selected base liquid. We recently reported on the rheological behavior of ethylene glycol (EG)-based nanofluids containing spherical-shaped silicon carbide (SiC) nanoparticles. In this study, we focused on the stability and thermo-physical property of EG/SiC nanofluids to investigate the enhanced thermal conductivity with respect to the effect of volume fraction and temperature. A series of SiC nanofluids with volume fraction up to 1.0vol.% were made with this purpose. The results of sedimentation experiment and zeta potential analysis confirmed that the nanofluids exhibited good stability. In addition, enhancement up to 16.21% in thermal conductivity of nanofluids with volume fractions was found compared to base fluids and theoretical model. The thermal conductivity also increased with the measured temperature ranged from 20 to 50°C. We do hope that our current work could be useful for future research of SiC nanofluids as sharing a desirable direction of nanofluids research.

Experimental study of ethylene glycol-based Al2O3 nanofluid turbulent heat transfer enhancement in the corrugated tube with twisted tapes

In this study, fluid flow of the Al2O3/ethylene glycol (EG) nanofluid in a corrugated tube fitted with twisted tapes were experimentally studied under turbulent flow conditions. The experiments with different twists ratio and different nanofluid concentration were performed under similar operation condition. The investigated ranges are (1) three different Al2O3 concentrations: 0.5, 1 and 1.5 % by volume (2) three different twist ratios of twisted tape: y/w = 2, 3.6 and 5 and (3) Reynolds number from 6000 to 30,000. Regarding the experimental data, utilization of twists together with nanofluids tends to increase heat transfer and friction factor as compared with the base fluid. In addition, heat transfer performances were weakened by using for high nanoparticle concentration. The thermal performances of the heat exchanger with nanofluid and twisted tapes were evaluated for the assessment of overall improvement in thermal behavior. Over the range studied, the maximum thermal performance factor 4.2 is found with the use of Al2O3/EG nanofluid at concentration of 0.5 % by volume in corrugated tube together with twisted tape at twist ratio of 2.

Co3O4 ethylene glycol-based nanofluids: Thermal conductivity, viscosity and high pressure density

This work contributes with experimental information of the properties of ethylene glycol-based Co3O4 nanofluids. Thermal conductivity, high-pressure density and rheological characterization were performed in the temperature range T=(283.15–323.15)K. Thermal conductivity and rheological behaviour were studied for nanofluid samples with concentrations of Co3O4 nanoparticles up to 25% in weight fraction whereas the densities of the nanofluid were analysed up to 5% at pressures up to 45MPa. Thermal conductivity showed in the range studied an increase with weight fraction and a decrease with temperature. A volumetric contractive behaviour was observed, and an increment in the nanoparticles concentration leads to a clear departure from ideal behaviour. The tests performed to analyse rheological properties showed that the viscosity of the nanofluids is nearly independent of the shear rate, thus evidencing the characteristic behaviour of a Newtonian fluid. Experimental viscosity and thermal conductivity were also compared with the estimations provided by several semiempirical equations proposed in the literature.

Rheological behavior of ethylene glycol-based SiC nanofluids

With the purpose to get more fundamental understanding of the rheological behavior of nanofluids as filling the research gap in the literatures, the rheological behavior of ethylene glycol-based nanofluids containing spherical-shaped SiC nanoparticles have been conducted using a HAAKE MARS III rheometer at different volume fractions and temperatures. The results showed that the nanofluids exhibited an interesting rheological behavior of the viscosity curves. Attempts were made to explain this phenomenon in this paper and the theoretical analyses revealed that the rheological behavior of the studied nanofluids had a strong relationship with shear rates and particle concentration. In addition, this work concluded that viscosity of the studied nanofluids increased with volume fractions but decreased with temperatures. In addition, the theoretical analyses also lead to a classification of nanofluids into dilute nanofluids and concentrated nanofluids on particle concentration.

An Experimental Investigation into the Thermal Properties of Nano Fluid

In this paper, the results of the experimental investigation on the thermal properties of Nano fluid are presented. The effect of sonication time, settling time and temperature on the thermal conductivity, viscosity and specific heat of zinc oxide (ZnO, 14 nm and 25 nm size) and single walled carbon nanotube (SWCNT, 10nm size) based Nano fluid are investigated and the results of ZnO with DI water and ethylene glycol (EG) as base fluids are compared. The experimental results indicate that the studied parameters have a remarkable effect on the thermal properties of Nano fluid. The rate of enhancement in thermal conductivity of EG based Nano fluid is found to be less than that of water based Nano fluid. The SWCNT based DI water Nano fluid found to be very unstable i.e. the nanoparticles settle down very rapidly. The 0.02% volume fraction of SWCNT nanoparticles suspension results in 10% increase in the specific heat of DI water. A decrement of 24% and 13% in the specific heat of 14 nm size ZnO based Nano fluid were obtained at a volume fraction of 0.001% and 0.002% respectively.

Influence of CuO Nanostructures on the Thermal Conductivity of DI Water and Ethylene Glycol Based Nanofluids

The influence of cupric oxide (CuO) nanostructures on the thermal conductivity of deionized (DI)water and ethylene glycol (EG) was investigated here. CuO nanospheres (average diameter 7 nm) and nanorods (L × W = ∼120 nm × 4 nm) have been synthesized; their structural and morphological characterizations have been done by powder x-ray diffraction (XRD), UV-visible spectrophotometer, and transmission electron microcopy (TEM). The CuO nanospheres and nanorods have been dispersed separately in DI water and EG with four different volume fractions (0.005–0.1%). The results showed that an enhancement in thermal conductivity for CuO nanospheres and CuO nanorods was found to be 15% and 17% with respect to DI water, 19% and 21% with respect to EG. The enhancement in thermal conductivity in case of CuO nanorods is due to large surface area, crystallinity, and network formation of nanorods in base fluids which directly help in the transfer of phonon vibrations rapidly from one atom to another atom and increase the heat-transfer rate. Thus, the CuO–EG based-nanofluids exhibited 4–5% higher thermal conductivity than CuO–DI water based nanofluids, nanorods always showed higher thermal conductivity (2–3%) than nanospheres in both base fluids.

Strong enhancement in thermal conductivity of ethylene glycol-based nanofluids by amorphous and crystalline Al2O3 nanoparticles

In the present work, the temperature and concentration dependence of thermal conductivity (TC) enhancement in ethylene glycol (EG)-based amorphous and crystalline Al2O3 nanofluids have been investigated at temperatures ranging from 0 to 100 °C. In our prior study, nanometer-sized particles of amorphous-, γ-, and α-Al2O3 were prepared via a simple sol-gel process with annealing at different temperatures and characterized by various techniques. Building upon the earlier study, we probe here the crystallinity, microstructure, and morphology of the obtained α-Al2O3 nanoparticles (NPs) by using X-ray powder diffraction with Rietveld full-profile refinement, scanning electron microscopy, and high-resolution transmission electron microscopy, respectively. In this study, we achieved a 74% enhancement in TC at higher temperature (100 °C) of base fluid EG by incorporating 1.0 vol. % of amorphous-Al2O3, whereas 52% and 37% enhancement is accomplished by adding γ- and α-Al2O3 NPs, respectively. The amorphous phase of NPs appears to have good TC enhancement in nanofluids as compared to crystalline Al2O3. In a nutshell, these results are demonstrating the potential consequences of Al2O3 NPs for applications of next-generation efficient energy transfer in nanofluids.

Sunlight absorbing potential of carbon nanoball water and ethylene glycol-based nanofluids

Solar thermal collectors are applicable in the water heating or space conditioning systems in which surface-based absorption of incident solar flux cause high heat losses. Therefore, an enhancement in the efficiency of solar harvesting devices is a basic challenge which requires great effort. Adding nanoparticles to the working fluid in direct absorption solar collector, which has been recently proposed, leads to improvement in the working fluid thermal and optical properties such as thermal conductivity and absorption coefficient. This results certainly in collector efficiency enhancement. In this paper, the characteristics of nanofluids consisting carbon nanoball in water- and ethylene glycol-based suspensions in consideration of their use as sunlight absorber fluid in a DASC are investigated. It was found that by using of 300 ppm carbon nanoballs, the extinction coefficient of pure water and ethylene glycol is increased by about 3.9 cm−1 and 3.4 cm−1 in average, respectively. With these significantly promising optical properties, a direct absorption solar collector using carbon nanoball-based nanofluids can achieve relatively higher efficiencies, compared with a conventional solar collector.

Thermophysical profile of ethylene glycol-based ZnO nanofluids

This work presents values of the experimental thermal conductivity, viscosity and density of homogeneous and stable nanofluids consisting of both synthesized and commercial ZnO nanoparticles dispersed in ethylene glycol (EG). The influence of variables such as particle size, temperature and volume fraction on their thermophysical properties were studied at concentrations up to 6.2%. The experimental results provide the evidence that thermal conductivity increases non-linearly with concentration and temperature within the range studied. Viscosity increases with concentration as usual for this type of dispersion and decreases with temperature. Density as a function of pressure has been also examined. The mixing volumes show little dependence on temperature and pressure over the range studied. Nevertheless, these results show a contractive behaviour on mixing and a departure from ideal behaviour, and this effect increases with concentration. The influence of particle size is significant for the measured properties, especially on viscosity. Finally, experimental values of thermal conductivity and viscosity have been compared to estimations provided by several simple theoretical models.

Measurement of the viscosity coefficient of an ethylene glycol-based nanofluid with silicon-dioxide particles

Measurement of the viscosity coefficient of an ethylene glycol-based nanofluid with silicon-dioxide particles

Sunlight Absorbing Potential of Carbon Nanoball Water- and Ethylene Glycol-Based Nanofluids

Sunlight Absorbing Potential of Carbon Nanoball Water- and Ethylene Glycol-Based Nanofluids

Thermal conductivity, rheological behaviour and density of non-Newtonian ethylene glycol-based SnO2 nanofluids

The thermal conductivity, rheological behaviour and the high-pressure density of several non-Newtonian ethylene glycol-based SnO2 nanofluids were analysed. The thermal conductivity and density were measured at 283.15, 303.15 and 323.15K whereas rheological characterization was performed at 303.15K. Nanofluids with concentrations of SnO2 nanoparticles up to 25% in weight fraction were designed for thermal conductivity and rheological studies while density behaviour were analysed up to 5% at pressures up to 45MPa. Thermal conductivity increases as usual with weight fraction showing an enhancement up to 14% in the range studied, and the experimental values were compared with available theoretical models. The volumetric behaviour shows a contractive behaviour and a departure from ideal behaviour, which is incremented with the concentration of the nanoparticles. The temperature and pressure dependence on this contractive behaviour is also studied. The rheological tests performed evidence shear thinning behaviour. In addition, the viscosity at a given shear rate is time dependent, i.e. the fluid is rheopectic. Finally, using strain sweep and frequency sweep tests the storage modulus, G′, and loss modulus, G″, were determined, showing viscoelastic behaviour for all samples, a fact that must be carefully taken into account for any application involving nanofluid flow.

Heat transfer characteristics of multiwall carbon nanotube suspensions (MWCNT nanofluids) in intertube falling-film flow

Multiwall carbon nanotube suspensions (MWCNT nanofluids) are used in an intertube falling-film flow to explore the nanofluid effects on heat transfer characteristics. Water-based and ethylene–glycol-based nanofluids are prepared at concentrations of 0, 0.05, 0.14 and 0.24vol%. Thermal conductivity and viscosity of these nanofluids is measured. Falling-film heat transfer behavior of these nanofluids is also investigated and the results are compared to those of the base fluids. Based on the same liquid feeding flow rate, it is observed that the heat transfer coefficients of the water-based nanofluids decreases then increases as the MWCNT concentration increases, and the heat transfer coefficient of the ethylene–glycol-based nanofluids decreases with an increased MWCNT concentration. A model is provided for predicting the heat transfer enhancement of the nanofluids in intertube falling-film flow, and an agreement between predictions and experimental data is obtained for nanofluids with larger MWCNT concentrations. When comparing the heat transfer coefficient based on the same Reynolds number, up to 20% or higher heat transfer enhancement can be observed for ethylene–glycol based nanofluids.