Nanofluids For Heat Transfer Applications Research Articles

A review on thermo-physical properties and heat transfer applications of single and hybrid metal oxide nanofluids

Nanofluids have been widely explored by various investigators for different types of nanomaterials either the single nanoparticles or hybrid types. This is due to their advantages in thermal properties as well as contribution to the enhancement in the heat transfer performance. Numerous numbers of studies were performed mostly on oxide nanofluids until today. However, the review on oxide nanofluids and their applications is limited. Hence, this paper highlights the most recent development solely on the oxide nanofluids for heat transfer applications. In addition, a comprehensive review is carried out on the recent studies of thermo‑physical properties on oxide nanofluids and their heat transfer applications. The numerical and experimental studies related to forced convection heat transfer using oxide nanofluids were presented. Most of the literatures confirmed the capability of nanofluids to improve the heat transfer performance and simultaneously insignificant increments in pressure drop. Hence, the oxide nanofluids is recommended for applications in various engineering systems.

Enhancing the performance of automotive radiators using nanofluids

Advanced heat removal technologies are critical for high-performance automotive engines. The conventional fluids being used today are based on a mixture of distilled water (DW) and ethylene glycol (EG), which widens the operational temperature range but at the same time limits the heat removal. Therefore, the use of nanofluids for improving heat transfer performance has soared over the past few years. The problem is that most of the reports highlight the short-term heat transfer results which may not be true over time. In this paper, a suggested best practice for analyzing the usage of nanofluids in heat transfer applications is presented, specifically for an actual car radiator. This work investigates the use of aluminum oxide (Al2O3) and titanium dioxide (TiO2) nanoparticles dispersed in DW and EG at 50:50 volumetric proportions. The choice of these oxide-based nanofluids is motivated by their anti-corrosive properties that are usually not analyzed or discussed in most of the articles. Furthermore, the emphasis is given on the presentation of a comprehensive characterization of the nanofluids including thermophysical properties (size, density, viscosity, thermal conductivity, corrosive behavior) and long-term stability (zeta potential) which are essential for an end-user to have. The results showed a maximum enhancement of the thermal performance by 24.21% using Al2O3 at a volume fraction of 0.3%. Friction factor and performance evaluation criterion (PEC) for the radiator experiments are calculated in order to determine the penalty in the pressure drop and to evaluate it properly. Finally, it is found that the values of PEC lie in the range of 1.03–1.31 which indicates significant flow enhancement.

Thermo-physical properties of pure ethylene glycol and water–ethylene glycol mixture-based boron nitride nanofluids

Nanofluids are suspensions of solid nanoparticles in conventional heat transfer fluids, and they often exhibit improved heat transfer characteristics. Different nanoparticles (metals, oxides, nitrides, etc.) have been used for the synthesis of nanofluids. The nanosized hexagonal form of boron nitride (BN) has versatile properties, such as chemical inertness, electrically insulating and high in-plane thermal conductivity (~ 600 W m−1 K−1) making it a prospective dispersoid in nanofluids for heat transfer applications. The present study reports the synthesis of pure ethylene glycol (EG)- and ethylene glycol–water mixture (EG/W, 40/60 vol. ratio)-based nanofluids containing a dispersion of BN nanoparticles. Form the study, it emerged that with the increase in particle concentration, the BN nanofluids showed an increment in the thermal conductivity manifesting a maximum of 15.5% and 12.5% for 3 vol.% of BN dispersion in EG- and EG/W-based nanofluids, respectively. Also, the thermal conductivity enhancement of BN nanofluids was found to be nearly independent of temperature in the temperature range of 30–60 °C. The viscosity of BN nanofluids increased with the increase in particle concentration showing a maximum of 41 and 33% for 2 vol.% of BN in EG-based and EG/W-based nanofluids, respectively. Further, BN nanofluids exhibited shear-thinning behaviour at lower shear rates and a Newtonian nature at higher shear rates. A new correlation has been developed to estimate the thermal conductivity and viscosity of BN nanofluids on the basis of experimental data.

Investigation On Heat Transfer Properties Of Water Based TiO2-ZnO Nanofluids

Nanofluids in heat transfer applications exhibit effective performance over conventional heat transfer fluids. High thermal loads due to miniaturization in a wide variety of applications offers technological challenges in designing efficient thermal management systems. Traditional heat transfer fluids such as air, water, engine oil, and ethylene glycol (EG) have very low thermal conductivities of 0.03, 0.613, 0.145 and 0.253 W/mK respectively. The poor thermal conductivity of these fluids is an obstacle in improving heat transfer and compactness of the heat exchangers. Determination of properties of nanofluids and its performance in water based base fluids has been studied by many researchers. However the heat transfer performance of mixed nanofluids ie., hybrid nanofluids is yet to be explored. TiO2 and ZnO nanofluids were prepared at 0.5%, 1.5% and 2.0% volume concentration. Thermal conductivity estimated for temperature range of 30-70°C. Significant enhancement of both heat transfer rate and effectiveness of heat exchanger was noticed with TiO2 nanofluids at 2.0% volume concentration and with 1.5% volume concentration of TiO2-ZnO hybrid nanofluids.

Heat transfer capability of the hybrid nanofluids for heat transfer applications

In this paper, the heat transfer capabilities of the hybrid nanofluids and their behavior in heat transfer applications under laminar and turbulent flows were investigated. The study is based on both experimental data and theoretical analyses. Heat transfer capability of the hybrid nanofluids was evaluated on different figures of merit both in laminar and turbulent flows at various temperatures and volume fractions of hybrid nanoparticles. Finally, two possible applications of the hybrid nanofluids, other than those frequently studied, namely the forced convective heat transfer in the parallel flow over isothermal flat plates and the natural convection over vertical plate in laminar and turbulent flows which occurs in numerous engineering applications were analyzed and detail discussed.

Influence of surfactant and volume fraction on the dispersion stability of TiO2/deionized water based nanofluids for heat transfer applications

Nanofluids are the implausible outcome of nanotechnology which fascinates many researchers by owing incredible thermal transport properties in different domains, including heating-cooling of systems, power generation, nuclear and space technology. Due to the higher surface area of nanomaterials, their suspension in traditional heat transfer fluids extensively enriches the heat transfer characteristics. In this research work, commercially available bulk Titania (TiO2) powder is used for the synthesis of TiO2 nanoparticles (NPs). Scanning electron microscopy confirmed the spherical shape of NPs with an average diameter of 18.88 nm. X-ray Diffraction (XRD) and Thermal Gravimetric analysis (TGA) is performed for material characterization. Dispersion stability of TiO2/Deionized water nanofluids for 0.05 vol% and 0.5 vol% concentration of NPs has been studied, using UV–vis Spectrometry. Sodium dodecyl sulfate (SDS) is used as a surfactant and its effect on the stability of nanofluids is analyzed. Experimental results revealed that the addition of surfactant to the nanofluids at a given volume concentration increase the dispersion stability.

Synthesis of stable waste palm oil based CuO nanofluid for heat transfer applications

This article aims at preparation of novel copper oxide nanofluid using waste palm oil as a base solvent without using any surfactants/stabilizers for its suitability in heat transfer applications. Copper oxide nanoparticles were synthesized using co-precipitation technique and were subjected to structural and morphological studies using X-ray diffraction and Transmission Electron Microscope. UV-vis and FTIR studies were conducted to confirm the formation CuO nanoparticles and adsorption of oleic acid groups on the surface of CuO nanoparticles. These nanoparticles were dispersed in waste palm oil at different concentrations (0.1% – 0.9% wt.) using ultrasonication, resulting in stable solution. CuO nanofluids were observed to be stable for at least 6 months without any sign of aggregation. The synthesized CuO nanofluid was found to exhibit enhanced thermal properties as compared to base fluid. The thermal conductivity of nanofluid (0.7% by wt. of nanoparticle) shows maximum enhancement (upto 190%) as compared to pure palm oil. Thus, it can be considered as a suitable candidate for many heat transfer applications.

Modified Two-Step Method to Prepare Long-Term Stable CNT Nanofluids for Heat Transfer Applications

CNT nanofluids are getting attention in heat transfer applications due to their very high thermal conductivity in comparison with conventional fluids. For commercial exploitation of CNT nanofluids as heat transfer media, they must have long-term stability. In this study, the two-step method was modified to prepare dynamically stable CNT nanofluids by utilizing commercial grade multiwalled carbon nanotubes and SDBS as a surfactant. The modified technique consists of separation of coarse agglomerates of CNT from the CNT nanofluids by applying centrifugal action after its preparation. The effect of relative centrifugal force was also studied for the very first time on the stable concentration of CNT nanofluids. The stability of CNT nanofluids was analyzed by measurement of their CNT concentration and Zeta potential. Results showed that CNT nanofluids possess good stability and remain stable for more than 15 months. In addition to stability, thermo-physical properties such as thermal conductivity, density, and viscosity of CNT nanofluids were also measured. The results of this study elucidated the effect of RCF on the stable concentration of CNT nanofluids. It is expected that the results obtained in this study may significantly contribute to the proper tailoring of CNT nanofluids, by providing long-term stable CNT nanofluids which are suitable for industrial heat transfer applications.

Nanofluids for heat transfer applications: a review

Since diluted suspensions of nanoparticles were first called nanofluids and presented as viable solutions for heat transfer applications, this subject has received much attention and related investigations have expanded to many paths. In order to comprehend how nanoscale-related effects could influence the macroscopic transport behavior of nanofluids under single or phase-change conditions, researchers have studied, for example, the stability of these solutions, variation of thermal and rheological properties, and the convective heat transfer behavior of a great variety of nanofillers in common fluids, mainly water. The deposition of nanofillers over heated surfaces has also been investigated due to the role of surface nanostructuring in modifying wettability, thermal resistance, and delaying the occurrence of critical heat flux. Despite the considerable number of publications regarding nanofluids, scattered results for transport properties or convective behavior of nanofluids under similar experimental conditions are often found, which hinders their applications due to a lack of comprehension on the mechanisms related to the behavior of these fluids and, consequently, to the difficulty in predicting it. In this context, this work concerns a review about the heat transfer behavior of nanofluids under single-phase flow, pool boiling, and flow boiling conditions. In general, there is a consensus that the heat transfer coefficient of single-phase flow is enhanced by the addition of nanoparticles to base fluids, although overall benefits of their application cannot be assured due to increases in viscosity. In contrast, either increase or decrease in heat transfer coefficient could be observed for pool and flow boiling conditions. Such behavior can be attributed to surface modifications due to interactions between the bare surface texture and the deposited nanoparticles; however, information on the surface texture is commonly missing in most works. Finally, the main mechanisms reported in the literature pointed out as responsible for the heat transfer coefficient behaviors are summarized, where it can be seen that modifications of transport properties and particles movements impact single-phase flow, while phase-change heat transfer is also influenced by variations of surface characteristics.

Thermophysical properties of CNT and CNT/Al 2 O 3 hybrid nanofluid

This work presents the thermophysical properties of carbon nanotubes (CNT) and CNT/Al2O3 hybrid nanofluids for heat transfer applications. An equal proportion of nanoparticles CNT (50%) and Al2O3 (50%) were added to the base fluid for two different concentration of 0.05 and 0.1%. Results show that addition of Al2O3 nanoparticles with CNT nanofluid improves the thermophysical properties. The thermal conductivity of hybrid nanofluids improved by 20% with a maximum concentration of 0.1%, while the thermal conductivity of CNT alone improved by only 8% with the base fluid. Similarly, density and viscosity of hybrid nanofluid increased up to 7 and 10%, respectively, while comparing it with the base fluid. The result of specific heat energy capacity of hybrid nanofluids increases to about 138% than CNT nanofluid with a maximum concentration of 0.2%.

TiO2/CuO Water Based Nanofluid for Heat Transfer Applications

TiO₂/CuO Water Based Nanofluid for Heat Transfer Applications

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 1.0wt% 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 0.5wt%, the surface tension was lower than the surface tension of the water, while at 1.0wt% 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.

Evaluation of thermal and power performances of nanofluid flows through square in-line cylinder arrays

In this paper, the thermal and power performances of nanofluid flows through square in-line cylinder arrays are examined; and these performances are compared with those from the flowrate approach by increasing the base fluid flowrate. Effects of nanoparticle size, concentration, pitch distance of the cylinder array, and flow Reynolds number are investigated. Results show that a maximum thermal enhancement state and a critical nanoparticle concentration exist for nanofluids, and the best performance state should be chosen with both considered. Nanofluids of smaller nanoparticles can yield better thermal improvement, and a large nanoparticle concentration can depress the thermal efficiency even at a same flowrate. The pitch distance appears to have no major effect on the nanofluid performance, and a better thermal improvement can be obtained for high Reynolds flows. In particular, the effects of individual nanoparticle properties (including density, specific heat, and thermal conductivity) on the nanofluid performance are investigated. A counter-intuitive finding is noticed from our results: the nanoparticle density has the most significant influence on the nanofluid thermal enhancement, and a larger nanoparticle density is more desirable for better heat transfer of nanofluids. On the other hand, the nanoparticle thermal conductivity has negligible effect on the nanofluid performance. These findings as well as the analysis and discussions could be useful for the selection and development of nanofluids in heat transfer applications.

A novel, eco-friendly technique for covalent functionalization of graphene nanoplatelets and the potential of their nanofluids for heat transfer applications

In this study, a facile and eco-friendly covalent functionalization technique is developed to synthesize highly stable graphene nanoplatelets (GNPs) in aqueous media. This technique involves free radical grafting of gallic acid onto the surface of GNPs rather than corrosive inorganic acids. Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy are used to confirm the covalent functionalization of GNPs with gallic acid (GAGNPs). The solubility of the GAGNPs in aqueous media is verified using zeta potential and UV–vis spectra measurements. The nanofluid shows significant improvement in thermo-physical properties, indicating its superb potential for various thermal applications.

Thermo-physical property evaluation of diathermic oil based hybrid nanofluids for heat transfer applications

Diathermic oil has high boiling point, low vapor pressure and low pour point, so it has been widely used as a heat carrier in heat transfer systems. Due to the excellent thermo-physical property of nanofluids, a kind of hybrid nanoparticles (SiC/TiO2) was dispersed in diathermic oil to fabricate nanofluids with concentration up to 1vol% in this paper. And there was no visually observable sedimentation or stratification even after ten days. As two characteristics of thermo-physical property, the thermal conductivity and viscosity were measured under the same conditions respectively, and the experimental results showed that the thermal conductivity of nanofluids increased with increasing volume fractions of nanoparticles and increasing of temperature. With the loading further increasing, the thermal conductivity of SiC/TiO2 nanofluids is higher than SiC or TiO2 nanofluids’, and the maximum of thermal conductivity enhancement ratio is 8.39% at 1vol%. Thermal conductivity enhancement ratio was a linear relationship with the volume fraction. Suspending SiC/TiO2 nanoparticles can enhance thermal capacity of the system. In rheological experiment, the shear viscosity almost maintained constant with shear rate increasing at the given temperature, which means that the samples are Newtonian fluid. And the higher the nanofluids concentration was, the larger value of their shear viscosity. There were some anomalous phenomena occurred in rheological behavior, which may be caused by the breaking up of hybrid of two types of nanoparticles.

Effective viscosity of nanofluids — A modified Krieger–Dougherty model based on particle size distribution (PSD) analysis

Nanofluids (colloidal suspensions of nano-sized metallic and non-metallic particles in conventional cooling liquids) are well known for their potential to enhance the thermal transport. Excessive attempts have been made to utilize these nanofluids in heat transfer applications and energy conversion systems, etc. Effective viscosity of nanofluids is a pivotal parameter in determining the flow and heat transfer performance of nanofluids. The prime aim of this work is to develop a new model for effective viscosity of nanofluids. The influences of aggregation and interfacial layer formation have been incorporated into the Krieger–Dougherty (K–D) equation to predict the effective viscosity of nanofluids. This is accomplished by characterizing the clusters based on particle size distribution (PSD) analysis. Furthermore, attention has been paid to showcase the effects of cluster volume fraction, particle diameter and surfactants on effective viscosity of nanofluids. The predicted results are in good agreement with a wide variety of experimental data from literature consisting of different combinations of nanoparticles and basefluid. The accuracy and ease of application of the newly proposed model make it more interesting and useful for practical engineers in design and development of heat transfer systems using nanofluids.

An ecofriendly graphene-based nanofluid for heat transfer applications

Herein, a new ecofriendly approach to generate a graphene-based nanofluid was established. Specifically, a novel mode of graphene oxide reduction through functionalization with polyphenol extracted from red wine was introduced. Comprehensive characterization methods were employed to confirm and understand the reduction process of graphene oxide in the red wine polyphenol solution. It was noted, that the deoxygenation level of the reduced graphene oxide is comparable with the levels obtained by conventional and non-ecofriendly methods. The physical and thermal properties of the generated nanofluid including chemical stability, viscosity, wettability, electrical conductivity and thermal conductivity were investigated in a comprehensive manner. A significant thermal conductivity enhancement amounting to 45.1% was obtained for a volume fraction of 4%. In addition, the convective heat transfer coefficient of the nanofluid in a laminar flow regime with uniform wall heat flux was investigated to estimate its cooling capabilities. These results, firmly confirm that the generated graphene-based nanofluid is a formidable transporter of heat and yet ecofriendly. Therefore, it's anticipate that the generated nanofluid will open a new avenue in the pursuit of ecofriendly thermal conductors for heat transfer applications.

Effect of volume concentration and temperature on viscosity and surface tension of graphene–water nanofluid for heat transfer applications

In the present study, the effect of volume concentration (0.05, 0.1 and 0.15 %) and temperature (10–90 °C) on viscosity and surface tension of graphene–water nanofluid has been experimentally measured. The sodium dodecyl benzene sulfonate is used as the surfactant for stable suspension of graphene. The results showed that the viscosity of graphene–water nanofluid increases with an increase in the volume concentration of nanoparticles and decreases with an increase in temperature. An average enhancement of 47.12 % in viscosity has been noted for 0.15 % volume concentration of graphene at 50 °C. The enhancement of the viscosity of the nanofluid at higher volume concentration is due to the higher shear rate. In contrast, the surface tension of the graphene–water nanofluid decreases with an increase in both volume concentration and temperature. A decrement of 18.7 % in surface tension has been noted for the same volume concentration and temperature. The surface tension reduction in nanofluid at higher volume concentrations is due to the adsorption of nanoparticles at the liquid–gas interface because of hydrophobic nature of graphene; and at higher temperatures, is due to the weakening of molecular attractions between fluid molecules and nanoparticles. The viscosity and surface tension showed stronger dependency on volume concentration than temperature. Based on the calculated effectiveness of graphene–water nanofluids, it is suggested that the graphene–water nanofluid is preferable as the better coolant for the real-time heat transfer applications.

Specific heat of metal oxide nanofluids at high concentrations for heat transfer

In this work isobaric specific heat capacity measurements were performed for five different nanofluid sets designed as dispersions up to 15% mass concentrations of MgO, ZnO and ZrO2 in pure ethylene glycol as well as ZnO and ZrO2 in an ethylene glycol+water mixture at 50:50% in volume. Isobaric specific heat capacities for the three dry metallic oxide nanopowders and the two base fluids were also studied with the aim of contributing to elucidate on the heat capacity behavior of nanofluids for heat transfer applications. Measurements were carried out by using a quasi-isothermal Temperature-Modulated Differential Scanning Calorimetry (TMDSC) method in the temperature range from 243.15 to 473.15K. Base fluid results were compared with literature data to validate the measurement procedure. The specific heats for nano-sized materials here presented were also compared with literature data for bulk-sized of the same metallic oxides. In addition, the experimental values were used to evaluate the goodness of different models existing in literature to predict or correlate the specific heat capacities. A new fitting equation was also proposed to correlate specific heats of nanofluids as a function of the base fluid, nanoparticles as well as nanoparticle concentration.

Experimental investigation on thermophysical properties of ethylene glycol based copper micro- and nanofluids for heat transfer applications

ABSTRACTThe present work reports on the fabrication, experimental and theoretical investigation of thermal conductivity (TC) and viscosity of ethylene glycol (EG) based nanofluids/microfluids (NFs/MFs) containing copper nanoparticles (Cu NPs) and copper microparticles (Cu MPs). Cu NPs (20-40 nm) and Cu MPs (0.5-1.5 μm) were dispersed in EG with particle concentration from 1 wt% to 3 wt% using powerful ultrasonic agitation, and to study the real impact of dispersed particles the use of surface modifier was avoided. The objectives were to study the effect of concentration and impact of size of Cu particles on thermo-physical properties, including thermal TC and viscosity, of EG based Cu NFs/MFs. The physicochemical properties of NPs/MPs and NFs/MFs were characterized by using various techniques. The experimental results exhibited higher TC of NFs and MFs than the EG base liquid. Moreover, Cu NFs displayed higher TC than MFs showing their potential for use in some heat transfer applications. Maxwell effective medium theory as well as Einstein law of viscosity was used to compare the experimental data with the predicted values for estimating the TC and viscosity of Cu NFs/MFs, respectively.