Carbon-based Nanofluids Research Articles

On evaluation of thermophysical properties of transformer oil-based nanofluids: A comprehensive modeling and experimental study

Transformer oil-based nanofluids are known to have higher thermal conductivity and heat transfer performance compared to conventional transformer oils. In this study, four different types of transformer oil-based nanofluids are synthesized using the well-known two-step method. The first nanofluid contains pure multi-walled carbon nanotubes (MWCNTs), while other samples consist of 20 Vol% of MWCNTs and 80 Vol% of different oxide nanoparticles (i.e., Al2O3, TiO2, and SiO2). The dynamic viscosity and thermal conductivity of prepared samples are investigated in seven different volume fractions of 0.001, 0.0025, 0.005, 0.01, 0.025, 0.05, and 0.1%. Besides, the breakdown voltage of the pure transformer oil and nanofluids containing 0.05 and 0.1 Vol% of nanoparticles is investigated. The outcomes show that dielectric properties of hybrid carbon-based nanofluids are far better compared to those properties of the pure MWCNTs nanofluids. Finally, eight different soft computing approaches, including group method of data handling (GMDH), support vector machine (SVM), radial basis function (RBF) neural network, multilayer perceptron (MLP), and MLP and RBF models optimized with bat and grasshopper optimization algorithm (GOA), are used to model the viscosity and thermal conductivity of synthesized nanofluids. The outcomes show that the GMDH approach significantly outperforms all other models in terms of predicting the thermal conductivity and dynamic viscosity of transformer oil-based nanofluids.

Application of Carbon-based Nanofluids in Heat Exchangers: Current Trends

The thermal performance of a heat exchanger can be enhanced by adding carbon nanostructured materials such as carbon nanotubes and graphene to the conventional working fluid. When nanomaterials are suspended in the working fluid, the fluid is known as Nanofluid. The enhancement in the thermal and rheological properties of the fluid is responsible for the augmentation in heat transfer performance. The influence of carbon nanomaterial on the thermophysical properties, heat transfer characteristics and flow properties are reviewed. The current trends on the utilization of carbon-based nanofluids in heat exchangers were reported. The study shows that carbon-based nanofluids have the potential to improve the performance of heat exchanger and reduce the cost of fabrication by reducing heat exchange area. The study identifies the scope for future study.

A review of heat transfer application of carbon-based nanofluid in heat exchangers

Heat exchangers are very important equipment for cooling and heating processes in different industrial fields and applications. Nanofluids were employed to replace conventional working fluids of the same kind as water, ethyl-glycol and oil, with the aim to improve the heat transfer performance of heat exchange device. Nanofluids of different nanomaterials such as metal oxides, ceramic oxides and carbon nanomaterials have been widely used to enhance heat transfer. However, none improves the thermophysical properties as much as that of carbon nanomaterials such as Graphene and Carbon nanotubes. This study reviews and summarizes investigations on the application of carbon-based nanofluid in heat exchangers. It was observed that the thermal characteristics of the nanofluid depend on the type of base fluid, nanomaterial concentrations, temperature and surfactants used. The heat transfer characteristics and flow properties of the heat exchanger utilizing carbon-based nanofluids were also affected by nanomaterial concentration, Reynolds number, flow rates and inlet fluid temperature. It concluded by presenting challenges and scope for future studies.

Polyethylene Glycol Addition as Non-ionic Surfactant in Water-based Carbon Microfluid for Quench Medium in Heat Treatment Process

The mechanical properties of a material depend on the quenching process. In this process, there is a rapid cooling from elevated to room temperature in a short time by using a quench medium. Therefore, the phase transformation from austenite to martensite occurs. The common medium used in the quenching process is water, oil, polymer, and gas. Nanofluids are started to be used as a quench medium because they offer better thermal conductivity compared with the conventional medium. Selection of carbon-based nanofluids as a quenching process medium aims to obtain high thermal conductivity values and controllable cooling rates. Thereby, the expected microstructure of the material could be relatively easier to form. In this paper, carbon particles were obtained using a top-down method with a planetary ball mill for 15 hours at 500 rpm. Based on the electron microscope and spectroscopy results, the particle dimension was average at 15 μm after milling, and the carbon purity of the powder used in this research was 99%. Carbon particles at 0.1%, 0.3%, and 0.5% with variation of non-ionic surfactant Polyethylene Glycol of 1%, 2%, 3%, 4% and 5% respectively was used in this research. AISI 1045 or JIS S45C carbon steel was used as a steel sample, and austenized at 1000°C for 1 hour and then quenched in the microfluid. The hardness obtained was up to 811 HV for the sample quenched in 0.5% carbon and 1% Polyethylene Glycol. The improvement was more than 100 HV, compared with the sample quenched in distilled water, which had a hardness only 666 HV.

A review of solar collectors using carbon-based nanofluids

Abstracts The quest to enhance the thermal efficiency of solar collectors by improving the working or absorbing fluid led to the synthesis of nanofluids. Numerous studies have highlighted different nanomaterials such as copper oxide, alumina, silica and so on for dispersion in working fluid and subsequent application in solar collectors. However, carbon nanomaterials have been adjudged as the most promising for preparing nanofluids and heat transfer application. This is because carbon nanomaterials possess remarkable thermophysical properties. These properties contribute a notable enhancement in the thermophysical properties of the working fluid and consequently improve the performance of solar collectors. This study succinctly presents an overview of the performance of various solar collectors utilizing carbon-based nanofluids. The influence of nanofluid concentration, temperature and flow rate on the collector efficiency of the solar collectors were highlighted. This research outcome showed that carbon-based nanofluids with a low concentration of about 0.3 vol% improved the collector efficiency of flat-plate, evacuated-tube, parabolic trough and hybrid photovoltaic thermal solar collector up to 95.12%, 93.43%, 74.7% and 97.3% respectively. Also, direct absorption solar collector using carbon-based nanofluid with a low concentration of at least 0.01 vol% achieved a photothermal efficiency of up to 122.7%. The study further revealed that there is a huge potential to achieve the application of carbon-based nanofluid on a commercial scale. The challenges and prospects for further research were identified.

Surfactant-aided dispersion of carbon nanomaterials in aqueous solution

Carbon nanomaterials such as graphene and carbon nanotubes possess great thermophysical properties which make them very good candidates for heat transfer application. However, the major challenge of these nanomaterials is their tendency to agglomerate and bundle together when dispersed in base fluids. This study reviews the homogeneous dispersion of these nanomaterials in aqueous solution with the aid of surfactants. The different surfactants and their characterization methods for stable dispersion of carbon nanomaterials have been examined. The influence of surfactants on the thermophysical and rheological properties of carbon-based nanofluids was also highlighted. The usefulness of noncovalent functionalization using surfactants is due to its ability to efficiently unbundle carbon nanomaterials and sustain homogeneity of the nanofluids without compromising the integrity of their structure. Sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfate (SDBS), Gum Arabic (GA), Triton X-100, and cetyltrimethylammonium bromide (CTAB) are the commonly used surfactants. Unlike SDS, SDBS, and CTAB, GA does not foam when agitated. Various authors have investigated the stability of carbon-based nanofluids. Both physical and chemical techniques have been used to stabilize nanofluids. Mixed surfactants were found to stably disperse nanomaterials at lower concentrations compared to individual surfactants. However, limited studies exist for long term stability of carbon-based nanofluids.

Improving the efficiency and recognizability of the spectroscopy method for measuring nanofluid stability

This study proposed a method to improve the efficiency and recognizability of the spectroscopy method for measuring nanofluid stability. The 0.2 wt% and 0.4 wt% carbon-based nanofluids (CBNFs) were used as samples. The volumes of three test types of samples in the cuvette were 2.5 mL (Case 1), 1.8 mL (Case 2), and 1.8 mL (Case 3), respectively. In addition, an opaque black tape covered the lower half of the original area spotted by the probe beam in Case 3. The spectrometer was used to measure absorbance at wavelengths of 400–800 nm at fixed time interval. The results indicate that reducing the distance between the area spotted by the probe beam and the liquid level can improve the efficiency and recognizability of CBNF stability detection. For the optimal condition, the time to detect CBNF settling reduces by 50% and recognizability improves by 34.9% in the design of Case 2.

Carbon-based Nanofluid Applications in Solar Thermal Energy

Renewable energy sources such as solar, wind and geothermal are proposed as an alternative to fossil fuels whose excessive use causes global warming. The most popular one of the renewable energy sources is considered as solar energy due to the fact that required energy is provided by the sun entire year around the world. Solar energy systems convert the solar radiation to the useful heat or electricity. In order to achieve better performance in solar thermal systems many studies have been conducted. Some of these studies suggest that heat transfer fluid could be changed with the nanofluids which can be defined as new generation heat transfer fluid. Nanofluids are suspensions of nano-sized particles such as metals, metal-oxides, and Carbon-allotropes (C), in the conventional base-fluids (water, ethylene glycol and oil). Using nanofluid enhances the efficiency and thermal performance of solar systems due to their better thermophysical and optical properties. Recently, C-based nanofluids are getting attention due to their enhanced thermal conductivity and absorptivity at even low concentrations. The results show that C-based nanofluids have a potential to use in solar energy systems: solar collectors, solar stills, photovoltaic/thermal systems.

Thermal design improvement of a double-layered microchannel heat sink by using multi-walled carbon nanotube (MWCNT) nanofluids with non-Newtonian viscosity

In the present study, numerical optimization of a double layer micro channel heat sink is addressed. Carbon based nanofluids with a non-Newtonian viscosity is assumed as the coolant. A conjugate numerical model based on finite volume method and two-phase mixture model is used to simulate the heat and fluid flow through the two three-dimensional domains; the solid walls and the coolant. A direct search method is applied to find the optimal design of the micro channel heat sinks such that the thermal resistance of the heat sink is minimized under the constraint of fixed pumping powers. The numerical model is validated against experimental data. A comprehensive sensitivity analysis is undertaken to properly bracket the optimum design point of the heat sink and the optimum point is directly searched for several pumping powers. It is shown that using carbon based nanofluid results in the reduction of overall thermal resistance of the double layer microchannel heat sink in comparison with oxide-metallic nanofluid (with Newtonian rheological behavior). The superior thermal performance of MWCNT/water nanofluids is attributed to the high conductivity of the carbon nano particles and the shear thinning behavior of the nanofluid. Up to 14% enhancement in the thermal performance of the micro channel heat sink is reached by the use of non-Newtonian carbon base nanofluids.

Characteristics of carbon-based nanofluids and their application in a brazed plate heat exchanger under laminar flow

In this study, a graphite-powder-based heating and cooling processing method (GP-HCPM) was used to produce carbon-based nanofluids (CBNFs) as working fluid for a brazed plate heat exchanger (BPHE) system. Sodium dodecyl benzenesulfonate (SDBS) was added to CBNFs as a dispersant to enhance their stability, and the CBNF concentration was adjusted to 0.2 wt% (S1) and 0.6 wt% (S2). The thermal conductivity, viscosity, density, specific heat, and contact angle of the CBNFs were measured and analyzed. Finally, the CBNFs were tested in a BPHE system to evaluate the average heat exchange capacity (Q̇ex,avg), pumping power consumption (Pp), and system efficiency factor (SEF) under various temperatures (35, 40, and 45 °C) and laminar flow conditions. Results show that the Q̇ex,avg of S1 and S2 was higher than water under all experimental parameters, indicating that CBNFs exhibit a higher heat exchange performance than water. The Pp of S1 was slightly lower than that of water. The maximum Q̇ex,avg and SEF enhancement ratio of S1 and S2 was 7.54% and 7.98% and 9.19% and 7.28%, respectively. Considering the overall system efficiency of experimental parameters of the BPHE system, S1 was deemed more suitable than S2.

Thermophysical properties and stability of carbon nanostructures and metallic oxides nanofluids

A pioneer idea for increasing the thermal performance of heat transfer fluids was the use of ultrafine solid particles suspension in the basefluid. Nanofluids, synthesized by mixing solid nanometre-sized particles at low concentrations with the basefluid, were used as a new heat transfer fluid which developed a remarkable effect on the thermophysical properties and heat transfer coefficient. For any nanofluid to be usable in heat transfer applications, the main concern is its long-term stability. In this investigation, pentaethylene glycol-treated graphene nanoplatelets (PEG-GnP), pentaethylene glycol-thermally treated graphene (PEG-TGr), Al2O3 and SiO2 were synthesized. The thermophysical properties of PEG-GnP, PEG-TGr, Al2O3 and SiO2 were measured experimentally by using different devices and equipment. Dispersion stabilities of carbon-based nanofluids and metallic oxides nanofluids were observed for 30 days, and the results showed the higher dispersibility of the nanofluids in an aqueous media with very low sedimentation. Thermal conductivity, viscosity and density were increased, while specific heat decreased as mass concentration increased. The temperature effect on the nanofluids was directly proportional to their thermal conductivity and inversely to the viscosity, density and specific heat.

Study on the Phase Change Characteristics of Carbon-Based Nanofluids

In this study, carbon-based nanofluids (CBNFs) with the minimized carbon materials (MCMs) were prepared using a graphite powder-based heating and cooling processing method (GP-HCPM). In addition, sodium dodecyl benzenesulfonate (SDBS) was added as a dispersant to enhance the stability of the CBNFs. Two methods, one involving fixed heating and cooling rates and the other involving fixed heating and cooling temperatures, were used to measure and analyze the phase change characteristics of the CBNFs and SDBS aqueous solution in order to evaluate the feasibility of employing CBNFs as phase change materials (PCMs) for cold storage applications. Results revealed that SDBS reduced the thermal conductivity (k) and increased the viscosity (μ), density (ρ), and specific heat (cp) of the samples; the CBNFs tended to increase the k, μ, and ρ values but reduce the cp values of the samples, compared with water. Furthermore, the SDBS aqueous solution and CBNFs significantly reduced the contact angle of droplets, compared with water. Phase change experiments conducted for all samples revealed that the CBNF sample S4 demonstrated the greatest reduction ratios in onset nucleation time, solidification time, and subcooling degree (38.98%, 11.05%, and 35.41%, resp.); thus, S4 was determined to be the most suitable CBNF for use as a PCM in cold storage applications.

Acid-functionalized carbon nanofibers for high stability, thermoelectrical and electrochemical properties of nanofluids

Carbon-based nanofluids are viewed as promising thermal fluids for heat transfer applications. However, other properties, such as electrical conductivity and electrochemical behavior, are usually overlooked and rarely investigated despite their importance for the overall performance characterization of a given application. In this study, we synthesized PAN-based carbon nanofibers (CNF) by electrospinning, and characterized them using electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Thermoelectrical and electrochemical measurements were carried out on nanofluids. We found that, although CNF nanofluids exhibit good thermal and electrical properties with a negligible corrosive effect, the suspensions tend to sediment within a few days. However, acid treatment of CNF (F-CNF), which resulted in the shortening of the fibers and the appearance of surface-oxygenated species, made F-CNF-based nanofluids exhibit superior stability in water that extended for more than 90 days, with consistent and superior thermal and electrical properties.

Development of a new density correlation for carbon-based nanofluids using response surface methodology

Density is among the fundamental thermo-physical characteristics of fluids that are examined prior to carrying out performance analysis of the fluid. In this study, the effect of the design variables on the density of nanofluids was studied using response surface methodology (RSM). The quadratic model produced by RSM was employed to determine the performance factors, i.e., mass concentration and temperature with reasonably good accuracy. Improved experimental correlations were proposed for the density prediction of the carbon-based nanofluids based on the experimental data. Experimentally measured densities of two different nanofluids at the nanoparticle mass concentration of up to 0.1% and the temperature range of 20–40 °C were examined. The improvement in densities compared to the density of base fluid at 20 and 40 °C is approximately 0.15% for 0.1% fraction of MWCNT–COOH nanoparticles. Additionally, the densities of F-GNP nanofluids are increased by 0.056% compared to the density of distilled water. As a final point, the RSM results were compared with the results which got from the empirical data. It was detected that the optimal RSM model is accurate and the absolute maximum deviation measured values from the predicted densities of MWCNT–COOH and F-GNP nanofluids are 0.012 and 0.009%, respectively.

Fabrication and Characterization of Carbon-Based Nanofluids through the Water Vortex Trap Method

This study designed an efficient one-step method for synthesizing carbon-based nanofluids (CBNFs). The method employs the vortex trap method (VTM) and an oxygen-acetylene flame, serving as a carbon source, in a manufacturing system of the VTM (MSVTM). The flow rate ratio of O2 and C2H2 was adjusted to form suitable combustion conditions for the reduced flame. Four flow rate ratios of O2 and C2H2 were used: 1.5 : 2.5 (V1), 1.0 : 2.5 (V2), 0.5 : 2.5 (V3), and 0 : 2.5 (V4). The morphology, structure, particle size, stability, and basic physicochemical characteristics of the obtained carbon-based nanomaterials (CBNMs) and CBNFs were investigated using transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, Raman spectrometry, ultraviolet–visible–near-infrared spectrophotometry, and a particle size-zeta potential analyzer. The static positioning method was utilized to evaluate the stability of the CBNFs with added EP dispersants. The evaluation results revealed the morphologies, compositions, and concentrations of the CBNFs obtained using various process parameters, and the relation between processing time and production rate was determined. Among the CBNMs synthesized, those obtained using the V4-0 flow rate ratio had the highest stability when no EP dispersant was added. Moreover, the maximum enhancement ratios of the viscosity and thermal conductivity were also obtained for V4-0: 4.65% and 1.29%, respectively. Different types and concentrations of dispersants should be considered in future research to enhance the stability of CBNFs for further application.

Experimental investigation of dispersion characteristics and thermal conductivity of various surfactants on carbon based nanomaterial

The surfactants sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and dodecyl betaine (DB) are used in graphene and carbon nano-tube (CNT) aqueous solutions, to develop an improved method that increases dispersion, creates long-term stability, and increases thermal characteristics. To evenly disperse the nanoparticles in the base liquid, an ultrasound was applied for 40m. The nanoparticle dispersion of solutions was compared using UV spectroscopy. Zeta potential was used to indicate the colloidal stability of each solution. The thermal conductivities of the nanofluid solutions were measured using a transient hot wire method, and the three different surfactants were compared Good stability and nanoparticle dispersion was observed for nanofluids with surfactants. However, the thermal conductivities of the nanofluid solutions decreased with increasing surfactant concentrations. Carbon-based nanofluids with SDS had better thermal conductivity than nanofluids with other surfactant dispersants. We found the nanofluid has less weight percent of surfactant have better heat transfer than without surfactant. However, DB produced better dispersion than other surfactants, and carbon-based nanofluids with SDBS and SDS have anionic surfactant both had a better stability than nanofluids has amphoteric surfactant DB.

Bottom up Approach Toward Prediction of Effective Thermophysical Properties of Carbon-Based Nanofluids

ABSTRACTCarbon-based nanofluids, mainly suspensions of carbon nanotubes or graphene sheets in water, are typically characterized by superior thermal and optical properties. However, their multiscale nature is slowing down the investigation of optimal geometrical, chemical, and physical nanoscale parameters for enhancing the thermal conductivity while limiting the viscosity increase at the same time. In this work, a bottom up approach is developed to systematically explore the thermophysical properties of carbon-based nanofluids with different characteristics. Prandtl number is suggested as the most adequate parameter for evaluating the best compromise between thermal conductivity and viscosity increases. By comparing the Prandtl number of nanofluids with different characteristics, promising overall performances (that is, nanofluid/base fluid Prandtl number ratios equal to 0.7) are observed for semidilute (volume fraction ⩽ 0.004) aqueous suspensions of carbon nanoparticles with extreme aspect ratios (larger than 100 for nanotubes, smaller than 0.01 for nanoplatelets) and limited defects concentrations (<5%). The bottom up approach discussed in this work may ease a more systematic exploration of carbon-based nanofluids for thermal applications, especially solar ones.

Potential Heat Transfer Fluids (Nanofluids) for Direct Volumetric Absorption-Based Solar Thermal Systems

Nanoparticle dispersions or more popularly “nanofluids” have been extensively researched for their candidature as working fluid in direct-volumetric-absorption solar thermal systems. Flexibility in carving out desired thermophysical and optical properties has lend the nanofluids to be engineered for solar thermal and photovoltaic applications. The key feature which delineates nanofluid-based direct absorption volumetric systems from their surface absorption counterparts is that here the working fluid actively (directly) interacts with the solar irradiation and hence enhances the overall heat transfer of the system. In this work, a host of nanoparticle materials have been evaluated for their solar-weighted absorptivity and heat transfer enhancements relative to the basefluid. It has been found that solar-weighted absorptivity is the key feature that makes nanoparticle dispersions suitable for solar thermal applications (maximum enhancement being for the case of amorphous carbon nanoparticles). Subsequently, thermal conductivity measurements reveal that enhancements on the order of 1–5% could only be achieved through addition of nanoparticles into the basefluid. Furthermore, dynamic light scattering (DLS) and optical measurements (carried out for as prepared, 5 h old and 24 h old samples) reveal that nanoclustering and hence soft agglomeration does happen but it does not have significant impact on optical properties of the nanoparticles. Finally, as a proof-of-concept experiment, a parabolic trough collector employing the amorphous carbon-based nanofluid and distilled water has been tested under the sun. These experiments have been carried out at no flow condition so that appreciable temperatures could be reached in less time. It was found that for the same exposure time, increase in the temperature of amorphous carbon based nanofluid is approximately three times higher as compared to that in the case of distilled water.

Hydrodynamic and thermal performance prediction of functionalized MWNT-based water nanofluids under the laminar flow regime using the adaptive neuro-fuzzy inference system

ABSTRACTAdaptive Neuro-Fuzzy Inference System (ANFIS) opens a new gateway in understanding the complex behaviors and phenomena for different fields such as heat transfer in nanoparticles. The ANFIS method is a shortcut to find a nonlinear relation between input and output and results in valid outcomes, especially in engineering phenomena, which is used here for determining the convective heat transfer coefficient. Using the ANFIS, the critical parameters in heat transfer including convective heat transfer coefficient and pressure drop are determined. To realize this issue, the thermophysical properties of non-covalently and covalently functionalized multiwalled carbon nanotubes-based water nanofluid were investigated experimentally. The results of simulation and their comparison with the experimental results showed an excellent evidence on the validity of the model, which can be expanded for other conditions. The proposed method of ANFIS modeling may be applied to the optimization of carbon-based nanostructure-based water nanofluid in a circular tube with constant heat flux.