Multi-walled Carbon Nanotube Nanofluids Research Articles

Forced convection heat transfer of non-Newtonian MWCNTs nanofluids in microchannels under laminar flow

Heat transfer process in micro/mini-scales becomes an urgent need for many applications where size and weight are severe constraints such as electronics. However, the latter led to developing new thermal fluids, the so-called nanofluids, with enhanced thermophysical properties to cover the high heat dissipation requirements due to the devices' miniaturization. In this work, a validated computational model is used to establish guidelines for the compact heat exchanger with microchannels, as well as to assist nanofluid properties tailoring. A finite volume method (FVM) approach is built considering laminar fluid flow conditions in a circular microchannel. The latter is used and validated against available experimental data, and the influence of temperature-dependent thermophysical properties and non-Newtonian behaviour of the MWCNTs (Multi-walled carbon nanotubes) nanofluids are considered. The results show that MWCNTs nanofluids enhance the heat transfer performance of the micro heat exchanger by up to 33%. Moreover, particular operating conditions are seen to improve the system energy efficiency, mainly near to Reynolds number (Re) equal to 1000, when taking into account both heat transfer performance and pressure drop. Additionally, a correlation of the average Nusselt number is proposed to estimate the heat transfer performance of nanofluids in microchannels.

On grinding force ratio, specific energy, G-ratio and residual stress in SQCL assisted grinding using aerosol of MWCNT nanofluid

In the present investigation, water based multi-walled carbon nanotube (MWCNT) dispersed nanofluid was produced and used as a cutting fluid in small quantity cooling lubrication (SQCL) assisted grinding of hardened AISI52100 steel. The work material was ground by an alumina wheel. The SQCL technology utilizes atomized aerosol of liquid grinding fluid. Use of MWCNT nanofluid aerosol in place of soluble oil was found to be substantially beneficial in reduction of specific energy and development of compressive residual stress on ground surface. The steady and lower value of the force ratio (tangential to normal grinding force, Ft/Fn) was suggestive of the superior lubrication and grit sharpness retention ability of the aerosol of MWCNT nanofluid. Higher compressive residual stress on the ground surface under MWCNT nanofluid environment suggests lesser grinding zone temperature, which can be attributed to its superior wettability, lubricity and heat dissipation ability of the MWCNT nanofluid. The consumption rate of grinding fluid in SQCL was varied. It could be reduced to 200 ml/h for MWCNT nanofluid to obtain an almost similar or better effect to that of 500 ml/h for soluble oil. Lesser surface tension of MWCNT nanofluid, compared to its counterpart, seemed to facilitate wetting, thus improving lubrication and heat transfer capability further.

A New Effective Multiwalled Carbon Nanotube-Foam System for Mobility Control

SummaryNanoparticles have improved a surfactant's ability to create long-lasting foam. Recent studies have widely recommended the use of silica nanoparticles to enhance foam stability. This paper presents an experimental investigation of a new and highly effective alpha olefin sulfonate (AOS)–multiwalled carbon nanotube (MWCNT) system for mobility control during gas enhanced oil recovery (EOR) operations.The new AOS–MWCNT system was evaluated for its foam stability at 150°F using a high-pressure view cell. The MWCNT was obtained as solid particles of aspect ratio up to 100 and silica nanoparticles of median size of 118 nm. The foam system was optimized for its maximum half-life by varying the concentration of the AOS and the nanotube from 0.2 to 1% and 250 to 1,000 ppm, respectively. Compatibility testing with salts was done as well. Coreflood experiments with 1.5-in.-diameter, 6-in.-long Berea sandstone cores were run to calculate the mobility reduction factor at 150°F. Nitrogen foam was injected into the core at 80% foam quality in the tertiary recovery mode, and the pressure drop across the core was measured. The formation brine had a salinity of 5 wt% sodium chloride (NaCl), and the foaming solutions were prepared with 2 wt% NaCl.The optimal concentrations of the AOS solution and the nanotubes for maximum foam stability were determined to be 0.5% and 500 ppm, respectively. The optimized AOS–MWCNT system yielded 60% greater nitrogen foam half-life (32 minutes) than an optimized AOS–silica system at 150°F. The foam half-life of a stand-alone 0.5% AOS solution was 7 minutes. In the presence of crude oil, the foam half-life decreased for all the tested systems. Coreflood experiments at 150°F showed a significant increase in the mobility reduction factor when the new AOS–MWCNT system was used as the foamer instead of stand-alone AOS or AOS–silica system. The new foaming system was stable through the duration of the experiment, yielding foam in the effluent samples. There was no formation damage observed. Salt tolerance for the MWCNT nanofluid was higher than the silica nanofluid.Foam needs to be stable for long periods of time to ensure effective mobility control during gas injection for EOR. This paper investigates a new highly effective AOS-multiwalled carbon nanotube system that outperforms the AOS–silica foaming systems in terms of foam stability and mobility control at 150°F.

Experimental study on heat transfer, entropy generation, and exergy destruction of Ag, MWCNT, and GO water-based nanofluids in helical tubes

Heat transfer convection, pressure loss, and entropy generation analysis for nanofluid flow through helical tubes are experimentally investigated. A test setup was fabricated, and three types of nanofluid, including silver (Ag), multi-walled carbon nanotube (MWCNT), and graphene oxide (GO), were prepared. Experiments were carried out in the laminar regime through four helically coiled tubes, while uniform heat flux was applied on the wall surface. The results show that Ag nanoparticles improve thermal conductivity and heat transfer coefficient between 8 and 25%, MWCNT/water enhances the heat transfer rate up to 10%, but GO nanoplates decrease heat transfer rate. Comparing entropy generation and exergy destruction for water and nanofluids reveals that utilizing nanoparticles of Ag and MWCNT reduces entropy production and exergy loss due to better thermal performance, but GO/water increases entropy production because of lower thermal conductivity compared to water. Maximum reduction in non-dimensional total entropy generation around 15% was achieved for Ag/water nanofluid. Variation of entropy generation due to heat transfer and fluid friction in addition to Bejan number and non-dimensional total entropy generation for water and nanofluids is discussed in detail.

Experimental study of thermophysical properties of MWCNT and graphene coolant nanofluids for automotive application

The present study reports on an experimental investigation regarding thermal conductivity and dynamic viscosity of multi-walled carbon nanotubes (MWCNT) and graphene coolant nanofluids at four volumetric concentrations (0.025%, 0.050%, 0.1% and 0.15%), with focus on automotive applications. The base fluid was composed of a mixture of water–ethylene glycol (70:30). The nanofluids were prepared using the high-pressure homogenization method, which presents long-term stability. Thermal conductivity of nanofluids was measured using the transient hot bridge method, at temperatures ranging from 20 to 50 °C and dynamic viscosity from 20 to 80 °C using a rotational viscometer. Experimental results revealed that nanoparticle concentration and temperature significantly affect the thermophysical properties. Increases in thermal conductivity were found of up to 7.7% for MWCNT nanofluid at a 0.15% concentration. Graphene nanofluids presented thermal conductivity similar to MWCNT, with its highest augmentation found at 5.9% for a 0.1% volumetric concentration. MWCNT nanofluids presented discrete increments on viscosity relative to base fluid for temperatures lower than 50 °C (up to 9.2%) and more pronounced increments at higher temperatures (29.7% at 80 °C). Graphene nanofluids’ viscosity was close to base fluid over the entire analyzed temperature range. The maximum increase was 4.7% for 0.05% concentration at 30 °C, and viscosity was lower than base fluid for some conditions, with a maximum decrease of 3.9%. The experimental results on thermal conductivity and viscosity were compared with proposed correlations found in the literature and showed good agreement. Finally, the increase in thermal conductivity combined with similar viscosity compared to base fluid indicates that the use of nanofluids, as an alternative coolant for automotive applications, is certainly feasible.

Systematical study of multi-walled carbon nanotube nanofluids based disposed transformer oil

In this paper, the electrical, dielectric, Raman and small angle X-ray scattering (SAXS) structure behavior of disposed transformer oil in the presence of multi-walled carbon nanotube (MWCNT) were systematically tested to verify their versatility for preparing better alternative transformer oil in future. MWCNT nanofluids are prepared using a two-step method with concentrations ranging from 0.00 to 0.02 g/L. The test results reveal that 0.005 g/L concentration possesses the most optimum performance based on the electrical (AC breakdown and lightning impulse) and dielectric (permittivity, dissipation factor and resistivity) behavior. According to the trend of AC breakdown strength and lightning impulse pattern, there were 212.58% and 40.01% enhancement indicated for 0.005 g/L concentration compared to the disposed transformer oil. The presence of MWCNT also yielding to the decrement of dissipation factor, increased on permittivity and resistivity behavior of disposed transformer oil which reflected to the performance of electrical properties. Furthermore, it is found that these features correlated to the structural properties as systematically verify by Raman and SAXS analysis study.

Radiative Non-Coaxial Rotation of Magnetohydrodynamic Newtonian Carbon Nanofluid Flow in Porous Medium with Heat and Mass Transfer Effects

Non-coaxial rotation system has encountered in various fields such as engineering field in designing advanced cooling and heating system, food processing and mixer machines. In the present study, the effect of the non-coaxial rotation of a vertical disk on the heat and mass transfer of Newtonian nanofluids in a porous medium is analytically discussed. The influence of the magnetic field and thermal radiation is also taken into the consideration. Two different types of nanofluids which are single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) with water as the base fluid are analyzed and compared. Suitable dimensionless variables are utilized to convert the governing partial differential equations associated with the initial and boundary conditions into the dimensionless form. Then, the exact solutions of the dimensionless governing equations are calculated by using the Laplace transform method. A limiting case study of the obtained analytical solutions is constructed to compare with the previously published results to verify its validity. The distributions of the velocity, temperature, and concentration along with the Skin friction, Nusselt number, and Sherwood number due to the variation of the pertinent parameters are displayed and scrutinized through graphs and tables. In the frame of non-coaxial rotation, the nanofluid with the SWCNTs nanoparticles have illustrated a higher rate of heat transfer as compared to MWCNTs nanofluid. Moreover, the heat transmission in the nanofluid has been enhanced by increasing the volume fraction of the nanoparticle and also the intensity of the radiation. This suggests that heating or cooling in a system such as a nuclear reactor can be improved by properly selecting the type of the nanofluid and also the volume fraction of the nanoparticle.

Analysis of Multiwalled Carbon Nanotubes Porosimetry And Their Thermal Conductivity with Ionic Liquid-Based Solvents

The suspension of nanoparticles with common heat transfer fluids like Ethylene glycol and water yields nanofluid exhibits superior thermal properties than their host fluids. Ionic liquids have the potential to demonstrate remarkable thermophysical properties (especially thermal conductivity) that ordinary nanofluids cannot achieve. On the other hand, the quantity and structure of nanoparticles porosity affects the nanofluid’s thermal conductivity considerably. Various investigations have revealed the improved thermophysical characteristicts of Multiwalled Carbon nanotubes (MWCNTs) nanofluids containing common solvents or base fluids. However, only limited studies are available on the impact of thermal conductivity in Ionic liquid-based nanofluids (Ionanofluids) owing to their high cost and viscosity. Ultrasonication technique is employed in preparing the three different Ionanofluids containing 0.5 Wt.% via the two-step method to achieve a greater stability and thermal conductivity without utilizing surfactants. Experimental investigations are performed to boost the thermal conductivity of MWCNT/Propylene glycol nanofluid using 1,3-dimethyl imidazolium dimethyl phosphate [Mmim][DMP], 1-ethyl-3-methyl imidazolium octyl sulfate [Emim][OSO4] and 1-ethyl-3-methyl imidazolium diethyl phosphate [Emim][DEP] at a temperature ranging from 295 K to 355 K. The acquired results illustrated that the thermal conductivity of MWCNT Ionanofluids incorporated with [Mmim][DMP], [Emim][OSO4] and [Emim][DEP] increased by 37.5%, 5% and 2% respectively. This unique class of Ionanofluids shows incredible capacity for use in high temperature applications as conventional heat transfer fluids.

Comparative evaluation on the thermal properties and stability of MWCNT nanofluid with conventional surfactants and ionic liquid

Conventional surfactants such as CTAB (cetrimonium bromide), SDS (sodium dodecyl sulphate), SDBS (sodium dodecyl sulphonate) are combined with nanofluids to improve the stability and thermal conductivity of nanofluids. These nanofluids are mainly used for heat transfer applications where heating and cooling are usual courses of action which result in surfactants producing foams and polluting the heat transfer media, affecting the total system performance. Besides, the common surfactant molecules that augment the thermal resistance between the nanoparticles and base fluid also affect the thermophysical properties of the nanofluid. In this paper, [Bmim][Cl] (1-butyl-3-methylimidazolium chloride), a high purity ionic liquid (IL) with higher thermal stability was used to provide a comparative study on the stability and thermal properties with that of the conventional surfactants (CTAB, SDS, SDBS) on multiwalled carbon nanotubes (MWCNT)/propylene glycol (PG) nanofluid. The transient hot-wire based KD2-Pro and zeta potential results demonstrated that the inclusion of ionic liquid improved the thermal conductivity and stability of the formulated nanofluid. However, much like the conventional surfactants, the strong electrostatic repulsive force created by the ionic liquid was found to decrease when the temperature is increased. The outcome demonstrated the most extreme thermal conductivity upgrade of 33.7% at 303 K and maximum dispersion stability of more than one month without any aggregation for the nanofluid containing ionic liquid.

Darcy Forchheimer electromagnetic stretched flow of carbon nanotubes over an inclined cylinder: Entropy optimization and quartic chemical reaction

Carbon nanotubes (CNTs) are characterized with exceptional electrical, thermal, mechanical, chemical, and optical properties (e.g., electrical conductivity, large specific surface area, high thermal conductivity, high hardness and stiffness, light weight, special electronic structure, high aspect ratio and chemical stability, and low specific gravity). Because of such outstanding properties, CNTs are being considered as prime candidate materials in multidisciplinary fields comprising of automotive, material science, aerospace, optical, electrical, biomedical, and energy conversion for nanoscale applications. In view of such advantages, electromagnetic influence on the Darcy Forchheimer flow of single‐walled CNT (SWCNT)/multi‐walled CNT (MWCNT) nanomaterials over an inclined‐extended cylinder subject to quartic chemical reactions has been explored in the present study to improve the performance of existing heat transfer systems. The heat transportation model is enriched with nonlinear thermal radiation, dissipation, and Ohmic heating. This article is more specific about improving the efficiency of thermal‐flow systems through entropy minimization. The dimensionless nonlinear PDEs are solved via Runge–Kutta–Fehlberg approach with shooting technique. The outcome of our investigation reveals that curvature parameter augments the flow field and rate of heat and mass transfer from the cylindrical and flat surfaces. Greater electromagnetic influence favors the flow and viscous drag of SWCNT/MWCNT‐water nanofluids and rate of heat transportation from the extended cylindrical surface. Augmented volume fraction of solid nanoparticles upsurges the entropy generation and Bejan numbers appreciably. The rate of heat transportation from the extended cylindrical surface for MWCNT nanofluid is greater than that of SWCNT nanofluid.

Simulation and Experimental Investigation Quenching Behavior of Medium Carbon Steel in Water Based Multi Wall Carbon Nanotube Nanofluids

Experiments were conducted to study the effect of quenching medium carbon steel in water-based MWCNTs nanofluids at 0.05 % wt. concentration quenchant, a large cylindrical sample with 46 mm diameter and 40 mm length made from medium carbon steel used with three K-type thermocouples with a diameter of 1.5 mm inserted in three locations for sample (center of the sample, mid-point between center and surface and 1 mm from the surface). A time-temperature reading data system was used to read temperature history during cooling stage.The same experiments were simulated using ANSYS Workbench with Thermal Transient Version 19, the cooling curves at three locations for the cylindrical steel sample calculated during quenching in MWCNTs nanofluids. Quench factor analysis was used to predict the hardness results from the calculated and measured cooling curves, and these results compared with the hardness test results conducted in the significant sample from the center to the surface. The results show excellent compatibility when compared between the hardness results from cooling curves, and it also shows a good agreement with the results of the hardness test, especially at the sample surface.

Nusselt number and friction factor variations in a capsule heat exchanger filled with eco‐friendly jatropha seed oil–based multi walled carbon nanotubes nanofluid

The present 3‐D numerical paper investigates Nusselt number and friction factor variations in a capsule heat exchanger filled with eco‐friendly jatropha seed oil–based MWCNTs nanofluid. For all studied models, inlet nanofluid temperature is Tin = 310 K, and the hot source with q = 650 W/m2 is adopted. Due to achieve the most efficient Newtonian nanofluid in present study, solid nanoparticles of MWCNT are added to the base fluid in volume concentration of 0.2% to 0.8%. Also, different riser heights (25, 35, and 50 cm) and different emissivity values of capsule walls (ε = 0.3 and 0.7) are studied in this paper. In the current modeling, the SST k – ω turbulence model has been assumed as the turbulence model. Based on achieved results in this paper, the model with capsule angle of β = 30° has better heat transfer than the other studied slopes, which is followed with models with β = 60° and β = 90°, respectively. Also, it is seen that gravity has a significant influence on velocity contours, and in model with β = 90° more pressure drop may be seen, which is followed with models with β = 60° and β = 90°, respectively. Moreover the predicted pressure drop values from inlet to outlet always increase by increase of Reynolds numbers; therefore, there is an optimum Reynolds number during the studied range of flow velocities which leads to the minimum pressure drop penalty. Also, it is realized that usage of nanofluid at higher nanoparticles volume concentrations leads to higher Nusselt numbers during all studied Reynolds numbers. The model with nanoparticles volume fraction of ϕ = 0.8% has the highest values of predicted average Nusselt number which is followed with the models with ϕ = 0.6%, ϕ = 0.4%, and ϕ = 0.2%, respectively. Besides, it is clearly found that usage of walls with different emissivity values has not a significant influence on thermal–hydraulic characteristics of studied capsule heat exchanger.

Aqueous nanofluids containing paraffin-filled MWCNTs for improving effective specific heat and extinction coefficient

This paper presents measurements of the effective specific heat and the extinction coefficient for aqueous nanofluids dispersed with paraffin-filled Multi-Walled Carbon NanoTubes (MWCNTs). The MWCNTs were filled with paraffin wax by capillary action. Centrifugal decanting was used to modify the traditional two-step method so as to produce a nanofluid dispersion that was more stable than that produced by the traditional method. The stability of each suspension was quantitatively evaluated with a laser scattering method over 7 days. A differential scanning calorimetry (DSC) and the three-slap method were used to measure the effective specific heat and the extinction coefficient of the nanofluids, respectively. The measured effective specific heat of the water-based paraffin-filled MWCNTs nanofluid, with a volume fraction of 1%, was up to 5.1% larger than that for the water-based MWCNT nanofluids without paraffin wax. The nanofluid extinction coefficient was shown to increase linearly with the volume fraction for data within the independent scattering regime, which occurred when the nanoparticle-distance/wavelength ratio (c/λ) was less than 2.

MWCNT and COOH–MWCNT aqueous nanofluids: thermophysical and rheological characterization

The nanofluids characterization is of fundamental importance to predict their applicability in a real heat transfer situation. In addition to the transport properties, the nanofluid stability is an important factor to be studied, due to the long pumping, heating, cooling and resting cycles the fluids are usually subjected to. Carbon nanotubes have great potential to be used in nanofluids, due to their high thermal conductivity and low density. However, for aqueous medium, stability requires the use of stabilization methods. This work carried out the study of the transport properties and stability of nanofluids with multiwalled carbon nanotubes (MWCNT), using three stabilization methods: Triton X-100 (TrX–MWCNT) and Arabic gum (AG–MWCNT) as surfactants and functionalized carbon nanotubes with COOH group (COOH–MWCNT). These three nanofluids were compared to investigate the best configuration for heat transfer processes. The thermal conductivity was studied using the hot wire method; rheology was studied through three curves in rotational rheometer of concentric cylinders; specific heat was studied by the differential scanning calorimetry method; density was measured by the Coriolis Effect method; nanoparticles size and zeta potential were measured by the dynamic light scattering method. The COOH–MWCNT nanofluids present the highest thermal conductivity increase reaching 15% at 60 °C and 12% at 30 °C with 1wt% while the A.G–MWCNT and TrX–MWCNT reach 11% and 7.5%, respectively, at 30 °C. A.G–MWCNT nanofluids showed greater stability after long sonication times, while COOH–MWCNT presents best dispersion at 0.125 and 0.25 wt%, from 40 to 160 min of sonication. The specific heat increases with temperature and decreases with MWCNT concentration; however, it presents a peculiar increase in the concentration of 0.25 wt%, increasing about 0.5% and 4.5% for A.G–MWCNT and COOH–MWCNT, respectively at 60 °C. COOH–MWCNT nanofluids showed a thixotropic behavior for 0.5 and 1.0 wt% and large viscosity increase reaching 3.75 and 5.5 times the base fluid viscosity at 5 °C and 60 °C, respectively, with 1 wt%. The nanofluids A.G–MWCNT and COOH–MWCNT present good stability, as well as an increase in transport properties, optimized at a concentration close to 0.25 wt% and the COOH–MWCNT nanofluids can be stabilized simply by changing the water pH.

Optimum Electrical and Dielectric Performance of Multi-Walled Carbon Nanotubes Doped Disposed Transformer Oil

This paper intends to prepare a nanofluid sample by suspending Multi-walled Carbon Nanotubes (MWCNTs) at 0.005g/L concentration and analyze the behavior of electrical and dielectric properties based on the International Electrotechnical Commision test method. In order to validate the effectiveness of MWCNT nanofluid, alternating current breakdown voltage (BDV), negative polarity lightning impulse (LI), dielectric permittivity, dissipation factor (DF), DC resistivity and Raman structural measurement are executed accordingly. In the following, an analysis of the statistical distribution using the two-parameter Weibull distribution law of BDV and LI are evaluated at four experimental conditions to predict the probability of breakdown occurring at different percentages. Based on the observation, the MWCNT filler has a substantial effect in improving the BDV and LI characteristics of disposed mineral oil. The permittivity, DF and resistivity performance of MWCNT nanofluid from 25 °C to 90 °C also produces comparable and reliable performance as a fresh transformer oil. As for Raman structure, the revolution of transformer oil by doping MWCNT does not disrupt the original chemical structure of mineral oil. Hence, this study proves the improvement of the electrical and the behavior of dielectric properties and chemical structure of nanofluid, providing a huge contribution towards the development of insulating materials for transformer application.

An Artificial Intelligence Approach to Predict the Thermophysical Properties of MWCNT Nanofluids

Experimental data of thermal conductivity, thermal stability, specific heat capacity, viscosity, UV–vis (light transmittance) and FTIR (light absorption) of Multiwalled Carbon Nanotubes (MWCNTs) dispersed in glycols, alcohols and water with the addition of sodium dodecylbenzene sulfonate (SDBS) surfactant for 0.5 wt % concentration along a temperature range of 25 °C to 200 °C were verified using Artificial Neural Networks (ANNs). In this research, an ANN approach was proposed using experimental datasets to predict the relative thermophysical properties of the tested nanofluids in the available literature. Throughout the designed network, 65% and 25% of data points were comprehended in the training and testing set while the other 10% was utilized as a validation set. The parameters such as temperature, concentration, size and time were considered as inputs while the thermophysical properties were considered as outputs to develop ANN models of further predictions with unseen datasets. The results found to be satisfactory as the (coefficient of determination) R2 values are close to 1.0. The predicted results of the nanofluids’ thermophysical properties were then validated with experimental dataset values. The validation plots of all individual samples for all properties were graphically generated. A comparison study was conducted for the robustness of the proposed approach. This work may help to reduce the experimental time and cost in the future.

Thermal Conductivity and Viscosity of TiO2/MWCNTs (doped 10wt% graphene) - Ethylene Glycol Based Nanofluids for Different Ratio of Nanoparticle

The use of nanofluids to boost the thermal performance of conventional work fluids has recently shown considerable interest. This paper aims to analyse the thermal conductivity, viscosity and stability of titanium dioxide (TiO2)-multi-walled carbon nanotubes (MWCNTs) nanofluid in the presence of sodium dodecyl benzene sulfonate (SDBS) as a surfactant. The enhancement of thermal physical properties of nanofluids in this study investigated under different concentrations and ratios of the nanoparticle. Ethylene glycol (base fluid), TiO2 and CNTs nanoparticle mixed to produce hybrid nanofluid with concentration 0.02 to 0.1 wt.% with 0.02 wt% interval. The mixing ratio of TiO2: MWCNTs was 90:10 and 80:20, meanwhile the ratio of SDBS: MWCNTs was 10:1. The stability of nanofluid was confirmed by using the observation method and zeta potential analysis. The thermal conductivity and viscosity of suspension were measured to determine the relationship between concentration on nanofluid and thermal physical properties. Based on results obtained, zeta potential value for both nanofluid with different ratios range from -50 to -70 mV indicates excellent stability of the suspension. Thermal conductivity of nanofluid increase as nanofluid concentration and temperature increase and also shows enhancement compared to the base fluid. However, the increment in thermal conductivity for nanofluid with ratio 90:10 was more stable and higher throughout the increasing temperature compared to nanofluid with ratio 80:20. Meanwhile, the viscosity value of nanofluid shows decrements over increased temperature and increment over increase volume concentration. In conclusion, the developed nanofluid with both ratios in this study found to be stable, with enhanced thermal conductivity and viscosity.

Preparation of stable metal/COOH-MWCNT hybrid nanofluid

Multiwall carbon nanotube (MWCNT) nanofluid have potential to deliver high rate of heat transfer due to the presence of MWCNT which are having high thermal conductivity. Dispersion of MWCNT in polar basefluid is a difficult task because MWCNT are hydrophobic in nature which makes their utilization as a heat transfer fluid challenging. Metal nanoparticles can be attached with MWCNT which can possibly improve their dispersion. These nanofluid are called as hybrid nanofluid. The present study investigates the dispersion stability of hybrid of COOH-functionalized multi-walled carbon nanotubes (COOH-MWCNT) with different metals such as silver (Ag/COOH-MWCNT), copper (Cu/COOH-MWCNT), iron (Fe/COOH-MWCNT) and zinc (Zn/COOH-MWCNT) dispersed in distilled water as a basefluid. Chemical reduction method was used to synthesize hybrid nanoparticles by reducing metal cations in the presence of MWCNT. Dispersion of hybrid metal-MWCNT hybrid has been investigated by spectra analysis method (UV–Vis spectrophotometer) and zeta potential. Scanning electron microscope imaging with EDAX confirmed distribution of metal nanoparticle on the MWCNT surface. Thermal conductivity was measured using KD2 pro thermal analyzer. Results revealed that the sequence of dispersion stability and thermal conductivity of prepared nanofluid was Cu/COOH-MWCNT > Fe/COOH-MWCNT > Ag/COOH-MWCNT > Zn/COOH-MWCNT in distilled water.

Comparative investigation of efficiency sensitivity in a flat plate solar collector according to nanofluids

The performance characteristics of a flat plate solar collector were investigated experimentally by applying various nanofluids in the solar collector and comparing the sensitivity of its performance under different operating conditions. The experimental results revealed that the efficiency of the flat plate solar collector was highest (87%) when a multi-walled carbon nanotube (MWCNT) nanofluid was applied and lowest (62%) when basefluid(water) was applied. When the nanofluid concentration was decreased from that of the maximum efficiency, the performance sensitivity was highest for CeO2 nanofluid and lowest for Fe3O4 nanofluid. The reduction in performance attributable to nanoparticle size was the largest when CuO nanofluid was applied and lowest when Fe3O4 nanofluid was used. Overall, when nanofluids were used in the flat plate solar collector, high efficiency was observed, and the sensitivity of performance under the various operating parameters was found to be lower than in the case of water. In particular, when MWCNT nanofluid was used as the working fluid, the highest efficiency was observed; however, the efficiency sensitivity according to operating conditions was the largest.

Performance of Functionalized MWCNT–Water Nanofluids for Heat Transfer Applications

The higher level of performance, compactness and integration of modern electronic components often results in heat dissipation issues. Hence, there is an increasing interest in multiwalled carbon nanotubes (MWCNTs) due to their very attractive thermal properties. In this study, functionalized MWCNT (F-MWCNT) and different types of surfactants—Arabic gum (AG), dodecylbenzenesulphonic acid (DBSA) and Chinese ink (CI)—are incorporated into water-based nanofluids to improve the stability and dispersion behavior of the nanofluids. A two-step approach was used to prepare the nanofluids, and 0.5 vol% of F-MWCNT was used in the nanofluids formulation. Nanofluids prepared using 0.5 vol% of F-MWCNT with DBSA surfactant exhibited the highest thermal conductivity enhancement of 48% compared to other nanofluids. The results are supported by stability tests using visual observation and zeta potential. Notably, the F-MWCNT nanofluids with AG and DBSA exhibited an improvement in stability compared to those MWCNT and F-MWCNT nanofluids without surfactant. On the other hand, the experimental work on the closed-loop electronic cooling system revealed that nanofluids prepared with 0.5 vol% of F-MWCNT without surfactants exhibited better performance than F-MWCNT nanofluids with surfactants. This indicates that 0.5 vol% of F-MWCNT is sufficient for use as a nanofluid for a closed-loop electronic cooling system without the addition of surfactant.