Experimental study of thermal properties and dynamic viscosity of graphene oxide/oil nano-lubricant

This experimental study was carried out based on the nanotechnology approach to enhance the efficacy of engine oil. Atomic and surface structures of graphene oxide (GO) nanoparticles were investigated by using a field emission scanning electron microscope and X-ray diffraction. The nano lubricant was produced by using a two-step method. The stability of nano lubricant was analyzed through dynamic light scattering. Various properties such as thermal conductivity, dynamic viscosity, flash point, cloud point and freezing point were investigated and the results were compared with the base oil (Oil-SAE-50). The results show that the thermal conductivity of nano lubricant was improved compared to the base fluid. This increase was correlated with progressing temperature. The dynamic viscosity was increased by variations in the volume fraction and reached its highest value of 36% compared to the base oil. The cloud point and freezing point are critical factors for oils, especially in cold seasons, so the efficacy of nano lubricant was improved maximally by 13.3% and 12.9%, respectively, compared to the base oil. The flash point was enhanced by 8%, which remarkably enhances the usability of the oil. It is ultimately assumed that this nano lubricant to be applied as an efficient alternative in industrial systems

A new experimental correlation for non-Newtonian behavior of COOH-DWCNTs/antifreeze nanofluid

In this paper, the rheological behavior of nano-antifreeze consisting of 50%vol. water, 50%vol. ethylene glycol and different quantities of functionalized double walled carbon nanotubes has been investigated experimentally. Initially, nano-antifreeze samples were prepared with solid volume fractions of 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1% using two-step method. Then, the dynamic viscosity of the nano-antifreeze samples was measured at different shear rates and temperatures. At this stage, the results showed that base fluid had the Newtonian behavior, while the behavior of all nano-antifreeze samples was non-Newtonian. Since the behavior of the samples was similar to power law model, it was attempted to find the constants of this model including consistency index and power law index. Therefore, using the measured viscosity and shear rates, consistency index and power law index were obtained by curve-fitting method. The obtained values showed that consistency index amplified with increasing volume fraction, while reduced with enhancing temperature. Besides, the obtained values for power law index were less than 1 for all samples which means shear thinning behavior. Lastly, new correlations were suggested to estimate the consistency index and power law index using curve-fitting

Effects of graphene oxide‑silicon oxide hybrid nanomaterials on rheological behavior of water at various time durations and temperatures: Synthesis, preparation and stability

The present empirical study investigates the synthesis of graphene oxide nanoparticles, preparation of water/graphene oxide‑silicon oxide hybrid nanofluid, and parameters affecting viscosity of the nanofluid. Graphene oxide nanoparticles are synthesized using the modified Hummer's method. Surface structure and atomic structure of the nanoparticles were studied using SEM and XRD tests. The nanofluid was then prepared using the two step method. DLS tests with various patterns were used, in addition to sedimentation photograph capturing method, to measure stability of the nanofluid. Results suggested that the nanofluid has a fairly suitable nanostructure. Viscosity of the nanofluid was measured and studied using Brookfield DV2EXTRA-Pro Viscometer, in the temperature range of 20–60 °C with volume concentrations of 0, 0.5, 0.1, 0.2, 0.4, 0.6, 0.8, and 1%. Furthermore, effects of parameters such as shear rate, and period of applying constant shear rate on viscosity of the nanofluid were investigated. The test results showed that viscosity behavior of the nanofluid is independent of the shear rate and time of shearing. Numerical viscosity measurement results show that viscosity of the nanofluid with volume concentration of φ = 1%, in temperature of 20 °C, increased considerably to μ = 2.42 mPa·s. Viscosity changes ratio increases intensively in higher concentrations. Comparing empirical results of water/graphene oxide nanofluid viscosity to results of the present study shows that, due to the modification of surface structure in nanoparticles, the viscosity values have improved considerably. An empirical equation is provided to measure the viscosity of the nanofluid using this data, which can be used to calculate viscosity of the base fluid under effect of temperature, and viscosity of the nanofluid under effect of temperature and volume concentration variables

An experimental study on stability and thermal conductivity of water/silica nanofluid: Eco-friendly production of nanoparticles

In the present experimental study, an eco-friendly process (synthesized from rice plant source) was used to produce silica nanoparticles. Silica nanoparticles are environmentally friendly nanoparticles that have high heat transfer potential due to its abundant natural resources, low cost synthesis and mass production. The surface and atomic structure of the nanoparticles have been investigated through SEM and FTIR tests. After production of nanoparticles, water/silica nanofluid samples were prepared using two-step method that called eco-friendly nanofluid. Stability and thermal conductivity of the eco-friendly nanofluid were examined. Investigating the stability of the prepared samples, the DLS and TEM tests have been conducted as well as periodic visual observation of possible sedimentation over a period of six months through photography. The stability results indicated that the prepared samples possess excellent nano-structure and it showed long-time stability even after six months of preparation. The thermal conductivity measurement of the samples has been done in different temperatures ranging from 25 to 55 °C and solid volume fractions of 0.1, 0.25, 0.5, 1, 1.5, 2, 2.5, and 3%. The results showed the maximum thermal conductivity enhancement of 38.2% which took place at the temperature of 55 °C and solid volume fraction of 3%. Moreover, new precise correlation to predict the thermal conductivity of the eco-friendly nanofluid has been proposed with the maximum deviation of 2.72%. Finally, according to the results, it can be claimed that synthesis of environmentally friendly nanoparticles of silicon oxide with a plant source for nanofluid production is important, and this type of nanofluid can be introduced as an environmentally friendly alternative fluid with high heat transfer potential in thermal systems

Experimental investigation of heat transfer and friction coefficient of the water/graphene oxide nanofluid in a pipe containing twisted tape inserts under air cross-flow

The water/graphene oxide nanofluid effect in a pipe equipped by twisted tape inserts under air cross-flow is investigated and the optimal tape geometry is determined. The range of internal and external Reynolds numbers are: 3800<21500 and 550<2000. Heat transfer and pressure drop increase by increasing Re and inserts width and heat transfer performance coefficient increased up to 1.4, indicating enhanced heat transfer compared to undesirable pressure drop. On the other hand, the heat transfer coefficient is 26% higher when compared with water in a plain tube. According to the results, this method is a good alternative in heat exchangers

Effects of cobalt ferrite coated with silica nanocomposite on the thermal conductivity of an antifreeze: New nanofluid for refrigeration condensers

The purpose of the present study was to study the process of development, stability and measurement of thermal conductivity of nanofluid combination of antifreeze-CoFe2O4/SiO2. The results of photography capturing technique showed that the use of CMC surfactant with a mass ratio of 0.1 nanoparticles produced the best long-term stability conditions. Thermal conductivity measurement of nanofluid was performed using KD2-Pro thermal analyzer in a temperature range of 25–50°C with 0.1–1.5% of mass fraction. The results show that the nanofluid thermal conductivity enhanced with increasing the mass fraction of the nanoparticles up to 37.7%. In order to calculate the nano-antifreeze thermal conductivity using curve fitting method of laboratory data, an experimental correlation with high precision was presented. Finally, regarding thermal properties of this nano-antifreeze, it can be introduced as an alternative with high heat transfer potential in thermal and refrigeration systems

An experimental study on heat transfer and pressure drop of water/graphene oxide nanofluid in a copper tube under air cross-flow: Applicable as a heat exchanger

The effect of using water/graphene oxide nanofluid as a working fluid on heat transfer and pressure drop was studied experimentally. For this purpose, subsonic wind tunnel and a closed heat transfer cycle were used at the same time. The effect of different concentrations (0, 0.05, 0.1, 0.2% by volume) of water/graphene oxide nanofluid at different Reynolds numbers in a tube under air cross-flow was evaluated in wind tunnel tests. The range of Reynolds number of the flow around the tube was between 3800 and 21500 3800⩽Reo⩽21500. The friction factor of the nanofluid flow inside the tube and the mean Nusselt number of the external air flow around the copper tube were calculated by measuring the variables. Results showed that by using water/graphene oxide nanofluid, the average Nusselt number enhanced by up to 51.4% compared to pure water. The use of nanofluid increased the friction factor by 21% in comparison with pure water. Because of changes in heat transfer and friction factor, heat transfer performance coefficient increased by up to 42.2%, indicating enhanced heat transfer compared to undesirable pressure drop in the test. According to the results, this nanofluid can be a good alternative in similar applications such as heat exchangers

Empirical analysis of heat transfer and friction factor of water/graphene oxide nanofluid flow in turbulent regime through an isothermal pipe

Nanofluid flow is considered one of the most important solutions for improving heat transfer systems. In this study, an isotherm heat transfer system has been designed and built in order to investigate the effect of utilizing water/graphene oxide nanofluid flow on heat transfer and the friction coefficient in a circular profile copper tube. The range of nanofluid concentration is considered as 0%, 0.025%, 0.05%, 0.075%, and 0.1% of volume fraction and Reynolds number of the turbulent flow is chosen between 5250 and 36,500. The nanofluid is made through a two-step method. The absolute value of Zeta potential equals 41 mV, which is measured experimentally and shows acceptable stability. The thermal conductivity of nanofluid has a maximum of 28% increase in comparison to the base fluid. Considering the experiential data from this study, the Nusselt number, the convective heat transfer coefficient, the pressure loss, the friction factor, and the coefficient of performance are investigated. In order to achieve validation, the results of this study are compared with former studies. Maximally, the nanofluid has a 40.3% augmentation in the convective heat transfer coefficient in comparison to the base fluid. In addition, a minor augmentation takes place during pressure loss and friction coefficient by utilizing the nanofluid that reaches a maximum of 16%. However, the thermal performance coefficient maximally increases by 1.148. According to the achieved results, the present nanofluid can be used in coolant systems like air cooling heat exchangers

Numerical investigation on the effect of four constant temperature pipes on natural cooling of electronic heat sink by nanofluids: A multifunctional optimization

In the present study, natural-convective heat transfer along with the effects of radiation of aluminum/water nano-fluid between two blades of a heat sink, which is under the impact of a uniform magnetic-field, is studied numerically. The space between two blades of the heat sink is considered as a two-dimensional square enclosure. In the square cavity, there are four pipes with constant temperature Th with a circular cross section. The RSM method is used to optimize the geometric parameters of the pipes. The results show that the heat transfer rate from the pipes and the irreversibility generation augment and the Bejan number reduces by augmenting the Rayleigh number. The heat transfer intensified 7% and 16% by doubling of the aspect ratio of the pipes at the Rayleigh number of 103 and 106, respectively. As the distance between constant-temperature pipes intensified, Nusselt number augments. As the horizontal enclosure rotates 90°, i.e., it becomes a vertical enclosure, the heat transfer decreases by 22% and total irreversibility decreases by 21%. The optimum physical conditions of the pipes are is in the diameter of 0.15 and 0.25 of distance from each other to have maximum heat transfer and the minimum irreversibility generation

Hybrid GMDH-type neural network to predict fluid surface tension, shear stress, dynamic viscosity & sensitivity analysis based on empirical data of iron(II) oxide nanoparticles in light crude oil mixture

The effects of different parameters including nanoparticles mass fraction and temperature were investigated on rheological behavior and surface tension of iron(II) oxide/light crude oil nanofluid. Iron(II) oxide was dispersed in light crude oil by using ultrasonic processor. TEM images was provided in order to assess the size and morphology of iron(II) oxide nanoparticles. In addition, DLS analysis and Zeta potential test were performed on nanofluid for estimation of nanoparticles size distribution within the basefluid and stability of nanoparticles, respectively. The results of this study showed that for iron(II) oxide/light crude oil nanofluid the value of surface tension reach to its minimum value at the condition where nanoparticles mass fraction was chosen to be 2.0 wt% and temperature was set on 70 °C. These results showed that for iron(II) oxide/light crude oil nanofluid the rheological behavior of nanofluid is non-Newtonian at temperature of 40 °C and the suspension behave as a rheoplexy fluid in which by increasing the shear rate higher dynamic viscosity of nanofluid observed. Furthermore, nanofluid behaves as a Newtonian fluid for the temperature of higher than 55 °C. Finally, a comprehensive correlation was obtained for estimation of relative dynamic viscosity of nanofluid by hybrid group method of data handling (GMDH)-type neural network method. The correlation presented in this study shows that for the relative dynamic viscosity of iron(II) oxide/light crude oil as a function of nanoparticles mass fraction and temperature, the amount of the total deviation of calculated data from experimental values is less than 10%