Experimental investigation on thermophysical properties of solar glycol dispersed with multi-walled carbon nanotubes

This article deals with well-dispersed solar glycol-based nanofluids containing multi-walled carbon nanotube (MWCNT) nanoparticles with different particle volume concentrations of 0.1%, 0.2%, 0.3%, and 0.4% prepared by typical two-step method. Thermal conductivity, viscosity and specific heat capacity of solar glycol (SG)-based MWCNT nanofluids, in the temperature range of 30°C–70°C were measured. The values of density showed a noticeable deviation from the predictions of Pak and Cho correlation. Hence, correlations are developed for thermal conductivity and viscosity from the experimental results obtained from the various range parameters of interest. The presence of MWCNT enhanced the thermal conductivity of the nanofluids by 17.26% at 0.4 vol.% particle concentration at 70°C. The relative viscosity of MWCNT nanofluids depends on the nanoparticles percentage concentration and decreases significantly with increase in temperature for higher concentrations. The presence of MWCNT enhances the specific heat of the nanofluids significantly, and this enrichment decreases with the increase of the MWCNT concentration. MWCNT/SG represents a new and innovative class of heat-transfer fluid, which possesses excellent thermophysical properties. The MWCNT/SG-based nanofluids could be suitable working fluids for solar thermal and automobile applications.     

Preparation,characterization, viscosity,and thermal conductivity of nitrogen-doped graphene aqueous nanofluids

Nanofluids perform a crucial role in the development of newer technologies ideal for industrial purposes. In this study, Nitrogen-doped graphene (NDG) nanofluids, with varying concentrations of nanoparticles (0.01, 0.02, 0.04, and 0.06 wt%) were prepared using the two-step method in a 0.025 wt% Triton X-100 (as a surfactant) aqueous solution as a base. Stability, zeta potential, thermal conductivity, viscosity, specific heat, and electrical conductivity of nanofluids containing NDG particles were studied. The stability of the nanofluids was investigated by UV–vis over a time span of 6 months and concentrations remain relatively constant while the maximum relative concentration reduction was 20 %. The thermal conductivity of nanofluids was increased with the particle concentration and temperature, while the maximum enhancement was about 36.78 % for a nanoparticle loading of 0.06 wt%. These experimental results compared with some theoretical models including Maxwell and Nan’s models and observed a good agreement between Nan’s model and the experimental results. Study of the rheological properties of NDG nanofluids reveals that it followed the Newtonian behaviors, where viscosity decreased linearly with the rise of temperature. It has been observed that the specific heat of NDG nanofluid reduced gradually with the increase of concentration of nanoparticles and temperature. The electrical conductivity of the NDG nanofluids enhanced significantly due to the dispersion of NDG in the base fluid. This novel type of fluids demonstrates an outstanding potential for use as innovative heat transfer fluids in medium-temperature systems such as solar collectors.     

Stability,viscosity, thermal conductivity,and electrical conductivity enhancement of multi-walled carbon nanotube nanofluid using gum arabic

This experimental investigation discussed on the stability and rheological behavior of multi-wall carbon nanotubes (MWCNTs) nanofluids with and without gum arabic (GA). The stability of MWCNT in the presence of GA dispersant in solar glycol is systematically investigated by taking into account the combined effect of different parameters, such as sonication time, temperature, dispersant and particle concentration. The concentrations of MWCNT and GA have been varied from 0.2 to 0.6% volume concentration and from 0.25 to 1.25 wt%, respectively, and the sonication time has been varied in between 30 and 120 min. The effect of sonication time on viscosity was discussed. It was perceived that the shear thinning behavior is exhibited by all the nanofluid samples. The stability of nanofluid is measured in terms of MWCNT concentration as a function of sediment time using UV-Vis spectrophotometer. Rheological behavior of MWCNT nanofluids is measured using Bohlin CVO Rheometer in the temperature range of 30–50°C, with step sizes of 5°C. Optimal GA concentration is obtained for the entire range of MWCNT concentration and 0.25–1.25 wt% of GA is found to be sufficient to steady all MWCNT range in solar glycol. Rapid sedimentation of MWCNTs is observed at higher GA concentration and sonication time. The presence of MWCNT and GA enhanced the thermal conductivity of the nanofluids by 30.59% at 0.6 vol.% particle concentration and 1.25 GA wt% at 50°C. The electrical conductivity is enhanced in a linear manner with respect to the loading of MWCNT and GA. Nevertheless, the electrical conductivity is increased linearly with increasing the temperature of the nanofluid. At particle concentration of 0.6 vol.% of MWCNT and 1.25 wt% of GA, the electrical conductivity of the nanofluid is improved by 190.57% at a temperature of 50°C.     

Thermal Conductivity and Viscosity Measurements of Water-Based TiO<Subscript>2</Subscript> Nanofluids

In this study, the thermal conductivity and viscosity of TiO₂ nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO₂ nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO₂ nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3ω method for measuring the thermal conductivity. The 3ω method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO₂ nanoparticles in deionized water was measured at temperatures of 13 °C, 23 °C, 40 °C, and 55 °C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO₂ nanoparticles at 13 °C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.     

Characterization and stability analysis of oil‐based copper oxide nanofluids for medium temperature solar collectors

Thermal oils are widely used as heat transfer fluids in medium temperature applications. Addition of small amounts of nanoparticles in such fluids can significantly improve their thermophysical properties. This paper presents experimental investigation of an oil‐based nanofluids prepared by dispersing different concentrations (0.25 wt%–1.0 wt%) of copper oxide nanoparticles in Therminol‐55 oil using two‐step method. Shear mixing and ultrasonication were used for uniform distribution and de‐agglomeration of nanoparticles to enhance the stability of the suspensions. The effect of nanoparticles concentrations on thermophysical properties of the nanofluids was analysed by measuring thermal conductivity, dynamic viscosity, effective density and specific heat capacity at different temperatures (25 °C–130 °C). Thermal conductivity exhibited increasing trend with rising temperature and increase in nanoparticles loading. A significant decrease in dynamic viscosity and effective density against increasing temperature makes it suitable for medium temperature applications. Nano‐oils with improved thermal properties are expected to increase the efficiency of concentrating solar thermal collectors.     

Experimental evaluation of thermophysical properties of oil-based titania nanofluids for medium temperature solar collectors

Thermal oils are widely used as working fluids in the medium temperature heat transfer applications including concentrating solar thermal collectors. However, the weak thermal characteristics of these oils are major drawbacks in their successful application in the medium-high temperature solar collectors. Fortunately, the emergence of nanotechnology has provided the opportunity to alter thermo-physical properties of base fluids by adding small amount of sub-micron size solid particles possessing better properties. This paper presents an experimental investigation of thermophysical properties of an oil-based nanofluid to be used in the medium temperature solar collector for enhanced thermal energy transport. The colloidal suspensions were prepared by dispersing different weight fractions (0.25 wt.%, 0.5 wt.%, 0.75 wt.% and 1.0 wt.%) of Titania nanoparticles in Therminol-55 oil using two-step method. Shear mixing and high energy ultrasonication was employed to achieve uniform mixing and de-agglomeration of the nanoparticles in order to enhance the stability of the colloidal suspensions. Thermophysical properties of the nanofluids were determined as a function of nanoparticles concentrations in the temperature range of 25 °C–130 °C. The experimental results demonstrated substantial improvement in thermal conductivity of the nano-oils with an increase in nanoparticles loading which further enhanced at higher temperatures. Dynamic viscosity and effective density displayed a decreasing trend against rising temperature which indicate the effectiveness of these nanofluids for medium temperature heat supply. Nano-oils with superior thermal properties can improve the performance of medium temperature solar thermal collectors.     

Al2O3纳米粉体悬浮液热物性实验研究

分别采用瞬态热线法、比较量热法和旋转粘度计测试了不同温度、粒子浓度和粒径下的Al2O3-DW（蒸馏水）纳米流体的导热系数、比热容、粘度等热物性参数。试验结果表明,粒子浓度、粒径和温度都是影响Al2O3-DW纳米流体热物性参数的重要因素。与水相比,纳米流体导热系数和粘度增加,常温4％体积份额下增幅分别为21．5％和52．3％;纳米流体比热容随着粒子体积份额增加而降低,并推导出了常温下低浓度纳米流体比热容的预测公式。     

A facile and green approach to prepare monodispersion nanonickel nanofluids

This paper first develops a novel approach to prepare solvent-free nanonickel (Ni) nanofluids via hydrogen bonding between poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) and 3-(Trimethoxysilyl)-1-propanethiol-modified Ni powder with average diameter of 80?nm to solve the problem of nanoparticles agglomerating due to the anisotropic dipolar attraction. It is interestingly found that Ni nanofluid is solid at room temperature while it undergoes solid–liquid transition without solvent at 50.7°C. The content of Ni is up to 12.1?wt%. The average diameter of core-shell structure of Ni nanofluids is 182?nm without agglomerations. It is worth noting that incorporation of Ni powder can elevate remarkably initial decomposition temperature of block copolymer due to high dispersity of Ni powder after modification. In addition, the viscosity of Ni nanofluids is found to be less than 10?Pa?·?s at 100°C, which is between that of water and honey, 0.001 and 10?Pa?·?s, respectively, at 20°C. More importantly, the Ni nanofluids exhibit excellent dispersion in water and other organic solvents for 2 months due to amphiphilic properties of the modifier molecule. These unique properties of Ni nanofluids may offer new scientific and technical opportunities for application of Ni powder in the form of liquid-like status.     

Measurement of volumetric thermal expansion coefficient of various nanofluids

Experiments were carried out for studying volumetric thermal expansion behavior of various nanofluids in order to evaluate their potential application in heat removal systems employing natural convection as mode of heat removal. For this purpose, various nanoparticles such as Al₂O₃, CuO, SiO₂ and TiO₂ were used, which were suspended in the base fluid (water) by ultrasonication. All nanofluids had the same concentration of 1 wt %. Each nanofluid was heated from room temperature to a maximum of about 60°C and the increase in volume due to heat addition was recorded. The volumetric thermal expansion due to heating for each nanofluid was compared to that for the base fluid for same increase in the temperature. The volumetric thermal expansion coefficient was evaluated from the measured data. Surprisingly, it was found that the nanofluids have greater volumetric thermal expansion coefficients as compared to that of the base fluid. 1The text was submitted by the authors in English.     

Transport properties of alumina nanofluids

Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50?°C). Alumina nanoparticles with a mean diameter of 36?nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003?inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351?W?m(-1)?K(-1) was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6?°C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314?μS?cm(-1), was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901?42?mm(2)?s(-1), was obtained at 0?°C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models.     

Influence of nanofluids application on contact length during hard turning

The length of tool–chip contact area (L_c) is considered as a considerable parameter in metal cutting process. Mechanical stresses and high temperature at this region may easily lead to abrasion or even breakage of cutting tool. Up to now, several solutions have been presented to overcome these limitations. Using cutting fluids is one of the solutions to reduce friction, stresses, and temperature over this area. This paper presents experimental investigation and finite element simulation of tool–chip interface in hard turning AISI 4140 using TiO₂ nanofluids. Nanofluids are newly class of engineering fluids developed by distributing nanometer solid particles in a base fluid. The main reason to use nanofluids in cutting process is to increase heat transfer capabilities and also its tribological attributes. At first, the effects of cutting speed, nanoparticles’ size, and nanofluid concentration on L_c have been experimentally investigated. Then, a numerical model has been developed to simulate the contact area length in case of nanofluids application. Comparing the results with that of the experimental tests shows that TiO₂ nanofluids are able to decrease L_c, about 35%, in feed rate of 0.11 mm/rev, nanoparticle size equal to 10 nm, and nanofluid concentration equal to 3.0 wt%.     

Electrical conductivity measurements of nanofluids and development of new correlations

In this study the electrical conductivity of aluminum oxide (Al2O3), silicon dioxide (SiO2) and zinc oxide (ZnO) nanoparticles dispersed in propylene glycol and water mixture were measured in the temperature range of 0 degrees C to 90 degrees C. The volumetric concentration of nanoparticles in these fluids ranged from 0 to 10% for different nanofluids. The particle sizes considered were from 20 nm to 70 nm. The electrical conductivity measuring apparatus and the measurement procedure were validated by measuring the electrical conductivity of a calibration fluid, whose properties are known accurately. The measured electrical conductivity values agreed within +/- 1% with the published data reported by the manufacturer. Following the validation, the electrical conductivities of different nanofluids were measured. The measurements showed that electrical conductivity of nanofluids increased with an increase in temperature and also with an increase in particle volumetric concentration. For the same nanofluid at a fixed volumetric concentration, the electrical conductivity was found to be higher for smaller particle sizes. From the experimental data, empirical models were developed for three nanofluids to express the electrical conductivity as functions of temperature, volumetric concentration and the size of the nanoparticles.     

MgO nanofluids: higher thermal conductivity and lower viscosity among ethylene glycol-based nanofluids containing oxide nanoparticles

Five kinds of oxides, including MgO, TiO₂, ZnO, Al₂O₃ and SiO₂ nanoparticles were selected as additives and ethylene glycol (EG) was used as base fluid to prepare stable nanofluids. Thermal transport property investigation demonstrated substantial increments in the thermal conductivity and viscosity of all these nanofluids with oxide nanoparticle addition in EG. Among all the studied nanofluids, MgO–EG nanofluid was found to have superior features, with the highest thermal conductivity and lowest viscosity. The thermal conductivity enhancement ratio of MgO–EG nanofluid increases nonlinearly with the volume fraction of nanoparticles. In the experimental temperature range of 10–60°C, thermal conductivity enhancement ratio of MgO–EG nanofluids appears to have a weak dependence on the temperature. Viscosity measurements showed that MgO–EG nanofluids demonstrated Newtonian rheological behaviour, and the viscosity significantly decreases with the temperature. The thermal conductivity and viscosity increments of the nanofluids are much higher than the corresponding values predicted by the existing classical models for the solid–liquid mixture.     

A comprehensive study of the performance of a heat pipe by using of various nanofluids

In this paper, a two-dimensional numerical model is developed to simulate the performance of a heat pipe using various nanofluids. The effect of different nanofluids (prepared using alumina, copper oxide, and silver nanoparticles) at different concentrations and particle diameters on the performance of heat pipe is also studied by through finite volume method. The obtained results show that using a nanofluid instead of water leads to the increased thermal efficiency and reduction in heat at wall of the heat pipe. Also, the temperature difference between the evaporator and the condenser is a function of input power; this means that by an increase in the input capacity, the temperature difference between the evaporator and the condenser increases. It was observed that the use of nanofluid reduces the axial-flow pressure of the fluid inside the wick. As a result, the transmission of fluid flow inside the wick from the condenser to the evaporator is easily done with the cost of using a nanofluid. Moreover, with an increase in thermal capacity, fluid pressure drop becomes maximum and thus temperature difference between the evaporator and the condenser increases.     

On the dependence of the viscosity coefficient of nanofluids on particle size and temperature

The dependence of the viscosity coefficient of nanofluids based on ethylene glycol with SiO₂ particles on nanoparticle size and temperature is experimentally studied. The experiments are conducted for nanofluids with an average particle size of 18.1, 28.3, and 45.6 nm. Their volume concentration is varied from 0.2 to 8%. The temperature of the fluid is varied in a range of 20–60°C. It is shown that the viscosity of nanofluids heavily depends on particle size: the smaller the particles, the higher the viscosity. On the other hand, the viscosity of all the studied nanofluids decreases with increasing temperature.     

Influence of ultrasonication energy on the dispersion consistency of Al2O3–glycerol nanofluid based on viscosity data,and model development for the required ultrasonication energy density

Achieving homogenised and stable suspensions has been one of the important research topics in nanofluid investigations. Preparing nanofluids, especially from the two-step method, is often accompanied with varying degrees of agglomerations depending on some parameters. These parameters include the physical structure of the nanoparticle, the prevalent particle charge, the strength of van der Waals forces of attraction and repulsiveness strength. Amongst the methods of deagglomeration, the use of ultrasonic vibration is most popular for achieving uniform dispersion. However, there are very few works related to its effect on the thermo-physical properties of nanofluids, and above all, standardising the minimum required ultrasonication time/energy for nanofluids synthesis. In this work, the optimum energy required for uniform and initially stable nanofluid has been investigated through experimental study on the combined influence of ultrasonication time/energy, nanoparticle size, volume fraction and temperature on the viscosity of alumina–glycerol nanofluids. Three different sizes of alumina nanoparticles were synthesised with glycerol using ultrasonication-assisted two-step approach. The viscosities of the nanofluid samples were measured between temperatures of 20–70?°C for volume fractions up to 5%. Based on the present experimental results, the viscosity characteristics of the nanofluid samples were dependent on particle size, volume fraction and working temperature. Using viscometry, the optimum energy density required for preparing homogenous nanofluid was obtained for all particle sizes and volume fractions. Finally, an energy density model was derived using dimensionless analysis based on the consideration of nanoparticle binding/interaction energy in base fluid, particle size, volume fraction, temperature and other base fluid properties. The model's empirical constants were obtained using nonlinear regression based on the present experimental data.     

Influence of nanolubricant particles’ size on flank wear in hard turning

This paper presents the effects of cutting speed, nanoparticles’ size, and their concentration in water-based TiO₂ nanofluid on the magnitude of tool flank wear and tool wear rate. The types of nanoparticles and base fluid, nanoparticle size, and nanoparticle concentration can affect the tribological and heat transfer properties of nanofluids, and thereupon, these parameters can affect the cutting forces and temperatures during the metal cutting process, thereby affecting tool wear and nanolubricant consumption. According to the achieved results, with an increase in the size of nanoparticles from 10 to 50 nm, the average decrease in cutting tool flank wear reduces from 46.2% to 34.8%.     

Effect of temperature on rheological properties of copper oxide nanoparticles dispersed in propylene glycol and water mixture

This paper reports on experimental investigation of the rheological behavior of copper oxide nanoparticles dispersed in a 60:40 propylene glycol and water mixture. Nanofluids of a particle volume concentration from 0 to 6% have been tested in this study. The experiments were conducted over a temperature range of -35 degrees C to 50 degrees C to establish their behavior for use as a heat transfer fluid in cold climates. The experiments reveal that this nanofluid in the range of particle volume percentage tested exhibits a Newtonian behavior. A new exponential correlation has been developed from the experimental data, which expresses the viscosity as a function of particle volume percent and the temperature of the nanofluid. The slope of relative viscosity curve was found to be higher at lower temperatures.     

Experimental investigation of heat transfer enhancement in helical coil heat exchangers using water based CuO nanofluid

The present work deals with the study of heat transfer enhancement using water based CuO nanofluids in the helical coil heat exchanger. Nanofluids were prepared using two-step method by using wet chemical method. Nanofluids with various volume percentage between 0 and 0.5 of CuO nanoparticles and their flow rate between 30 and 80 LPH (Reynolds number ranging from 812 to 1895, Laminar flow regime) were considered in the present study. The setup consists of a test section (helical coil), cooler, reservoir, pump, flow meter, thermocouples and flow controlling system. The temperature measurements were carried out with the help of thermocouples. The investigation was carried out to study the effect of particle loading and flow rate on heat transfer coefficient and Nusselt number. It has been found that the increase in the loading of CuO nanoparticles in base fluid shows a significant enhancement in the heat transfer coefficient of nanofluid. In the present study, at 0.1 vol% concentration of CuO nanoparticles in nanofluid, enhancement in heat transfer coefficient was 37.3% as compared to base fluid while at 0.5 vol%, it is as high as 77.7%. Also with the increase in the flow rate of the CuO nanofluid, significant increase in heat transfer coefficient was observed.     

Stability and thermal conductivity enhancement of carbon nanotube nanofluid using gum arabic

This experimental study reports on the stability and thermal conductivity enhancement of carbon nanotubes (CNTs) nanofluids with and without gum arabic (GA). The stability of CNT in the presence of GA dispersant in water is systematically investigated by taking into account the combined effect of various parameters, such as sonication time, temperature, dispersant and particle concentration. The concentrations of CNT and GA have been varied from 0.01 to 0.1?wt% and from 0.25 to 5?wt%, respectively, and the sonication time has been varied in between 1 and 24?h. The stability of nanofluid is measured in terms of CNT concentration as a function of sediment time using UV-Vis spectrophotometer. Thermal conductivity of CNT nanofluids is measured using KD-2 prothermal conductivity meter from 25 to 60°C. Optimum GA concentration is obtained for the entire range of CNT concentration and 1–2.5?wt% of GA is found to be sufficient to stabilise all CNT range in water. Rapid sedimentation of CNTs is observed at higher GA concentration and sonication time. CNT in aqueous suspensions show strong tendency to aggregation and networking into clusters. Stability and thermal conductivity enhancement of CNT nanofluids have been presented to provide a heat transport medium capable of achieving high heat conductivity. Increase in CNT concentrations resulted in the non-linear thermal conductivity enhancement. More than 100–250% enhancement in thermal conductivity is observed for the range of CNT concentration and temperature.