Corrigendum: Analysis on thermal conductivity of green processed alumina nanofluid for thermal industries (2022 Adv. Nat. Sci.: Nanosci. Nanotechnol. 13 025011)

The dual mechanism played by curry leaf extract on synthesis of alumina nanoparticles contributes a significant enhancement in thermal conductivity of alumina nanofluid with appreciably small volume fraction from 0.01%–0.05%. The most probable particle size of alumina nanoparticle dispersed in water of 3.12 nm observed from particle size analyser along with a strong absorption peak at λ max around 238 nm confirms the alumina nanoparticles in the fluid. The increase of energy band gap from 4.8 to 5.12 eV indicates the decrease in size of the nanoparticle solely attributed to contribution of curry leaf extraction method of preparation of nanoparticles. The spherical shaped alumina nanoparticle has got high thermal conductivity with enhancement from 1.8% to 21.44% which is attributed to the significant contribution of H-atom as energy storage unit in water. With increase of sonication time, thermal conductivity varies appreciably from 0.531 W mK−1 to 0.736 W mK−1 with volume fraction of nanofluid. Therefore, the novel combinations of characterised properties of Al2O3 nanofluid have proved to be the best thermally stable heat transfer fluid compared to conventional cooling fluids.

An experimental investigation on thermal properties of molybdenum disulfide nanofluids

Recently, there has been considerable interest in the use of nanofluids for enhancing thermal performance. It has been shown that carbon nanotubes (CNTs) are capable of enhancing the thermal performance of conventional working liquids. Although much work has been devoted on the impact of CNT concentrations on the thermo-physical properties of nanofluids, the effects of preparation methods on the stability, thermal conductivity and viscosity of CNT suspensions are not well understood. This study is focused on providing experimental data on the effects of ultrasonication, temperature and surfactant on the thermo-physical properties of multi-walled carbon nanotube (MWCNT) nanofluids. Three types of surfactants were used in the experiments, namely, gum arabic (GA), sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS). The thermal conductivity and viscosity of the nanofluid suspensions were measured at various temperatures. The results showed that the use of GA in the nanofluid leads to superior thermal conductivity compared to the use of SDBS and SDS. With distilled water as the base liquid, the samples were prepared with 0.5 wt.% MWCNTs and 0.25% GA and sonicated at various times. The results showed that the sonication time influences the thermal conductivity, viscosity and dispersion of nanofluids. The thermal conductivity of nanofluids was typically enhanced with an increase in temperature and sonication time. In the present study, the maximum thermal conductivity enhancement was found to be 22.31% (the ratio of 1.22) at temperature of 45°C and sonication time of 40 min. The viscosity of nanofluids exhibited non-Newtonian shear-thinning behaviour. It was found that the viscosity of MWCNT nanofluids increases to a maximum value at a sonication time of 7 min and subsequently decreases with a further increase in sonication time. The presented data clearly indicated that the viscosity and thermal conductivity of nanofluids are influenced by the sonication time. Image analysis was carried out using TEM in order to observe the dispersion characteristics of all samples. The findings revealed that the CNT agglomerates breakup with increasing sonication time. At high sonication times, all agglomerates disappear and the CNTs are fragmented and their mean length decreases.

Thermal tuning properties of nanofluid from lower to higher value is a challenging issue in the field of thermal industries and microelectronic industries as well as in medical sciences. Nanofluids of aluminum oxide has been prepared with different volume fraction varies from 0.01– 0.05 vol%. The crystal structure and surface shape of the synthesized aluminum oxide nano powder has been studied using X-ray diffraction technique (XRD), scanning-electron-microscopy (SEM) and electron transmission microscopy (TEM). The nanofluids are characterized by experimental technique such as FTIR, UV-visible, photoluminescence and particle distribution with particle size analyzer. Thermal conductivity of the alumina nano fluid was found to vary from 0.5378–0.7299 W/mK for volume percentage 0.01–0.05 respectively with enhancement from 1.8 % to 21.44% which is better than other works in the literature. With increase of sonication time, thermal conductivity varies appreciably from 0.531–0.736 W/mK with volume fraction of nanofluid. This significant increase in thermal conductivity of alumina nanofluid in different operating condition may be attributed to extraction and oxidation of alumina nitrate assisted with leaf extracted surfactants.

In this study we present new data for the thermal conductivity enhancement in four nanofluids containing 11, 25, 50, and 63 nm diameter Aluminum oxide (Al2O3) nanoparticles in distilled water. The nanofluids were prepared using single step method (that is, by dispersing nanoparticle directly in base fluid) which was gathered in ultrasonic device for approximately 7 h. The transient hot-wire laser beam displacement technique was used to measure the thermal conductivity and thermal diffusivity of the prepared nanofluids. The thermal conductivity and thermal diffusivity were obtained by fitting the experimental data to the numerical data simulated for Al2O3 in distilled water. The results show that, the thermal conductivity and thermal diffusivity enhancement of nanofluids increases as the particle size increases. Thermal conductivity and thermal diffusivity enhancement of Al2O3 nanofluids was increase as the volume fraction concentration increases. This enhancement attributed to the many factors such as, ballistic energy, nature of heat transport in nanoparticle, and interfacial layer between solid/fluids. Key words: Thermal conductivity, thermal diffusivity, effect of particle size, effect of volume fraction.

Experimental investigation in a forced draft wet cooling tower using aluminum oxide nano particles

This paper presents experimental and theoretical determination of the effective thermal conductivity of various base fluids and nano TiO2 composition. Ultrasonically assisted sol–gel method was used for synthesising anatase TiO2 nanoparticles and dispersing them into base fluids using sonication for the synthesis of nanofluids. It is observed that thermal conductivity enhancement is significantly higher than that of base fluid. The thermal conductivity shows an increment with the addition of nanoparticles and confirms a 22% enhancement achievable in base fluids. The effect of base fluids is a complex idea and difficult to understand; lower base fluid viscosities were supposed to contribute higher in enhancement of thermal conductivity, but another important factor; i.e. fluid nanoparticles surface interaction, nanoparticles crystal type also contributes in enhancement. In the further study, as the sonication time increases; an improvement in the thermal conductivity of nanofluids is also observed. Except water-based nanofluids, all others show reasonably good agreement with the data predicted by Bruggeman model and the prediction is in the range of 5%. This study is important since it covers base fluids with a wide range of thermal conductivity and viscosity.

Present work aims to study the dispersion characteristics of Al2O3 nano-dispersoid in water following different periods of ultrasonication and its impact on the thermal conductivity and viscosity of the nanofluid. Nanofluids with 0.5–2 vol% of Al2O3 nanoparticles have been prepared by ultrasonication for varying period. Al2O3 nanofluids reported a maximum thermal conductivity enhancement of 16.1% for 2 vol% of nanoparticle concentration, after an optimum ultrasonication of 2 h beyond which the thermal conductivity decreases with further ultrasonication. The optimum ultrasonication time required for uniform dispersion of nanoparticles increases with the increase in the Al2O3 volume fraction. For 1.5 vol% Al2O3 nanoparticle loading, the viscosity of nanofluid decreased by 33% with an increase in the sonication time from 30 to 90 min. Further increase in sonication time by 30 min resulted in 13% increase in the viscosity of Al2O3 nanofluid. This decrease in the thermal conductivity enhancement and increase in the viscosity beyond the optimum ultrasonication period have been attributed to the re-agglomeration of nanoparticles which are confirmed by TEM, and DLS results carried out after different instants of ultrasonication. The occurrence of re-agglomeration is explained in terms of the convective flow associated with the ultrasonication process. Various theoretical models like Maxwell or Hamilton–Crosser models which when used to predict the thermal conductivity of nanofluid, underestimate the thermal conductivity. A new correlation is, therefore, developed on the basis of experimental results. With an R2 value of 0.9924, the correlation showed a good agreement with the present thermal conductivity data.

Organic phase change materials like paraffin possess high latent heat yet incredibly low thermal conductivity. For improving the thermal conductivity, nanomaterials are introduced into the phase change materials. Thermal energy storage applications benefit from the use of phase transition materials with high thermal conductivity and latent heat of fusion. In this work to increase the dispersion of the alumina and graphene nanoparticles, a novel nanocomposite phase change material was produced by utilizing sodium oleate as a surfactant. The surfactant sodium oleate is prepared with oleic acid and methanol, The mixture is prepared using sodium oleate, Alumina Nanoparticle, and Graphene in the mass ratio of 1:3:0.5 is mixed with paraffin in the weight percentage of 7.5 and 10 and thermal stability study was carried out. Alumina nanoparticles were synthesized and prepared by using a microwave-assisted chemical precipitation approach which is more effective and graphene nanoparticles were prepared by using modified hummer’s method. Thermocycling was used for up to 100 cycles to determine the melting point, latent heat, and long-term thermal stability of nanocomposites with phase change material. Differential Scanning Calorimetry (DSC) was used to evaluate the heat storage behaviour of the samples, and the heating rate of nanocomposites containing PCMs was investigated. The transient hot wire method was then utilised to assess the PCM’s actual thermal conductivity. From the obtained results, nanocomposite with 7.5 wt% additives show maximum thermal stability and latent heat (161.09 KJ Kg−1) for 100 cycles with an increase in 42% effective thermal conductivity, Nanocomposite with 10 wt% shows 57% higher thermal conductivity. But shows lower thermal stability and very low latent heat (120.44 KJ Kg−1). It is understood from the results that nanoparticle and surfactant addition gives a positive rise in latent heat.

Vegetable oils (Ground nut) are being investigated to serve as a possible substitute for non-biodegradable mineral oils, which are currently being used as metal-cutting fluids in machining processes. In this study, thermophysical properties of hybrid nanofluids (vegetable oil) to be used as metalworking cutting fluids are investigated. In-situ synthesis of copper (Cu) and zinc (Zn) combined hybrid particles is performed by mechanical alloying with compositions of 50:50, 75:25, and 25:75 by weight. Characterizations of the synthesized powder were carried out using X-ray diffraction, a particle size analyzer, FE-SEM, and TEM. Hybrid nanofluids with all the three combinations of hybrid nanoparticles were prepared by dispersing them into a base fluid (vegetable oil). The thermophysical properties, such as thermal conductivity and viscosity, were studied for various volume concentrations and at a range of temperatures. Experimental results have shown enhancement in thermal conductivity in all cases and also an increase in viscosity. The enhancement in viscosity is similar in all three combinations, as the particle size and shape are almost identical. The enhancement in thermal conductivity is higher in Cu–Zn (50:50), resulting in better enhancement in thermal conductivity due to the Brownian motion of the particles and higher thermal conductivity of the nanoparticles incorporated.

Comprehensive review of principle factors for thermal conductivity and dynamic viscosity enhancement in thermal transport applications: An analytical tool approach

Recent studies have showed that nanofluids have significantly greater thermal conductivitycompared to their base fluids. Large surface area to volume ratio and certain effects ofBrownian motion of nanoparticles are believed to be the main factors for the significantincrease in the thermal conductivity of nanofluids. In this paper all three transportproperties, namely thermal conductivity, electrical conductivity and viscosity, were studiedfor alumina nanofluid (aluminum oxide nanoparticles in water). Experiments wereperformed 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. Theeffect of particle size was not studied. The transient hot wire method as describedby Nagaska and Nagashima for electrically conducting fluids was used to testthe thermal conductivity. In this work, an insulated platinum wire of 0.003 inchdiameter was used. Initial calibration was performed using de-ionized water andthe resulting data was within 2.5% of standard thermal conductivity values forwater. The thermal conductivity of alumina nanofluid increased with bothincrease in temperature and concentration. A maximum thermal conductivity of0.7351 W m−1 K−1 was recorded for an 8.47% volume concentration of alumina nanoparticles at46.6 °C. The effective thermal conductivity at this concentration and temperature was observed tobe 1.1501, which translates to an increase in thermal conductivity by 22% when comparedto water at room temperature. Alumina being a good conductor of electricity, aluminananofluid displays an increasing trend in electrical conductivity as volumetric concentrationincreases. A microprocessor-based conductivity/TDS meter was used to perform theelectrical conductivity experiments. After carefully calibrating the conductivitymeter’s glass probe with platinum tip, using a standard potassium chloride solution,readings were taken at various volumetric concentrations. A 3457.1% increase in theelectrical conductivity was measured for a small 1.44% volumetric concentrationof 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 thekinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constanttemperature bath was used. Calibrated capillary viscometers were used to measure flowunder gravity at precisely controlled temperatures. The capillary viscometers werecalibrated with de-ionized water at different temperatures, and the resulting kinematicviscosity values were found to be within 3% of the standard published values. An increaseof 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration ofalumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid,2.901 42 mm2 s−1, wasobtained at 0 °C for an 8.47% volumetric concentration of alumina nanoparticles. The experimentalresults of the present work will help researchers arrive at better theoretical models.

We present new data for the thermal conductivity enhancement in seven nanofluids containing 8–282 nm diameter alumina nanoparticles in water or ethylene glycol. Our results show that the thermal conductivity enhancement in these nanofluids decreases as the particle size decreases below about 50 nm. This finding is consistent with a decrease in the thermal conductivity of alumina nanoparticles with decreasing particle size, which can be attributed to phonon scattering at the solid–liquid interface. The limiting value of the enhancement for nanofluids containing large particles is greater than that predicted by the Maxwell equation, but is predicted well by the volume fraction weighted geometric mean of the bulk thermal conductivities of the solid and liquid. This observation was used to develop a simple relationship for the thermal conductivity of alumina nanofluids in both water and ethylene glycol.

Thermal conductivity of mixed nanofluids under controlled pH conditions

Enhanced thermal conductivity in Ag-H2O nanofluids by nanoparticles of different shapes: Insights from molecular dynamics simulation