This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

The past decade has seen a boom in environmental adsorption studies on the adsorptive removal of pollutants from the aqueous phase. A large majority of works treat kinetic modeling as a mere routine to describe the macroscopic trend of adsorptive uptake by using common models, often without careful appraisal of the characteristics and validity of the models. This review compiles common kinetic models and discusses their origins, features, modified versions (if any), and applicability with regard to liquid adsorption modeling for both batch adsorption and dynamic adsorption systems. Indiscriminate applications, ambiguities, and controversies are highlighted and clarified. The appropriateness of linear regression for correlating kinetic data is discussed. This review concludes with a note on the current scenario and the future of kinetics modeling of liquid adsorption.

Insight into the adsorption kinetics models for the removal of contaminants from aqueous solutions

Introduction to Nanotechnology

Solar energy systems (SESs) are considered as one of the most important alternatives to conventional fossil fuels, due to its ability to convert solar energy directly into heat and electricity without any negative environmental impact such as greenhouse gas emissions. Utilizing nanofluid as a potential heat transfer fluid with superior thermophysical properties is an effective method to enhance the thermal performance of solar energy systems. The purpose of this review paper is the investigation of the recent advances in the nanofluids’ applications in solar energy systems, i.e., solar collectors (SCs), photovoltaic/thermal (PV/T) systems, solar thermoelectric devices, solar water heaters, solar-geothermal combined cooling heating and power system (CCHP), evaporative cooling for greenhouses, and water desalination.

Applications of nanofluids in solar energy: A review of recent advances

A review of recent advances in thermophysical properties at the nanoscale: From solid state to colloids

Preparation and evaluation of stable nanofluids for heat transfer application: A review

This study aims to report Batch adsorption study of hexavalent chromium, Cr (VI) on zeoliteNaX. Kinetics of Cr (VI) adsorption and adsorption isotherms were determined by varying operating parameters such as pH, initial concentration, temperature and contact time. ZeoliteNaX was found to remove Cr (VI) in acidic solutions down to ppm level at pH of about 4. Removal rate of Cr (VI) was found to decrease as pH rises above 4.0. Langmuir, Freundlich, Temkin and Redlich-Peterson models were applied to adsorption equilibrium data to find the best amongst these models. Langmuir model with R 2 = 0.9711 best fits the adsorption data. The kinetics of adsorption was found to follow the first order reversible reaction. The separation parameter, R L values of less than 1.0 i.e., 0.7369, 0.5834 and 0.4828 corresponding to initial concentrations of 10, 20 and 30 mg/L, respectively indicated that adsorption of Cr (VI) on zeoliteNaX is favoured. The estimated values of thermodynamic parameters such as heat of adsorption and standard gibbs free energy confirmed the exothermic nature of adsorption of Cr (VI) on zeoliteNaX.

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Kinetics and equilibrium study of chromium adsorption on zeoliteNaX

Carbon nanotubes (CNT) represent one of the most unique materials in the field of nanotechnology. CNT are the allotrope of carbon having sp2 hybridization. CNT are considered to be rolled-up graphene with a nanostructure that can have a length to diameter ratio greater than 1,000,000. CNT can be single-, double-, and multi-walled. CNT have unique mechanical, electrical, and optical properties, all of which have been extensively studied. The novel properties of CNT are their light weight, small size with a high aspect ratio, good tensile strength, and good conducting characteristics, which make them useful for various applications. The present review is focused on the structure, properties, toxicity, synthesis methods, growth mechanism and their applications. Techniques that have been developed to synthesize CNT in sizeable quantities, including arc discharge, laser ablation, chemical vapor deposition, etc., have been explained. The toxic effect of CNT is also presented in a summarized form. Recent CNT applications showing a very promising glimpse into the future of CNT in nanotechnology such as optics, electronics, sensing, mechanical, electrical, storage, and other fields of materials science are presented in the review.

Carbon nanotubes: synthesis, properties and engineering applications

In this work sorption of Pb(II) on zeolite-NaX was studied. Zeolites NaX is characterized by large surface area because of its highly porous nature. High surface area and ordered pore structure of zeolite-NaX result in adsorption of large quantities of adsorbate depending on adsorbate size, aperture size, temperature and surface acidity of zeolites. Therefore, equilibrium isotherms were obtained using batch study by varying operating parameters such as pH, initial concentration, temperature, adsorbent dosage and the contact time. The optimum condition thus obtained are: pH-6, concentration 10 mg/L and temperature of 303 K. The adsorption mechanism and the characterizing parameters were analyzed using two parameter (Dubinin–Radushkevich (DR), Temkin, Freundlich–Langmuir) and three parameter (Khan, Toth, Sips and Redlich–Peterson) isotherm models. Kinetics of the process was studied using Pseudo first order, Pseudo second order, First order reversible reaction, Elovich equation, intra-particle diffusion and Bangham equation. Dubinin–Radushkevich (DR) fitted the experimental data very well amongst the two parameter models. The three parameter isotherms show high determination coefficient compared to two parameter isotherms in the following order i.e., Sips > Toth > Pedlich–Peterson > Khan. The separation parameter, RL, values of less than 1.0 indicate that adsorption of Pb(II) on zeolite-NaX is favorable. The estimated values of thermodynamic parameters indicate the exothermic nature of adsorption of Pb(II) on zeolite-NaX. This study supports the view that zeolite-NaX could be an efficient adsorbent for removal of Pb(II) form aqueous solution.

Removal of lead(II) from waste water on zeolite-NaX

This study aimed to investigate the biosorption potential of Na2CO3-modified Aloe barbadensis Miller (Aloe vera) leaf (MABL) powder for removal of Ni(II) ions from a synthetic aqueous solution. Effects of various process parameters (pH, equilibrium time, and temperature) were investigated in order to optimize the biosorptive removal. The maximum biosorption capacity of MABL was observed to be 28.986 mg/g at a temperature of 303 K, a biosorbent dose of 0.6 g, a contact time of 90 min, and a pH value of 7. Different kinetic models (the pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models) were evaluated. The pseudo-second-order kinetic model was found to be the best fitted model in this study, with a coefficient of determination of R2 = 0.974. Five different isotherm models (the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Brunauer-Emmett-Teller (BET) models) were investigated to identify the best-suited isotherm model for the present system. Based on the minimum chi-square value (χ2 = 0.027) and the maximum coefficient of determination (R2 = 0.996), the Langmuir isotherm model was found to represent the system well, indicating the possibility of monolayer biosorption. The sticking probability (S*) was found to be 0.41, suggesting a physisorption mechanism for biosorption of Ni(II) on MABL. The biosorbent was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), zeta potential, and BET surface area, in order to understand its morphological and functional characteristics.

S. K. Sharma

Papers

Preparation and evaluation of stable nanofluids for heat transfer application: A review

Kinetics and equilibrium study of chromium adsorption on zeoliteNaX

Carbon nanotubes: synthesis, properties and engineering applications

Removal of lead(II) from waste water on zeolite-NaX

Biosorption of Ni(II) ions from aqueous solution using modified Aloe barbadensis Miller leaf powder