Abstract
Many studies have shown the remarkable enhancement of thermo-physical properties with the addition of a small quantity of nanoparticles into conventional fluids. However, the long-term stability of the nanofluids, which plays a significant role in enhancing these properties, is hard to achieve, thus limiting the performance of the heat transfer fluids in practical applications. The present paper attempts to highlight various approaches used by researchers in improving and evaluating the stability of thermal fluids and thoroughly explores various factors that contribute to the enhancement of the thermo-physical properties of mono, hybrid, and green nanofluids. There are various methods to maintain the stability of nanofluids, but this paper particularly focuses on the sonication process, pH modification, and the use of surfactant. In addition, the common techniques to evaluate the stability of nanofluids are undertaken by using visual observation, TEM, FESEM, XRD, zeta potential analysis, and UV-Vis spectroscopy. Prior investigations revealed that the type of nanoparticle, particle volume concentration, size and shape of particles, temperature, and base fluids highly influence the thermo-physical properties of nanofluids. In conclusion, this paper summarized the findings and strategies to enhance the stability and factors affecting the thermal conductivity and dynamic viscosity of mono and hybrid of nanofluids towards green nanofluids.
Highlights
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Green nanofluids are categorized under green nanotechnology, which is one of the branches under green technology introduced by the government of Malaysia
The results reveal that the thermal conductivity of SiC/ethylene glycol (EG) nanofluids increases as temperatures increase, where the highest thermal conductivity was found at maximum temperature, 50 ◦ C, augmented by up to 16.21% relative to the base fluids
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The utilization of nanoparticles is expected to increase the efficiency of thermal systems in different industrial applications [1]. According to Maksimović and Omanović-Mikličanin [7], green, environmental, or clean technology comprise methods and techniques that continuously evolve without risking the environment, conserving natural resources, and creating sustainable development methods. According to Malaysia’s Ministry of Energy, Green Technology and Water (KeTTHA) [8], “green technology” can be defined as the development and application of products, equipment, and systems used to conserve the environment and resources, which. Green nanotechnology represents an effort to utilize nature to eliminate or minimize the risk posed by the use of nanomaterials to the environment and humans and promote the replacement of existing products with more environmentally friendly nanoproducts [9]. The hydrothermal dehydration method is environmentally friendly, but it is capable of producing nanoparticles in bulk and maintaining the purity of the products
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