Stability Analysis of Alumina-Water Nanofluid Prepared with Different Surfactants

Stability Analysis of Alumina-Water Nanofluid Prepared with Different Surfactants

• Autor
• Eliel Wellington Marcelino
• Co-autores
• Humberto Naoyuki Yoshimura , Sydney Ferreira Santos
• Resumo

• Nanofluids are built with a mass fraction of nanoparticles dispersed into a base fluid in the order of 0-100nm. They represent an interesting alternative for the enhancement of conventional fluid properties (e.g., thermal conductivity, electric conductivity, etc.). Nanoparticle materials can be metallic, metallic oxide, ceramic, polymeric, or hybrid when there is a joining of two or more materials to form a nanoparticle. Base fluids are conventional fluids used in industrial systems and research, for example, water, ethylene-glycol, oils, etc. Nanoparticle’s structure, shapes, and geometry are diversified and depend on the material synthesis for obtaining the nanoparticles. The preparation of nanofluids is made through either a one-single-step method or a two-step method. The one-single-step method considers dispersing the nanoparticles into the base fluid through chemical vapor deposition (CVD), which is a process that demands high costs and time for nanofluid production. Conversely, the two-step method considers the dispersion of nanoparticles into the base fluid at room pressure and room temperature with a low cost and time for nanofluid production. The enhancement level of a nanofluid is related to the stability level of the nanoparticles dispersed into the base fluid. Thus, improved nanoparticle dispersion into the base fluid tends to enhance the stability of the nanofluid. However, during the nanofluid lifetime, sedimentation can occur or a change for agglomeration can occur as well, which will generate low stability.

  Mechanical and chemical methods for nanofluid preparation are applied to improve the stability level of nanofluid during its lifetime. Mechanical methods are related to the use of stirring action, such as magnetic or mechanical mixing, sonication bath, and sonication probes. Chemical methods are related to the change in the nanoparticle surface area and nanoparticle-base fluid interfaces, among others, by the application of surfactants. The stability of nanofluids generated through chemical methods can be categorized as steric, electrostatic, and electro-steric. Usually, chemical methods use a surfactant to cause steric or electro-steric stability. The surfactants can be either ionic, categorized by anionic (negatively charged), cationic (positively charged), amphoteric (positive and negative charges), or non-ionic, in which molecules contain no charge. Usually, mechanical methods are the first to be used for proper nanoparticle dispersion then chemical methods are used for the enhancement of the nanofluid stability. Thus, for obtaining longer periods of nanofluid stability, the use of chemical methods of preparation is required. The most common monitoring methods of nanofluid stability are the analysis of the pH value, zeta potential, and UV-Vis spectrometry.

  This work considered an alumina-water nanofluid with the surfactants Tween®20, Tween®80, Span®80, and Lauril. The first three surfactants, Tween-20, Tween-80, and Span-80, are non-ionic, while Lauril is an anionic surfactant, in which the molecules do not ionize in an aqueous solution. Each nanofluid sample was prepared with 0.003M of a chosen surfactant, and then, comparisons were made among all the results. For each nanofluid sample, it was considered a mass fraction of 0.1 wt.% of Al2O3 dispersed in deionized water. The samples were firstly stirred for 10min at 1000rpm in a mechanical stirrer, then an ultrasonic bath was applied for 32min, and finally, probe sonication was applied for 30min. The nanofluid stability level was analyzed by measuring the samples' pH, UV-Vis spectrometry, and zeta potential. The nanofluid pH analysis demonstrated that samples with surfactants Tween-20 and Tween-80 showed enhanced results. The nanofluid zeta potential analysis showed that surfactants Span-80 and Lauril demonstrated higher stability results with -32.6mV and -33.2mV, respectively. Finally, the surfactants Tween-20 and Tween-80 demonstrated better results for the UV-Vis analysis. To summarize, based on the conditions considered in this work, the surfactants Tween-20 and Tween-80 tend to demonstrate enhanced results for nanofluid stability when compared to the other surfactants of this work.

• Palavras-chave
• Nanofluids, Nanofluid Stability, Surfactants, Zeta potential.
• Modalidade
• Pôster
• Área Temática
• Materias Funcionais Avançados