BIBLIOS

Document type
Conference papers

Document subtype
Abstract/Full paper of Invited talk

Title
How to validate nanofluids?

Participants in the publication
Maria José V. Lourenço (Author)
Dep. Química e Bioquímica
CQE

Summary
The International Organization for Standardization defines the term "nanomaterial" as "material with any external dimensions in the nanoscale or having internal structure or surface structure in the nanoscale". The term "nanoscale" is defined as size range from approximately 1 nm to 100 nm “The increasing use of nanomaterials in industry and society means that their utility, risks and benefits throughout their life-cycle are important topics for discussion” [1].\nWhat about nanofluids? Nanofluids are not simply mixtures of nanomaterials in fluids. The simpler nanofluids are bi-phasic systems with a solid phase dispersed in a liquid phase to be stable over a long period of time with different roperties from those of the base fluids. These useful nanofluids can replace, with advantages, fluids used in many ngineering applications.\nThe results show that good and coherent experimental results can be obtained when well planned experiments are used, demonstrating that nanofluids can be used in many applications with success [2]. Until now the published results on nanofluids exhibit several problems about the characterization of nanomaterials used, preparation and short/long term stability of the prepared dispersions, and the adequacy of the experimental techniques used to measure the\nthermophysical properties, namely thermal conductivity, due to the scatter/availability of published data. However, optical properties have considerable contribution to heat absorbance in nanofluids. Simple light absorption measurements in UV-Vis may be used to follow the stability of nanofluids using just the dispersion of light caused by the nanomaterial, even for systems that do not have any absorption bands in the visible range. The experimental results\nrevealed that the transmittance of nanofluids has indirect relation with nanoparticle size, volume fraction, and path length [3]. Overall, results of various elements showed that the presence of large particles and particle agglomerates leads to significant amount of scattered light. \nIt is fundamental to be aware of the difference between agglomerate and aggregate. An agglomerate is defined as a collection of weakly or medium strongly bound particles where the resulting external surface area is similar to the sum of the surface areas of the individual components (the forces holding an agglomerate together are weak forces, for example van der Waals forces or simple physical entanglement). An aggregate is defined as particles comprising strongly bonded or fused particles where the resulting external surface area is significantly smaller than the sum of surface areas of the individual components (the forces holding an aggregate together are strong forces, for example covalent or ionic bonds, or those resulting from sintering or complex physical entanglement, or otherwise combined former primary particles) [1].\nThe special case of IoNanofluid defined by C. A. Nieto de Castro et al.[4] as a nanomaterial stable dispersion in an ionic liquid have an enormous potential for many applications, due to their properties, namely HTF’s. The fundamental is to achieve kinetically stable dispersions. Two-step methods and sonication probes are the most convenient techniques for its preparation. The toxic effect of the system ionic liquid /nanomaterial in biota is a challenging endeavour.\nThe use of surfactants or any other additives to stabilize the nanofluids should be avoid. Understanding the molecular interactions cation/anion/nanomaterial is critical. There are other special and essential requirements, for example, the durability of the suspension, the prevention of agglomeration and/or aggregation, and the constancy of the fluid chemistry [5].

Editor(s)
S. M. Sohel Murshed, C. A. Nieto de Castro and Enrique Juliá


Institution
FACULDADE DE CIÊNCIAS DA UNIVERSIDADE DE LISBOA

Event
1st European Symposium on Nanofluids (ESNf2017)

Publication Identifiers
ISBN - 9789729665356

Address
Lisboa, Portugal

Organizers
Centro de Química Estrutural, Faculdade de Ciências da Universidade de Lisboa

Publisher
FACULDADE DE CIÊNCIAS DA UNIVERSIDADE DE LISBOA

Collection
Abstract Book



Document Identifiers
URL - http://esnf2017.campus.ciencias.ulisboa.pt/

Keywords
Nanofluid Validation Standardization Stability Thermal Properties