Recent Patents on Nanotechnology - Volume 7, Issue 3, 2013

As innovative nanotechnology-based heat-transfer media, nanofluids have evoked considerable interest among researchers owing to their improved thermal properties as well as their extendable applications to various high-power thermal systems. This paper presents a comprehensive review of recent research developments and patents pertaining to nanofluid boiling heat transfer. Nanofluids definitely offer a wide range of potential improvements in boiling heat-transfer performance. However, experimental data available from different studies are currently beset by numerous contradictions, suggesting that the fundamental mechanisms of nanofluid boiling heat transfer are not yet well understood. Consequently application of these technologies has been limited in some aspects. Only a small number of patents related to nanofluid boiling heat transfer have thus far been reported in the literature. Based on the present review, future technological development and research requirements in this area are outlined in line with technical challenges. To utilize nanofluid boiling heat-transfer technologies for practical applications, more systematic and fundamental studies are required to understand the physical mechanisms involved.

This paper presents the most recent review of research articles and patents on thermal conductivity on nanofluids. Larger portion of literature accounts for experimental investigations, which is a sign of the preference for hands-on work by experimentalists. Metallic, non-metallic as well as ceramic nanoparticles of different sizes and shapes were suspended in common heat transfer liquids and their thermal conductivities were measured. In contrast to previous belief, it has now been proven that when the nanoparticle concentration is kept low the degree of enhancement falls reasonably within the boundaries predicted by the effective medium theories. There are strong evidences to suggest that the main mechanisms driving the thermal conductivity behavior are nanoparticle aggregation and the particle Brownian motion in suspension.

Fluids with suspended nanoparticles, commonly known as nanofluids, may be formulated to improve the thermal performance of industrial heat transfer systems and applications. Nanofluids may show enhanced thermal and electrical properties such as thermal conductivity, viscosity, heat transfer coefficient, dielectric strength, etc. However, stability problems may arise as nanoparticles usually have the tendency to agglomerate and sediment producing deterioration in the increment of these properties. In this review, we discuss patents that report advances in the formulation of nanofluids including: production methods, selection of components (nanoparticles, base fluid and surfactants), their chemical compositions and morphologies, and characterization techniques. Finally, current and future directions in the development of nanofluid formulation are discussed.

Nanofluids- a new class of heat transfer fluids have recently been a very attractive area of research due to their fascinating thermophysical properties and numerous potential benefits and applications in many important fields. However, there are many controversies and inconsistencies in reported arguments and experimental results on various thermal characteristics such as effective thermal conductivity, convective heat transfer coefficient and boiling heat transfer rate of nanofluids. As of today, researchers have mostly focused on anomalous thermal conductivity of nanofluids. Although investigations on boiling and droplet spreading are very important for practical application of nanofluids as advanced coolants, considerably fewer efforts have been made on these thermal features of nanofluids. In this paper, recent research and development in boiling heat transfer and droplet spreading of nanofluids are reviewed together with summarizing most related patents on nanofluids published in literature. Review reveals that despite some inconsistent results nanofluids exhibit significantly higher boiling heat transfer performance compared to their base fluids and show great promises to be used as advanced heat transfer fluids in numerous applications. However, there is a clear lack of in-depth understanding of heat transport mechanisms during phase change of nanofluids. It is also found that the nanofluids related patents are limited and among them most of the patents are based on thermal conductivity enhancement and synthesising processes of specific type of nanofluids.

Due to the rapid elevation of health standards and the limited water resources, decontamination and disinfection have become a challenging aspect of water/wastewater treatment. Traditional disinfection in water/wastewater treatment is associated with limitations, such as the production of toxic disinfection by-products. With the development of nanofluids, there is more and more interest in using nanofluids in environmental sectors, especially in water/wastewater treatment. Nanofluids are not strong oxidants and are not expected to produce harmful disinfection by-products. Nanofluids exhibit good disinfection properties against a wide range of bacteria, including Gram-negative, Gram-positive and spore bacteria. Several patents disclose the typically used types of nanofluids and their possible disinfection/ decontamination mechanisms. The use of different nanofluids and their applications in different water/wastewater treatment have also been reviewed in this paper.

The rheological behavior of nanofluids published in recent research papers and the relevant patents are reviewed in this article. Effects of various factors such as preparation, nanoparticle and base fluid properties, concentration, temperature, surface charge, and aggregation etc. on the rheological behavior of nanofluids are discussed. Brownian motion and nanoparticle aggregation are found to be the major mechanisms for rheological properties of nanofluids compared to the micro-sized suspensions. The importance of microstructure as means of understanding the mechanisms behind the rheological and heat transfer behavior of nanofluids is also disclosed.

In the last fifteen-years, the application of metal nanoparticles as catalysts in organic synthesis has received a renewed interest. Therefore, much attention is currently being paid to the synthesis of metal nanoparticles in order to achieve the control of their characteristics in terms of size, shape and surface chemistry. Besides this, the recyclability as well as the recovery from the reaction medium still remain the major drawbacks to widespread the use of nanoparticles in catalysis. To overcome these problems, the immobilization of metal nanoparticles on solid supports appears as a promising alternative. In that context, carbon materials offer several advantages as solid supports such as availability, relatively low cost, high mechanical strength, chemical stability, and a pore structure along with an attractive surface chemistry which allows easy modifications, such as its functionalization, to suit the nanoparticles immobilization needs. Among the transition metals Palladium and Ruthenium are widely employed as efficient catalysts in many reactions. Herein, the most recent advances, from recent papers and patents, in relation to the preparation of carbon-supported Pd or Ru nanoparticles systems as well as their application as catalysts in alcohol oxidation, cross-coupling or hydrogenation reactions, are reviewed.