Nanofluids have been receiving great attention in recent years due to their potential usage, not only as an enhanced thermophysical heat transfer fluid but also because of their great importance in applications such as drug delivery and oil recovery. Nevertheless, there are some challenges that need to be solved before nanofluids can become commercially acceptable. The main challenges of nanofluids are their stability and operational performance. Nanofluids stability is significantly important in order to maintain their thermophysical properties after fabrication for a long period of time. Therefore, enhancing nanofluids stability and understanding nanofluid behaviour are part of the chain needed to commercialise such type of advanced fluids. In this context, the aim of this article is to summarise the current progress on the study of nanofluids, such as the fabrication procedures, stability evaluation mechanism, stability enhancement procedures, nanofluids thermophysical properties, and current commercialisation challenges. Finally, the article identifies some possible opportunities for future research that can bridge the gap between in-lab research and commercialisation of nanofluids.

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One practical solution for utilizing hydrogen in vehicles with proton-exchange fuel cells membranes is storing hydrogen in metal hydrides nanocrystalline powders. According to its high hydrogen capacity and low cost of production, magnesium hydride (MgH2) is a desired hydrogen storage system. Its slow hydrogenation/dehydrogenation kinetics and high thermal stability are the major barriers restricting its usage in real applications. Amongst the several methods used for enhancing the kinetics behaviors of MgH2 powders, mechanically milling the powders with one or more catalyst species has shown obvious advantages. Here we are proposing a new approach for gradual doping MgH2 powders with Ni particles upon ball milling the powders with Ni-balls milling media. This proposed is-situ method showed mutually beneficial for overcoming the agglomeration of catalysts and the formation of undesired Mg2NiH4 phase. Moreover, the decomposition temperature and the corresponding activation energy showed low values of 218 °C and 75 kJ/mol, respectively. The hydrogenation/dehydrogenation kinetics examined at 275 °C of the powders milled for 25 h took place within 2.5 min and 8 min, respectively. These powders containing 5.5 wt.% Ni performed 100-continuous cycle-life time of hydrogen charging/discharging at 275 °C within 56 h without failure or degradation.

Heat exchangers are key components in many of the devices seen in our everyday life. They are employed in many applications such as land vehicles, power plants, marine gas turbines, oil refineries, air-conditioning, and domestic water heating. Their operating mechanism depends on providing a flow of thermal energy between two or more mediums of different temperatures. The thermo-economics considerations of such devices have set the need for developing this equipment further, which is very challenging when taking into account the complexity of the operational conditions and expansion limitation of the technology. For such reasons, this work provides a systematic review of the state-of-the-art heat exchanger technology and the progress towards using nanofluids for enhancing their thermal-hydraulic performance. Firstly, the general operational theory of heat exchangers is presented. Then, an in-depth focus on different types of heat exchangers, plate-frame and plate-fin heat exchangers, is presented. Moreover, an introduction to nanofluids developments, thermophysical properties, and their influence on the thermal-hydraulic performance of heat exchangers are also discussed. Thus, the primary purpose of this work is not only to describe the previously published literature, but also to emphasize the important role of nanofluids and how this category of advanced fluids can significantly increase the thermal efficiency of heat exchangers for possible future applications.

This study demonstrates an electron beam physical vapour deposition approach as an alternative stainless steel thin films fabrication method with controlled layer thickness and uniform particles distribution capability. The films were fabricated at a range of starting electron beam power percentages of 3–10%, and thickness of 50–150 nm. Surface topography and wettability analysis of the samples were investigated to observe the changes in surface microstructure and the contact angle behaviour of 20 °C to 60 °C deionised waters, of pH 4, pH 7, and pH 9, with the as-prepared surfaces. The results indicated that films fabricated at low controlled deposition rates provided uniform particles distribution and had the closest elemental percentages to stainless steel 316L and that increasing the deposition thickness caused the surface roughness to reduce by 38%. Surface wettability behaviour, in general, showed that the surface hydrophobic nature tends to weaken with the increase in temperature of the three examined fluids.

This study investigates the shelving stability of dispersed aluminium nanoparticles in water mixtures fabricated by the conventional and the controlled bath temperature two-step methods. The nanofluids were prepared with water of pH 9 and nanoparticles of 0.1–1.0 vol.%. A bath type ultrasonicator was employed for dispersing the nanoparticles into the base fluid. The sonication process, for all as-prepared samples, lasted for 4 hours and was either device bath temperature uncontrolled or controlled in the range of 10–60°C. Furthermore, the stability of the as-produced nanosuspensions was evaluated using the sedimentation photograph capturing method by capturing images at equal intervals of time for 12 hours then analysing the data based on the sample sedimentation height ratios. It was found that the sedimentation behaviour of the nanofluids fabricated via the controlled temperatures of less than 30°C was of dispersed sedimentation type, while those produced by the conventional method and the fixed temperatures of 30°C and higher were of flocculated sedimentation type. In addition, increasing the controlled sonication temperature has shown to increase the settling process of the sediments. Moreover, the rise in nanoparticle concentration was seen to reduce the variation in sedimentation height ratio between the fixed temperature samples. A comparison between the two fabrication methods has shown that the 30°C nanofluids had better short- and long-term stability than the conventionally produced suspensions.

Throughout human history, any society’s capacity to fabricate and refine new materials to satisfy its demands has resulted in advances to its performance and worldwide standing. Life in the twenty-first century cannot be predicated on tiny groupings of materials; rather, it must be predicated on huge families of novel elements dubbed “advanced materials”. While there are several approaches and strategies for fabricating advanced materials, mechanical milling (MM) and mechanochemistry have garnered much interest and consideration as novel ways for synthesizing a diverse range of new materials that cannot be synthesized by conventional means. Equilibrium, nonequilibrium, and nanocomposite materials can be easily obtained by MM. This review article has been addressed in part to present a brief history of ball milling’s application in the manufacture of a diverse variety of complex and innovative materials during the last 50 years. Furthermore, the mechanism of the MM process will be discussed, as well as the factors affecting the milling process. Typical examples of some systems developed at the Nanotechnology and Applications Program of the Kuwait Institute for Scientific Research during the last five years will be presented in this articles. Nanodiamonds, nanocrystalline hard materials (e.g., WC), metal-matrix and ceramic matrix nanocomposites, and nanocrystalline titanium nitride will be presented and discussed. The authors hope that the article will benefit readers and act as a primer for engineers and researchers beginning on material production projects using mechanical milling.

Nanofluids have opened the doors towards the enhancement of many of today’s existing thermal applications performance. This is because these advanced working fluids exhibit exceptional thermophysical properties, and thus making them excellent candidates for replacing conventional working fluids. On the other hand, nanomaterials of carbon-base were proven throughout the literature to have the highest thermal conductivity among all other types of nanoscaled materials. Therefore, when these materials are homogeneously dispersed in a base fluid, the resulting suspension will theoretically attain orders of magnitude higher effective thermal conductivity than its counterpart. Despite this fact, there are still some challenges that are associated with these types of fluids. The main obstacle is the dispersion stability of the nanomaterials, which can lead the attractive properties of the nanofluid to degrade with time, up to the point where they lose their effectiveness. For such reason, this work has been devoted towards providing a systematic review on nanofluids of carbon-base, precisely; carbon nanotubes, graphene, and nanodiamonds, and their employment in thermal systems commonly used in the energy sectors. Firstly, this work reviews the synthesis approaches of the carbon-based feedstock. Then, it explains the different nanofluids fabrication methods. The dispersion stability is also discussed in terms of measuring techniques, enhancement methods, and its effect on the suspension thermophysical properties. The study summarizes the development in the correlations used to predict the thermophysical properties of the dispersion. Furthermore, it assesses the influence of these advanced working fluids on parabolic trough solar collectors, nuclear reactor systems, and air conditioning and refrigeration systems. Lastly, the current gap in scientific knowledge is provided to set up future research directions.