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Thermal oils due to their high ability in cooling and lubricating have many applications in high-tech industries such as automotive industry. Dispersing nanoparticles in a thermal oil (which the resulted new liquid is called nanofluid) can modify further the cooling and lubrication efficiencies. This review paper aims to present the recent advances in the preparation methods and thermophysical properties measurements of oil-based nanofluids. Effects of various parameters such as nanoparticle concentration, size, and temperature on the values of properties including thermal conductivity, viscosity, density, and specific heat are reviewed. The correlations available for the properties of oil-based nanofluids are gathered from the literature that could be a worthy source for those who aim to work on oil-based nanofluids. Unlabelled Image [ABSTRACT FROM AUTHOR]

This paper aims to investigate the electrical, thermal and exergy efficiencies of a photovoltaic/ thermal (PV/T) system cooled by Ag/water nanofluid. The utilized nanofluid was prepared by a one-step method of electrical explosion of wire (EEW) and was tested for long-term stability and uniformity. The performance of the PV/T system was measured by considering a wide range of parameters to determine key performance indicators such as electrical and thermal energy efficiency as well as exergy efficiency of the system. The effects of mass flow (i.e. different flow regimes of laminar, transient, and turbulent) on efficiencies were studied. The results showed that using nanofluids for cooling of the PV/T system can enhance both the energy and exergy efficiencies of the system significantly. It was also found that this positive impact is more pronounced by increasing the concentration of the nanofluid and increasing the flow rate (i.e. moving towards a turbulent flow). By using 4 wt% nanofluid (with turbulent flow) the power output of the panel increased by ∼35% and ∼10% compared to when no cooling and water cooling were applied respectively; and the exergy efficiency was also determined to be 50% and 30% higher than when no cooling and water cooling were used, respectively. [ABSTRACT FROM AUTHOR]

The present work aims to study heat transfer performance and pumping power of MgO–MWCNT/ thermal oil hybrid nanofluid. Using a KD2 Pro thermal analyzer, the thermal conductivity of the samples has been measured. The results showed an increasing trend for the thermal conductivity of the nanofluid by increasing the mass concentration and temperature, in which the maximum enhancement of thermal conductivity was approximately 65%. Predicting the thermal conductivity of the nanofluid, a highly accurate correlation in terms of solid concentration and temperature has been proposed. Moreover, the heat transfer efficiency and pumping power in all the studied range of solid concentrations and temperatures have been theoretically investigated, based on the experimental data of dynamic viscosity and thermal conductivity, for both the internal laminar and turbulent flow regimes. It was observed that the studied nanofluid is highly efficient in heat transfer applications as a coolant fluid in both the laminar and turbulent flow regimes, although it causes a certain penalty in the pumping power. [ABSTRACT FROM AUTHOR]

• Latest developments in solar thermal applications using nanofluids are reviewed • Low to medium temperature solar collectors are summarized • Improvements in solar collectors using nanofluids as working fluid is compiled • Application of solar collectors in buildings is reviewed The efficient exploitation of solar irradiation is one of the most encouraging ways of handling numerous environmental concerns. Solar collectors are suitable devices that capture solar irradiation and convert it into thermal energy and electricity. In the last years, the nanofluids used in solar thermal systems have been studied as a useful technique for enhancing the solar collectors' performance and establishing them as viable and highly efficient systems. The present review paper aims to summarize and discuss the most important numerical and experimental studies in nanofluid-based solar systems for application at low and medium temperature levels, while the emphasis on the fundamental physical phenomena that occur. In the first part, numerous numerical models and the principal physical phenomena affecting the heat transfer rate in the nanofluid have been analyzed. More specifically, the importance of different forces in nanofluid flows that exist in particulate flows such as drag, lift (Magnus and Saffman), Brownian, thermophoretic, Van der Waals, electrostatic double-layer forces are considered. Moreover, an overview of the thermophysical properties, physical models, heat transfer models, and evaluation criteria of nanofluids are included in this work. In the second part, which is the main part of this work, a comprehensive review is performed to gather and discuss the new advantages in the nanofluid-based solar collectors that operate at low and medium temperatures. More specifically, the examined solar systems are the flat plate collectors, the evacuated tube collectors, the direct absorption collectors, and the thermal photovoltaic systems, while the investigated applications are space-heating, space-cooling, household hot water production, desalination, industrial activities, and power generation. The aforementioned collectors and applications are the most usual in the real systems, indicating the importance of the present work. Moreover, the emphasis is given in the thermal, exergy, economic, and environmental evaluation of the studied systems, as well as in the discussion of the possible limitations of the use of nanofluids like the lack of long-term stability, the agglomeration of nanoparticles, and the increased pumping work due to the increased pressure drop. Finally, it is found that the nanofluid utilization usually enhances the collector efficiency up to 5%, while higher enhancements can be found in thermal photovoltaics. Moreover, it is concluded that there is a need to emphasize issues such as stability and the use of eco-friendly solar systems. Lastly, the field's future trends are highlighted, and a clear image of the present situation and the next steps in the field are given. [ABSTRACT FROM AUTHOR]