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Vanadium redox flow batteries (VRFBs) are increasingly used in different large-scale stationary applications. In particular, this state-of-the-art energy storage system is used to deal with power management, peak shaving and load leveling and to support a large-scale renewable power grid. VRFBs offer many benefits such as long lifetime, flexibility, and relatively high performance; however, their high capital and operation costs haveremained to be their major drawback compared to other more conventional energy storage systems (ESSs). Thus, significant efforts have been dedicated to modifying VRFB components in order to enhance their economic competitiveness while improving their performance. The present paper comprehensively reviews and discusses various electrode modification approaches, and electrolyte retainment techniques by focusing on their pros and cons and effects on the performance of VRFBs and the research gaps to be addressed. This paper also aims to explore another approach, known as the nanofluidic electrolyte technique , to simultaneously modify electrode and electrolyte. In addition, novel materials with different affecting properties suitable to be utilized in "nanofluidic electrolyte" technique for improving the performance of VRFBs are introduced and discussed. • VRFB electrode-improving techniques, drawbacks and the research gap are discussed. • Recent progress in vanadium electrolyte are deeply discussed and overviewed. • Novel and rarely studied "Nanofluidic Electrolyte" method is introduced and discussed. • Possible advanced materials that can be used in this method are introduced. [ABSTRACT FROM AUTHOR]

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 study aims to experimentally investigate and introduce a new model for enhancing convective heat transfer in the presence of Ag/ oil nanofluid. An annular tube was designed with a turbine element attached to the inner tube. The inner tube was a bearing shaft which could rotate with the rotation of turbine element. As the previous works by authors, the setup was conducted with a fully developed laminar flow regime with the Reynolds numbers less than 160. The outer surface of the annular tube was heated by an element with constant heat flux of 204 W. Ag/ oil nanofluid was used in different volume concentrations of 0.011%, 0.044% and 0.171%. The new model could enhance the convective heat transfer coefficient up to 54% (compared to the simple annular tube in the case of base fluid) for the best studied case (nanofluid with the volume concentration of 0.171%) while the friction factor remained low. The new model can be applied for related applications regarding Ag/ oil nanofluid as a new step in enhancing the convective heat transfer coefficient. [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]

In this work, an experimental study on nanofluid preparation stability, thermo-physical properties, heat transfer performance and friction factor of Al/ Oil nanofluids has been carried out. Electrical Explosion Wire (E.E.W) which is one of the most reliable one-step techniques for nanofluids preparation has been used. An annular tube has been considered as the test section in which the outer tube was subject to a uniform heat flux boundary condition of about 204 W. The utilized nanofluids were prepared in three different volume concentrations of 0.011%, 0.044% and 0.171%. A wide range of parameters such as Reynolds number Prandtl number, viscosity, thermal conductivity, density, specific heat, convective heat transfer coefficient, Nusselt number and the friction factor have been studied. The experiment was conducted in relatively low Reynolds numbers of less than 160 and within a hydrodynamically fully-developed regime. According to the results, thermal conductivity, density and viscosity increased depending on the volume concentrations and working temperatures while the specific heat declined. More importantly, it was observed that convective heat transfer coefficient and Nusselt number enhanced by 28.6% and 16.4%, respectively, for the highest volume concentration. Finally, the friction factor (which plays an important role in the pumping power) was found to be increased around 18% in the volume fraction of 0.171%. [ABSTRACT FROM AUTHOR]

This study aims to first introduce a formulation which is quite simple for obtaining dielectric-barrier discharge plasma spatial body force. This new model comprises a combination of an empirical model and a numerical one. Although there are still some limitations in the new model (restriction to specific geometry, maximum voltage amplitude of 30 kV, maximum frequency of 30 kHz, dielectric coefficient of 2.8 and Debye length of 0.0001 m), it is straightforward compared to the existing ones. The model possesses a high accuracy for the abovementioned band. It is proposed an approximate integral solution for the wall jet problem which is associated with the induced jet produced by dielectric barrier discharge plasma actuator. The approximate integral solution for the wall jet is verified by similarity, and the details are extensively discussed. [ABSTRACT FROM AUTHOR]

The present work provides an empirical investigation on the thermal characteristics of Ag/oil nanofluids flow inside a sinusoidal tube under a constant heat flux boundary condition. Ag/oil nanofluids have been prepared in low-volume concentrations of 0.011%, 0.044%, and 0.171%. The average size of the nanoparticles was 20 nm. A heated coil was attached to the upper and lower surface of the tube that satisfied the constant thermal boundary condition of 204 W. The experiment has been pursued at low Reynolds numbers less than 160. A loop was designed to keep the flow hydrodynamically fully developed during the experiment. The test case was a sinusoidal tube. Upper and lower surfaces of the tube have been designed sinusoidally. Moreover, the width of the plates was long enough, so the problem was not considerably affected by the three-dimensional releasing effect. Convective heat transfer coefficient and Nusselt number were calculated. It has been observed that based on the acquired data of the present work, convective heat transfer coefficient increased up to 23% for the best case (nanofluid with a volume concentration of 0.171%) compared to the base fluid. This happened while the rise of the friction factor was very low. In addition, a comparison between the new results and the previous work by authors showed the positive performance of sinusoidal tubes in increasing the convective heat transfer coefficient (the average increase was calculated to be about 82%) compared to the annular tube. [ABSTRACT FROM AUTHOR]

The present study aims to experimentally investigate heat transfer performance of rectangular and semicircular tubes in the presence of Ag / water nanofluids. The nanoparticles of Ag (silver) were used in seven different volume concentrations of 0.03%, 0.07%, 0.1%, 0.2%, 0.4%, 1% and 2%. The experiment was conducted in relatively low Reynolds numbers of 301 to 740. A heater with the power of 200 W was used to keep the outer surface of the tubes under a constant heat flux condition. In addition, the rectangular tube has been designed within the same length as the semicircular one and also within the same hydraulic diameter. Moreover, the average nanoparticles size was 20 nm. The outcome results of the present empirical work indicate that, for all the examined Reynolds numbers, the semicircular tube has higher convective heat transfer coefficient for all the utilized volume concentrations of Ag nanoparticles. The possible reasons behind this advantage are discussed through the present work mainly by taking the boundary effect on Brownian motions into account. Coming to this point that the conventional design for cooling system of photovoltaic cells is a heat sink with the rectangular graves, it is discussed that using a semicircular design may have the advantage over the rectangular one in convective heat transfer coefficient enhancement and hence a better cooling performance for these solar cells. [ABSTRACT FROM AUTHOR]

The present study indicates the impact of different arrangements of dielectric barrier discharge (DBD) plasma actuators on temperature field in a channel flow. The modified lumped circuit element electro-static model was used to calculate induced Lorentz body force and plasma dissipation of the actuators. Different distributions of temperature in the modeled channel flow for each arrangement of actuators (one, two, and three attached actuators) are discussed. According to the numerical simulation, DBD plasma actuators are beneficial devices for increasing temperature in the channel flow, especially near the location of the actuators that can be considered for related applications. The actuators are modeled under an incompressible flow regime with low Reynolds number of 335, and the configurations of the actuators are set to be 3 KV for the peak voltage amplitude, 10,000 Hz for the voltage frequency, and Kapton as the dielectric. [ABSTRACT FROM AUTHOR]

In this study, thermo-physical properties including thermal conductivity, viscosity, density and specific heat capacity of an oil based nanofluid including silver as to be nanoparticles have been experimentally studied. The results indicate an enhancement in thermal conductivity which was depended on bulk temperature and volume fraction of utilized nanofluids. Viscosity data show a significant increment through volume fraction increasing. In addition, the specific heat capacity and density of nanofluids were studied experimentally and it was found that, all measured rheological properties of these nanofluids, were not in agreement to published correlations. [ABSTRACT FROM AUTHOR]

This study deals with an empirical investigation on the convective heat transfer of Cu/oil nanofluid flow inside a concentric annular tube with constant heat flux boundary condition and suggests a correlation to predict the Nusselt number. The average size of particles was 20 nm and the applied nanofluid was prepared by Electrical Explosion of Wire technique with no nanoparticle agglomeration during nanofluid preparation process and experiments. The nanofluid flowing between the tubes is heated by an electrical heating coil wrapped around it. The effects of different parameters such as the flow Reynolds number, tube diameter ratio, and nanofluid particle concentration on heat transfer coefficient are studied. Using the acquired experimental data, a correlation is developed for the estimation of the Nusselt number of nanofluid flow inside the annular tube. This correlation has been presented by using the exponential regression analysis and least-squares method. The correlation is valid for Cu/base oil nanofluid flow with weight concentrations of 0.12, 0.36, and 0.72 in the hydrodynamically full-developed laminar flow regime with Re <140, which is applicable in mini- and microchannel heat exchangers, and it is in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

An oil based nanofluid including silver as to be nanoparticles was created by EEW method as a one-step method in three different volume fractions have been experimentally studied. Assessing the stability and viscosity of the nanofluids was involved in this work. The results show that the nanofluids behave in both of Newtonian and non-Newtonian in different volume concentrations. Also, an enhancement in viscosity of nanofluids has been recognized. In addition, based on the experimental results of this study and the other previous published studies on the oil based nanofluids, a correlation for predicting viscosity of oil based nanofluids has been developed and a good agreement between the experimental viscosity of applied nanofluids in this study and the predicted one has been achieved. [ABSTRACT FROM AUTHOR]

• A novel highly stable and well-oxidized EGO/ vanadium electrolyte based nanofluid was prepared. • Rheological evaluation showed an optimum mass fraction of 0.05% to be applicable in VRFBs. • A model to predict the viscosity of the utilized nanofluid was developed accurately. • Electrical conductivity assessment confirmed 0.05% as the optimum concentration. • Thermal conductivity reached a maximum enhancement of 4% for the optimum 0.05 wt% The use of electrolyte-based nanofluid is a new approach for enhancing the performance of Vanadium Redox Flow Batteries (VRFBs). This paper, for the first time in the literature, presents an experimental study to comprehensively investigate the rheological behaviour, electrical conductivity, and thermal conductivity of a newly prepared electrochemical graphene oxide (EGO)/ vanadium (IV) electrolyte-based nanofluid in different weight concentration and bulk temperatures. SEM, FT-IR and X-ray Diffraction (XRD) characterizations were performed and different functional groups, smooth 2D layered structures, and low crystallinity were detected in our tailored oxidation EGO which are amongst the enhancing features for VRFBs electrode materials. It was observed that the optimum weight concentration of nanoparticles in the electrolyte-based nanofluid is 0.05 wt% with strong colloidal stability, enhanced electrical and thermal conductivities, and an optimal viscosity. The maximum feasible enhancements in electrical and thermal conductivities that were achieved were 12%, and 4%, respectively, which can positively affect the performance of flow battery in terms of electrochemical activity on the electrode surface and thermal management of the flow battery system. In addition, the rheological evaluation showed that the behaviour of the electrolyte-based nanofluid tends to change from Newtonian to non-Newtonian for weight concentrations higher than 0.05%. The results obtained from rheological behaviour can provide useful insights in choosing an optimum pumping system of the flow batteries working with electrolyte-based nanofluid. [ABSTRACT FROM AUTHOR]

In this study, the flow of Cu/oil nanofluids over an impermeable semi‐infinite plate was investigated. A complete single‐phase modeling of nanofluids flowing over a semi‐infinite plate was performed, bringing into account, real experimental data of oil‐based nanofluids. The empirical correlations revealed that the viscosity and thermal conductivity of the pure oil and oil‐based nanofluids strongly depend on temperature. The similarity transformation method was utilized to transform governing partial differential equations into coupled nonlinear ordinary differential equations solved by employing the standard Runge–Kutta. The results showed that even low volumetric fraction of copper/oil nanofluids noticeably enhanced the heat transfer; however, such behavior was not predicted accounting the classic modeling of nanofluids. Furthermore, both hydrodynamics and thermal characteristics were reliant on the thermal boundary conditions, which this seems to have received a marginal focus in the existing literature. [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]

About 130,000,000 and 4,500,000 million people live at an altitude between 2000‐2500 and 3500–5200 above sea level respectively. Although, there are lots of water resources at high altitude which most of them are raw/impure/saline water. Also, there is not enough research on the performance of small-scale solar desalination systems at highlands. The main purpose of this paper is to present the impact of altitude on the performance of a single slope single basin solar still. Two identical passive solar still at the top of Mount Tochal and city of Tehran with 3964 and 1171 m of height are tested respectively. A series of experiments during four days from 24.07.2018 to 27.07.2018 are performed. All experiments are conducted by considering the effect of all important environmental conditions and performed by two separate teams at the mountain and Tehran simultaneously. All experiments were started and ended at the same time. Findings show that maximum hourly yield at the summit of Tochal and Tehran reaches to 720 and 500 ml/m2/h respectively. Total productivity at the mountain is higher by about 56.1% rather than that in Tehran. The cost of produced water at Tochal and Tehran evaluated about 0.0112 and 0.0087 $/liter/m2 respectively. • Performance of a solar distillation system in highlands for the first time is investigated • A comparative study on basin-type solar still at summit of Tochal and Tehran with 3964 and 1171 meters altitude is performed • Effect of different environmental conditions of both locations on the performance is examined • Total productivity at the summit is higher about 56.17% rather than that Tehran-located setup • Economic assessment showed that the cost of water in mountain is higher than Tehran [ABSTRACT FROM AUTHOR]

In recent years utilizing nanoparticles in black paint (nano-paint) of solar desalination absorbers has become a topic growing interest. However, in most of studies, only the effect of using different types of nanoparticles brought into the spotlight, while in those limited studies that discussed on optimum concentration of nanoparticles, the results were controversial and not conclusive. Herein, an experimental study to find the optimum concentration of nanoparticles (silver, 1–5%) in solar absorbers in summer, spring and autumn with/without reflectors was conducted. To find the optimum concentration, performance of the systems from different viewpoints including energetic, exergetic, economic, productivity, exergoeconomic, energy-matrices, and environmental (amount of CO 2 /SO 2 /NO emission/reduction) analysis for each season and thorough its lifetime was examined thoroughly. Ascribe the highly variable of parameters; two Matlab codes have been developed to precisely calculate the economic and exergoeconomic parameters for different scenarios. The results showed that increasing the nanoparticle concentration to 5% from an economic viewpoint was reasonable just in summer, while for autumn and spring, 2.5% was optimum. The same was valid for productivity and exergy analysis. Importantly, the embodied energy of nanoparticles for the first time considered in calculation to obtain more accurate results in terms of environmental analysis and energy-matrices. Finally, it was concluded that even though using 5% nanoparticle in limited cases led to better results, the 2.5% concentration with reflector was optimum for all seasons and through the lifetime. This work would be a cornerstone for future researches in the context of using nano-paint in solar absorbers. [Display omitted] • Optimum concentration of nanoparticle in solar absorber in autumn, spring and summer. • Productivity, energy, exergy, economic, environmental, exergoeconomic, energy-matrices consider as criteria assessment. • Improvements for nanoparticle at 1%–2.5% is higher than 2.5%–5% for all seasons. • Negative effect on increasing nanoparticle from 2.5% to 5% in autumn and spring observed. • Although 5% in limited cases has better results, 2.5% regarding all criteria proposed for real-world applications. [ABSTRACT FROM AUTHOR]

The heat transfer and flow characteristics of Cu-heat transfer oil nanofluid during mixed convection through horizontal annular tubes under uniform heat flux as boundary condition are investigated experimentally. Data were acquired at low Reynolds number ranged from about 26 to 252. The applied nanofluid prepared by Electrical Explosion of Wire technique with no nanoparticles agglomeration during nanofluid preparation process and experiments. Pure heat transfer oil and nanofluids with nanoparticles weight concentrations of 0.12, 0.36 and 0.72% were used as the working fluids. Based on these results, Effects of nanoparticles concentration, heat flux and free convection on the thermal field development are studied under buoyancy assisted flow condition for Grashof number, Richardson number between 2820 and 12,686, and 0.1-10, respectively. Results show that Nusselt number increases with an increase of nanoparticles weight concentrations from 0 to 0.72% under certain Richardson numbers. [ABSTRACT FROM AUTHOR]

The present study examined the performance of different modifications of identical solar stills (SSs) with heating/cooling and nanofluid. The first system is SS with thermoelectric heating (TEH) in the basin. The second system used TEH in the basin and loaded with nanofluid. The third SS used TEH as well as nanofluid and equipped with a double-slope symmetric external condenser that one side of it cooled by film of water and the other side with thermoelectric. Silver nanoparticle due to well-known characteristics in water disinfection was used with 0.03% weight. A series of experiment performed during one week in June 2019. Findings revealed that the daily yield and efficiency for SS with nanofluid/condenser and with nanofluid without condenser compared with SS without nanofluid/condenser improved by about 100.5%, 26.7% and 50.8%, 30.6% respectively. The highest productivity obtained by SS with nanofluid/condenser with 7760 cc/m2/day where the productivity from the glass-side increase by about 16.5% and 47.6% compared to SS with nanofluid without condenser and SS without nanofluid/condenser. Also it revealed that the contribution of external condenser in productivity is 26.3% of total productivity. Findings showed that the productivity of thermoelectric-side of condenser is more than 5 times higher than water film-side. • A modified solar desalination system with double-slope condenser and internal heater with nanofluid experimentally studied • Total yield and efficiency of SS with nanofluid and condenser is improved about 100.5% and 50.8% respectively. • The contribution of external condenser is 26.3% of total productivity. • Condenser increases the yield of glass-side while productivity of thermoelectric-side is 5.5 times higher than water-side. • Silver nanoparticle increased the rate of heat and mass transfer while it act as an anti-bacterial agent. [ABSTRACT FROM AUTHOR]