In this paper, the thermal conductivity of Fe3O4 magnetic nanofluids has been investigated experimentally. The nanofluid samples were prepared using a two-step method by dispersing Fe3O4 ...nanoparticles into the water with the solid volume fractions of 0.1%, 0.2%, 0.4%, 1%, 2% and 3%. Thermal conductivity measurements were performed by employing a KD2 Pro thermal properties analyser under temperatures ranging from 20°C to 55°C. Then, using experimental data, a new correlation was proposed to predict the thermal conductivity ratio of the magnetic nanofluid. Finally, an optimal artificial neural network was designed to predict the thermal conductivity ratio of the magnetic nanofluid. The experimental results indicated that the maximum enhancement of thermal conductivity of nanofluid was about 90%, which occurred at solid volume fraction of 3.0% and temperature of 55°C. The comparative results showed that there are deviations of 5% and 1.5%, respectively, for correlation and ANN from the experimental data. It was found from comparisons that the optimal artificial neural network model is more accurate compared to empirical correlation.
•Preparing the stable SiO2-MWCNTs/SAE40 hybrid nanofluids by the two-step method.•Measuring the viscosity for various concentrations under different temperatures.•Comparing the nanofluid viscosity ...with the existing well-known models.•Viscosity enhances with increasing the solid volume fraction.•Proposing an accurate correlation to predict the viscosity of the hybrid nanofluid.
In this study, an experimental investigation on the effects of temperature and concentration of nanoparticles on the dynamic viscosity of SiO2-MWCNTs/engine oil (SAE40) hybrid nanofluid is presented. The experiments were performed in the solid volume fraction range of 0–1.0% and temperature ranging from 25°C to 60°C. Viscosity measurements showed that SiO2-MWCNTs/SAE40 hybrid nanofluid behaves as a Newtonian fluid at all considered solid volume fractions and temperatures. Experimental results also revealed that the dynamic viscosity enhances with an increase in the solid volume fraction and decreases with increasing temperature. Moreover, results indicated that the maximum enhancement of viscosity of the hybrid nanofluid was 37.4%. Finally, an accurate correlation with maximum deviation of 0.75% has been proposed to predict the dynamic viscosity of SiO2-MWCNTs/SAE40 hybrid nanofluids.
The application of nanofluid in cooling systems is increasing. The nanofluid consists of a mixture of nanometallic and nonmetallic particles, which dispersed in a base fluid. In this study, an ...overview on fuel cell types and their applications and how they work are presented. In the main part of this paper, the previous articles on the application of nanofluid in fuel cell cooling are reviewed. Their general results indicate that fuel cells with nanofluids have a higher cooling capability than those with pure fluids. This increase has only been achieved by adding a limited volume fraction of nanoparticle. Studies show that the use of hybrid nanofluids increases the thermal conductivity compared to conventional nanofluids. Also, the economic and functional analyses provided by the researchers and their proposed relationships suggest that the use of nanofluids in a fuel cell has acceptable performance, and therefore they can be used as industrial fluids. Finally, the challenges of using nanofluids and fuel cells are discussed. It was found that limited studies have been conducted in the field of economic and exergy evaluation of fuel cell systems, including their impact on the environment, so it is suggested to address this issue in future studies.
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In the current work, we investigate the dynamic viscosity of Ag/Ethylene glycol nanofluid within the temperature range of 25–55 ° C with volume fraction of nanoparticles range of 0.2%–2%. The ...experimental data includes 42 samples. At first, an Artificial Neural Network (ANN) is designed to predict the dynamic viscosity of this nanofluid and finally the results of ANN and correlation has been compared. The algorithm of generating the best architecture of ANN has been proposed and the best ANN has been used to predict the dynamic viscosity of Silver/Ethylene glycol nanofluid. It is found that the ANN can predict the viscosity of Ag/Ethylene glycol nanofluid with good precision compared to the correlation method. Also, in the correlation method, MSE is 0.0012, SSE is 0.0512 and the maximum value of error is 0.0858.
The building sector is the major energy consumer, accounting for over 40% of global energy demand. Heating and cooling together with domestic hot water energy consumption are estimated to account for ...60% of the required energy for buildings’ maintenance and operation. Energy recovery is a suitable technique to tackle high energy consumption in the building. In this study, a new layout of heat recovery units installation (i.e., primary and secondary) is investigated. The main objective of this study is to reduce energy consumption in an air handling unit through the exergy analysis. Owing to adding heat recovery units, cooling and heating coil loads reduced by 7.8% and 43%, which in turn decreased the total required load of AHU by 17.84%. From the viewpoint of the second law and based on the results, incorporating the primary and secondary heat recovery units into the base AHU in hot and dry climate regions led to decrease in the total irreversibility up to 26.29%, while in hot and humid climate this figure is 14.25%. Consequently, the positive effect of using heat recovery units in the hot and dry climate region is superior to the hot and humid one.
In this paper, the effect of the presence of radiation on the convection heat transfer rate and the nanofluid entropy generation within a diagonal rectangular chamber is investigated numerically in ...the presence of a magnetic field. The governing equations have been solved via finite volume method using the simple algorithm. In this paper, the effects of Rayleigh number, Hartmann number, magnetic field angle changes, chamber angle changes, entropy parameter, radiation parameter and volume percent of nanoparticles on the entropy generation and heat transfer have been investigated. The results show that with increasing Rayleigh number and decreasing the Hartmann number, the Nusselt number and entropy generation increase and the Bejan number decreases. By increasing the angle of the magnetic field, the heat transfer rate and the entropy generation are reduced and the Bejan number increases. By increasing the angle of the chamber at high Rayleigh numbers, the heat transfer rate increases, or by adding 6% of the nanoparticles to the base fluid, the heat transfer rate increases by 9.3% and the entropy generation increases by 15.5% in the absence of radiation. This increase in the Rd = 3 radiation parameter is 5.4% and 6.2%, respectively. It was also observed that the Nusselt number and the entropy generation increased, and with increasing the radiation parameter, the Bejan number decreased. Increasing the heat transfer rate is more significant at higher Rayleigh numbers by increasing the radiation parameter.
•Experimental study on thermal conductivity of MgO-FMWCNTs/EG hybrid nanofluid.•Performing tests in temperature range of 25–50°C and concentration range of 0–0.6%.•Maximum enhancement of thermal ...conductivity of nanofluid is 21.3%.•Proposing a new correlation to predict the thermal conductivity of the nanofluid.
In this paper, an experimental investigation on the effects of hybrid nano-additives, composed of magnesium oxide (MgO) and functionalized multi-walled carbon nanotubes (FMWCNTs), on the thermal conductivity of ethylene glycol (EG) is presented. The experiments performed at temperatures ranging from 25°C to 50°C and the solid volume fraction range of 0–0.6%. The measurements revealed that the thermal conductivity of nanofluids significantly enhances with an increase in the percentage of the solid volume fraction. Moreover, the thermal conductivity of EG considerably increased with increasing temperature, while thermal conductivity of hybrid nanofluid slightly enhanced. The thermal conductivity measurements showed that the maximum enhancement of thermal conductivity of nanofluid is 21.3%, which occurred at solid volume fraction of 0.6% and temperature of 25°C. Finally, efforts were made to provide an accurate correlation for estimating the thermal conductivity at various temperatures and concentrations. Deviation analysis of the thermal conductivity ratio was performed. The comparison between experimental results and correlation outputs showed a good agreement.
This is a numerical study of heat transfer and flow in a counter-flow sinusoidal parallel-plate heat exchanger using metal foam in the channels’ divergent sections. The cold water fluid with Reynolds ...number of 100 and hot oil fluid with Reynolds number of 2 enter the downer and upper channels of the heat exchanger, respectively. The sinusoidal heat exchanger is investigated with two-wave amplitudes (0.3 and 0.6 cm), two wavelengths (6 and 12 cm) inserting the porous media with three particle diameters (0.1, 0.05 and 0.01 mm) and three thicknesses (
A
/3, 2
A
/3, and
A
). Darcy–Brinkman–Forchheimer and local thermal non-equilibrium models are used. To evaluate the increased heat transfer versus the increased pumping power, a dimensionless number called performance evaluation criteria (PEC) has been defined in the current study. The obtained results showed that the heat transfer rate, effectiveness and overall heat transfer coefficient of the heat exchanger are increased up to 19.2%, and the PEC number is enhanced to 1.171 in the optimum case with wave amplitude, wavelength, metal foam particle diameter and thickness equal to 0.6 cm, 6 cm, 0.01 mm and 2
A
/3, respectively. Moreover, since the metal foam is embedded in the wake region of the heat exchanger or channels’ divergent sections, its effect on pumping power is subtle, which is an advantage of using the porous medium at these regions.
In this study, a new design for energy recovery from the return air has been introduced to improve the air handling unit (AHU) performance through the energetic analysis. The main objective is ...defined as the reduction in cooling and heating coils energy demand. In the novel AHU, the coldness from the exhaust air is transferred to the fresh air through the primary heat exchanger to reduce the cooling coil energy usage, while in the secondary heat exchanger, the warmness from the return air is recovered to the outlet cold air of the cooling coil to reduce the heating coil energy usage. Results showed that using air-to-air heat exchanger in hot and dry climate regions, the total energy consumption decreased up to 26.38%, which in turn increased the first law efficiency up to 35.84%, while in hot and humid climate these figures are 13.11% and 10.57%, respectively. It is concluded that the effect of using the air-to-air heat exchangers in hot and dry climate has priority over the hot and humid one.
Nanoparticles (NPs) are known as important nanomaterials for a broad range of commercial and research applications owing to their physical characteristics and properties. Currently, the demand for ...NPs for use in enhanced oil recovery (EOR) is very high. The use of NPs can drastically benefit EOR by changing the wettability of the rock, improving the mobility of the oil drop and decreasing the interfacial tension (IFT) between oil/water. This paper focuses on a review of the application of NPs in the flooding process, the effect of NPs on wettability and the IFT. The study also presents a review of several investigations about the most common NPs, their physical and mechanical properties and benefits in EOR.
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