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In the present study, the application of six engine oil-based Nano fluids (NFs) in a solar concentrating photovoltaic thermal (CPVT) collector is investigated. The calculations were performed for different values of nanoparticle volume concentration, receiver tube diameter, concentrator surface area, receiver length, receiver actual to the maximum number of channels ratio, beam radiation, and a constant volumetric flow rate. Besides, two novel soft computing paradigms namely, the cascaded forward neural network (CFNN) and Multi-gene genetic programming (MGGP) were adopted to predict the first law efficiency (η I) and second law efficiency (η I I ) of the system based on the influential parameters, as the input features. It was found that the increase of nanoparticle concentration leads to an increase in η I and a decrease in η I I . Moreover, the rise of both the concentrator surface area (from 5 m2 to 20 m2) and beam irradiance (from 150 W/m2 to 1000 W/m2) entails an increase in both the η I (by 39% and 261%) and η I I (by 55% and 438%). Furthermore, it was reported that the pattern of changes in both η I and η I I with serpentine tube diameter, receiver plate length, and absorber tube length is increasing-decreasing. The results of modeling demonstrated that the CFNN had superior performance than the MGGP model. • Six engine oil based Nanofluids were examined as the coolant. • Two soft computing paradigms used to predict the first and second law efficiencies. • CuO-engine oil Nanofluid provides highest useful thermal energy. • MWCNT-engine oil Nanofluid has the highest first and second law efficiencies. • The highest and lowest electrical performances belong to CuO and SiO2, respectively. [ABSTRACT FROM AUTHOR]

The work focuses on an experimental evaluation of the changes of thermal conductivity (TC) of ethylene glycol-based nanofluid containing SiO2 nanoadditives against volume concentration of nanoadditives (φ) and temperature. The experiments are carried out in the φ range of 0–2.5% and temperature range of 30–55 °C. The dynamic light scattering method is used to obtain the particle size distribution, while the transmission electron microscopy technique is utilized to visualize agglomerated particles in the prepared nanofluid samples. The outcomes revealed that the TC of the nanofluid grows by boosting both the φ and temperature. The percentage enhancement varied in the range of 0.72–26.66%. Furthermore, the curve-fitting method was utilized to model the TC of the nanofluid using experimental data. It was found that the developed model is able to properly forecast the TC of nanofluid with the maximum percentage error of 1.75%. [ABSTRACT FROM AUTHOR]

• Energetic and exergetic performances of a nanofluid-based PVT unit are assessed. • The unit is equipped with a sheet-and-grooved serpentine tube collector. • Aqueous suspension of magnetite nanoparticles is considered as coolant. • Energetic and exergetic performance of the unit intensify with boosting φ and m ̇ nf . • The rise of groove pitch causes an increase in the performance of the PVT system. In this experimental investigation, an effort is executed to evaluate and compare the energetic and exergetic performances of three nanofluid-based photovoltaic/thermal (PVT) systems, namely a PVT system with a sheet-and-serpentine tube collector (case-I), a PVT system with a sheet-and-grooved serpentine tube type collector with a groove pitch of 8 mm (case-II), and a PVT system with a sheet-and-grooved serpentine tube type collector with a groove pitch of 5.4 mm (case-III). The water-Fe 3 O 4 nanofluid was considered as the working fluid. The influences of nanoadditive concentration (Ø) (0–1%) and flow rate (m f) of nanofluid (10–40 kg/h) on the performance features were then examined. It was found that at any given Ø , the overall energy, overall exergy, and electrical performances of the case-I, II, and II improved with an increase in nanofluid m f (10–40 kg/h) and vice versa. Thus, the case-III yielded 15% and 6% better overall energy efficiency, 4.6% and 2.3% better overall exergy efficiency, and 3.3% and 1.9% better electrical energy efficiency than the case-I and II at a Ø and nanofluid m f of 1.0% and 40 kg/h. The maximum electrical energy of case-I, II, and III is 9.5%, 11%, and 13.1% higher than those achieved by the PV panel in absence of cooling. The findings obtained from this study can be used to design photovoltaic systems with significant energetic and exergetic performance. [ABSTRACT FROM AUTHOR]

This experimental study aims to energetically and exergetically compare the performance of a PVT system with sheet-and-plain serpentine tube collector (base PVT system) with two cases of modified PVT systems. The modified PVT systems are the replacements of plain serpentine tube with rifled serpentine tube with 3 ribs (3-start rifled PVT system) and 6 ribs (6-start rifled PVT system). The electrical parameter of the PV module without cooling is compared with the three cases of the PVT system with cooling. The cooling fluid is water/magnetite nanofluid. The effect of nanofluid flow rates (20–80 kg/h) and nanoadditive volume concentrations (0–2%) over the three cases of the PVT system is investigated to propose a suitable combination of flow rate and NA concentration offering the best energetic and exergetic performances. Thus, the 6-start rifled PVT system achieved a maximum of 22.5% and 3.8% higher overall energy efficiency, and 5.9%, and 1.9% higher overall exergy efficiency than the base and 3-start rifled PVT systems at flow rate and concentration of 80 kg/h and 2%. Finally, the electrical power generated by the base, 3-start rifled, and 6-start rifled PVT systems achieved maximum enhancement of 27.5%, 29.5%, and 31.5% compared to the PV module without cooling. • Energetic and exergetic performances of a nanofluid-based PVT unit are assessed. • The unit is equipped with a sheet-and-rifled serpentine tube collector. • Aqueous suspension of magnetite nanoparticles is considered as coolant. • Energetic and exergetic performances of the unit intensify with boosting ϕ and m ˙ n f . • Overall energy and exergy efficiencies of rifled PVT unit is better than base unit. [ABSTRACT FROM AUTHOR]

In the present work, the entropy production of Al 2 O 3 -water nanofluid in an oblique cavity enclosure is examined. The side edges of the enclosure are at lower temperature and the top and down ones are insulated. Two thick conductive walls are placed on the low temperature edges. Furthermore, the center of the enclosure is equipped with a constant high temperature heat source. The enclosure is exposed to an inclined magnetic field. The governing nonlinear partial differential equations are continuity, Navier–Stokes and energy equations. These equations are solved using an open-source CFD software package (OpenFOAM). The influence of effective parameters includes Ra number, Hartman number, the angles of magnetic field and enclosure, nanoadditives concentration, and aspect ratio on the entropy production and the Bejan (Be) number are investigated. The results show that the minimum entropy production happened at low power magnetic fields. With the increase of the slope of the cavity, the entropy production rises. The addition of nanoadditives leads to an intensification in the entropy production and a reduction in the Be number. [ABSTRACT FROM AUTHOR]

The aim of the present experimental investigation is to study the impact of duration of various stages of nanofluid preparation on its thermal conductivity. The considered nanofluid is the Al 2 O 3 /liquid paraffin. Oleic acid is used to ensure proper stability of prepared nanofluid samples. The nanofluid is prepared using a two-step method. The influences of duration of magnetic stirring and the sonication time on the thermal conductivity of nanofluid at different nanoadditive concentrations and temperatures are evaluated. It was found that the optimal sonication time is 3 h and 15min, and a further intensification in this time breaks the bond between the nanoadditives and the surfactant, resulting in a less thermal conductivity. Moreover, the outcomes indicated that the proper duration for magnetic stirring in the first and second stages are 20 and 40min, respectively. Unlabelled Image • Preparing the alumina-liquid paraffin nanofluid by two-step method. • Examining influence of sonication time on the thermal conductivity of nanofluid. • Evaluating impact of stirring time on the thermal conductivity of nanofluid. • Suspension of Al 2 O 3 -liquid paraffin is considered as nanofluid. • The optimal duration for sonication is 3 h and 15 min. [ABSTRACT FROM AUTHOR]

• MHD natural-convective heat transfer of aluminum/water nano-fluid between two blades of a heat sink. • Irreversibility generation augments and the Bejan number reduces by augmenting the Rayleigh number. • The heat transfer enhanced up to 16% by doubling of the aspect ratio of the pipes. • As the distance between constant-temperature pipes intensified, Nusselt number enhances. • When cavity became vertical, the heat transfer and total irreversibility decreased by 22% and 21%. In the present study, natural-convective heat transfer along with the effects of radiation of aluminum/water nano-fluid between two blades of a heat sink, which is under the impact of a uniform magnetic-field, is studied numerically. The space between two blades of the heat sink is considered as a two-dimensional square enclosure. In the square cavity, there are four pipes with constant temperature T h with a circular cross section. The RSM method is used to optimize the geometric parameters of the pipes. The results show that the heat transfer rate from the pipes and the irreversibility generation augment and the Bejan number reduces by augmenting the Rayleigh number. The heat transfer intensified 7% and 16% by doubling of the aspect ratio of the pipes at the Rayleigh number of 103 and 106, respectively. As the distance between constant-temperature pipes intensified, Nusselt number augments. As the horizontal enclosure rotates 90°, i.e., it becomes a vertical enclosure, the heat transfer decreases by 22% and total irreversibility decreases by 21%. The optimum physical conditions of the pipes are is in the diameter of 0.15 and 0.25 of distance from each other to have maximum heat transfer and the minimum irreversibility generation. [ABSTRACT FROM AUTHOR]

A new optimization/statistical approach of "Robust Weighted Least Squares Support Vector Regression" algorithm (RWLS-SVR) is provided for the first time. The experimental achieved amounts of the thermal conductivity for a new hybrid nanofluid of water/Graphene Oxide–Silicon Carbide, are examined at different values of temperature and nanoparticles volume fraction. A Support Vector Regression is a supervised learning regression algorithm based on the Support Vector Machine methodology. However in the Least Squares Support Vector Machine method, the inequality constraints are converted to equality constraints and the sum squared error function is employed. Moreover a LS-SVR is applied to the problem in order to calculate the error variables. Afterwards, the weights computed based on the error variables are applied to the optimization problem in order to reduce the effects of outliers on the final results. As a result, the WLS-SVR method does not significantly increase the computational burden, but it provides sparseness and robustness. • Providing new optimization/statistical approach of RWLS-SVR algorithm. • Estimate thermal conductivity of water/Graphene Oxide-Silicon Carbide nanofluid. • A LS-SVR is applied to the problem in order to calculate the error variables. • WLS-SVR method provides sparseness and robustness. [ABSTRACT FROM AUTHOR]

• Application of solar thermal collectors. • Utilizing nanofluids and phase change materials for improving performance of STCs. • The influences of nanofluids and PCMs on the performance of STCs are examined. • Energy, exergy, economic, and environmental considerations are evaluated. Solar energy is broadly utilized in various applications, including solar thermal collectors (STCs), heating, desalination, etc. The SCs are employed to convert solar energy into thermal one. Utilizing nanofluids (NFs) and phase change materials (PCMs) can improve the performance of STCs by enhancing the rate of heat transfer. The present review paper describes NFs and PCMs, explains STCs, and provides different advances in these subjects. The influences of NFs and PCMs on the performance of STCs are examined. In addition, energy, exergy, economic, and environmental considerations are evaluated, and finally, current challenges and future directions are discussed. It was observed that the use of NF and PCM leads to a significant improvement of the energy and exergy functions of STCs. Also, Also, it was found that a limited number of studies have been done on the performance of NF-based STCs from an economic and environmental point of views, and all of them have reported the positive effect of NFs on the performance of these systems. Moreover, it was revealed that the employment of NFs in the STCs depends on their long-term stability and preparation costs. Therefore, more laboratory investigations are required to characterize thermophysical properties of NFs. [ABSTRACT FROM AUTHOR]

• Effect of mechanical vibration on the ferrofluid flow in a rifled tube is examined. • Flow of ferrofluid is studied in the presence of two rotating magnetic fields. • Effect of vibration acceleration and magnetic field configuration is assessed. • Using vibration and magnetic field boosts the cooling performance of ferrofluid. • The PEC parameter increases with boosting vibration acceleration. Vibration can enhance the hydrothermal performance by disturbing the thermal boundary layer. Also, the magnetic field increases the ferrofluid mixing, thereby enhancing the heat transfer rate. In this study, an experimental analysis of ferrofluid flow inside a rifled tube under the vibration and rotational magnetic field (RMF) effects was conducted by considering different Reynolds numbers (Re), nanoparticle concentrations (φ), and rifled tube pitches (P). In the first stage, the effect of Re and φ on the hydrothermal performance of the system in the absence of the vibration and RMF was explored. In the second stage, the effect of vibration on the performance evaluation criterion (PEC) of the system was investigated. Finally, the RMF effect was considered. Based on the results, the system with P = 5 mm showed the highest PEC in all experiments. The highest PEC without the vibration and RMF effects was obtained as 1.62 for P = 5 mm and φ = 0% at Re = 2000. The highest PEC under the vibration effect (1.28) was also found for Re = 2000 but at φ of 2%, when the highest vibration acceleration (5 m/s2) was applied. Among the RMFs examined, the RMF with the counter clock-wise along with the counter clock-wise fluid flow inside the rifled tube resulted in the highest PEC of 1.62. RMF improved the PEC of the system from 1.28 to 1.62, corresponding to a 21.32% increase, under the vibration. [ABSTRACT FROM AUTHOR]

A hybrid solar photovoltaic-thermal collector is the combination of a solar thermal unit and a photovoltaic panel for the simultaneous generation of heat and electricity. In these systems, a fluid is used to cool photovoltaic panels and, thus, prevent their reduction of electrical efficiency. The hot fluid leaving the system can also be used in various kinds of engineering applications, from agriculture to heating, ventilation and air conditioning units, and process heat in utilities. Coolants used in photovoltaic-thermal units include air, water and nanofluids, among which air is less efficient than water and nanofluids due to its low specific heat capacity. Although extensive research has been done on the exergy performance of photovoltaic-thermal units, the number of published review articles in this field is very limited. This paper presents a critical review with some recommendations for future research on the topic of exergy examination of water-based and nanofluid-based photovoltaic-thermal units. As a first step, the concept and mathematical exergy relations are introduced. Then, water-based and nanofluid-based photovoltaic-thermal units are exergetically discussed in detail, followed by the description of novel units. At the end of each section, some suggestions are presented for future exergy examination of those types of photovoltaic-thermal units. • Exergetic performance of liquid-based PV/T systems are critically reviewed. • Exergy efficiency of nanofluid-based PV/T unit is higher than the water-based unit. • Unglazed PV/T unit has a higher exergy output than the glazed unit. • Exergetic output of a PV/T unit is higher than a separate PV and thermal unit. [ABSTRACT FROM AUTHOR]

• Effect of nanoparticle shape on entropy generation in a heat sink is examined. • Simulations are conducted for both laminar and turbulent flow. • Spherical particles have the most insignificant impact on entropy generation. • Thermal entropy generation is reduced up to 43% by using platelet shaped particles. • Platelet nanoparticles increase frictional entropy generation up to 6.32 folds. Entropy generation characteristics of different nanoparticle shapes are explored considering a nanofluid-cooled helical heat sink system for both laminar and turbulent flow regimes. For each flow regime, four different Reynolds numbers are considered, ranging from Re =500 to 20,000. Five different particle shapes (spherical, bricks, blades, cylindrical and platelets) are included for this comparative study, and their thermal, frictional, and total entropy generation characteristics are evaluated for four different nanoparticle volume concentrations (ϕ =0.5, 1.0, 1.5, and 2.0%), and the outcomes are compared to the base fluid case (ϕ =0%) as well as a comparison is considered among the investigated nanoparticles. Obtained results revealed that in the turbulent flow regime, the thermal entropy generation tends to decrease with increasing particle volume fraction, and the highest decrements are obtained for platelet shape (43%). The frictional entropy generation shows an opposite trend, and the platelet nanoparticles yield the highest increment, around 6.32 folds in both laminar and turbulent flow. In both flow regimes, the spherical particles have the smallest impact on the entropy generation among the examined ones. In addition to that, increment in Re results in a decrement in the thermal entropy generation, while it causes a remarkable increase in the frictional entropy generation. [Display omitted] [ABSTRACT FROM AUTHOR]

The intent of the present investigation is to conduct; experimentally, the effects of nanofluid of water/magnetite and flow channel arrangement on photovoltaic thermal (PVT) systems. Three different configurations of the collector in PVT were researched in various nanofluid's flow rate of M ˙ = 20.0 − 80.0 (k g / h r) , and nano concentration of φ = 0.0 − 2.0 %. The studied arrangements of flow channels in the collector are a sheet-and-plain serpentine tube (PVT-0S), a sheet-and-finned serpentine tube with four fins (PVT-4S) and a sheet-and-finned serpentine tube with eight fins (PVT-8S). The electrical efficiency is compared between the cited three cases and the PV panel without cooling system. The maximum energetic, exergetic and electrical performances were found at the flow rate of M ˙ = 80 (k g / h r) and nano concentration of φ = 2.0 %. It was observed that the PVT-8S system provides the most efficient configuration since the overall energy efficiency (η) in the PVT-8S system are 5.87 % , and 15.59 % higher than the PVT-4S, and PVT-0S systems. Further, the PVT-8S system demonstrated the maximum value of exergy efficiency (Γ = 14.51 %) compared to other studied systems. It was also shown that the electrical efficiency (Λ) augments significantly with the adding the cooling systems to the PV panel. The increase in the electrical efficiency was 12.06 % , 10.87 % , and 8.40 % for the PVT-8S, PVT-4S, and PVT-0S systems; respectively. • The maximum energetic performance is obtained at the flow rate, and volume fraction of 80 (kg/hr) and 2.0%. • The highest overall energy and exergy efficiencies were achieved for the PVT-8S system. • PVT-8S, PVT-4S, and PVT-0S have 12.06%, 10.87%, and 8.40% higher electrical efficiency than PV panel. [ABSTRACT FROM AUTHOR]

In this study, an experimental assessment is presented on the effects of employing serpentine tubes with three different cross-sections of circular, triangular, and rectangular, on the characteristics of a photovoltaic/thermal (PV/T) unit in terms of energy and exergy efficiencies compared with a conventional PV system. The influences of adding magnetite nanoparticle to the base-fluid and employing a higher mass flow rate of the cooling fluid are examined. The results demonstrated that by comparing PV and PV/T units with a circular serpentine tube, the electrical efficiency improves by almost 12% due to adding coolant tube in addition of getting 22.6W extra thermal energy power. Furthermore, by changing the cooling tube configuration from conventional circular form to rectangular, electrical efficiency eases by 2% to reducing PV module temperature. Moreover, it was found that by adding nanoparticle to pure water to employ nanofluid as coolant fluid, overall energy and exergy efficiencies enhance by 6.6% and 0.7%, respectively, using nanoparticles with a volume concentration of 2% for the case of the rectangular serpentine tube for the flow rate of 20 kg/h. Furthermore, enhancing the mass flow rate has a positive trend on the PV/T performance in terms of both energy and exergy efficiencies. Image 1 [ABSTRACT FROM AUTHOR]

In the current study, the two-phase mixture model is employed to assess the influences of nanoparticle shape on the hydrothermal aspects and entropy production of turbulent forced convection of MoS 2 /water nanofluid (NF) flow through a flat plate solar collector. The considered nanoparticle shapes include blade, brick, platelet and cylinder. The studied performance features include the heat transfer, outlet fluid temperature, pressure loss, friction factor, performance evaluation criterion (PEC) and entropy production. In addition, the effect of volume fraction of nanoparticles (ϕ) on the above-mentioned parameters is evaluated at two different NF mass flow rates (ṁ). According to the results, the maximum PEC corresponds to the case of ϕ = 3%, ṁ = 0.5 kg/s and brick-shaped nanoparticles, while the minimum entropy production corresponds to the case of φ = 4%, ṁ = 0.5 kg/s and blade-shaped ones. [ABSTRACT FROM AUTHOR]

This study aims at experimentally investigating the influence of magnetic field on the rheological behavior of water–carbon nanotube (CNT)/magnetite (Fe 3 O 4) nanofluid. Tetramethylammonium hydroxide (TMAH) and Gum arabic (GA) are respectively used to stabilize the nanofluid. Scanning Electron Microscope (SEM), Dynamic Light Scattering (DLS) and X-ray Diffraction (XRD) methods were used to characterize the prepared nanofluid samples. Experiments were performed to evaluate the viscosity of water–CNT/magnetite nanofluid in the shear rate range of 1–100 s−1, volume fraction range of 0.5-1.5%, and magnetic field strength range of 0–480 mT. It was found that the presence of an external magnetic field causes an increase in the viscosity of the water–CNT/magnetite nanofluid. In addition, the results depicted that the viscosity of the nanofluid augments by boosting the concentration of the nano-materials. Moreover, it was reported that increasing the magnetic field strength to more than 360 mT has a negligible influence on the augmentation of nanofluid viscosity. Furthermore, the non-Newtonian shear thinning behavior was depicted because of the decrease in viscosity with intensifying the shear rates. • Experimental study of rheological behavior of Water–Carbon-nanotube/magnetic particles. • Presence and absence of magnetic field. • MCR300 rheometer is used to measure viscosity and the magnetic field system up to 480 G. • Diagrams of dynamic viscosity versus shear rate are obtained based on different volume fractions and applied magnetic fields. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the entropy generation and natural convection of water- Al2O3 nanofluid in an inclined cavity which consists of two connected inclined triangular enclosures under a horizontal magnetic field. The horizontal diameter of the cavity is small in thickness and has the temperature Tc. Half of the bottom wall and also the right wall are at the temperature Th. The rest of the walls are adiabatic. The governing equations of the nanofluid flow are algebrized and solved using the FVFEM method. The effective parameters are 103

In this study, the rheological behavior of ethylene glycol (EG)-graphene nanosheet nanofluid is examined experimentally. The impacts of mass concentration of nanoparticles (0–5%), temperature (5–65 ° C) and shear rate (0–90 1 s) on the dynamic viscosity of EG-graphene nanofluid are examined. The obtained results showed that incorporating graphene nanoparticles into EG causes fluid behavior to change from Newtonian to power-law non-Newtonian. In addition, it was found that the dynamic viscosity of EG-graphene nanofluid augments by boosting nanoparticle concentration and decreasing temperature. Moreover, the regression technique is utilized to develop predictive correlations of consistency-index and power-law index of the power-law model. The results demonstrated that the R-squared value for the obtained correlations for consistency index and power-law index are 0.925and 0.982, respectively. Unlabelled Image • Rheological behaviour of EG-graphene nanofluid is evaluated experimentally. • Effects of nanoparticle concentration and temperature on the results are assessed. • Correlations are developed to predict the consistency index and power-law index. • The EG-graphene nanofluid follows the Newtonian and non-Newtonian behaviour. • R2 for the obtained correlations for m and n are respectively 0.925 and 0.982. [ABSTRACT FROM AUTHOR]

• Simulation of nanofluid in a heat exchanger equipped with twisted tape using a two-phase mixture model. • Studying effect of nanofluid and twisted tape on the thermal performance of heat exchanger. • Evaluating effect of material type of twisted tape on heat transfer and pressure drop in the heat exchanger. • The use of twisted tape improved the Nusselt number up to 22%. • Alumina nanoparticles increased heat transfer and pressure drop up to 30% and 40%, respectively. The present study dealt with the numerical simulation of nanofluid flow in a double tube heat exchanger equipped with twisted tape. Alumina/water nanofluid and pure water are considered to be working fluids. A two-phase mixture model was employed for nanofluid flow simulation. The effect of nanofluid and twisted tape on the hydrodynamic and thermal performance of the heat exchanger was studied. Next, the focus was placed on the effect of the surface roughness (material type) of twisted tape on heat transfer and pressure drop in the heat exchanger. The results are presented as the temperature distribution, velocity field, Nusselt number, and pressure drop for various Reynolds numbers, nanofluid concentrations, pitch ratios, and tape insert materials. The results revealed that the use of twisted tape improved the Nusselt number up to 22%; also, adding alumina particles to water augmented heat transfer up to 30% and increased pressure drop up to 40%. Tapes with more roughness provided heat transfer enhancement of up to 16%, whereas the friction factor increased up to 21%. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• The naturally cooled baffled U-shaped cavity is examined under the magnetic field. • The power-law non-Newtonian water-Fe 3 O 4 nanofluid is considered as coolant. • The average Nu rises with boosting aspect ratio and nanoparticle volume fraction. • The impact of n and Ra on average Nu is significant only for Ra =106. • The effect of Ha and n on average Nu is considerable only for the cases where Ha <30. This numerical work examines the impact of an external magnetic field on the hydrothermal aspects of natural convection of a power-law non-Newtonian nanofluid inside a baffled U-shape enclosure. The enclosure is heated from the bottom and cooled from the baffles while the other walls are thermally insulated. Sinusoidal profile is chosen to describe the temperature distribution along the bottom wall. A comprehensive analysis is conducted to study the influence of pertinent parameters including Rayleigh number (Ra), Hartmann number (Ha), nanoparticle volume fraction (ϕ), aspect ratio of cold baffles (AR), inclination angle, and power-law index (n) on the flow and heat transfer characteristics in detail by using Galerkin finite element method. The obtained results show that the impact of n on the Nusselt number (Nu) is considerable for Ra =106 and inappreciable below this value. The influence of n and Ha on the heat transfer is significant when Ha is smaller than 30. For Ha <30, there is a threshold value of nanoparticle after which the rise of n augments heat transfer, which is 5% for AR =0.4 and 7% for AR =0.6. The analysis of heat transfer and fluid flow in open cavities is important because of the diverse applications in thermal engineering. In this work, magnetic field, non-Newtonian power-law nanofluid, and sinusoidal heat flux are used to improve the performance of a naturally cooled U-shape cavity. It was found that the cooling performance of cavity augments with the rise of aspect ratio, nanoparticle volume fraction, Rayleigh number, while it reduces with boosting Hartmann number. Finally, it was revealed that the best cooling performance of cavity occurs at Ra =106, Ha= 0, ϕ =5% and AR =0.6 Image, graphical abstract [ABSTRACT FROM AUTHOR]