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In the present numerical simulation, laminar single‐phase and two‐phase nanofluid flows are investigated inside a rectangular microchannel with the vortex generators. Rhombic vortex generators with different attack angles are used for a better mixture of fluid. Water/MgO nanofluid is used as the working fluid in the volume fractions of nanoparticles φ = 0‐4% in Reynolds numbers of Re = 1‐300 at the two‐dimensional space. The presence of vortex generators with attack angles of λ = 0‐45°, and simultaneous investigation of heat transfer and flow hydrodynamic parameters distinguish this research from other similar studies. Obtained results revealed that using nanofluid with higher volume fractions, slip boundary condition on the hot wall, and using vortex generator with higher λ lead to significant enhancement of heat transfer. Also, the value of pressure drop augmentation is caused by the increase of φ and λ is significant at higher Reynolds numbers. Unlike the increase of φ, by increasing Reynolds number, the effect of slip boundary condition becomes considerable on the reduction of entropy generation. The behavior of entropy generation graphs with slip velocity boundary condition on the wall is different from the no‐slip boundary condition at Re = 300. The behavior of average entropy generation is different in the various φ, Reynolds numbers, and λ in the no‐slip boundary condition for single‐phase and two‐phase models. Also, the two‐phase model estimates flow behavior with less irreversibility. [ABSTRACT FROM AUTHOR]

In this study, a numerical investigation of fluid flow and heat transfer of Al2O3‐water nanofluids in a pillow plate heat exchanger with a two‐phase model is investigated. The flow regime studied in this study is in the laminar flow regime such that the Reynolds numbers are 250, 500, 750, and 1000 and the volume fraction of the nanoparticles remained so that the fluid stayed in Newtonian. The volume fraction of nanoparticles is ϕ=$\phi = $ 0, 1, 2, and 3 %. In this study, the effect of the shape of the welding points used in the pillow plate has also been investigated in such a way that three modes of circular welding point, large‐diameter elliptic welding point along with the flow and large‐diameter elliptic welding point perpendicular to the stream have been investigated. Numerical simulation results show that using nanofluid and increasing Reynolds number improves heat transfer, as well as circular welding point, shows the best heat transfer rate. The shape of the welding points has a direct relationship with the pressure drop and heat transfer, as well as the wake created behind the welding points, which have the highest wake and pressure drop respectively for the elliptic welding points perpendicular to the flow, circular and elliptical parallel to the flow. On the other hand, the addition of nanoparticles increases the friction factor and, on the contrary, increases the Reynolds number, which reduces the friction factor. Finally, the highest Reynolds number, the highest volume fraction of nanoparticles, and the circular welding point state show the highest PEC. [ABSTRACT FROM AUTHOR]

In the present research, heat transfer behavior and Ag/water two-phase laminar nanofluid flow as cooling fluid in volume fraction of nanoparticles 0–6 % and Reynolds numbers of 200–500 in a tube with curvature angle of 270° are simulated utilizing finite volume method. 3-D simulations of laminar mixed convection two-phase nanofluid flow considering Grashof numbers of 5,000, 50,000 and 100,000 are carried out numerically. The results of the present research indicate that adding solid nanoparticles causes periodic behavior with particular repeat length on the axial velocity profile and maximum and minimum values shift every 60°. Also, after the curvature angle of 30° because of fluid motion, centrifugal forces importance, fluid rotation, and hydrodynamic field, local friction factor increases considerably up to channel outlet. In all diagrams, the maximum friction factor is related to the Grashof number of 100,000, this value will have more significant augmentation by the increase of volume fraction. Due to better fluid mixing and increase of temperature line slop at Reynolds number of 500, heat transfer enhances at the regions of the bottom bend of the channel. Higher volume fractions of nanoparticles reinforce the heat transfer mechanism and heat absorption from the hot surface. In the regions where fluid is influenced by thermal boundary layer growth, entropy generation is augmented. This entropy generation is due to heat transfer. On the other hand, entropy generation is reduced in the regions where the effect of inlet fluid temperature is dominated. [ABSTRACT FROM AUTHOR]

With recent technological advances in nanotechnology, solid particles in nanometer dimensions are being produced. Researchers have created a new nanofluid (NF) fluid with excellent thermal properties using these nanoparticles (NPs). This study examines the influence of the CuO NPs' length on the atomic conduct and phase transition duration of water-based fluid in a nanochannel with Cu walls using molecular dynamics simulation (MDS). The outcomes show that the phase transition duration decreases by adding CuO NP in the simulated base fluid (BF). Numerically, the phase transition duration decreased from 6.78 ns to 6.01 ns by adding CuO NPs with a 1.5 nm length. As the length of CuO NPs enhances from 1.5 to 5 nm, the phase transition duration decrease to 4.33 ns. Also, increasing the length of NPs to 5 nm leads to a decrease in the total energy (TE) from −44924.5 to −64214.3 eV. Finally, it was found that the highest density of BF/NF was detected in final and initial bins with 0.0187/0.01944 atom/Å3 values. Also, the maximum velocity and temperature (T) of BF/NF were detected in middle-bins with 0.0011/0.0021 Å/fs and 688.25/753.69 K values. This atomic evolution shows that the CuO NPs have appropriate performance in the phase transition procedure. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulation of graphe nanoplatelet (GNP) – sodium dodecylbenzene sulfonate (SDBS) – water nanofluid with volumetric mass fractions of ϕ equal to 0–0.1%. The new microchannel is made of 2 layers and has sinusoidal cavities along with the heat sink. The study was conducted for Re = 50, 300, 700 and 1000 (laminar flow). Based on the results, higher Re leads to more convective heat transfer coefficient. Therefore, the value of temperature gradients decreases and on the other hand the effect of cooling fluid temperature in warm areas near solid wall becomes important. Using a higher value of Re results in the penetration of heat in the fluid layer decreases which in general will reduce the temperature of the outlet section in larger Re values. Also, larger Re value results in larger development length which is also a cause for lack of thermal development and dominance of the temperature of the coolant flow in the heat sink resulting in decreased outlet section temperature for higher Reynolds numbers. For Re = 50 and 300 because of lower fluid velocity, the effect of surface geometry factors such as sinusoidal paths or hollow parts (cavities) has a smaller influence on the pressure loss or friction factor of the flow. [ABSTRACT FROM AUTHOR]

In this investigation, fluid flow and heat transfer of the nanofluid in a tube with helical ribs are surveyed at a different volume fraction of nanoparticles ϕ = 0%, 1%, 2%, and 3% and Eulerian–Eulerian two-phase approach (mixture model) is used for simulating the water/Al2O3 nanofluid. The fluid flow is laminar, and simulation is done at Re = 250, 500, 750, and 1000. Also, four different geometric cases, including a plain tube and a tube with one, two, and three helical ribs, are used in this research. The most important surveyed parameters are the Nusselt number and friction factor. The results revealed that as Reynolds number increases, heat transfer increases, and friction factor decreases. The relative increase in Nusselt number and the relative decrease in friction factor at Re = 1000 than Re = 250 were calculated, respectively, 82% and 72% at ϕ = 0% in the plain tube. Helical ribs enhance the Nusselt number and friction factor and relative increase in Nusselt number, and friction factor in the tube with three helical ribs than the plain tube was calculated, respectively, 40% and 86% at ϕ = 0% and Re = 250. Finally, using nanofluid causes to increase in heat transfer and friction factor, and the relative increase in Nusselt number at ϕ = 3% than ϕ = 0% was calculated 6% at Re = 250 in the plain tube. [ABSTRACT FROM AUTHOR]

In the present paper, nanofluid mixed convection is investigated in a square cavity with an adiabatic obstacle by using the Lattice Boltzmann method (LBM). This enclosure contains Fe–ethylene-glycol nanofluid and three constant temperature thermal sources at the left wall and bottom of the enclosure through a lateral wall. The fluid is incompressible, laminar, and Newtonian. The obtained results are presented in the constant Ra = 104 and a Pr = 0.71 for different Ri = 0.1, 1, and 10. The effects of the slope of the enclosure, volume fraction of nanoparticles φ , the location of adiabatic obstacles, and nanoparticle diameter in the fluid are investigated on the value of heat transfer. A change in the attack angle of the enclosure leads to changes in the movement distance for fluid between hot and cold sources and passing fluid through case E, which affects the flow pattern strongly. In each attack angle, on colliding with an obstacle, the fluid heat transfers between two sources, which leads to uniform heat transfer in the enclosure. By increasing the velocity of the lid, the Richardson number decreases leading to improvement of the convective heat transfer coefficient and Nusselt number enhancement. The results so obtained reveal that by augmenting φ value the effect of Richardson number reduction can augment Nusselt number and the amount of absorbed heat from the hot surface. Consequently, in each state where a better flow mixture and lower depreciation of fluid velocity components, due to the penetration of lid movement and buoyancy force, occurs higher heat transfer rate is accomplished. Furthermore, it is shown that when Ri = 0.1, the effect of cavity angle is more important but when Ri = 10, the effect of the position of obstacle is more visible. [ABSTRACT FROM AUTHOR]

In this study, the numerical simulation of heat transfer of Al2O3-water nanofluid in a pipe equipped with helically twisted tapes is investigated. The volume fraction of nanoparticles in this study is equal to 0, 1, 2, and 3%, and a two-phase mixture method has been used to simulate the nanofluids. The flow regime is laminar in the present study, and Reynolds numbers are Re = 250, 500, 750, and 1000. The helical twisted tapes are in three different types, single, double, and triple. The same heat flux 5000Wm-2 is applied to the walls. The simulation results showed that increasing the Re increases the Nusselt number and decreasing the friction factor. Nusselt number in case 1 and volume fraction of nanoparticles 0% for Re = 250, 500, 750 and 1000 are equal to 95.8, 57.11, 56.13 and 22.15, respectively. The average friction factor is equal to 0.18, 0.09, 0.07, and 0.05. The presence of helical twisted tapes increases the Nu ave . The friction factor due to secondary flows and increases the contact of the fluid and the solid surface, so that the Nusselt number in volume fraction of nanoparticles 0%, Re = 250 for case 1, case 2, case 3, and case 4 are 95.8, 46.10, 58.11, and 51.12, respectively, and the friction factor are 18.0, 29.0, 0.38 and 0.48, respectively. [ABSTRACT FROM AUTHOR]

In the present study, heat transfer in a lid-driven square cavity in the existence of four rotating cylinders having harmonic motion was investigated numerically for different parameters such as Richardson number (0.1 ≤ Ri ≤ 10), the volume fraction of the nanoparticles (0 ≤ ϕ ≤ 0.03) and Reynolds number (86.2 ≤ Re ≤ 862). The enclosure filled with water–Cu nanofluids. Seven different cases were studied to find the best position and diameter ratio of cylinders. The results of this study presented in term of contours, Nusselt number, velocity profile, PEC number, entropy generation. This study demonstrated that heat transfer affected by the inertial force, buoyancy force, and changing in thermophysical properties of the base-fluid. Also, we found that the combination of harmonic motion and decrease in space between walls and cylinders makes the heat transfer behavior and trend, unpredictable. Another outcome of this numerical study is the effect of adding nanoparticle to pure water. In general, increasing the concentration of nanoparticles in pure water improved the thermophysical properties of the fluid. However, in some cases, shear effects and buoyancy forces changed this improvement. [ABSTRACT FROM AUTHOR]

This study numerically investigates the heat and mass transfer characteristics of water—silver nanofluid flowing in a spiral heat exchanger (HX) using the two-phase mixture model. The hot side of the HX is pure water at the temperature of 343 K and Re = 500, while the cold side is nanofluid with volume fraction up to 5% at 305 K and Re number ranging from 500 to 2000. The cold and hot tubes are concentrically twisted 3.5, 5.5 and 7.5 turns in order to explore the heat transfer effectiveness of the heat exchanger as a function of the spiral turns. The results indicate that increasing the volume fraction of nanoparticles, Re number and the number of turns increases the overall heat transfer coefficient, heat rate absorbed by the cold fluid and pumping power of the HX noticeably. The above-mentioned factors also improve the temperature stability of the input fluid along with the heat exchanger. The effectiveness of the HX decreases by increasing the Re number, the volume fraction of nanoparticles and turning rounds due to the greater pressure drop of the coolant fluid. At a constant Re number, increasing the volume fraction and number of turns enhances the NTU parameter to a great extent. [ABSTRACT FROM AUTHOR]

Present work studies the effects of microchannel height and Reynolds number on the temperature distribution behavior, pressure drop, and Nusselt number of a non-Newtonian nanofluid. The nanofluid is an aqueous solution of carboxy-methyl cellulose with a 1 percent volume fraction of copper oxide (CuO) nanoparticle, which is flowed at four Reynolds numbers of 250, 500, 750 and 1000, respectively, inside a rectangular microchannel with different heights size. Three dimensions in the order of H = 1 mm, H = 1.5 mm, and H = 2 mm are used for the microchannel height. Generally, it is concluded that increment of channel height and Reynolds number reduce temperature, whereas they increase heat transfer rate and Nusselt number due to their role in reducing thermal and hydrodynamics boundary layers thickness and flow concentration within the microchannel. Moreover, this phenomenon increases collision between hot and cold fluids due to decreasing their interval layer thickness. Also, increasing Reynolds number amplifies the pressure drop along the microchannel as well as increasing microchannel height. Therefore, it is concluded that the maximum temperature value of 430 K and maximum pressure drop of 7000 Pa have belonged to the case of studies with minimum and maximum microchannel height, respectively. On the other side, the maximum value of temperature is related to the minimum Reynolds number of 250, whereas maximum pressure drop is related to the maximum Reynolds number of 1000. [ABSTRACT FROM AUTHOR]

In this work, the molecular dynamics method is implemented to study the time evolution of water/Fe3O4 nanofluid dynamics with constant and time-dependent magnetic fields. The nanochannel with four walls is simulated to carrier water base-fluid and spherical Fe3O4 nanoparticles in a nanochannel. Simulations reveal that the density, velocity, and temperature profiles of nanofluid inside copper nanochannel are increased by increasing the nanoparticle numbers. Our results show that the simulated nanofluids with magnetic forces agglomerate faster. Furthermore, the effects of nanoparticles' number on the aggregation process are examined. Also, when the magnetic fields are subjected to nanofluid atomic structure, this external parameter prevents the aggregation of Fe3O4 nanoparticles, and so the assembly rate decreases and needed longer time for this phenomenon to occur. Physically, our results show that the magnetic field with normal direction to the nanofluid flow affects to the simulation process. This external parameter avoids the movement of nanoparticles along the fluid flow direction, and aggregation of these nanostructures occurs at a long time. [ABSTRACT FROM AUTHOR]

Optimization of the cooling processes by fluids in many industries such as power generation, transportation, machining, and electronics is very important. Heat transfer equipment to achieve higher efficiency, need to downsizing of the equipment, and increase the heat transfer rate per unit of surface. The aim of this paper is to investigate the effect of MHD mixed convection flow of Cu-water nanofluid in a trapezoidal lid-driven cavity with different tilt angles in a range of 0° to 60°. The cavity consists of the non-uniformly heated bottom wall, insulated top wall, and isothermal sidewalls. The governing equations of the flow by using the finite volume method and the SIMPLE algorithm have been numerically solved. The studies for the wide range of Richardson number (Ri) from 0.01 to 10, volume fraction of nanoparticles from 0.1% to 4% and Hartman number (Ha) from 0 to 40 in the steady-state have been done. Result in the form of streamline, vorticity and temperature contours for three geometry, local Nusselt number graphs for non-uniformly heated bottom surface and velocity profile on the vertical centerline of the cavity in different geometry have been investigated. The results show that the average Nusselt number on the non-uniformly heated bottom wall is dependent on dimensionless parameters and tilt angles. Also, applying a magnetic field, reduce the velocity profile changes, and using nanoparticles will cause increasing the Nusselt number. [ABSTRACT FROM AUTHOR]

In present numerical study, water/NDG (nitrogen-doped graphene) nanofluid flow in different arrangements of rhombic tube banks is investigated in a two-dimensional space. Water/NDG nanofluid is considered in mass fractions of 0, 1, 2, 4 and 6% and Re numbers of 10, 100 and 450 as cooling fluid. The arrangements of tube banks are considered as ET (equilateral triangle), RS (rotated square) and ES (equal spacing) arrangements. Results revealed that the enhancement of mass fraction causes heat transfer enhancement which is due to the increase in thermal conductivity coefficient of cooling nanofluid compared to base fluid. The increase in Re causes the enhancement of average Nu which is due to better mixture of fluid layers with the enhancement of fluid velocity in higher Re which causes the reduction in temperature gradients among fluid layers away from tubes and homogeneous temperature distribution in these areas. Among investigated arrangements, RS has the highest Nu. Also, ET arrangement, compared to ES arrangement, has higher Nu. In all of the studied arrangements, the increase in Re causes the reduction in friction factor and the maximum values of friction factor are related to RS and ET arrangements, respectively. [ABSTRACT FROM AUTHOR]

In the current study, turbulent flow and heat transfer in a three-dimensional channel is simulated numerically. The main purpose of this study is investigating the effect of using dimpled fin and CuO nanoparticles on the heat transfer enhancement and the improvement in cooling performance in a channel under the heat flux (100 kW m−2). Pure water flow is simulated at Reynolds numbers of 5000, 10,000, 15,000 and 20,000 with nanoparticles volume fractions 2 and 4%, and the effect of dimpled fins is investigated. To ensure the accuracy of the numerical solving procedure, the obtained results are compared with other experimental results and acceptable coincidence is observed. The results show that dimpled fins cause the improvement in heat transfer and using nanoparticles inside a dimpled fin causes better cooling performance than using pure water flow in a smooth channel. According to the obtained results at lower Reynolds numbers, the dimpled fin has more efficient performance in heat transfer enhancement than higher Reynolds numbers. Hence, using dimpled fin at lower Reynolds numbers flow is recommended. [ABSTRACT FROM AUTHOR]

This paper presents the effects of a non-uniform magnetic field on the hydrodynamic and thermal behavior of ferrofluid flow in a wavy channel by 3D numerical simulation. The wavy surfaces at the top and bottom of the channel are heated by constant heat fluxes. Moreover, the sidewalls are adiabatic. In the wavy section, in the perpendicular direction of the main flow, the magnetic field that linearly varies along the direction of the main flow is applied. The mathematical model that is consistent with the principles of ferrohydrodynamics and magnetohydrodynamics is used for the problem formulation. The results indicate that the wavy wall enhances the heat transfer rate on the bottom of the channel in comparison with the plain wall, while it does not have any significant effect on the top wall where the natural convection is weak. Furthermore, it can be found that the influence of the magnetic field on the flow field and heat transfer in the channel with the wavy walls is greater than one for the channel with the plain walls. This is due to the elimination of the recirculation zones in the sinusoidal cavities of the wavy walls by applying the magnetic field. The rise of the magnetic gradient value from 0 to 1.5 × 105 increases the skin-friction factors on the top and bottom wavy walls by factors of 11 and 1.6, respectively. In addition, it changes the Nusselt number 40% and 300% for the bottom and top walls, respectively. [ABSTRACT FROM AUTHOR]

In the present study, turbulent flow and heat transfer inside a three-dimensional wavy microchannel with different wavelengths have been numerically simulated. The main purpose of this study is to investigate the effects of changing the wavelength of the sinusoidal microchannel and CuO nanoparticle concentration on flow and heat transfer properties. For this reason, flow is simulated at Reynolds numbers of 3000, 4500, 6000, and 7500 with volume fractions of 0, 1.5, and 3% in three different geometries and the effects of each parameter have been investigated. Validation of the results showed there is an excellent agreement between the presented results with the previous studies. The average Nusselt number, pressure loss ratio, performance evaluation criterion, and local Nusselt number have been presented. Moreover, the distribution of the static temperature contour has been presented. In the flow with lower Reynolds numbers, the Nusselt number is not changed significantly; however, in flow with Reynolds number of 7500, the Nusselt number is increased. The performance evaluation criterion has the highest value in nanofluid flow with the volume fraction of 3%, indicating the effects of heat transfer with pressure drop caused by nanoparticles, and from engineering and economic perspectives, using nanoparticles in the wavy microchannel is recommended. [ABSTRACT FROM AUTHOR]

In this paper, the hydrodynamics and heat transfer parameters of nanofluids are investigated using CFD analysis. Laminar convective heat transfer of alumina–water nanofluids with 0, 1%, and 2% volume fraction in a straight microtube heat sink under constant wall heat flux condition is studied. This work is performed in two parts. In the first part, the single-phase and two-phase approaches have been used for modeling heat transfer of pure water and alumina–water nanofluids in a straight microtube. The results of simulation are compared with the experimental data. The results showed that CFD predictions via a two-phase model show better agreement with the experimental measurements. For nanofluid with 1% concentration, the average relative error between the experimental data and CFD result based on a two-phase model is 5.85%, while for nanofluid with 2% concentration that is 2.54%. In the second part of this work, the effects of ribs through the microtube are investigated. The effect of the geometry on the Nusselt number and friction factor in the microtube is studied. We found that spiral pitch increment increases the thermal performance by an average of 19.8%. Finally, the best performance is obtained for the ribs height 1 mm and the pitch 1.5 mm. [ABSTRACT FROM AUTHOR]

In this paper, we studied heat transfer characteristics in the developing and the developed flow of nanofluid inside a tube with different entrances in the transition regime. A range of Reynolds numbers from Re = 500 to 13,000 was stimulated to examine flow characteristics in the tube. Effect of entrance, diameter of nanoparticles, nanoparticle type, Reynolds number and concentration of nanoparticles on onset of transition were studied. The results show that heat transfer coefficient and Nusselt number of base fluid and the nanofluid increase with increasing Reynolds number. Also, convective heat transfer coefficient of nanofluid increases by increasing Reynolds number, and the rate of increase in heat transfer coefficient varies depending on diameter, volume fraction and type of nanoparticles. Furthermore, the results show that local Nusselt number and local convective heat transfer coefficient slightly decrease with increasing particle diameter at constant volume fraction of nanoparticles. [ABSTRACT FROM AUTHOR]

Unfortunately, in the original publication of the article, the third author, Özgür Bayer, was included in the author group by mistake. The corrected author group is given in this correction article. The e-mail address of second corresponding author, Amin Asadi was incorrectly published. The corrected e-mail is given in this correction article. [ABSTRACT FROM AUTHOR]

Recent progress in nanoparticle construction can be seen as a breakthrough in increasing heat transfer methods. The small size of particles and low volume fraction of particles leads to solving agglomeration and pressure drop problems and reduce the cost of storing and transporting nanofluids. Molecular dynamics simulation is one of the essential branches of computational physics that can predict various structures' atomic behavior. In this study, the effects of external electrostatic force and external electrical field on the density, velocity, temperature of atomic structures, and agglomeration of Fe 3 O 4 nanoparticles in a copper microchannel are investigated. The results of the physical properties of this structure are estimated using molecular dynamics simulation and LAMMPS software. The results show that with increasing the applied external electrostatic force the maximum velocity is converged to 0.0071 Å /ps. Also, adding an external electrical field to the simulated nanofluid, the maximum values of density, velocity, and temperature are estimated to 1.32 g/cm3, 0.0078 Å /ps, and 345 K, respectively. The external electrical field has a significant and essential role in the agglomeration process in atomic structures. Finally, it is observed that by increasing the external electrical field, the time required for the agglomeration process increases to 2.26 ns. [ABSTRACT FROM AUTHOR]

In the computational study, the MD approach is used. MD simulations express that by adding Fe nanoparticles to base-fluid the highest rate of velocity/ temperature of base fluid 12%/37% increases. This atomic behavior has importance in industrial applications of nanofluids. Further, our simulations express that the temperature, velocity and density profiles of water/Fe nanofluid in Fe microchannel are enhanced by the radius of nanoparticles rising. Numerically, by nanoparticle radius enhancing from 10 Å to 20 Å, the maximum density of nanofluid rises from 0.033 to 0.048. Further, the highest rate of nanofluid particle velocity enhances from 0.038 Å /fs to 0.054 Å /fs. Through velocity enhancing, the temperature of simulated structures increases to 954 K, and phase transition occurring on the nanofluid structure. Physically, the size of simulated nanoparticle has an important effect on fluid flow and transition phase of this atomic structure. The time of transition in the simulation box varies from 0.5 ns to 0.38 ns. Hence, we underestand adding nanoparticle to base fluid improves the thermal manner of this structure. [ABSTRACT FROM AUTHOR]

In this study, the molecular dynamics method is used to study the atomic behavior of water and water/Fe nanofluid within a microchannel. In our simulations, the microchannel walls have atomic porosity with various values. The results show that the values of density, velocity, and temperature vary by inserting atomic porosity into the microchannel. Numerically, by increasing the porosity value from 1% to 5%, the maximum densities of water and water/Fe nanofluid decrease to 0.03 atom/Å3 and 0.032 atom/Å3. Further, the maximum values of water and water/Fe nanofluid velocities converged to 0.038 and 0.053 Å/fs. The temperatures of water and water/Fe nanofluid are other parameters which reach to 535 K and 803 K by inserting the porosity into the microchannel walls. Physically, we conclude that the porosity value has an important effect on the fluid/nanofluid atomic and thermal behavior such as phase transition phenomena. Numerically, by inserting the atomic porosity into microchannel walls, the phase transition time in water/Fe nanofluid structure varies from 402,000-time steps to 282,000-time steps (Δt = 1 fs). So, the atomic porosity improves the thermal behavior of nanofluid. • Molecular dynamics method is used to study the atomic behavior of nanofluid within microchannel. • Microchannel walls have atomic porosity with various values. • Porosity value has an important effect on fluid/nanofluid atomic and thermal behavior. • By atomic porosity inserting to microchannel walls, the phase transition time in water/Fe nanofluid structure varies. [ABSTRACT FROM AUTHOR]

In this computational research, we study the electric field and microchannel type effects on H2O/Fe3O4 nanofluid dynamical manner. The dynamical characteristics of this atomic structure are calculated using molecular dynamics method and we reported physical parameters such as total temperature, total energy, radial distribution function, velocity, density and temperature profiles of H2O/Fe3O4 nanofluid with 2 spherical nanoparticles. Physically, inserting external electric field causes phase transition (boiling process) in H2O/Fe3O4 nanofluid in shorter simulation time. Further, our results show that magnitude of external electric field is a significant parameter in nanofluid dynamical manner in microchannels. By external electric field magnitude increasing, the highest rate of velocity, temperature and density of nanofluid enhance to 0.0071 Å·ps−1, 714 K and 0.038 atom·Å−3 rates, numerically. Further, by microchannel atomic type variation from Pt to Au one, the rate of temperature and velocity of nanofluids reach to maximum rate at Au microchannel. So we conclude that phase transition of nanofluid in Au microchannel occurs in shorter MD simulation time. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation of Water-Copper nanofluid flow in a three-dimensional nanochannel with different types of surface roughness geometry using Molecular dynamics simulation (MDS) is performed. NVT ensemble is used to keep the particle number, volume, and temperature constant in the simulated system. The results show that as the volume fraction of nanoparticles (φ) increases, an increase in the amplitude of the fluctuations was observed. Also, the maximum velocity decreases, but there is no particular change in the amount of slip velocity. Increasing external force as well as reducing the surface roughness somehow increases the mean velocity. • Numerical simulation of Water-Copper nanofluid flow in a three-dimensional Copper nanochannel • Different types of surface roughness geometry • Using molecular dynamics simulation • NVT ensemble is used to keep the particle number, volume, and temperature constant. • Increasing external force increases the mean velocity in the channel. [ABSTRACT FROM AUTHOR]

In this work, the computational method is implemented to study the atomic barrier effects on water/Fe 3 O 4 nanofluid manner in the presence external magnetic field. The Copper nanochannel by 3 atomic barriers is simulated to flow of water/Fe 3 O 4 nanofluids. Results show that the density, velocity, and temperature profiles of water/Fe 3 O 4 nanofluid inside Cu nanochannel changed by adding atomic barriers to the interior surface of the nanochannel. Furthermore, the effects of nanoparticle number variation on the dynamical manner of nanofluids calculated. From a numerical perspective, the aggregation time of Fe 3 O 4 nanoparticles in simulated systems varies from 1 ns to 0.75 ns by adding a magnetic field to simulated nanofluid. This mechanical manner arises from external force powering by adding constant and time-dependent magnetic field to the simulation box. Finally, we reported that the constant and time-dependent external magnetic field cause nanofluids agglomerates in a short time rather than magnetic field-free models. • Molecular dynamics simulation is implemented to study the atomic barrier effects on the nanofluid manner. • Flow of water /Fe3O4 nanofluids is investigated. • Effects of nanoparticles number on dynamical manner of nanofluids are calculated. • Constant and time-dependent external magnetic fields cause the nanofluids agglomerate in the short time. [ABSTRACT FROM AUTHOR]

In the present study, the flow and heat transfer of CuO-water nanofluid in different solid concentrations (1–4 vol%) in a tube have been simulated by using the single- and two-phase (mixture) models. The simulations have been conducted under the turbulent flow regime in different Reynolds numbers ranging from 3000 to 36,000. The effects of using CuO-water nanofluid on the Nusselt number, friction factor, and performance evaluation criterion have been investigated. It is found that employing the two-phase mixture model leads to having closer results in reality compared to the single-phase model. The results revealed that the maximum performance efficiency coefficient in the tube with one twisted tape is 2.18 (for the two-phase model, Re = 36,000 and φ = 4%), while for a tube with two twisted tapes under the same conditions, it is 2.04. Thus, the use of one twisted tape is more favorable from the thermal-fluid dynamics viewpoint. [ABSTRACT FROM AUTHOR]

The optimization of MgO-water nanofluids in order to reduce the cost and increase the heat transfer coefficient is investigated in this study. At first, the heat transfer coefficient is obtained at various values of solid volume fractions, diameters of nanoparticles, and Reynolds numbers based on empirical data. The cost amount is also determined in terms of solid volume fractions and diameters of nanoparticles. Then, the heat transfer coefficient function and the cost function are attained via RSM (Response Surface Method) and with a regression coefficient of over 0.997. The optimization is performed by the non-dominated sorting genetic algorithm which has a significant capability of achieving optimal response. Finally, the Pareto front, the optimal heat transfer coefficient, and their corresponding minimum cost have been obtained. An appropriate correlation is also provided to achieve the optimal model of the minimum cost in terms of the maximum heat transfer coefficient. Optimization results have shown that, compared to the first optimization, the cost has decreased about 38% in the best case. [ABSTRACT FROM AUTHOR]

In this study, the rotating twisted tape and its effect on fluid flow and heat transfer as well as Performance Evaluation Criterion (PEC) in a tube under constant heat flux is investigated. The twisted tapes are examined in two rotating and stationary cases, namely four geometric cases of Plain Tube (PT), tube equipped with Stationary Twisted Tape (STT), tube equipped with Rotating Twisted Tape- Clockwise (RTT-C) and the tube is equipped with Rotating Twisted Tape-Counterclockwise (RTT-CC). The used nanofluid is Al 2 O 3 /water nanofluid in volume fraction of nanoparticles 0, 1, 2, and 3% and is considered as Newtonian, and two-phase mixture method is used to simulate the nanofluid. The flow regime in this study is laminar and the Reynolds numbers are 250, 500, 750, 1000, and heat flux of 5000 W/m2 is applied to the wall of the tube. The height of the twisted tape is 90% of the height of the channel and they act as thermal insulation and are only responsible for creating the secondary flow. The results show that increasing the Reynolds number increases Nu ave and increases the pumping power, and by using nanoparticles and changing the volume fraction of nanoparticles from 0 to 3%, heat transfer, pumping power, and pressure drop are increased. [ABSTRACT FROM AUTHOR]

In the present numerical analysis, the forced convection of nanofluid flow is investigated in a microtube with twisted porous blocks while existing a uniform magnetic field based on the first and second laws of thermodynamics with various geometries. Using the finite volume technique and SIMPLE algorithm, the governing equations are discretized and solved. The governing equations are solved using a two-phase mixture model and second-order upwind technique. With the heat flux of 5000 W.m−2, the effects of Hartmann number, Reynolds number, the volume fraction of nanoparticles, as well as porosity percentage of twisted porous blocks are investigated on pressure drop, heat transfer rate, and flow fields. The values of the Hartmann and Reynolds numbers are different within the range of Ha = 0 to Ha = 20 and Re = 250 to Re = 1000, respectively, and the volume fraction of nanoparticles is different within φ = 0 to 2%. The findings indicate that placing the porous blocks in the microtube leads to protrusions in the local diagrams, moreover, by increasing the number of twisted porous block layers, the vertices value of these protrusions increments. By incrementing the Reynolds number, the pressure drop and convective heat transfer coefficient are increased, and the friction factor is decreased. Incrementing φ and the thermal conductivity of the fluid increase the heat transfer rate. Moreover, by increasing the Hartmann number, the local friction factor and the Nusselt number are increased. According to the results, by increasing the number of twisted porous block layers in the highest φ , the average pressure drop becomes 38.171 Pa. The performance evaluation criterion in Ha = 20 and microchannel with three twisted block layers possess the highest value of 1.717. [Display omitted] • This study investigates the nanofluid flow in a microtube with twisted porous blocks. • The effect of porosity percentage of twisted porous blocks is analyzed. • As the Hartmann number increases, friction factor and the Nusselt number increase. • The PEC in Ha = 20 and with three layers of twisted blocks have a maximum value. [ABSTRACT FROM AUTHOR]

In this study, the molecular dynamics method is applied for condensation flow inside rough and smooth nanochannels by attaching the roughness on the lower walls. The influence of roughness geometry and height on the condensation characteristics is studied, and the corresponding distribution of density, velocity, and temperature are obtained. Also, the influence of rough surfaces on the condensation rate and the number of atoms that shift the liquid phase is investigated. Results indicate that the rough surface decreases the density fluctuations in its neighboring as well as the velocity level and temperature near the lower wall. Moreover, rough surfaces trap more atoms in the liquid film, which empower the condensation process of flow. It is concluded that the behavior of condensation flow in rough nanochannels is dependent on the roughness geometry and height so that by enhancement of the roughness height, the flow is more affected. [ABSTRACT FROM AUTHOR]

In this investigation, laminar flow with a hybrid nanofluid as a working fluid in a newly designed double layer microchannel with sinusoidal walls is investigated. The nanofluid is Al 2 O 3 -Cu/water hybrid nanofluid. Results indicate that changing the geometry of fluid route (wavelength of the sinusoidal wall), usage of nanofluid and increasing fluid velocity can alter Nusselt number, the maximum temperature distribution in the microchannel, Performance Evaluation Criterion and friction factor. The presence of sinusoidal wavelength across the entire microchannel can improve mixing between surface and fluid, and this mixing happens because of the slow flow of fluid in low Reynolds number (Re = 50) and the average Nusselt number variation is the same for similar wavelengths. For Re = 300, 700 and 1200, the decrease in PEC is the same for the higher volume concentration of solid nanoparticles and the change in the level of curves for each wavelength are close together compared with Re = 50. When the difference temperature between surface and fluid is reduced, the heat transfer value is reduced, and the maximum temperature of the lower layer increases sharply so that for Re = 50 the value of maximum temperature is noticeable compare with Re = 1200. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of Solid Volume Fraction (SVF) and temperature on the dynamic viscosity of a hybrid antifreeze composed of MWCNTs and aluminum oxide in a mixture of water (80%) and ethylene-glycol (20%). An Artificial Neural Network (ANN) is used to predict the viscosity of the nanofluid, which was generated at different SVFs ranging from 0.25% to 1% and temperatures ranging from 25 °C to 50 °C. This study aims to establish a correlation between viscosity and input parameters in the antifreeze. Results demonstrate that Shear Rate (SR) and SVF have opposite effects on the viscosity of the nanofluid. Increasing SVF leads to a strong increase in viscosity deviation and higher mean values of viscosity while increasing SR results in a sharp decline in both the mean value and variation of the viscosity. The temperature has a smaller impact on viscosity variance than SR and SVF. The proposed ANN model with a two-layer network and 13 neurons having nonlinear activation functions in the hidden layer shows an accurate prediction of viscosity versus inputs. The proposed methodology offers an improvement of up to 10 times in predicting viscosity accuracy as compared to GMDH and decision tree techniques. The findings of this study can have important implications for the design of heat exchangers using nanofluids especially in portable devices. [ABSTRACT FROM AUTHOR]

• The properties of nanofluid in nanochannel in the presence of surfactant molecules are investigated in rectangular atomic channel. • Water molecules are considered as the base fluid, copper atoms as nanoparticles and CTAB molecules were considered as surfactant. • The Atomic stability of simulated nanofluid don't disrupted by surfactant molecules adding to MD simulation box. • Cu nanoparticles and CTAB molecules adding to base fluid molecules improve their thermal behavior. • MD simulation results which calculated by using the Drieding UFF force, and Charm force fields have similar form. The poor heat transfer properties of the base fluid are the first effective obstacle to improving heat exchangers' efficiency. The key point of using very high conductivity of solid particles (in nanometer dimension) is hundreds of times more than common fluids in heat transfer in the composition of these fluids. Therefore, adding nanoparticles (NPs) to base fluids has been a solution to increase the heat transfer (HT) properties of common energy-carrying fluids. On the other hand, adding surfactants prevents the sedimentation and instability of NPs and improves the thermal performance of nanofluids (NF). So, this study surveyed the thermal properties of water-copper NF with/without surfactant molecules in a rectangular nanochannel using molecular dynamics (MD) simulation. Cetryltrimethylammoniu Bromide (CTAB) molecules were used as surfactants, copper structure as NPs, and water molecules as a base fluid in this simulation. In the present study, the effect of nanochannel wall temperature, copper nanoparticle (NP) size, and force field type (DREIDING, Universal Force-Field (UFF), and CHARM) on thermal conductivity (K nf) of water-copper NF were studied. The results show that as the wall temperature decreased from 80 to 30 K, K nf decreased from 0.783 to 0.753 Wm-1K−1. On the other hand, by increasing the radius of NPs from 0.5 to 2 nm, K nf and heat flux (HF) increase from 0.77 to 0.798 Wm-1K−1 and 5734 to 6352 W.m−2, respectively. One of the important purposes of researchers and engineers in various industries is to increase efficiency and reduce the systems' size. Therefore, it is expected that the results of this study will be effective in many different thermal industries. [ABSTRACT FROM AUTHOR]

The objective of present research is to investigate the effect of temperature, the volume fraction of nanoparticles (φ) and shear rate (γ ̇) to predict the dynamic viscosity (µ nf) of MWCNT-ZnO (50–50)/oil SAE50 nano-lubricant by using an artificial neural network (ANN). The second principal component was used as an indicator of variance and various statistical characteristics of all the data. This is used to identify outliers. Due to the Principal Component Analysis (PCA) minimizing quadratic norms, it has the same least-squares problems, or it becomes Gaussian the sensitivity to outliers. Sensitivity analysis was used to evaluate the importance and role of temperature, γ ̇ , and φ in experimental µ nf variations. The results show that the estimated values of the ANN simulation have a strong correlation with the experimental data and the predicted data extracted from the ANN are similar to the targets close to µ nf of MWCNT-ZnO (50–50)/oil SAE50 nano-lubricant by ANN simulation with 7 neurons model. Finally, ANN was generated and tested with experimental data sets and the results show that there was a good agreement between the actual and predicted ANN values. [Display omitted] [ABSTRACT FROM AUTHOR]

• Molecular Dynamics simulation method is implemented. • Atomic behavior of H 2 O-CuO nanofluid inside Pt microchannel is described. • H 2 O-CuO nanofluid inside Pt microchannel is represented by UFF, TIP4P, and EAM. • Total energy of atomic structures converged to −509910 eV value after 10 ns. • Aggregation time of CuO nanoparticles reach to 2.11 ns by microchannel thickness enlarging. Microchannels are promising structures for the different processes such as mass and heat transfer processes. Previous researches indicated the atomic behavior of nanofluids in these structures improved appreciably. In the current numerical study, the atomic behavior of H 2 O-CuO nanofluid inside Pt microchannel is described using Molecular Dynamics simulation. The results are reported by calculating physical properties such as temperature, total energy, density, velocity, temperature profile, and aggregation time. In our simulations, H 2 O-CuO nanofluid inside Pt microchannel is represented by Universal Force Field, TIP4P, and Embedded Atom Model. The simulation results show that the total energy of atomic structures converged to −509910 eV value after 10 ns. This calculation estimated the atomic stability of structures. Also, simulations predicted microchannel thickness is an important parameter for nanofluid flow. By increasing microchannel thickness, the absorption force between Pt atoms and nanofluid particles increases. Numerically, by increasing microchannel thickness to 15, the maximum density, velocity, and temperature profiles reach 1.23 g/cm3, 0.0065 Å/ps, and 264 K, respectively. Furthermore, by microchannel thickness increasing from 5 to 15, CuO nanoparticles' aggregation time and potential energy increase from 1.32 ns and −659328 eV to 2.11 ns and −721583 eV. Physically, because of the amplitude of the atomic displacement, this atomic process occurs and decreases with the enlargement of the atomic layers. The movement atomic of various particles of H2O/CuO nanofluid increases by microchannel walls thickening and nanoparticles aggregation phenomenon occur in higher time. [ABSTRACT FROM AUTHOR]

• Effect of the presence of Fe 3 O 4 nanoparticles on the behavior of fluid flow is investigated. • Effect of number of layers and wall material on fluid flow is investigated. • The material of walls is considered as platinum, copper and iron. • By changing the material from copper to iron and platinum, the interactions between particles increase. Due to the increasing development of nanotechnology and its wide applications, the flow of a nanofluid in a duct is also optimal geometric construction of ducts in the fabrication and production of various ducts to increase efficiency in nanofluid behavior are essential. In this paper, by using the molecular dynamics (MD) simulation process, the effect of Fe 3 O 4 nanoparticles on the behavior of water-based fluid is investigated. Physical parameters such as total temperature, potential energy, fluid, nanofluid density profiles, fluid velocity, nanofluid profiles, and fluid and nanofluid temperature profiles are reported. Also, the effect of the number of layers and wall material on fluid flow is investigated. Therefore, the channel wall material in the following simulations will be considered as platinum, copper, and iron. Over time, the temperature of atomic structures reaches 300 K, which indicates the temperature stability in the simulated atomic structures. The results show that by increasing the number of wall layers in nanochannels and similar microchannels, interactions between fluid particles and walls increase. As these interactions increase, the accumulation of fluid particles in the vicinity of the channel walls increases, which increases the density of the shelves adjacent to the channel walls. Also, by changing the microchannel material from copper to iron and platinum, the number of interactions between particles in the present structures increases. This increase in the number of interactions between the particles present in the microchannel wall and the base fluid causes the maximum density to be observed in the platinum microchannel. [ABSTRACT FROM AUTHOR]

In the present numerical study, the mixed convection of Cu-water and CuO-water nanofluids is modeled inside an inclined square-shaped cavity by utilizing the thermal model of the Lattice Boltzmann Method (LBM). A cold fluid flow enters into the cavity at the upper side of the left wall and, after being heated by the hot obstacle, exits from the lowest right side of the cavity The effective thermal conductivity and viscosity of nanofluids are computed by the KKL (Koo-Kleinstreuer-Li) equation. The results are presented in the constant Rayleigh number of 104 and the Richardson numbers of 0.1,1 and 10. Obtained results reveal that by incrementing Ri because of the augmentation of inlet fluid velocity from the left side, the gradient of isothermal lines decreases, and temperature distribution becomes more uniform, leading to Nusselt number reduction on hot wall. Although the Nu avg enhances considerably in Ri of 0.1, in Ri = 1 and 10, there is no sensible change. In the angle of 0o, by augmenting Ri, Nu avg decreases, but in the angle of 60o, by increasing Ri from 0.1 to 1, Nu avg increments up to 22%. This augmentation is due to the change of angle of the collision of flow with the hot obstacle. Furthermore, when the hot obstacle is located in the flow path, heat transfer improves. Application of such studies shows its importance in the design of electronic components cooling systems, solar energy storage, heat exchangers, and lubrication systems. [ABSTRACT FROM AUTHOR]

In this paper, the effect of nanoparticles on the annular condensation flow of Argon-Copper nanofluid passing inside a nanochannel is investigated by molecular dynamic method. Simulation is performed in a computational domain with two solid Copper walls for different saturation conditions with focusing on the thermal conductivity and flow characteristics of condensation process. By considering appropriate correlation length for heat flux autocorrelation function (HFACF) to decay to zero, Green-Kubo relation is utilized for calculation of thermal conductivity. It has been observed that adding nanoparticle disfigures the density profile and drives the liquid film closer to the walls towards the center of the nanochannel. With more Copper nanoparticles, correlation of heat flux is increased and decayed to zero in longer time. Also, with more particles, less time is required for condensation flow to reach equilibrium. Thermal conductivity of condensation flow of Argon-Copper nanofluid is obtained at different saturated temperatures. The results show that at a constant volume fraction, increasing the diameter of the nanoparticle has a better effect on the enhancement of thermal conductivity of nanofluid condensation than the increasing the number of nanoparticles. • Effect of nanoparticles on the annular condensation flow • Argon-Copper nanofluid passing inside a nanochannel. • Simulation is performed in a computational domain with two solid Copper walls. • ForGreen-Kubo relation is utilized for calculation of thermal conductivity. • Thermal conductivity of condensation flow of Argon-Copper nanofluid is obtained. [ABSTRACT FROM AUTHOR]

In this paper, the annular condensation of vapor Argon through a nanochannel is studied using the molecular dynamics method. Simulation is performed in a computational domain with two solid platinum walls for different saturation conditions with focusing on the flow characteristics and heat transfer. The density, surface tension, and velocity profiles are obtained for various axial locations. Also, the effect of different wall temperatures on the density profile and heat transfer of condensation flow is investigated. It is found that the wall temperature does not have a significant effect on the vapor and liquid density, while the heat flux value is dependent on the wall temperature. Finally, thermal conductivities for the two-phase flow of Argon are estimated at different saturated temperatures, and an equation is presented for calculating the thermal conductivity of the liquid-vapor Argon in terms of the thermal conductivity of each phase. The results show that the formula can predict the thermal conductivity of two-phase flow of Argon quite well. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation is one of the most common simulation methods which predict the dynamical and thermodynamical properties of atomic structures based on classical Newton's laws. In this study, the effect of copper nanoparticles on the thermal behavior of the fluid in zig-zag nanochannel was investigated using molecular dynamics simulation. In our simulations, water molecules were used to model the base fluid, and platinum atoms were used to model the nanochannel walls. To investigate the effects of copper nanoparticles on the base fluid, physical quantities such as potential energy, density, velocity, temperature profiles, and finally, the thermal conductivity has been reported. The results show that, by adding nanoparticles to the base fluid, the maximum density increases. On the other hand, the maximum velocity decreases from0.22°A/ps to 8°A/ps to. From the velocity behavior of the fluid particles, the temperature decreases from 363 K to 330 K. Furthermore, a study of the thermal conductivity of the simulated system by using the Green-Kubo method showed an increase in the thermal conductivity of water up to 0.679 W m−1 K−1. The increase of the nanofluid thermal conductivity is consistent with the increase in heat transfer, which can be a promising parameter in industrial applications. [ABSTRACT FROM AUTHOR]