This article introduces an innovative integration of a thermoelectric generator (TEG) module with a U-tube evacuated solar system, using paraffin as the phase change material (PCM). To enhance the PCM's melting rate and improve the system’s overall thermal efficiency, three advanced strategies were employed: (1) The addition of ternary nanoparticles—comprising MgO, ZnO, and MWCNT—into the paraffin to boost thermal conductivity; (2) Modification of the U-tube's geometry from a circular to a three-lobed design for improved heat transfer; and (3) The installation of tree-shaped fins to optimize heat distribution and accelerate the melting rate. The unsteady thermal behavior has been modeled using the finite volume method. The results demonstrated that these techniques significantly increased the melting rate and thermal efficiency, though they led to a slight decrease in the TEG's electrical power output. Four configurations were examined: (Case 1: Circular U-tube with pure paraffin; Case 2: Three-lobed U-tube with pure paraffin; Case 3: Three-lobed U-tube with ternary nanofluid; Case 4: Three-lobed U-tube with ternary nanofluid and tree-shaped fins). The incorporation of ternary nanoparticles accelerated the melting process, increasing the charging rate by 3.47 % at 150 s and 1.92 % at 450 s. Replacing the circular U-tube with a three-lobed design, combined with ternary nanomaterials, improved the liquid fraction by 57.76 % at 150 s and 22.28 % at 450 s. When all three techniques were applied together, the temperature of the system rose by 6.14 % at 150 s and 4.57 % at 450 s. However, in case 4, a decrease of 3.23 % in the TEG’s efficiency was observed at 900 s, yielding an electrical output of 2.28 kW.

To expedite melting within storage unit, the efficacy of nanoparticle with various configurations of fins and eccentricity of inner pipe on the free convection melting phenomena in the horizontal double-tubes storage system is numerically scrutinized. For this simulation, lattice Boltzmann method (LBM) with some correction is applied considering enthalpy-based approach. This modification helps to find the optimal code with minimum CPU execution time. The melting temperature of 220 degrees C with Prandtl number of 4.61 has been use for paraffin. The amounts of Ra and Ste. are 2 x 10(5) and 0.13. The outputs illustrated that the greatest rate of charging is obtained for the case with four perpendicular fins which are located on the inner tube. Also, it reveals that adding high thermal conductivity nanoparticles can increase 16 % melting rate while the total heat storage is slightly reduced. The zone influenced by buoyancy increases with increasing eccentric distance, but there is an optimal eccentricity ratio where the paraffin melts at the bottom and top of the inner pipe simultaneously.

This paper aims to study the effect of waves from gas channels on the interaction of liquid droplets growing from two micropores in a wavy gas channel of PEMFC. The computational domain consists of a wavy gas channel in which liquid water is injected from two micropores with different diameters from the bottom of the computational domain. Also, the airflow entering the gas channel is fully developed with Poiseuille velocity. A multi-component multiphase pseudopotential Lattice Boltzmann method with a multi-relaxation time collision operator is present to simulate it. The forcing term in the collision operator has been improved to reach the real conditions of liquid water and air component density ratio and thermodynamic consistency. The different parameters such as Capillary number, temperature effect, wave amplitude, micropore diameter, and distance between two micropores on growth, detaching, and movement of liquid in the gas channel are studied. The simulation results indicate that by enhancing the Capillary number, the drag shear force rises, and the droplet detaches faster and improves its movement in the gas channel. Also, it is found that when the micropore diameter increases, the flow pattern changes from dripping flow to a continuous jet regime and raises the water removal time. The simulation is performed for a higher amplitude wavelength ratio to increase the maximum velocity, thus facilitating the droplet exit from the gas channel.

In this paper, a multi-component multiphase pseudopotential Lattice Boltzmann method with multi relaxation time (MRT) collision operator is presented to examine the dynamic behavior of liquid droplets movement and coalescence process in the gas channel of PEMFC. In the numerical method, the forcing term is improved to achieve a high-density ratio and thermodynamic consistency. First, the density ratio, Laplace law, and contact angle are validated with previous studies. Then, different parameters, such as operating temperature, pressure difference, surface contact angle, the radius of droplets, and distance between two droplets on the droplet movement and coalescence process are studied. The results revealed by rising temperature from 30 to 80 degrees, the speed of drop increases around 6 percent. The simulation results indicated that the rising of pressure gradient increases the gas flow velocity on the channel and leads to increasing the shear force and eventually faster movement of the droplet on the gas channel. Also, investigation of various contact angles shows that a hydrophilic surface causes a resistance force between the droplet and the wall and delays the removal of droplets. Moreover, droplet coalescence is useful for droplet movement because of increasing the velocity gradient on top of the droplet; consequently, the shear force on the droplet is raised during coalescence.

Compression of the porous transport layers (PTLs) of Proton exchange membrane fuel cell affects the porosity and the the fraction of the pores occupied by liquid water. Therefore, by changing the compaction factor, the saturated water phenomena in the PTLs is different.The two-phase flow is simulated using Shan and Chen multi-component multiphase pseudopotential Lattice Boltzmann method with a multi relaxation time(MRT) collision operator. In this simulation, the forcing term is improved, in order to the physical properties of water and air achive to the real physical condition. It is known that saturation water transport is affected by the compression of porous transport layers(PTLs), microporous layer intrusion thickness(MPL), Capillary number, and the contact angle. The results indicate that different compression level, when the compression ratio increases, the water accumulated under the ribs increases while the amount of saturated water levels below the gas channel reduces. Furthermore, when the water injection rate enhances, the time to reach the steady state decreases, but the saturated water level is higher.

In this study, a multi-component multiphase pseudopotential Lattice Boltzmann method with multi relaxation time (MRT) collision operator is used to investigate liquid water transport in the compressed microporous layer (MPL) and gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells with interdigitated flow field. In this simulation, in order to achieve the real physical conditions of liquid water and air, such as viscosity ratio and high-density ratio, the forcing term is improved. Effect of parameters such as PTLs compression, intrusion thickness of the MPL, and operating temperature are studied. By studying four different compression levels (one without compression), when the PTL compression level is 85%, the water removal time is in the optimum state. Therefore, further increasing of compression level does not result in reduced water removal time. The simulation results indicated by rising temperature from 30 to 80 degrees The maximum level of saturated water is reduced by a factor of 5. Also, when the MPL thickness increases, the liquid water content is reduced in the PTL.

Many researches have been performed about Lab-On-Chip microfluidic systems experimentally and numerically. At the best of our knowledge, there are so few numerical assessments about Lab-On-Disk. Hence, aim of the present paper is numerical investigation of Lab-On-Disk (Laboratory-On-Disk or LOD) platforms because of its broadened usage in variety of assays in different fields of science particularly in biomedicine, drug delivery, biomedical and diagnostic assays. To fulfill this purpose, Lattice Boltzmann Method (LBM) has been employed to assess droplet generation in a T-junction through investigation of influential parameters such as Bond number (Bo), density ratio, viscosity ratio and some geometrical parameters such as width ratio of the channels (nuzzle) and height of the main channel at both sides of the junction. Results revealed that growing Bo number altered flow regime while viscosity ratio did not have any considerable effect. Incline in width of the nuzzle generated small droplet whereas its increment enlarged droplet size. Inequality in the height of the main channel at the junction postponed droplet formation but generated larger one.

In the present study, the melting phenomenon in a half horizontal cylinder cavity with rectangular heat sources is investigated using numerical lattice Boltzmann method. The cylinder is modeled two dimensionally and its boundaries are insulated. Also, the high temperature rectangular heat sources with constant area are located in radial position on cavity. The enthalpy-based lattice Boltzmann method is used for simulating the phase change problem in the cavity. Melting of lead with Stefan number of 0.86 and Prandtl number of 0.0236 is simulated in the cavity. The effects of pertinent parameters such as the aspect ratio of the fins 1,2.5,5,7.5, the Rayleigh number 103,104,105 and the angular position of the heat sources 0,15,45 are studied on the melting phenomenon. The results show that increasing the aspect ratio of the fin with constant area reduces the melting time and increases the liquid fraction at the same time. Also higher value of the Rayleigh number improves the natural convection effect and raises the rate of melting. Finally, it is observed that the highest rate of melting is obtained when two fins are positioned at 45 degrees with aspect ratio of 7.5 at Rayleigh number of 105.

In this study, phase field method of Lattice Boltzmann method (LBM) is employed to simulate the collision of a droplet with inclined dry walls under gravitational force. At first, dynamic behavior of moving droplet in a horizontal channel, through this method, has been investigated to verify convective boundary condition as the outlet one. Relatedly, falling of a droplet in vertical channel under gravity without any obstacle in certain Ohnesorge number (Oh) and Eotvos number (Eo), as related dimensionless numbers, is enquired. Then, breakup of a falling drop in the range of Eo [Formula: see text], Oh [Formula: see text], various angles of solid walls [Formula: see text], different sizes of the drop diameter [Formula: see text], influence of density ratio and parameter [Formula: see text] corresponding to surface tension are investigated. The results indicated that by increase in Eo, the breakup and deformation of droplet increased after collision while by growing Oh, the droplet retained its spherical shape. Change in the [Formula: see text] and [Formula: see text] has effect only on the size of generated fragments. Furthermore, higher density ratio reinforced gravitational force and resulted in more deformation of the droplet and its resistance was enhanced by higher parameter [Formula: see text].

Modeling of multi-component gas transport ( O2, N2, H2O) in a Proton exchange membrane fuel cell (PEMFC) cathode channel with heterogeneous porous gas diffusion layer (GDL) has been carried out using a two different lattice Boltzmann models. Generally, two passive and active methods are used for modeling single-phase, multi-component fluid flows in the Lattice Boltzmann method. In this study, the implementation of both models is described completely and their results are compared with experimental study. The results demonstrate that maximum error in active approach is only 2.5% at the common operating voltage of PEMFC and this model reaches to steady solution 33.3% faster than passive model. Also, that is found that the active method is more appropriate for complex geometry by using bounce back boundary condition on the obstacles in GDL and modify new bounce back on the reaction surface where the implementation of this boundary condition is so easy for complicated geometries.

We study the hydrodynamic forces acting on a fixed particle close to a corrugated wall experiencing tangential fluid flow, using the lattice Boltzmann method. To carry out a fundamental analysis, a single two-dimensional circular particle near a sinusoidal wall is selected as a case study. The influence of the particle distance from the wall, the particle Reynolds number, corrugation amplitude, and downstream particle position (relative to a corrugation-peak) on the drag, lift and torque acting on the particle are investigated. Our simulations reveal that the hydrodynamic forces change significantly by changing the particle distance from the wall. Even the direction of forces and torque may change, depending on the distance from the wall, downstream particle position and Rep number. We find an increase in magnitude of forces and torque by increasing the corrugation amplitude of the wall.

In this paper, the thermo-hydrodynamics of Al2O3-water nanofluid in a wavy U-turn channel with hot walls is numerically investigated by means of lattice Boltzmann modeling. At first, the numerical technique is validated by simulating fluid flow in a (non-)wavy straight channel. Then, the effects of various active parameters, e.g. pressure gradient in the channel, nanoparticles volume fraction, and number of sinusoidal waves along the channel, on the flow field and heat transfer is studied. Furthermore, the thermal-hydraulic performance factor is determined to investigate whether heat transfer enhancement outweighs the greater frictional losses caused by both complex wavy wall geometry and nanoparticles. The results show that the heat transfer rises by increasing pressure gradient in the channel while drops by increasing number of waves. Also, the effect of nanoparticles volume fraction on dimensionless Nusselt number becomes more pronounced at higher pressure gradients. The results indicate that the thermal-hydraulic performance factor grows by increasing nanoparticles volume fraction or decreasing the number of waves.

In this paper, natural convection heat transfer of Al2O3-Cu/water hybrid nanofluid within open wavy cavity and subjected to a uniform magnetic field is examined by adopting the lattice Boltzmann method scheme. The left wavy wall is heated sinusoidal, while the right wall is open and maintained to the ambient conditions. The top and the bottom horizontal walls are smooth and insulated against heat and mass. The influence of solid volume fraction of nanoparticles (phi = 0, 0.02, 0.04), Rayleigh number (Ra = 10(3), 10(4), 10(5)), Hartmann number (Ha = 0, 30, 60, 90) and phase deviation (Phi = 0, pi/4, pi/2, 3 pi/4) are investigated on flow and heat transfer fields. The results proved that the Nusselt number decreases with the increase of the Hartmann number, but it increases by the increment of Rayleigh number and nanoparticle volume fraction. The magnetic field rises or falls the effect produced by the presence of nanoparticles with respect to Rayleigh number. At Ra = 10(3), the effect of the raising phase deviation on heat transfer is erratic while it has a positive role in the improvement of nanoparticles effect at Ra = 10(5). (C) 2018 Published by Elsevier B.V.

In this study, lattice Boltzmann method is applied in order to simulate the magnetohydrodynamic (MHD) natural convection heat transfer and entropy generation of CuO–water nanofluid inside an inclined wavy cavity. The left wavy wall is heated sinusoidal, while the right flat wall is kept at a constant temperature. The top and the bottom horizontal walls are smooth and insulated against heat and mass. The effects of active parameters such as solid volume fraction of nanoparticles, Rayleigh number, Hartmann number and inclination angles are examined on flow, heat transfer and entropy generation. The results proved that the heat transfer and entropy generation decline significantly with increasing Hartmann numbers, while those rise with increasing Rayleigh numbers. The results show that the effect of nanoparticles volume fraction on dimensionless Nusselt number and entropy generation is more pronounced at high Rayleigh number than at low Rayleigh number. Also the results indicate that the mean Nusselt number and total entropy generation changes with inclination angle, while the minimum values of \(Nu_{\text{m}}\) and S belong to \(\theta = \pi /3\) and 0, respectively.

This investigation compared with other numerical studies and found to be in excellent agreement. The results depict the maximumtotal entropy generation due to the fluid friction and temperature gradient is generated in the vicinity of a high-temperature wall. Also, the results indicate that the average Nusselt number and entropy generation are an increasing function of the Rayleigh number, porosity, and Darcy number, but the entropy generation is a decreasing function of the volume fractions of the nanofluid.

دییامن هدافتسا لیذ ترابع زا هلاقم نیا هب عاجرا یارب : Please cite this article using: A. Shahriari, H. Ashorynejad, Numerical study of heat transfer and entropy generation of Rayleigh–B َ enard convection nanofluid in wavy cavity with magnetic field, Modares Mechanical Engineering, Vol. 17, No. 10, pp. 385-396, 2017 (in Persian) هعلاطم یددع یلیار ییاجباج یپورتنآ دیلوت و ترارح لاقتنا ظفحم رد لایسونان درانب ه یسیطانغم نادیم ریثأت تحت یجوم

In this paper, the lattice Boltzmann method is applied to investigate the effects of uniform vertical magnetic field on thermo-hydrodynamics of nanofluid in a partially porous channel. Cu-water nanofluid with constant pressure gradient is forced to flow into the channel while the top wall is heated by constant heat flux and bottom wavy wall of the channel is insulated against heat. The porous media is modeled using the Brinkman-Forchheimer model. Good agreements with the previous results verify that the selected numerical method is a capable method for simulating magnetic fluids in a porous media. The effects of active parameters, i.e. solid volume fraction of nanoparticles, pressure gradient, magnetic field and permeability of the porous layer, on thermo-hydrodynamics of flow are examined. The results reveal that the Nusselt number is an increasing function of nanoparticle volume fraction, Hartmann number, pressure gradient and Darcy number, although the effect of Darcy numbers and pressure gradient on the temperature profile are more noticeable than others. (C) 2017 Elsevier Ltd. All rights reserved.

• Unsteady squeezing nanofluid flow between parallel plates is investigated. • Adomian decomposition method is used to solve this problem. • Selecting silver as nanoparticle leads to obtain the highest Nusselt number . • Nusselt number has direct relationship with ϕ and Ec . • Nusselt number has reverse relationship with S when S < 0.