Farhad Talebi - Academia.edu (original) (raw)

Papers by Farhad Talebi

Heat transfer analysis of Viscoelastic fluids in noncircular channel has complication because of ... more Heat transfer analysis of Viscoelastic fluids in noncircular channel has complication because of nonlinear behavior of fluid consistency equation and channel geometry. In this paper a weak secondary flow is shown using generalized model CEF and numerical solution. Numerical solution is based on the Artificial Compressibility (Chorin method) and using staggered mesh. The effect of secondary flow on the forced and natural heat convection is studied. Effect of fast secondary flows at forced and free convection was assimilated. Quantities of static pressure and temperature distributions were obtained. Computer program was used for 3-D CFD technique.

Journal of Modeling in Engineering, Aug 15, 2011

The permeability and tortuosity of pore-scale two and three-dimensional random porous media were ... more The permeability and tortuosity of pore-scale two and three-dimensional random porous media were calculated using the Lattice Boltzmann method (LBM). Effects of geometrical parameters of medium on permeability and tortuosity were investigated as well. Two major models of random porous media were reconstructed by computerized tomography method: Randomly distributed rectangular obstacles in a unit-cell as two-dimensional porous media, and random granular media in a cubic unit-cell as three-dimensional porous media. Results were validated using available theoretical, experimental, and numerical results from the literature. It is observed that permeability is a weak function of porosity in low porosity regions, but a strong function of porosity at high porosities. It also depends on the aspect ratio and hydraulic diameter of obstacles.Permeability results were obtained regarding to 73 random two-dimensional samples with different porosities and obstacle aspect ratios. Also 29 random sph...

International Journal of Engineering, 2017

In this study, the stirring mechanism of shear-thinning fluids benefiting from four blades in tur... more In this study, the stirring mechanism of shear-thinning fluids benefiting from four blades in turbulent flow is considered. The fluid is studied inside a stirred cylindrical tank with a flat bottom. The height of fluid is equal to the cylinder’s diameter and the impeller is positioned centrally. A CFD simulation has been carried out and three-dimensional turbulent flow is numerically analyzed using the Shear Stress Transport k-ω (k- ω SST) model. The parameters related to power consumption including attack angle and flow index were studied. The power consumed during the mixing of the shear thinning liquids under a specific Reynolds number and attack angle is less than that consumed when the fluid used is water, which is a Newtonian fluid. As the power law index decreases, the corresponding power consumption also declines. At a certain attack angle and power law index, an increase in the Reynolds number first significantly decreases power consumption; beyond a given range, the consum...

International Journal of Heat and Mass Transfer, 2019

Cold box with plate-fin heat exchanger (PFHE) is extensively used in liquefied natural gas (LNG) ... more Cold box with plate-fin heat exchanger (PFHE) is extensively used in liquefied natural gas (LNG) refinery plants. In the present study, a CFD model in ANSYS FLUENT is developed for better understanding the transport phenomena, especially the phase change, in a quite complex plate-fin heat exchanger operated in a gas refining company. The flow channels, ducts and passes of the cold box, are considered in the computational geometry. The porous media technique is introduced in the computational domain due to the excessive increase in the number of computational grids when the fins accounted for in the numerical domain. The flash calculations (FC) technique is coupled with CFD in evaluation of chemical species in the cold box by a user defined function. This study examines the importance of local thermal equilibrium between the porous medium and fluid flow without mass transfer (LTE-non mass), local thermal equilibrium between the porous medium and fluid flow with mass transfer (LTE), and local thermal non equilibrium between the porous medium and fluid flow with mass transfer (LTNE) in simulation of an industrial cold box. Numerical results are compared with the corresponding operational data and the best agreement is obtained by the LTNE approach. The calculated mean relative errors of the LTNE approach for the outlet vapor fraction of streams A, hot stream, B and C, sided cold streams, are 0.15, 0.352, and 0.173%, respectively.

The forced convection heat transfer of turbulent Al2O3-water nanofluid flow inside the grooved tu... more The forced convection heat transfer of turbulent Al2O3-water nanofluid flow inside the grooved tubeswith the different aspect ratio of the rectangular grooves is numerically investigated. The governingequations have been solved using finite volume method (FVM) coupled with SIMPLE algorithm. It isassumed the heat flux is constant on the grooved walls. The Single-phase approach is applied for thecomputation of the nanofluid flow. The Nanoparticles volume fraction is in the range of 0-5% and flowReynolds number is in the range of 10,000-35,000. Comparisons between the numerical results andavailable experimental data show that among different turbulence models, k-e model with enhanced walltreatment gives the better results. The results show that the heat transfer coefficient increases withnanoparticles volume fraction and Reynolds number but it is accompanied by pressure dropaugmentation. From the results, it is concluded that the grooved tubes with Al2O3-water nanofluid floware thermod...

Majlesi Journal of …, 2011

يور ﺮﺑ ﻖﻴﻘﺤﺗ ﻪﺠﻴﺘﻧ ﺮﺿﺎﺣ ﻪﻟﺎﻘﻣ يﺎﻳﺎﭘ ﺖﻟﺎﺣ ﻪﺑ نﺪﻴﺳر نﺎﻣز ﺶﻫﺎﻛ ﻢﺘﺴﻴﺳ ﻫ ﻲﺗراﺮﺣ يﺎ ﺖﺳا . ﺗﺮﺗ ﻦﻳا ﻪﺑ ﺎـ... more يور ﺮﺑ ﻖﻴﻘﺤﺗ ﻪﺠﻴﺘﻧ ﺮﺿﺎﺣ ﻪﻟﺎﻘﻣ يﺎﻳﺎﭘ ﺖﻟﺎﺣ ﻪﺑ نﺪﻴﺳر نﺎﻣز ﺶﻫﺎﻛ ﻢﺘﺴﻴﺳ ﻫ ﻲﺗراﺮﺣ يﺎ ﺖﺳا . ﺗﺮﺗ ﻦﻳا ﻪﺑ ﺎـﺑ يزﺮـﻣ ﻂﻳاﺮـﺷ ﻪـﻛ ﺐﻴ ﻲﻣ راﺮﻗ لﺮﺘﻨﻛ ﺖﺤﺗ ﻢﺋاد ﺖﻟﺎﺣ ﻪﺑ لﻮﺻو ﺎﺗ ﻪﻧﺎﻣﺎﺳ ﻲﻜﻳﺰﻴﻓ تﺎﺼﺨﺸﻣ ﻪﺑ ﻪﺟﻮﺗ دﺮﻴﮔ . ﺶﻫوﮋﭘ ﻦﻳا رد ﻲﻫﺎﮕﺸـﻳﺎﻣزآ ﻲـﺗراﺮﺣ ﻪﻧﺎﻣﺎﺳ ﻚﻳ ... هﺪﺷ ﻲﺳرﺮﺑ يدﺪﻋ يزﺎﺳ ﻪﻴﺒﺷ زا هدﺎﻔﺘﺳا ﺎﺑ ﺞﻳﺎﺘﻧ ﺎﺑ يدﺪﻋ ﻞﺣ ﺞﻳﺎﺘﻧ و ﻪﺴﻳﺎﻘﻣ ﻲﺑﺮﺠﺗ ﺶﻳﺎﻣزآ ﺪﻨﭼ ياﺮﺟا مﺎﺠﻧا ﺖﺳا هﺪﺷ ...

The European Physical Journal Plus, 2016

Abstract.In this paper, the problem of developing forced convection flow of a nanofluid in a cons... more Abstract.In this paper, the problem of developing forced convection flow of a nanofluid in a constant-wall-temperature circular tube filled with a porous medium is considered. The flow is steady and Brinkman-Forchheimer-extended Darcy equation model is employed. The thermal-equilibrium model is assumed between nanofluid and solid phase. It is also assumed that nanoparticles are distributed non-uniformly inside the pipe, hence the particles volume fraction equation is also coupled with the governing equations. A numerical study has been performed using the Finite-Volume method to analyze heat transfer coefficient of Al2O3 -water nanofluid. The effects of nanoparticles volume fraction and porosity on fluid flow and heat transfer of nanofluids are studied. The results show that the Nusselt number is increased with increasing particles volume fraction. Moreover, the wall shear stresses are increased. Finally, the effect of porosity on particle volume fraction distribution is studied and discussed in detail. We are confident that the reported results are new and original.

Iranian Journal of Chemistry & Chemical Engineering-international English Edition, Sep 1, 2015

In this paper, convection heat transfer of Al2O3-water nanofluid turbulent flow through internall... more In this paper, convection heat transfer of Al2O3-water nanofluid turbulent flow through internally ribbed tubes with different rib shapes (rectangular, trapezoidal and semicircular) is numerically investigated. For each rib shape, the optimum geometric ratio and volume fraction were calculated using entropy generation minimization technique. The governing equations in steady state and axisymmetric form have been solved using Finite Volume Method (FVM) with the SIMPLE algorithm. A uniform heat flux was applied on the wall. A single-phase approach has employed to model the nanofluid. Nanoparticles size is 20 nm and nanoparticles volume fraction and Reynolds number were within the ranges of 0-5% and 10,000-35,000 respectively. Comparisons between the numerical results and experimental data show that among different turbulence models, k-ε model with enhanced wall treatment gives better results. The results indicate that the heat transfer increases with nanoparticles volume fraction and Reynolds number but it is accompanied by increasing pressure drop. The simulations demonstrate that trapezoidal and semi-circular ribbed tubes have higher Nusselt number than the rectangular ribbed tubes with the same diameters. Correlations of heat transfer have obtained for different ribbed tubes. In evaluation of thermal performance and pressure drop, it is seen that the ribbed tubes with Al2O3-water nanofluid flow are thermodynamically advantageous. For each rib shape, the optimum geometric ratios are also presented.

The Lattice Boltzmann method is employed for pore-level fluid flow simulation in 3D porous media.... more The Lattice Boltzmann method is employed for pore-level fluid flow simulation in 3D porous media. The base of study of a fibrous porous medium is an ordered arrangement of cylinders which is not investigated by LBM so far. LBM is well suited to the study of mesoscopic pore-level flow in porous media. Permeability, k, is the most important property which characterizes a porous medium. It is a measure of the frictional resistance of the material to flow. In the present paper, Lattice Boltzmann method is presented as a powerful tool in order to calculate some appropriate values of permeability in some porous media. A good representation of the pore structure can be in the form of ordered arrangements of sphere or cylinder obstacles. Regular array of sphere and, for the first time, cylinder packs domains were virtually reconstructed and input to a LBM algorithm based on a D3Q15 lattice. Then a pressure gradient was applied to induce fluid flow to the lattice, the Darcy velocity was calc...

In this study, natural convection inside a square cavity filled with nanofluids with several pair... more In this study, natural convection inside a square cavity filled with nanofluids with several pairs of heaters and coolers (HACs) inside is investigated numerically in the range of Rayleigh numbers between 10 4 and 10 7 . Walls of the cavity are insulated and heaters and coolers walls are isothermal with temperatures of T h and T c ( T h > T c ). Two-dimensional Navier–Stokes and energy equations are solved using finite volume discretization method. Effects of various design parameters on the heat transfer rate are investigated. Design parameters considered in this study are: position, surface area, shape and orientation of HACs, volume fraction and types of nanoparticles. The results show that the highest and the lowest impacts of design parameters, on the enhancement of heat transfer rate are caused by changing the HAC position and types of nanoparticles, respectively. Moreover, it is found that for a constant surface area of the HAC at the entire range of Rayleigh number, rat...

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

The cold box, which comprises of several plate-fin heat exchangers (PFHE), is largely utilized in... more The cold box, which comprises of several plate-fin heat exchangers (PFHE), is largely utilized in different industries. In this research, the computational fluid dynamics (CFD) technique has been used for investigating the impact of different fluid distributors on the rates of heat and mass transfer, in an industrial complex cold box equipped with plate-fins. While inlet and outlet fluid distributors and channels were taken into account in the computational domain, the porous media technique was applied to the channels as an alternative to the fins in the original cold box. The mass transfer model including the phase change was accounted for by the flash calculations. Local thermal non-equilibrium (LTNE) between the porous medium and fluid flow with a mass transfer was used in the simulations. Three principal side distributors, i.e. diagonals A, B, and C, were used, and their performance was evaluated by CFD. It was found that using each of these types of distributors led to differe...

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

This study investigated the vibrational behaviour of a rotating two-blade propeller at different ... more This study investigated the vibrational behaviour of a rotating two-blade propeller at different rotational speeds by using self-tracking laser Doppler vibrometry. Given that a self-tracking method necessitates the accurate adjustment of test setups to reduce measurement errors, a test table with sufficient rigidity was designed and built to enable the adjustment and repair of test components. The results of the self-tracking test on the rotating propeller indicated an increase in natural frequency and a decrease in the amplitude of normalized mode shapes as rotational speed increases. To assess the test results, a numerical model created in ABAQUS was used. The model parameters were tuned in such a way that the natural frequency and associated mode shapes were in good agreement with those derived using a hammer test on a stationary propeller. The mode shapes obtained from the hammer test and the numerical (ABAQUS) modelling were compared using the modal assurance criterion. The exa...

Transactions of FAMENA, Feb 12, 2018

In the present work, the mixing process of shear thinning liquids in a six-blade Rushton turbine ... more In the present work, the mixing process of shear thinning liquids in a six-blade Rushton turbine is studied. A finite volume based computational fluid dynamics (CFD) simulation has been carried out and the three-dimensional turbulent flow is numerically analyzed by using the Shear Stress Transport k-ω (k-ω SST) model. Shear thinning liquids were investigated and shear thinning behaviour was modelled by the Ostwald-de Waele law. The used stirred vessel has a cylindrical shape with a flat bottom and the liquid height was kept equal to the vessel diameter. Effects of the power law index and the angle of attack of the blade on power consumption have been investigated. The results show that decreasing the angle of attack from 90° to 45° not only results in an increase in the flow rate down to the bottom of the vessel, resulting in a better mixture qualification, but also reduces the power consumption of the stirring process. To verify the simulation, axial, radial and tangential velocity components were compared with other experimental data and satisfactory agreement was found.

Physica A: Statistical Mechanics and its Applications

Abstract Drag reduction of viscoelastic fluids under turbulent flow regime is an important phenom... more Abstract Drag reduction of viscoelastic fluids under turbulent flow regime is an important phenomenon and well observed by many researchers. In this paper, turbulent flow characteristics under drag reduction condition are compared using four different low-Reynolds number k- e models namely, Lam–Bremhorst, Launder–Sharma, Nagano–Hishida and Chien. The viscoelastic turbulence closure of Resende et al. (2011) is adopted. Time-averaged momentum and rheological constitutive equations based on finitely extensible nonlinear elastic-Peterlin (FENE-P) model are used and a polymeric contribution to the eddy viscosity equation is considered. The simulations are conducted for two sets of rheological parameters identified by Re τ 0 = 395, β = 0 . 9 , L2 = 900 and We τ 0 = 25, 100 corresponding to drag reductions of 18% and 37%. Validation against DNS data is carried out for profiles of mean velocity, viscoelastic stress tensor, turbulent kinetic energy and its rate of dissipation. The differences are mainly limited to the viscous and buffer layer regions. While Nagano–Hishida and Chien models overpredict the DNS drag reduction results in both cases, the two other models underpredict them. The Lam–Bremhorst has the most accurate drag reduction results as a consequence of better capturing the near-wall effects.

Advanced Powder Technology

Abstract In the present study, the problem of conjugate natural and mixed convection of nanofluid... more Abstract In the present study, the problem of conjugate natural and mixed convection of nanofluid in a square cavity containing several pairs of hot and cold cylinders is visualized using non-homogenous two-phase Buongiorno's model. Such configuration is considered as a model of heat exchangers in order to prevent the fluids contained in the pipelines from freezing or condensing. Water-based nanofluids with Cu, Al2O3, and TiO2 nanoparticles at different diameters ( 25 nm ⩽ d p ⩽ 145 nm ) are chosen for investigation. The governing equations together with the specified boundary conditions are solved numerically using the finite volume method based on the SIMPLE algorithm over a wide range of Rayleigh number ( 10 4 ⩽ Ra ⩽ 10 7 ), Richardson number ( 10 - 2 ⩽ Ri ⩽ 10 2 ) and nanoparticle volume fractions ( 0 ⩽ φ ⩽ 5 % ). Furthermore, the effects of three types of influential factors such as: orientation of conductive wall, thermal conductivity ratio ( 0.2 ⩽ K r ⩽ 25 ) and conductive obstacles on the fluid flow and heat transfer rate are also investigated. It is found that the heat transfer rate is significantly enhanced by incrementing Rayleigh number and thermal conductivity ratio. It is also observed that at all Rayleigh numbers, the total Nusselt number rises and then reduces with increasing the nanoparticle volume fractions so that there is an optimal volume fraction of the nanoparticles where the heat transfer rate within the enclosure has a maximum value. Finally, the results reveal that by increasing the thermal conductivity of the nanoparticles and Rayleigh number, distribution of solid particles becomes uniform.

Heat transfer analysis of Viscoelastic fluids in noncircular channel has complication because of ... more Heat transfer analysis of Viscoelastic fluids in noncircular channel has complication because of nonlinear behavior of fluid consistency equation and channel geometry. In this paper a weak secondary flow is shown using generalized model CEF and numerical solution. Numerical solution is based on the Artificial Compressibility (Chorin method) and using staggered mesh. The effect of secondary flow on the forced and natural heat convection is studied. Effect of fast secondary flows at forced and free convection was assimilated. Quantities of static pressure and temperature distributions were obtained. Computer program was used for 3-D CFD technique.

Journal of Modeling in Engineering, Aug 15, 2011

The permeability and tortuosity of pore-scale two and three-dimensional random porous media were ... more The permeability and tortuosity of pore-scale two and three-dimensional random porous media were calculated using the Lattice Boltzmann method (LBM). Effects of geometrical parameters of medium on permeability and tortuosity were investigated as well. Two major models of random porous media were reconstructed by computerized tomography method: Randomly distributed rectangular obstacles in a unit-cell as two-dimensional porous media, and random granular media in a cubic unit-cell as three-dimensional porous media. Results were validated using available theoretical, experimental, and numerical results from the literature. It is observed that permeability is a weak function of porosity in low porosity regions, but a strong function of porosity at high porosities. It also depends on the aspect ratio and hydraulic diameter of obstacles.Permeability results were obtained regarding to 73 random two-dimensional samples with different porosities and obstacle aspect ratios. Also 29 random sph...

International Journal of Engineering, 2017

In this study, the stirring mechanism of shear-thinning fluids benefiting from four blades in tur... more In this study, the stirring mechanism of shear-thinning fluids benefiting from four blades in turbulent flow is considered. The fluid is studied inside a stirred cylindrical tank with a flat bottom. The height of fluid is equal to the cylinder’s diameter and the impeller is positioned centrally. A CFD simulation has been carried out and three-dimensional turbulent flow is numerically analyzed using the Shear Stress Transport k-ω (k- ω SST) model. The parameters related to power consumption including attack angle and flow index were studied. The power consumed during the mixing of the shear thinning liquids under a specific Reynolds number and attack angle is less than that consumed when the fluid used is water, which is a Newtonian fluid. As the power law index decreases, the corresponding power consumption also declines. At a certain attack angle and power law index, an increase in the Reynolds number first significantly decreases power consumption; beyond a given range, the consum...

International Journal of Heat and Mass Transfer, 2019

Cold box with plate-fin heat exchanger (PFHE) is extensively used in liquefied natural gas (LNG) ... more Cold box with plate-fin heat exchanger (PFHE) is extensively used in liquefied natural gas (LNG) refinery plants. In the present study, a CFD model in ANSYS FLUENT is developed for better understanding the transport phenomena, especially the phase change, in a quite complex plate-fin heat exchanger operated in a gas refining company. The flow channels, ducts and passes of the cold box, are considered in the computational geometry. The porous media technique is introduced in the computational domain due to the excessive increase in the number of computational grids when the fins accounted for in the numerical domain. The flash calculations (FC) technique is coupled with CFD in evaluation of chemical species in the cold box by a user defined function. This study examines the importance of local thermal equilibrium between the porous medium and fluid flow without mass transfer (LTE-non mass), local thermal equilibrium between the porous medium and fluid flow with mass transfer (LTE), and local thermal non equilibrium between the porous medium and fluid flow with mass transfer (LTNE) in simulation of an industrial cold box. Numerical results are compared with the corresponding operational data and the best agreement is obtained by the LTNE approach. The calculated mean relative errors of the LTNE approach for the outlet vapor fraction of streams A, hot stream, B and C, sided cold streams, are 0.15, 0.352, and 0.173%, respectively.

The forced convection heat transfer of turbulent Al2O3-water nanofluid flow inside the grooved tu... more The forced convection heat transfer of turbulent Al2O3-water nanofluid flow inside the grooved tubeswith the different aspect ratio of the rectangular grooves is numerically investigated. The governingequations have been solved using finite volume method (FVM) coupled with SIMPLE algorithm. It isassumed the heat flux is constant on the grooved walls. The Single-phase approach is applied for thecomputation of the nanofluid flow. The Nanoparticles volume fraction is in the range of 0-5% and flowReynolds number is in the range of 10,000-35,000. Comparisons between the numerical results andavailable experimental data show that among different turbulence models, k-e model with enhanced walltreatment gives the better results. The results show that the heat transfer coefficient increases withnanoparticles volume fraction and Reynolds number but it is accompanied by pressure dropaugmentation. From the results, it is concluded that the grooved tubes with Al2O3-water nanofluid floware thermod...

Majlesi Journal of …, 2011

يور ﺮﺑ ﻖﻴﻘﺤﺗ ﻪﺠﻴﺘﻧ ﺮﺿﺎﺣ ﻪﻟﺎﻘﻣ يﺎﻳﺎﭘ ﺖﻟﺎﺣ ﻪﺑ نﺪﻴﺳر نﺎﻣز ﺶﻫﺎﻛ ﻢﺘﺴﻴﺳ ﻫ ﻲﺗراﺮﺣ يﺎ ﺖﺳا . ﺗﺮﺗ ﻦﻳا ﻪﺑ ﺎـ... more يور ﺮﺑ ﻖﻴﻘﺤﺗ ﻪﺠﻴﺘﻧ ﺮﺿﺎﺣ ﻪﻟﺎﻘﻣ يﺎﻳﺎﭘ ﺖﻟﺎﺣ ﻪﺑ نﺪﻴﺳر نﺎﻣز ﺶﻫﺎﻛ ﻢﺘﺴﻴﺳ ﻫ ﻲﺗراﺮﺣ يﺎ ﺖﺳا . ﺗﺮﺗ ﻦﻳا ﻪﺑ ﺎـﺑ يزﺮـﻣ ﻂﻳاﺮـﺷ ﻪـﻛ ﺐﻴ ﻲﻣ راﺮﻗ لﺮﺘﻨﻛ ﺖﺤﺗ ﻢﺋاد ﺖﻟﺎﺣ ﻪﺑ لﻮﺻو ﺎﺗ ﻪﻧﺎﻣﺎﺳ ﻲﻜﻳﺰﻴﻓ تﺎﺼﺨﺸﻣ ﻪﺑ ﻪﺟﻮﺗ دﺮﻴﮔ . ﺶﻫوﮋﭘ ﻦﻳا رد ﻲﻫﺎﮕﺸـﻳﺎﻣزآ ﻲـﺗراﺮﺣ ﻪﻧﺎﻣﺎﺳ ﻚﻳ ... هﺪﺷ ﻲﺳرﺮﺑ يدﺪﻋ يزﺎﺳ ﻪﻴﺒﺷ زا هدﺎﻔﺘﺳا ﺎﺑ ﺞﻳﺎﺘﻧ ﺎﺑ يدﺪﻋ ﻞﺣ ﺞﻳﺎﺘﻧ و ﻪﺴﻳﺎﻘﻣ ﻲﺑﺮﺠﺗ ﺶﻳﺎﻣزآ ﺪﻨﭼ ياﺮﺟا مﺎﺠﻧا ﺖﺳا هﺪﺷ ...

The European Physical Journal Plus, 2016

Abstract.In this paper, the problem of developing forced convection flow of a nanofluid in a cons... more Abstract.In this paper, the problem of developing forced convection flow of a nanofluid in a constant-wall-temperature circular tube filled with a porous medium is considered. The flow is steady and Brinkman-Forchheimer-extended Darcy equation model is employed. The thermal-equilibrium model is assumed between nanofluid and solid phase. It is also assumed that nanoparticles are distributed non-uniformly inside the pipe, hence the particles volume fraction equation is also coupled with the governing equations. A numerical study has been performed using the Finite-Volume method to analyze heat transfer coefficient of Al2O3 -water nanofluid. The effects of nanoparticles volume fraction and porosity on fluid flow and heat transfer of nanofluids are studied. The results show that the Nusselt number is increased with increasing particles volume fraction. Moreover, the wall shear stresses are increased. Finally, the effect of porosity on particle volume fraction distribution is studied and discussed in detail. We are confident that the reported results are new and original.

Iranian Journal of Chemistry & Chemical Engineering-international English Edition, Sep 1, 2015

In this paper, convection heat transfer of Al2O3-water nanofluid turbulent flow through internall... more In this paper, convection heat transfer of Al2O3-water nanofluid turbulent flow through internally ribbed tubes with different rib shapes (rectangular, trapezoidal and semicircular) is numerically investigated. For each rib shape, the optimum geometric ratio and volume fraction were calculated using entropy generation minimization technique. The governing equations in steady state and axisymmetric form have been solved using Finite Volume Method (FVM) with the SIMPLE algorithm. A uniform heat flux was applied on the wall. A single-phase approach has employed to model the nanofluid. Nanoparticles size is 20 nm and nanoparticles volume fraction and Reynolds number were within the ranges of 0-5% and 10,000-35,000 respectively. Comparisons between the numerical results and experimental data show that among different turbulence models, k-ε model with enhanced wall treatment gives better results. The results indicate that the heat transfer increases with nanoparticles volume fraction and Reynolds number but it is accompanied by increasing pressure drop. The simulations demonstrate that trapezoidal and semi-circular ribbed tubes have higher Nusselt number than the rectangular ribbed tubes with the same diameters. Correlations of heat transfer have obtained for different ribbed tubes. In evaluation of thermal performance and pressure drop, it is seen that the ribbed tubes with Al2O3-water nanofluid flow are thermodynamically advantageous. For each rib shape, the optimum geometric ratios are also presented.

The Lattice Boltzmann method is employed for pore-level fluid flow simulation in 3D porous media.... more The Lattice Boltzmann method is employed for pore-level fluid flow simulation in 3D porous media. The base of study of a fibrous porous medium is an ordered arrangement of cylinders which is not investigated by LBM so far. LBM is well suited to the study of mesoscopic pore-level flow in porous media. Permeability, k, is the most important property which characterizes a porous medium. It is a measure of the frictional resistance of the material to flow. In the present paper, Lattice Boltzmann method is presented as a powerful tool in order to calculate some appropriate values of permeability in some porous media. A good representation of the pore structure can be in the form of ordered arrangements of sphere or cylinder obstacles. Regular array of sphere and, for the first time, cylinder packs domains were virtually reconstructed and input to a LBM algorithm based on a D3Q15 lattice. Then a pressure gradient was applied to induce fluid flow to the lattice, the Darcy velocity was calc...

In this study, natural convection inside a square cavity filled with nanofluids with several pair... more In this study, natural convection inside a square cavity filled with nanofluids with several pairs of heaters and coolers (HACs) inside is investigated numerically in the range of Rayleigh numbers between 10 4 and 10 7 . Walls of the cavity are insulated and heaters and coolers walls are isothermal with temperatures of T h and T c ( T h > T c ). Two-dimensional Navier–Stokes and energy equations are solved using finite volume discretization method. Effects of various design parameters on the heat transfer rate are investigated. Design parameters considered in this study are: position, surface area, shape and orientation of HACs, volume fraction and types of nanoparticles. The results show that the highest and the lowest impacts of design parameters, on the enhancement of heat transfer rate are caused by changing the HAC position and types of nanoparticles, respectively. Moreover, it is found that for a constant surface area of the HAC at the entire range of Rayleigh number, rat...

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

The cold box, which comprises of several plate-fin heat exchangers (PFHE), is largely utilized in... more The cold box, which comprises of several plate-fin heat exchangers (PFHE), is largely utilized in different industries. In this research, the computational fluid dynamics (CFD) technique has been used for investigating the impact of different fluid distributors on the rates of heat and mass transfer, in an industrial complex cold box equipped with plate-fins. While inlet and outlet fluid distributors and channels were taken into account in the computational domain, the porous media technique was applied to the channels as an alternative to the fins in the original cold box. The mass transfer model including the phase change was accounted for by the flash calculations. Local thermal non-equilibrium (LTNE) between the porous medium and fluid flow with a mass transfer was used in the simulations. Three principal side distributors, i.e. diagonals A, B, and C, were used, and their performance was evaluated by CFD. It was found that using each of these types of distributors led to differe...

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

This study investigated the vibrational behaviour of a rotating two-blade propeller at different ... more This study investigated the vibrational behaviour of a rotating two-blade propeller at different rotational speeds by using self-tracking laser Doppler vibrometry. Given that a self-tracking method necessitates the accurate adjustment of test setups to reduce measurement errors, a test table with sufficient rigidity was designed and built to enable the adjustment and repair of test components. The results of the self-tracking test on the rotating propeller indicated an increase in natural frequency and a decrease in the amplitude of normalized mode shapes as rotational speed increases. To assess the test results, a numerical model created in ABAQUS was used. The model parameters were tuned in such a way that the natural frequency and associated mode shapes were in good agreement with those derived using a hammer test on a stationary propeller. The mode shapes obtained from the hammer test and the numerical (ABAQUS) modelling were compared using the modal assurance criterion. The exa...

Transactions of FAMENA, Feb 12, 2018

In the present work, the mixing process of shear thinning liquids in a six-blade Rushton turbine ... more In the present work, the mixing process of shear thinning liquids in a six-blade Rushton turbine is studied. A finite volume based computational fluid dynamics (CFD) simulation has been carried out and the three-dimensional turbulent flow is numerically analyzed by using the Shear Stress Transport k-ω (k-ω SST) model. Shear thinning liquids were investigated and shear thinning behaviour was modelled by the Ostwald-de Waele law. The used stirred vessel has a cylindrical shape with a flat bottom and the liquid height was kept equal to the vessel diameter. Effects of the power law index and the angle of attack of the blade on power consumption have been investigated. The results show that decreasing the angle of attack from 90° to 45° not only results in an increase in the flow rate down to the bottom of the vessel, resulting in a better mixture qualification, but also reduces the power consumption of the stirring process. To verify the simulation, axial, radial and tangential velocity components were compared with other experimental data and satisfactory agreement was found.

Physica A: Statistical Mechanics and its Applications

Abstract Drag reduction of viscoelastic fluids under turbulent flow regime is an important phenom... more Abstract Drag reduction of viscoelastic fluids under turbulent flow regime is an important phenomenon and well observed by many researchers. In this paper, turbulent flow characteristics under drag reduction condition are compared using four different low-Reynolds number k- e models namely, Lam–Bremhorst, Launder–Sharma, Nagano–Hishida and Chien. The viscoelastic turbulence closure of Resende et al. (2011) is adopted. Time-averaged momentum and rheological constitutive equations based on finitely extensible nonlinear elastic-Peterlin (FENE-P) model are used and a polymeric contribution to the eddy viscosity equation is considered. The simulations are conducted for two sets of rheological parameters identified by Re τ 0 = 395, β = 0 . 9 , L2 = 900 and We τ 0 = 25, 100 corresponding to drag reductions of 18% and 37%. Validation against DNS data is carried out for profiles of mean velocity, viscoelastic stress tensor, turbulent kinetic energy and its rate of dissipation. The differences are mainly limited to the viscous and buffer layer regions. While Nagano–Hishida and Chien models overpredict the DNS drag reduction results in both cases, the two other models underpredict them. The Lam–Bremhorst has the most accurate drag reduction results as a consequence of better capturing the near-wall effects.

Advanced Powder Technology

Abstract In the present study, the problem of conjugate natural and mixed convection of nanofluid... more Abstract In the present study, the problem of conjugate natural and mixed convection of nanofluid in a square cavity containing several pairs of hot and cold cylinders is visualized using non-homogenous two-phase Buongiorno's model. Such configuration is considered as a model of heat exchangers in order to prevent the fluids contained in the pipelines from freezing or condensing. Water-based nanofluids with Cu, Al2O3, and TiO2 nanoparticles at different diameters ( 25 nm ⩽ d p ⩽ 145 nm ) are chosen for investigation. The governing equations together with the specified boundary conditions are solved numerically using the finite volume method based on the SIMPLE algorithm over a wide range of Rayleigh number ( 10 4 ⩽ Ra ⩽ 10 7 ), Richardson number ( 10 - 2 ⩽ Ri ⩽ 10 2 ) and nanoparticle volume fractions ( 0 ⩽ φ ⩽ 5 % ). Furthermore, the effects of three types of influential factors such as: orientation of conductive wall, thermal conductivity ratio ( 0.2 ⩽ K r ⩽ 25 ) and conductive obstacles on the fluid flow and heat transfer rate are also investigated. It is found that the heat transfer rate is significantly enhanced by incrementing Rayleigh number and thermal conductivity ratio. It is also observed that at all Rayleigh numbers, the total Nusselt number rises and then reduces with increasing the nanoparticle volume fractions so that there is an optimal volume fraction of the nanoparticles where the heat transfer rate within the enclosure has a maximum value. Finally, the results reveal that by increasing the thermal conductivity of the nanoparticles and Rayleigh number, distribution of solid particles becomes uniform.