Ali Ahmadpour

Ali Ahmadpour
Amirkabir University of Technology | TUS · Department of Mechanical Engineering

PhD
Numerical Modeling of Complex Fluid Flows and Heat Transfer

About

46
Publications
4,775
Reads
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481
Citations
Citations since 2017
34 Research Items
436 Citations
2017201820192020202120222023020406080100
2017201820192020202120222023020406080100
2017201820192020202120222023020406080100
2017201820192020202120222023020406080100
Additional affiliations
September 2015 - December 2015
Amirkabir University of Technology
Position
  • Lecturer

Publications

Publications (46)
Article
The restart problem of pipelines filled with gelled waxy crude oils is investigated numerically using the finite volume method (FVM). Based on the rheological data obtained using the MCR-301 rheometer for a typical Iranian waxy crude oil, the Dullaert-Mewis (DM) rheological model was adopted to represent the viscoplastic/thixoelastic nature of such...
Article
The effect of a variable plastic viscosity is numerically investigated on the success of the restart operation for a pipeline filled with fully-gelled waxy crude oil. To investigate the separate effects of structure- and shear-dependent viscosity, waxy crude oil is assumed to obey the Houska rheological model. In order to precisely capture the shap...
Article
An exact solution is found for swirling flow of Bingham fluids above a rotating disk. The similarity parameter, first introduced by von Karman for Newtonian fluids, is found to be applicable for Bingham fluids effectively reducing the governing PDEs into a set of coupled ODEs. The system of nonlinear ordinary differential equations so obtained is s...
Article
Laminar flow of an incompressible thixotropic liquid which obeys the Houska model as its constitutive equation is investigated theoretically in a circular pipe under equilibrium (steady) conditions. Having derived the single differential equation governing fully-developed, unidirectional, pipe flow of this fluid model, it is shown that an analytica...
Article
The von Karman flow of an incompressible Bingham fluid is studied numerically under laminar and steady conditions. Boundary layer theory is used to simplify the equations of motion assuming that the flow is axisymmetric. A suitable similarity parameter is used to reduce the governing partial differential equations into a system of coupled ordinary...
Article
In the present research, a comparative study of improved Large-Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) closures are carried out with the focus on the influence of terms accounting for the effect of Non-Newtonian (NN) power-law fluid rheology. Using different available databases for shear-thinning turbulent pipe flows, a new...
Article
In the present study, the convective heat transfer of MWCNT/water nanofluid was investigated along microchannels with different cross-sectional geometries. This class of carbon-based nanofluid exhibited a notable non-Newtonian shear-thinning behavior, which made them suitable for different heat transfer applications. A two-phase mixture model with...
Article
Full-text available
In the present study, numerical simulation of the steady blood flow through the carotid artery with non-planar geometry model and considering mild (20%), moderate (50%), and severe (80%) occlusion was performed. In this research, the shear-thinning behavior of the blood fluid is incorporated by the Carreau-Yasuda model, and the viscoplasticity of b...
Article
Full-text available
In the present study, the Thermo-hydraulic performance evaluation of nano-encapsulated phase change material slurries was undertaken in a micro-channel heat sink. The present research was motivated by the urgent need for the performance enhancement of micro-sized heat sinks for the electronic cooling application. A micro-channel with sinusoidal cav...
Article
Large Eddy Simulation (LES) of turbulent non-Newtonian flows involves two additional closures, namely the Non-Newtonian SubGrid-Scale (NNSGS) stress tensor and filtered viscosity. Here, dynamic closures are proposed for NNSGS, eliminating the need for model calibration. In addition, for the primary evaluation of LES closures, two canonical case stu...
Article
In the present study, the two-phase gas–liquid convective heat transfer is numerically studied inside uniformly heated wavy micro-tubes in the Taylor flow regime. Both Newtonian and Shear-thinning rheological behavior for the liquid phase are considered. The volume of fluid method is employed to capture the gas–liquid interface throughout the flow...
Article
The present study introduces a microchannel heat sink (MCHS) with a new geometry entitled as flattened, which is used to dissipate heat flux form high heat flux generation devices and evaluates its hydrothermal performance. Three-dimensional conjugate heat transfer problem with the assumptions of laminar and steady-state fluid flow has been solved...
Article
In the present study, a low-cost solar fruit and vegetable dryer was designed, constructed, and tested for small-scale production, especially in households. An optimizing procedure was performed to convert a typical widely-used direct cabinet dryer into a new indirect dryer using experimental data and numerical simulations. Several well-designed ex...
Article
The laminar forced convective heat transfer of multi-walled carbon nanotubes (MWCNTs)/water nanofluids with shear-thinning rheological behavior inside curved tubes is addressed in the present study. The four-equation model was selected to model the fluid flow and heat transfer of the nanofluid accounting for the Brownian diffusion and thermophoresi...
Article
The laminar forced convective heat transfer of multi-walled carbon nanotubes (MWCNTs)/water nanofluids with shear-thinning rheological behavior inside curved tubes is addressed in the present study. The four-equation model was selected to model the fluid flow and heat transfer of the nanofluid accounting for the Brownian diffusion and thermophoresi...
Article
A numerical study is performed to investigate the effects of an external uniform and non-uniform magnetic field on the optimal geometric design and thermal performance of a microchannel heat sink. Fe3O4 nanoparticles suspended in water is used as the cooling fluid. The optimization process has been utilized for three cases: (1) in the absence of th...
Article
The forced convective heat transfer from multiple isothermal cylinders in tandem and staggered arrangements to the surrounding non-Newtonian Carreau fluid was studied. The study has been motivated by this fact that the Carreau viscosity function is one of the most accurate rheological models for the prediction of non-Newtonian inelastic behavior. A...
Article
In the present work, a 3D numerical study has been performed to investigate the core-annular flow of waxy crude oil/water in inclined pipes with a gradual expansion. Waxy crudes are highly viscous crude oils that exhibit non-Newtonian flow behavior, and their efficient transportation is still a technical challenge. In the current work, the use of t...
Article
In the present work, a 3D numerical study was carried out to investigate the stratified flow of waxy crude oil-water through a horizontal pipe with a contraction-expansion placed in its midsection. Moreover, a uniform heat flux was applied to the pipeline wall to investigate its effect on the overall pressure drop across the pipeline and the two-ph...
Article
In this study, natural convection of non-Newtonian power-law fluids around an array of elliptic cylinders has been investigated numerically. The governing equations have been solved using an in-house CFD code based on the well-known finite volume method. It is assumed that the flow and temperature fields are laminar, steady, and two-dimensional. Fu...
Article
In the present study, laminar natural convection of a non-Newtonian ferrofluid inside an elliptical porous cavity was numerically simulated in the presence of a non-uniform external magnetic field. This natural convection problem was relevant to the cooling of micro-sized electronic devices. The well-known finite volume method was employed to discr...
Article
The displacement flow inside a long pipeline filled with a stagnant thixoelastic fluid was investigated in the present study using the computational fluid dynamics (CFD). It was considered that the thixoelastic fluid was removed from the pipeline by a Newtonian incoming fluid which was injected at the pipeline inlet with constant pressure. This two...
Article
In this study, detailed three-dimensional (3D) numerical simulations of intermittent multiphase flows were carried out to investigate the slug initiation process and various features of intermittent flows inside a horizontal pipe. Air and water are used as working fluids. The domain used for simulations is a 14.4 m long pipe with 54 mm inner diamet...
Article
In the present study, the use of mechanical vibration for the enhancement of pool boiling heat transfer is evaluated theoretically. For this purpose, a vertical array of vibrating circular tubes is considered. The array is submerged in a pool of water under atmospheric conditions and electrically heated for boiling to occur on the tube surfaces. To...
Article
Turbulent gas-liquid multiphase flows with and without phase change in a vertical wavy channel are addressed. The multiphase flow field is resolved using the volume of fluid method (VOF), and the flow equations are discretized and numerically solved by the well-known finite volume method. As a multiphase system without mass transfer, air/water flow...
Article
This study investigates condensation of R141b in an 8mm ID horizontal smooth tube. Condensation of R141b is conducted at an average saturation temperature of  with mass fluxes ranging from 40 to 400 kg m-2 s-1. The plant runs with low vapor quality of refrigerant where intermittent flow is expected to be the dominant flow regime. visualization im...
Article
In the present study, natural convection heat transfer and its associated entropy generation in a porous trapezoidal enclosure saturated with a power-law non-Newtonian fluid has been numerically investigated. Horizontal walls of the enclosure are assumed to be adiabatic while the side walls are considered to be kept at a constant temperature. A con...
Article
In the present work, the rise of a single elongated gas bubble in a vertical tube filled with Newtonian or shear-thinning (CarboxyMethyl Cellulose or CMC) liquid is numerically studied in the presence of a sudden/gradual area expansion. The shear-thinning rheology was modeled using the well-known Carreau-Yasuda viscosity function. Governing equatio...
Article
In the present work, the rise of a single Taylor bubble through stagnant shear thinning liquids is numerically investigated. The non-Newtonian liquid rheology is modeled using the well-known Carreau–Yasuda viscosity function and the gas/liquid interface is captured by the volume of fluid method. 2D axisymmetric and 3D numerical results obtained by...
Article
The recent studies in biofluids of the cardiovascular system has put in front several apprehension for the diagnosis of atherosclerosis. Arterial stenosis is basically the fat accumulated over the inner walls of the artery. The stenosis are found mostly on the bifurcations of the large arteries and the junctions the curvatures. The stenosis is most...
Article
Full-text available
The recent studies in biofluids of the cardiovascular system has put in front several apprehension for the diagnosis of atherosclerosis. Arterial stenosis is basically the fat accumulated over the inner walls of the artery. The stenosis are found mostly on the bifurcations of the large arteries and the junctions the curvatures. The stenosis is most...
Article
Full-text available
In the present study, MHD laminar mixed convection of Cu/water nanofluid inside a lid driven cavity and in the presence of two rotating cylinders is numerically simulated. This mixed convection problem has found its applications in material processing, air conditioning, electronic cooling, solar heating/cooling and other natural and industrial proc...
Article
In the present study, numerical optimization of a double layer micro channel heat sink is addressed. Carbon based nanofluids with a non-Newtonian viscosity is assumed as the coolant. A conjugate numerical model based on finite volume method and two-phase mixture model is used to simulate the heat and fluid flow through the two three-dimensional dom...
Article
In the present study, a numerical simulation of atmospheric pool boiling on tandem, inclined, electrically heated circular tubes is performed. An Eulerian-Eulerian description of the two-phase flow formulations is adopted together with a Rensselaer Polytechnic Institute (RPI) nucleate boiling model to account for the heat and mass transfer in the b...
Article
In the present work, a numerical approach is proposed to simulate two phase pool boiling on a staggered tube bundle. The simulations are carried out using the Eulerian–Eulerian framework for two phase flows, accounting for the nucleate pool boiling on the surface of the tube bundle. A favourable agreement was reported between the numerical results...
Article
In the present study, the applicability of wall heating for facilitating the restart process of gelled pipelines by the injection of a secondary fresh fluid is evaluated using computational fluid dynamics (CFD). The secondary fluid is assumed to be injected with a constant pressure into the pipeline and at the same time the pipe wall is considered...
Article
In the present study, the combined effect of non-uniform heat source/sink, suction/injection , thermal radiation, and viscous dissipation is investigated on the unsteady squeezing flow and heat transfer of non-Newtonian Casson fluids. By means of a suitable similarity transformation, the governing equations are converted to a set of non-linear ordi...
Article
In this study, the steady pipe flow of a thixo-elastic fluid is considered. Thixo-elasticity is modeled using the modified Delaware thixotropic model (MDTM). In MDTM model, the total stress tensor is decomposed into a viscous part and an elastic part and each stress component is properly modeled using the concept of single structural parameter whic...
Article
In the present study, increasing the performance of thermo-compressors and steam turbines by volumetric cooling and inlet superheating is addressed. The efficacies of these two proposed methods are assessed using a numerical code developed based on Eulerian-Eulerian description of the two-phase fluid flow accounting for the spontaneous nucleation....
Article
In this study CFD-based shape optimization of a 3D nozzle and a 2D turbine blade cascade is undertaken in the presence of non-equilibrium condensation within the considered flow channels. A two-fluid formulation is used for the simulation of unsteady, turbulent, supersonic and compressible flow of wet steam accounting for relevant phase interaction...
Article
In the present study, the displacement of waxy crude oils is numerically/theoretically investigated in the water-flooding operation. The oil was assumed to obey the Houska model―a robust thixotropic fluid model which is often realized to well describe the rheology of waxy oils in different parts of the world. Based on the concept of effective visco...
Article
In the present work, turbulent two-phase flows of air and water are numerically simulated through a smooth area expansion/restriction with a constant opening angle. To model the multiphase flow, a two-fluid approach is adopted in which two sets of governing equations are solved simultaneously for continuous and dispersed phases and the coupling bet...
Article
In the present work, the dynamics of a single spherical gas bubble surrounded by an elastic thixotropic liquid is addressed at the presence of an acoustic pressure field. The well-known Dullaert and Mewis' rheological model is used to represent different aspects of the fluid's thixotropic and elastic behavior. A numerical method based on Gauss-Lagu...
Article
https://www.jstage.jst.go.jp/article/rheology/39/3/39_3_113/_article In the present work, nonlinear acoustic oscillation of a single spherical gas bubble immersed in an unbounded thixotropic fluid is studied numerically. Using Moore's structural model as the constitutive equation of the liquid surrounding the bubble, the general Rayleigh-Plesset i...
Article
Full-text available
In this study, the problem of natural convection and radiation heat transfer in a micro fin array heat sink is numerically investigated. A two-dimensional model is used to formulate the problem. The governing equations of the problem are mass, momentum and energy equations of the fluid along with conduction equation in the micro fin. The radiation...

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Projects (8)
Project
This project aimed to develop a solar fruit and vegetable dryer suitable for household usage with the highest standards to provide final acceptable mechanical, economical and environmental features. Now the patent and related article are just under preparation.