Majid Saffar-Avval

Amirkabir University of Technology | TUS · Department of Mechanical Engineering

This article investigates the effect of embedding the aluminum honeycomb structure in latent heat thermal energy storage (LHTES) of a solar air heater (SAH) and proposes an optimal arrangement of the partial honeycomb core. The effect of placing an aluminum honeycomb core in the LHTES of a solar air heater in mass flow rates of 0.02 and 0.04 kg/s i...

Numerical and experimental papers on the enhancement of evaporation from liquid surfaces due to the electrohydrodynamic flow are reviewed in this work. Impressive advances have been obtained during the last two decades in the augmentation of evaporation from liquid surfaces due to electrohydrodynamic flow, especially through numerical simulations....

In the oil and gas industry, sand particle erosion damage to elbows is a common problem. The ability to predict erosion patterns is of great importance for sizing lines, analyzing failures, and limiting production rates. Computational fluid dynamics (CFD) can be utilized to study the erosion behavior and mitigate the erosion problem for safety purp...

This paper presents experimental and numerical studies of heat transfer enhancement of water in an annulus under ultrasonic waves and fluid flow. An experimental setup is designed and built from two concentric pipes and a bolted Langevin ultrasonic transducer with a frequency of 25.7 kHz stuck to the inner pipe. Two new solvers are developed in Ope...

Overall heat transfer and pressure drop for three novel staggered tube banks with tubes partially wrapped with metal foam layers have been experimentally studied in an open circuit wind tunnel. The positions of the metal foam layers around the tubes are different in the studied tube banks, TB1, TB2, and TB3. In other words, the angles between inlet...

This paper is a thermo-economics and ecological study for solving the water shortage problem in the central and southern regions of Iran using solar energy. Bandar-e Jask in the south and Sirjan in the central region of Iran have been selected for the study. Water desalination units can be single solar still or solar still combined with solar pond....

Producing a desired level of fuel stratification has recently aroused much interest to improve performance of combustion systems. In the present work, an injection strategy is proposed by combining the rate-shaping (IRS) and split-injection approaches for regulating the level and quality of stratification. An Eulerian-Lagrangian numerical model is...

Basin-type solar stills lose their source of energy over nights which leads to very weak performance. In this paper, performance and energy consumption of an electrohydrodynamic desalination system for nightly production of fresh water in high-humidity regions are numerically examined. To solve the governing equations of a three-phase problem with...

In this paper, augmentation of water evaporation from saline water due to corona discharge generated EHD flow is numerically and experimentally examined. The effects of applied voltage and relative humidity of ambient air are considered. Relative humidity of ambient air affects both the corona discharge and the driving force of interfacial evaporat...

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...

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...

In many industrial applications, gas-liquid-particle three-phase flows are observed. Predicting erosion damage in this type of flow is a challenging issue, and so many factors, such as the liquid film behavior have significant effects on the erosion rate. In the present study, the Eulerian-Lagrangian approach was implemented to study the process of...

In this numerical study, flow driven by oscillating plates in a channel is investigated at the intermediate Reynolds regime by means of the arbitrary Lagrangian–Eulerian method. The effects of temporal asymmetry, Reynolds number, channel height, phase differences between adjacent plates, and orientation angle on pumping performance, which are uncle...

Sand erosion occurs in a host of industrial applications and accounts for one of the key factors in equipment failure. This study investigated sand particle erosion performance of different 90-degree fittings. To this end, a CFD-DEM model was employed and the erosion rates of various fittings carrying particle-laden flows were analyzed. Several cas...

In the oil and gas industry, predicting sand particle erosion damage is a challenging task as many factors have profound effects on the material losses. In this study, a computational modeling approach was used, and the sand erosion in gas-liquid-solid annular three-phase flows in pipe bends was analyzed. The Volume of Fluid (VOF) and the hybrid Eu...

Laminar forced convection heat transfer enhancement in a coaxial wire-tube corona system is numerically examined. Governing equations were solved using the finite volume method implemented in a developed solver using the OpenFOAM platform. The proposed corona system could change the flow pattern pushing the central high-velocity flow towards the ho...

In this study, first, the effect of different state-of-the-art dispersion and particle-wall collision models on the efficiency and erosion prediction are investigated. Second, the influence of particle size on the erosion pattern is explored. These assessments require reliable sub-model inputs, e.g. velocity statistics, which are provided through a...

Fracking (fracturing) is of great importance for enhancing oil and gas production from low permeability reservoirs. Since in fracking fluid, suspension of sand particles are used, the erosion failure of fracturing equipment has become an increasing concern. Accordingly, investigation of erosion of commonly used fittings such as ball seats in order...

This paper performs an economic evaluation study for different desalination scenarios to propose a solution to the water shortage problem in the central and southern regions of Iran. Bandar-e Jask in the south and Sirjan in the central region are selected to be studied. The desalination method utilizes a simple solar still or a combination of a sol...

This paper performs an economic evaluation study for different desalination scenarios to propose a solution to the water shortage problem in the central and southern regions of Iran. Bandar-e Jask in the south and Sirjan in the central region are selected to be studied. The desalination method utilizes a simple solar still or a combination of a sol...

Heat transfer enhancement of double-pipe heat exchanger in the presence of ultrasonic vibrations is experimentally and numerically studied. A novel experimental setup made of two concentric pipes is constructed and a bolted Langevin ultrasonic transducer is used for applying the ultrasonic vibrations to the inner pipe with a frequency of 26.7 kHz....

In this article, the current status of research in Iran has been evaluated with a focus on the field of engineering and especially mechanical engineering. To achieve this goal, the quantity and quality of research have been studied and compared with developed and developing countries. The number of scientific publications has been used as the main...

In many industrial applications, sand erosion wear is the main cause of equipment failure, particularly in the transferring pipeline fittings. In order to reduce the adverse consequences of erosion in bends, in this study the potential usage of plugged tees instead of standard elbows under a wide range of flow conditions is examined. A computationa...

Performance of the staggered and inline tube bundles with three rows covered by a porous layer has been numerically studied from the viewpoint of the first and second law of thermodynamics. The results indicate that wrapping tubes with a porous layer bring about Nu number augmentation as well as pressure drop increment in comparison with the bare t...

The efficient reduction of statistical error and achieving numerically convergent solutions in Eulerian-Lagrangian (EL) simulations necessitate the use of Parcel-Number-Density Control (PNDC) algorithms. Many PNDC algorithms have been proposed in other fields, like plasma simulations, which have not been evaluated for particle-laden two-phase flows...

Laminar forced convection heat transfer in an annulus partially filled with copper foam is enhanced using electrohydrodynamics (EHD) technique. A mathematical model for simulation of EHD conduction mechanism in an electrically conductive porous zone is developed. The flow patterns of the induced flow and electroconvection heat transfer are investig...

A two-phase electrohydrodynamic flow in a corona discharge system of a sharp needle and a water electrode is studied considering free interface deformation. The governing equations were solved using finite volume method implemented in a developed solver using the OpenFOAM platform. Recommendations are given about selection of equivalent electrical...

Laminar forced convection heat transfer from a constant temperature tube wrapped fully or partially by a metal porous layer and subjected to a uniform air cross-flow is studied numerically. The main aim of this study is to consider the thermal performance of some innovative arrangements in which only certain parts of the tube are covered by metal f...

In gas and oil industry, erosion damage to pipelines' bends and elbows due to the presence of sand particles has been a challenging issue. In this study, a computational model approach was used to evaluate the erosion rates at different vertical return bends: Sharp bend, standard elbow, 180° pipe bend, and long elbow. The airow in the pipe was simu...

Since curved pipes are widely used in industrial equipment, predicting multiphase ows in these geometries is of great importance. In the present study, a computational model for predicting the velocity profile is developed and used to study the developing turbulent gas-liquid ows in curved pipes. In order to discretize and solve the three-dimension...

Sand particle erosion is the main cause of the failure of bends in the natural gas pipelines. The rapid progress of computational power and modern numerical methods has provided the opportunity for developing realistic simulation of the erosion process. The goal of this paper is to predict the sand erosion rates with the use of computational fluid...

Erosion is a common problem in various parts of the pipeline industry. In this study, computational fluid dynamics is employed for analysis of pipeline erosion due to gas transported particles. Total removed volume and maximum erosion rate in different elbow geometries from 15° to 90°elbows, for a range of mass loadings are studied. Particle tracki...

In the present work, the hydrodynamics and heat transfer characteristics of water flow through a pipe with porous medium insert at the core were investigated numerically and experimentally. The pipe wall was subjected to a constant and uniform heat flux. The cylindrical porous medium was fabricated from copper wires woven together. The effects of v...

Heat transfer and pressure drop for a tube bank with 5 rows of tubes wrapped by metal foam layers has been numerically studied. The results show that covering the tubes with a thin metal foam layer could result in substantial heat transfer enhancement in comparison to the bare tube bank. Moreover, it is indicated that metal foam wrapped tube banks...

The augmentation of heat transfer and acoustic streaming due to high frequency ultrasonic waves are investigated numerically. The incompressible Navier-Stokes and energy equations are solved by perturbation method because of the great difference between ultrasonic time period and fluid flow time step. The model is implemented in OpenFOAM software a...

Using nano fluid and curved pipes are two efficient methods for improving heat transfer rate. In the present research, turbulent flow in curved tube and helically coiled tubes is numerically investigated in developing flow. In addition, convective heat transfer is investigated in helically coils under constant wall heat flux. Heat transfer in Nano...

Laminar forced convection heat transfer in an annulus is enhanced using electrohydrodynamics (EHD) technique. A novel EHD-enhanced double pipe heat exchanger is designed and incorporated with six pairs of electrodes. An experimental setup is constructed to investigate heat transfer enhancement, pressure drop and power consumption in the double pipe...

In the present study a rule-based fuzzy inference system is used to predict heat transfer and entropy generation of stratified air-water flow in horizontal mini-channel as a function of a wide range of important parameters. Numerical data of our recent study are used to develop and test the system. The GK clustering algorithm is used to cluster the...

In the present paper, a numerical study has been conducted to investigate the heat transfer from a constant temperature cylinder covered with metal foam. The cylinder is placed horizontally and is subjected to a constant mean cross-flow in turbulent regime. The Reynolds Averaged Navier-Stokes (RANS) and Darcy-Brinkman-Forchheimer equations are comb...

This study include experimental and three dimensional numerical analysis of conjugate steady state laminar forced ferroconvection of Newtonian incompressible ferrofluid through horizontal circular pipe under constant heat flux and in presence of transverse magnetic field. Magnetic field was applied by two fixed parallel magnet bars at the beginning...

In the present paper, an in-house CFD code is developed using Roe scheme to simulate a condensing two-phase flow in blade to blade passage of a steam turbine. Effects of condensation on the flow field of steam turbine rotor tip section are investigated for different outlet pressures. Firstly, comparison is performed between results of wet and dry c...

Application of ultrasonic waves for heat transfer augmentation has been proposed in the last few decades. Due to limited researches on acoustic streaming induced by ultrasonic oscillation, the effect of ultrasonic waves on natural convection heat transfer is the main purpose of this paper. At first, natural convection on up-ward-facing heating surf...

Helical coils and nanofluids are among efficient methods for heat transfer augmentation. The present study numerically investigates convective heat transfer with nanofluids in helically coiled tubes. Two boundary conditions are applied to the coil walls; constant temperature and constant heat flux. Heat transfer in nanofluids are mainly investigate...

In the present study, heat transfer and entropy generation of developing KOH-water solution is numerically examined by implementing a finite difference code to solve the governing equations. Effects of important parameters of heat transfer in both of the developing and fully developed regions are examined. The study reveals that alteration of the e...

In this paper, effects of non-equilibrium condensation on deviation angle and performance losses of wet stages of steam turbines are investigated. The AUSM-van Leer hybrid scheme is used to solve the two-phase turbulent transonic steam flow around a turbine rotor tip section. The dominant solver of the computational domain is the non-diffusive AUSM...

In this paper, the AUSM-van Leer hybrid scheme is extended to solve the governing equations of two-phase transonic flow in a steam turbine stage. The dominant solver of the computational domain is the non-diffusive AUSM scheme (1993), while a smooth transition from AUSM in regions with large gradients to the diffusive scheme by van Leer (1979) guar...

In the present paper, the hybrid AUSM-van Leer scheme is extended to solve the governing equations of twophase condensing flows. The method of moments with the classical homogeneous nucleation theory is used to model the non-equilibrium condensation phenomenon. Firstly, the hybrid method is validated using two test cases (i.e. Laval nozzle and roto...

In microfluidics, two important factors responsible for the differences between the characteristics of the flow and heat transfer in microchannels and conventional channels are rarefaction and surface roughness which are studied in the present work. An incompressible gas flow in a microchannel is simulated two dimensionally using the lattice Boltzm...

In this paper, convective heat transfer coefficient of Graphene–water nanofluid in a laminar flow through a circular pipe with uniform wall heat flux is investigated experimentally. To achieve this aim, the nanofluid is synthesized chemically in various concentrations, and a testbed is constructed. The effective thermal conductivity and viscosity o...

Heat transfer in two-phase flow boiling of a dilute mixture of TiO2 nanoparticles in R141b base fluid in a smooth tube is investigated experimentally. Examining the obtained results reveals that enhancement of the convective heat transfer coefficient for the particle volume fractions of 0.01% and 0.03% in comparison with pure R141b is more pronounc...

In this paper, effects of turbine blade roughness and steam condensation on deviation angle and performance losses of the wet stages are investigated. The steam is assumed to obey non-equilibrium thermodynamic model, in which abrupt formation of liquid droplets produces condensation shocks. An AUSM-van Leer hybrid scheme is used to solve two-phase...

In the present research, steady state turbulent forced convection developing flow of a CuO nano-fluid inside helically coiled tubes at constant wall surface temperature was investigated both numerically and experimentally. Both the pressure drop and convective heat transfer behaviors of the nano-fluid were investigated in detail and compared with t...

The current study focuses on numerical and experimental investigation of the laminar, steady state flow in helical tubes with constant wall heat flux boundary condition. Pressure drop and convection heat transfer behavior of water–silver nanofluid in helical coils were evaluated and compared to the pure water. In the numerical part of the study, in...

In this paper, conjugate heat transfer in a wavy walls microchannel with different geometrical parameters has been studied numerically to find the optimum geometry with maximum Nusselt number. A constant heat flux boundary condition has been applied on the bottom wall of the micro-device. Water used as working fluid and the body is made of silicon....

In the present study, the effects of wall roughness on erosion rate for gas–solid flows in horizontal annular pipes for different ratios of inner to outer radii and also for different values of solid particle concentration are investigated. The results are compared with earlier studies, and the effect of various parameters is discussed. The impinge...

Gas–solid flow in a pipe with different configurations (vertical, horizontal, and inclined positions) is studied experimentally. Air with temperature around 170°C and sand particles with mean diameter of 253 μm are used as gas and solid mediums, respectively. Effects of different parameters (pipe slope and solid particles feed rate) are studied on...

The effect of magnetic field on laminar forced convection of ferrofluid in a horizontal tube partially filled with porous media is investigated. Governing equations are solved numerically using the finite volume method and the SIMPLE algorithm, to obtain thermohydrodynamic characteristics and enhancement of heat transfer for different porous locati...

A modified model for prediction of erosion rate in pipe flows is presented based on the simulation of the fluid fluctuating velocities with the Discrete Random Walk model. Turbulence modulation of gas-solid flow in a horizontal pipe is investigated numerically using a four-way coupled Eulerian-Lagrangian approach. The particle impingement angle and...

The effects of wall surface roughness on the rate of heat transfer and temperature profiles in turbulent gas-solid flows in pipes at different inclination angles were studied. The earlier developed computational model for 3D flows including the four-way interactions was extended and used in this study for evaluating the mean flow, turbulence intens...

The effect of presence of solid particles on stratified wavy gas-liquid flows has been studied. The height of liquid phase in the natural gas pipeline is a key parameter in designing and can affect the corrosion/erosion rate. In present paper, the numerical four-way simulation of solid particles in gas-liquid wavy stratified flow has been used. The...

Turbulent convective heat transfer of graphene–water nanofluids with various concentrations inside a uniformly heated circular tube is studied experimentally. For this purpose, experiments are conducted to measure thermal conductivity, viscosity, pressure drop, and heat transfer coefficient. Results show enhancement of thermal conductivity and mode...

In this article, laminar forced convection of nanofluids in a parallel plate microchannel under constant wall temperature is numerically investigated. A Eulerian–Lagrangian two-phase method is employed to simulate the flow and heat transfer of nanofluid in the microchannel. Navier–Stokes equations were solved using a finite difference method based...

Curved pipes constitute essential components in engineering systems such as heat exchangers, and process pipelines. In curved pipes with 180� bends, the excess pressure drop, and the excess entropy generation (through heat and fluid flow) bring forth serious penalties. To overcome these difficulties a new partially curved pipe will be examined in t...

Due to demands for the economical operations of power plants and environmental awareness, performance control of a boiler-turbine unit is of great importance. In this paper, a nonlinear Multi Input-Multi Output model (MIMO) of a utility boilerturbine unit is considered. Drum pressure, generator electric output and drum water level (as the output va...

As a result of the worldwide concern about global warming, projects that target reduction of greenhouse gas emissions have gained a lot of interest. The idea of this paper is to recover exhaust hot gases of an existing gas turbine power plant to meet dynamic thermal energy requirements of a residential area (the new town of Parand) situated in the...

Heat transfer enhancement in presence of acoustic streaming in a closed cylindrical enclosure filled with water on a down-ward-facing horizontal heating surface was measured experimentally. Acoustic streaming is induced by the vibration of the lower plate by means of an ultrasonic Bolted Langevin transducer. Standing wave was generated between a la...

The thermodynamic and thermoeconomic analyses are investigated to achieve the optimum operating parameters of a dual pressure heat recovery steam generator (HRSG), coupled with a heavy duty gas turbine. In this regard, the thermodynamic objective function including the exergy waste and the exergy destruction, is defined in such a way to find the op...

The employment of a TES system to improve the performance of a DH network integrated with a CHP station is investigated. Thermal energy demand fluctuations is the main issue threatening the viability of CHP/DH projects; therefore, TES facility can be coupled with CHP plant by a smart operation strategy to match the production and consumption profil...

In the present research, laminar, steady state flow in helically coiled tubes at a constant wall temperature was studied numerically and experimentally. Pressure drop and the convective heat transfer behavior of nanofluid were investigated. In the experimental section, a heat exchanger was designed, capable of providing constant wall temperature fo...

Nowadays, dynamic analysis of air-conditioner units is essential to achieve satisfactory comfort conditions in buildings with low energy consumption and operation cost. In this paper, a nonlinear multi input–multi output model (MIMO) of an air-handling unit (AHU) is considered. In the presence of realistic harmonic disturbances, nonlinear dynamics...

In steam power-plants, to prevent over-heating of drum components or flooding of steam lines, perfect control of drum water level is of great importance. But during the operation, disturbances affecting water level, model uncertainties and parameter mismatch due to variant operating conditions lead to the variation of model parameters. In this pape...

In this paper, acoustic streaming generated by standing waves in a cylindrical enclosure filled with water is simulated. The effects of geometry, vibrating amplitude and frequency on formation of streaming structures are numerically investigated. The vibrating source is located at the central region of the lower plate. This source generates a plane...

Natural gas pressure has to be increased in natural gas distribution network; meanwhile, before entering the low-pressure lines, this high pressure must be reduced. Pressure let-down in city gate stations is traditionally performed as natural gas passes through a throttle valve, although this method is simple, a considerable irreversibility is impo...