Iman Zahmatkesh

Bio: Iman Zahmatkesh is an academic researcher from Islamic Azad University. The author has contributed to research in topics: Nanofluid & Heat transfer. The author has an hindex of 9, co-authored 34 publications receiving 384 citations. Previous affiliations of Iman Zahmatkesh include Shiraz University.

Free convection heat transfer analysis of a suspension of nano–encapsulated phase change materials (NEPCMs) in an inclined porous cavity

Abstract: In the current study, free convection heat transfer of a suspension of Nano–Encapsulated Phase Change Materials (NEPCMs) is simulated and discussed in an inclined porous cavity. The phase change materials are capsulated in nano-shells layers, while the core stores/releases large amounts of energy during melting/solidification in the vicinity of the hot/cold walls. The governing equations are introduced and transformed into non–dimensional form before being solved by using the finite element method. Simulation results are validated thoroughly. Thereafter, the consequences of the fusion temperature and the Stefan number on the distributions of streamlines, isotherms, and the heat capacity ratio, as well as the heat transfer characteristics, are analyzed for different inclination angles of the cavity. Inspection of the results demonstrates that the best heat transfer performance occurs for the non–dimensional fusion temperature of 0.5 and the inclination angle of 42°. It is found that a decrease in the Stefan number improves heat transfer. The results also show that the presence of the NEPCM particles generally leads to heat transfer improvement.

On the importance of thermal boundary conditions in heat transfer and entropy generation for natural convection inside a porous enclosure

Abstract: The aim of the present paper is to analyze the importance of thermal boundary conditions of the heated/cooled walls in heat transfer and entropy generation characteristics inside a porous enclosure, heated from below. Both the heating and the cooling are carried out uniformly and non-uniformly and the results are compared. The laminar, steady, natural convection heat transfer is calculated by solving numerically the mass, momentum, and energy conservation equations whilst viscous dissipation and the work of pressure forces are included in the energy equation. Moreover, the generation of entropy is calculated taking into account both heat transfer irreversibility and fluid friction irreversibility. As the thermal boundary conditions, sinusoidal temperature distributions are invoked for the non-uniformly heated/cooled walls. Comparison between the results of the present numerical model with the previously published works provides excellent agreement. Results are presented in terms of streamlines, isothermal lines, iso-entropy generation lines, and iso-Bejan lines. Additionally, variations of average Nusselt number, global entropy generation rate, and global Bejan number are analyzed over a wide range of Darcy-modified Rayleigh number ( 10 Ra 1000 ). Inspection of the results indicates that thermal boundary conditions are of profound influences on the induced flow as well as heat transfer characteristics and possess prominent consequences on entropy generation rates. It is demonstrated that, the optimum case with respect to heat transfer as well as entropy generation could be achieved by non-uniform heating.

Effect of nanoparticle shape on the performance of thermal systems utilizing nanofluids: A critical review

Abstract: Due to their superior thermophysical properties, there is a growing body of work on nanofluids in the field of thermal systems. However, there is no specific review of the role of the nanoparticle shape, which has been found crucial to their performance adjustment. A comprehensive literature review of the effect of nanoparticle shape on the hydrothermal performance of thermal systems utilizing nanofluids was compiled. The review covered the forced, mixed, and natural convection regimes and included heat exchangers, boundary layer flows, channel flows, peristaltic flows, impinging jets, cavity flows, and flows of hybrid nanofluids. It indicated that the control of nanoparticle shape is a promising technique for the optimization of heat exchange and the required pumping power. However, no uniform conclusion was reached for the role of nanoparticle shape on the hydrothermal performance of thermal systems. In most of the previous studies in the natural and forced convection regimes, the platelet–like nanoparticle acquired the highest heat transfer rate. However, most of the works in the mixed convection regime reported the best heat transfer performance for the blade–like nanoparticle. More research studies are required in future to determine the role of nanoparticle shape for thermal management of energy systems.

On the importance of thermophoresis and Brownian diffusion for the deposition of micro-and nanoparticles

Abstract: The aim of the present paper is to analyze the importance of thermophoresis as well as Brownian diffusion for the deposition of micro- and nanoparticles in the presence of temperature gradient. A hybrid Eulerian–Lagrangian procedure is invoked to evaluate the air flow and temperature distribution as well as particles dispersion and deposition. Inspection of the results indicates that, the dominant mechanism for the deposition of ∼ 100 μm particles belongs to inertial impaction. The results reveal that, ∼ 10 μm particles are mainly influenced by thermophoresis. For finer particles (10 nm

Influence of thermal radiation on free convection inside a porous enclosure

Abstract: ةيماسم ةدامب ءولمم زيح لخاد لمحلاب ةكرحلا لاجم ىلع عاعشلإاب ةرارحلا لاقتنا رثأ ةسارد ىلإ ثحبلا فدھي ةعئاملا ةداملل (Laminar) مظتنم نايرج فورظ تحت ةرارحلا لاقتنلا تاباسحلا لمع مت .ةعئاملا ةداملاب ةعبشم بيرقتو Darcy نوناق نم لاك مادختسا مت لحلا يف .ةقاطلاو ،مخزلا ،ةداملا ظفح تلاداعمل يددعلا لحلا قيرط نع نكل (gray) يدامرلا عونلا نم عئاملا رابتعا مت دقف يرارحلا عاعشلإا ثيح نم اما .Oberbeck-Bousinesg طباوضلا .ةقاطلا ظفح ةلداعم يف عاعشلإا رادقم باسحل راشتنلال Rosseland بيرقت مادختسا عمو ،تيتشت نودب نيطئاحلا امنيب ،ةفلتخم نكل ةتباث ةرارح تاجرد امھل نيلباقتملا نيطئاحلا نم نانثإ :يھ لحلا يف ةمدختسملا ةيدحلا قباطت ظحول دقف اقباس ةروشنم جئاتن عم ثحبلا اذھ جئاتن ةنراقمبو (Adiabatic) ايرارح امھلزع مت نيرخلآا لاجملاو (Flow) ةكرحلا لاجمب ؤبنتلل هئادأ ةحص نم ققحتلا مت مدختسملا ليدوملا نإف اذھبو .مھنيب زاتمم يرارحلا عيزوتلاو ايرارح نيلوزعملا ريغ نيطئاحلا ىلع Nusselt ددع يف تاريغتلا نإف كلذل ةفاضإ .يرارحلا .ةفلتخم عاعشإ فورظ تحت مھتسارد مت نيلوزعملا نيطئاحلا ىلع

A Benchmark Study on the Thermal Conductivity of Nanofluids

Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Effect of thermal radiation on magnetohydrodynamics nanofluid flow and heat transfer by means of two phase model

Abstract: In this study, effect of thermal radiation on magnetohydrodynamics nanofluid flow between two horizontal rotating plates is studied. The significant effects of Brownian motion and thermophoresis have been included in the model of nanofluid. By using the appropriate transformation for the velocity, temperature and concentration, the basic equations governing the flow, heat and mass transfer are reduced to a set of ordinary differential equations. These equations, subjected to the associated boundary conditions are solved numerically using the fourth-order Runge–Kutta method. The effects of Reynolds number, magnetic parameter, rotation parameter, Schmidt number, thermophoretic parameter, Brownian parameter and radiation parameter on heat and mass characteristics are examined. Results show that Nusselt number has direct relationship with radiation parameter and Reynolds number while it has reverse relationship with other active parameters. It can also be found that concentration boundary layer thickness decreases with the increase of radiation parameter.

MHD free convection of Al2O3–water nanofluid considering thermal radiation: A numerical study

Abstract: This article explores the effect of thermal radiation on Al2O3–water nanofluid flow and heat transfer in an enclosure with a constant flux heating element. KKL (Koo–Kleinstreuer–Li) correlation is used for simulating effective thermal conductivity and viscosity of nanofluid. The governing equations are solved via control volume based finite element method. The effects of Rayleigh number, Hartman number, viscous dissipation parameter, radiation parameter and volume fraction of nanoparticle on the flow and heat transfer characteristics have been examined. Results show that enhancement in heat transfer has direct relationship with Hartman number, viscous dissipation parameter and radiation parameter but it has reverse relationship for Rayleigh number. It is also observed that Nusselt number is an increasing function of Rayleigh number, volume fraction of nanoparticle and radiation parameter while it is a decreasing function of viscous dissipation parameter and Hartman number.

A review on slip models for gas microflows

Abstract: Accurate modeling of gas microflow is crucial for the microfluidic devices in MEMS. Gas microflows through these devices are often in the slip and transition flow regimes, characterized by the Knudsen number of the order of 10−2~100. An increasing number of researchers now dedicate great attention to the developments in the modeling of non-equilibrium boundary conditions in the gas microflows, concentrating on the slip model. In this review, we present various slip models obtained from different theoretical, computational and experimental studies for gas microflows. Correct descriptions of the Knudsen layer effect are of critical importance in modeling and designing of gas microflow systems and in predicting their performances. Theoretical descriptions of the gas-surface interaction and gas-surface molecular interaction models are introduced to describe the boundary conditions. Various methods and techniques for determination of the slip coefficients are reviewed. The review presents the considerable success in the implementation of various slip boundary conditions to extend the Navier–Stokes (N–S) equations into the slip and transition flow regimes. Comparisons of different values and formulations of the first- and second-order slip coefficients and models reveal the discrepancies arising from different definitions in the first-order slip coefficient and various approaches to determine the second-order slip coefficient. In addition, no consensus has been reached on the correct and generalized form of higher-order slip expression. The influences of specific effects, such as effective mean free path of the gas molecules and viscosity, surface roughness, gas composition and tangential momentum accommodation coefficient, on the hybrid slip models for gas microflows are analyzed and discussed. It shows that although the various hybrid slip models are proposed from different viewpoints, they can contribute to N–S equations for capturing the high Knudsen number effects in the slip and transition flow regimes. Future studies are also discussed for improving the understanding of gas microflows and enabling us to exactly predict and actively control gas slip.

A review on entropy generation in natural and mixed convection heat transfer for energy systems

Abstract: This paper reviews the second law analysis of thermodynamics in enclosures due to buoyancy-induced flow for energy systems It defines entropy generation minimization or thermodynamic optimization In addition, the article summarizes the recent works on entropy generation in buoyancy-induced flows in cavity and channels Studies on mixed convection were also included in the study Presentation was performed for flow in porous media and viscous fluid filled media at different shaped enclosures and duct under buoyancy-induced force