Search for: mixed-convection
Total 23 records
Modified Buongiorno's model for fully developed mixed convection flow of nanofluids in a vertical annular pipe, Article Computers and Fluids ; Vol. 89 , 2014 , pp. 124-132 ; ISSN: 00457930 ; Moshizi, S. A ; Soltani, E. G ; Ganji, D. D ; Sharif University of Technology
This paper deals with the mixed convective heat transfer of nanofluids through a concentric vertical annulus. Because of the non-adherence of the fluid-solid interface in the presence of nanoparticle migrations, known as slip condition, the Navier's slip boundary condition was considered at the pipe walls. The employed model for nanofluid includes the modified two-component four-equation non-homogeneous equilibrium model that fully accounts for the effects of nanoparticles volume fraction distribution. Assuming the fully developed flow and heat transfer, the basic partial differential equations including continuity, momentum, and energy equations have been reduced to two-point ordinary...
Numerical study of mixed convection heat transfer of various fin arrangements in a horizontal channel, Article Engineering Science and Technology, an International Journal ; Volume 20, Issue 3 , 2017 , Pages 1106-1114 ; 22150986 (ISSN) ; Barzegar Gerdroodbary, M ; Yeganeh, R ; Fallah, K ; Sharif University of Technology
Elsevier B.V 2017
The mixed convection of a three-dimensional square duct with various arrangements of fins in both laminar and turbulent flow is numerically characterized and studied. This study focuses on the ability of fin arrangements to enhance a heat transfer while flow is incompressible and the fluid is air. In our models, the lower duct wall is defined with a constant heat flux condition while the two side walls and upper wall are insulated. The finite volume method with the SIMPLE (Semi Implicit Method for Pressure Linked Equations) algorithm is used for handling the pressure–velocity coupling. The numerical results are validated with experimental data and show good agreement. The computations...
Article Microfluidics and Nanofluidics ; Vol. 16, issue. 1-2 , 2014 , pp. 207-224 ; ISSN: 16134982 ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
Consideration is given to the buoyancy effects on the fully developed gaseous slip flow in a vertical rectangular microduct. Two different cases of the thermal boundary conditions are considered, namely uniform temperature at two facing duct walls with different temperatures and adiabatic other walls (case A) and uniform heat flux at two walls and uniform temperature at other walls (case B). The rarefaction effects are treated using the firstorder slip boundary conditions. By means of finite Fourier transform method, analytical solutions are obtained for the velocity and temperature distributions as well as the Poiseuille number. Furthermore, the threshold value of the mixed convection...
M.Sc. Thesis Sharif University of Technology ; Saidi, Mohammad Hassan
In the study of heat transfer in micro-channels, free and force convections are two limit cases and these two methods of heat transfer are combined together generally, so to achieve the most accurate informations about the flow field they should be considered in combination. In the first part of the thesis the fully developed slip flow mixed convection in vertical micro-ducts of arbitrary shapes is investigated.Uniform axial heat flux and uniform peripheral wall temperature (H1) is considered. The method considered is analytical-numerical in which the governing equations and three of the boundary conditions are exactly satisfied but the remaining slip boundary condition on the duct wall...
Modeling and CFD simulation of a mixed-convection flow of regular fluids and nanofluids in vertical porous and regular channels, Article Heat Transfer - Asian Research ; Vol. 43, issue. 3 , May , 2014 , pp. 243-269 ; ISSN: 1523-1496 ; Dehkordi, A. M ; Sharif University of Technology
In this article, the problem of combined forced and free convection in vertical porous and regular channels for both regular fluids and nanofluids has been solved using the CFD technique in the entrance regions of momentum and heat transfer taking into account the influences of viscous heating and inertial force. In this regard, various types of viscous dissipation models reported in the literature such as the Darcy model, the power of the drag force model, and the clear fluid-compatible model were applied. In the case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered. The dimensionless distributions of velocity, temperature, and the volume...
Numerical investigation of nanofluid mixed-convection flow in the entrance region of a vertical channel partially filled with porous medium, Article Heat Transfer - Asian Research ; Vol. 43, issue. 7 , November , 2014 , p. 607-627 ; Dehkordi, A. M ; Jamshidi, S ; Sharif University of Technology
In this article, transient two-dimensional mixed convection of nanofluids in the entrance region of a vertical channel has been studied carefully. The geometry under consideration consisted of a parallel-plate channel partly filled with a porous medium with a constant wall temperature. In the free flow region, the two-dimensional flow field has been governed by the Navier-Stokes equations. The general formulation of the momentum equations accounting for the inertial and the viscous effects in the presence of a porous medium has been used. Viscous dissipation effects have also been incorporated in the thermal energy equation. Effects of Brownian diffusion and thermophoresis have also been...
Article Journal of Thermophysics and Heat Transfer ; Vol. 28, issue. 1 , 2014 , p. 105-117 ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
The fully developed longitudinal slip-flow mixed convection between a periodic bunch of vertical microcylinders arrangedin regular arraysis investigated inthe present work. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The rarefaction effects are taken into consideration using first-order slip velocity and temperature jump boundary conditions. The method considered is mainly analytical, in that the governing equations and three of the boundary conditions are exactly satisfied. The remaining symmetry condition on the right-hand boundary of the typical element is applied to the solution through the point-matching technique. The results...
Article Energy and Buildings ; Volume 43, Issue 6 , June , 2011 , Pages 1254-1263 ; 03787788 (ISSN) ; Bahadori, M. N ; Sharif University of Technology
Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools. They have been also employed in other buildings like bazaars or market places in Iran due to their favorable thermal performance. The aim of this research is to study about domed roofs thermal performance in order to determine how they can be helpful in reducing the maximum air temperature of inside buildings during the warm seasons considering all parameters like air flow around them, solar radiation, radiation heat transfer with the sky and the ground as well as some openings on the building. The results of the study show that the thermal performance of the...
Employment of algebraic multigrid as a preconditioner to solve fully implicit mixed convection equations, Article 44th AIAA Aerospace Sciences Meeting 2006, Reno, NV, 9 January 2006 through 12 January 2006 ; Volume 10 , 2006 , Pages 7055-7063 ; 1563478072 (ISBN); 9781563478079 (ISBN) ; Vakili, S ; Schneider, G. E ; Sharif University of Technology
The main purpose of the present work is to study the performance of an algebraic multigrid (AMG) algorithm as a preconditioner to the Krylov subspace methods, mainly GMRES methods. The method is used to solve the set of linear algebraic equations resulted from treating simultaneous simulation of fluid dynamics and heat transfer problems. The extended algorithm is fully implicit which results in a huge system of linear algebraic equations. Different parameters affecting the performance of the AMG are taken into account to enhance the performance of our extended algorithm. Because of high level of sparsity of the matrix of coefficients, the current results indicate that the AMG can be very...
LBM investigation of a Cu-water nanofluid over various configurations of pipes in the mixed convection flow, Article Heat Transfer ; Volume 50, Issue 2 , August , 2021 , Pages 1056-1072 ; 26884534 (ISSN) ; Sharif University of Technology
John Wiley and Sons Inc 2021
Increasing the heat capacity of heat exchangers is a crucial need for modern devices. The thermal conductivity of the usual fluids and the Nusselt (Nu) number of flows containing such fluids are two bottlenecks in the way of increasing heat delivery in the heat exchangers. For this reason, nanofluids have been introduced. The effect of utilizing a Cu-water nanofluid as a coolant of two hot pipes in a square cavity is investigated numerically with a two-component lattice Boltzmann method. The volume fraction of nanoparticles is assumed to be constant (0.03) while the Richardson (Ri) number varies from 0.02 to 20. Results show that the effectiveness of nanoparticles is better observed in the...
Transient behavior of fluid flow and heat transfer in vertical channels partially filled with porous medium: Effects of inertial term and viscous dissipation, Article Energy Conversion and Management ; Volume 61 , September , 2012 , Pages 1-7 ; 01968904 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
In this article, transient hydrodynamic and heat-transfer behavior of Newtonian fluid flow in vertical parallel-plate channels partially filled with a porous medium has been investigated numerically. In this regard, the influences of macroscopic local inertial term and the viscous heating due to the viscous dissipation were taken into account in the momentum equations of porous region and the thermal energy equations, respectively. Moreover, Forchheimer-Brinkman extended Darcy model was used to model fluid flow in the porous region. In addition, an analytical solution was obtained in the case of negligible Brinkman and Forchheimer number values at the steady-state conditions. The predicted...
Ph.D. Dissertation Sharif University of Technology ; Molaei Dehkordi, Asghar
In the present study, mixed-convective heat transfer of nanofluids in a vertical rectangular channel partially filled with open-cell metal foam has been investigated experimentally and numerically. Al2O3–H2O nanofluids with different concentrations were synthesized and their stability was inspected with UV-Vis spectroscopy. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature profiles were obtained using finite difference method. The Brinkman–Forchheimer extended Darcy model and the...
Two-phase, Two-component Simulation of Nanofluids in Natural Convection Applying Lattice Boltzmann Method, Ph.D. Dissertation Sharif University of Technology ; Saeedi, Mohammad Hassan
The advances of technology of microelectrical devices and their computational capacity and so, their heat rates, make the thermal control of them more complex. Utilizing nanopfluids is one of proposing options. The current research investigates the effectiveness of using nanoparticles on the heat transfer rate of fluids in the natural convection. A two-component two-phase lattice Boltzmann method (LBM) has been implemented for this purpose. A wide range of Rayleigh number (Ra), namely 103 to 109, 0 to 0.05 volume fraction s of nanoparticles and nanoparticle diameters below 100 nm has been investigated in this research. The method is optimized for complex geometries. Two and three dimensional...
Article Journal of Heat Transfer ; Vol. 136, issue. 3 , 2014 ; ISSN: 00221481 ; Baghani, M ; Saidi, M. H ; Sharif University of Technology
The present investigation is devoted to the fully developed slip flow mixed convection in vertical microducts of two different cross sections, namely, polygon, with circle as a limiting case, and rectangle. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first-order slip boundary conditions. The method considered is mainly analytical in which the governing equations in cylindrical coordinates along with the symmetry conditions and finiteness of the flow parameter at the origin are exactly satisfied. The first-order slip boundary...
Article International Communications in Heat and Mass Transfer ; Volume 45 , 2013 , Pages 137-145 ; 07351933 (ISSN) ; Nikravan Moghaddam, A. M ; Mohammadi, N ; Shafii, M. B ; Sharif University of Technology
Pulsating heat pipes (PHPs) are interesting heat transfer devices. Their simple, high maintaining, and cheap arrangement has made PHPs very efficient compared to conventional heat pipes. Rotating closed loop PHP (RCLPHP) is a novel kind of them, in which the thermodynamic principles of PHP are combined with rotation. In this paper, effect of rotational speed on thermal performance of a RCLPHP is investigated experimentally. The research was carried out by changing input power (from 25. W to 100. W, with 15. W steps) and filling ratio (25%, 50%, and 75%) for different rotational speeds (from 50. rpm to 800. rpm with an increment of 125. rpm). The results presented that at a fixed filling...
Overall thermal performance of ferrofluidic open loop pulsating heat pipes: An experimental approach, Article International Journal of Thermal Sciences ; Volume 65 , 2013 , Pages 234-241 ; 12900729 (ISSN) ; Mohammadi, M ; Afshin, H ; Saidi, M. H ; Shafii, M. B ; Sharif University of Technology
Pulsating heat pipes (PHPs) are simple, cheap, and efficient heat transfer devices. They have applications in electronic cooling. In the present research, an experimental investigation is conducted on startup and steady thermal performances of open loop pulsating heat pipes (OLPHPs). Effects of working fluid, heat input, non-condensable gases (NCGs), ferrofluid concentration, magnets location, and inclination angle on the thermal performance of OLPHPs have been considered. Obtained results show that using ferrofluid can improve the thermal performance in steady state condition. Furthermore, applying a magnetic field enhances the heat transfer characteristics of ferrofluidic OLPHPs in both...
Mixed convection in a vertical channel containing porous and viscous fluid regions with viscous dissipation and inertial effects: A perturbation solution, Article Journal of Heat Transfer ; Volume 133, Issue 9 , 2011 ; 00221481 (ISSN) ; Dehkordi, A. M ; Sharif University of Technology
In this paper, combined forced and natural convection in a vertical channel containing both porous and viscous regions taking into account the influences of inertial force and viscous dissipation has been studied. In this regard, fully developed fluid flow in the porous region was modeled using the Brinkman-Forchheimer extended Darcy model. To solve governing equations of both the porous and viscous regions including thermal energy and momentum equations, a two-parameter perturbation method was applied. The velocity and temperature distributions of both the regions were obtained in terms of various parameters such as inertial force, Grashof, Reynolds, and Brinkman numbers, as well as various...
Article 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, Darmstadt, 23 June 2008 through 25 June 2008 ; Issue PART B , 2008 , Pages 1371-1379 ; 0791848345 (ISBN); 9780791848340 (ISBN) ; Safari Mohsenabad, S ; Vakilipour, S ; ASME ; Sharif University of Technology
The analytical study of microchannels has been considered as a preliminary approach to alleviate the difficulties which are normally encountered in numerical and experimental studies. Among the analytical solutions, those with high robustness and low complexities are certainly more attractive. In this work, we present a theoretical approach to predict the temperature field in micro-Poiseuille channel flow with constant wall temperature. The use of power series method simplifies the solution in the current analytical approach. The current analytical derivations are examined for channels with both hot-wall and cold-wall conditions. The current solutions agree well with the numerical solutions...
Extended-fem Modeling of Advective-dispersive Transport under Variable-density Flow in Heterogeneous Fractured Porous Media, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza
This thesis aims to present a computationally efficient extended finite element model for the simulation of isothermal single-phase coupled advective-dispersive transport and variable-density/viscosity flow in a saturated, rigid, heterogeneous and fractured porous media with a particular application to miscible viscous fingering instabilities and dispersive mixing in subsurface formations. Density-driven flows arise from differences in salinity or temperature within a fluid body. The partial differential equations governing system is given by the mass conservation equation of the fluid phase, as well as by the advection-diffusion transport equation of the solute concentration. The...
Mixed-convection flow of Al2O3-H2O nanofluid in a channel partially filled with porous metal foam: Experimental and numerical study, Article Experimental Thermal and Fluid Science ; Vol. 53 , February , 2014 , pp. 49-56 ; ISSN: 08941777 ; Molaei Dehkordi, A ; Sharif University of Technology
Mixed-convection flow of nanofluids inside a vertical rectangular channel partially filled with open-cell metal foam and subject to a constant wall-heat flux was investigated experimentally and numerically. Al2O3-water nanofluids with different concentrations were prepared and their stability was examined using UV-Vis spectroscopy. Dynamic light scattering method was used to determine particle size distribution of the nanofluid feedstock. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature...