Showing 11 results for Mixed Convection
, Behzad Ghasemi,
Volume 12, Issue 2 (6-2012)
Abstract
ABSTRACT A numerical investigation of mixed convection heat transfer with nanofluid and pure water from a heat source in a horizontal channel is performed. The walls of the channel are adiabatic and the heat source is placed at the bottom wall of the channel. Free flow at cold temperature enters channel and takes heat from heat source. Discretization of the continuity, momentums and energy equations are achieved through a finite volume method and solved with SIMPLE method. The Brownian motion of nanoparticles is simulated to determine the thermal conductivity of the nanofluid.The results show that using the nanofluid caused to heat diffusion and average temperature of source to increase. Also, increase in solid volume fraction causes increase in heat transfer especially at high Reynolds number. It is understand that with increase in ratio of length to height of source in its constant area, heat transfer decreases first and then increases.
, Behzad Ghasemi,
Volume 13, Issue 7 (10-2013)
Abstract
Abstract- Mixed convection flow of a water-copper nanofluid in a channel under magnetic field effects has been numerically investigated. The fluid flow and temperature fields as well as the heat transfer rate have been determined by solving the Navier-Stocks and energy equations. In this study, the effects of various parameters such as the Richardson number, the Hartmann number, the solid volume fraction and the channel angle on the thermal performance of the channel have been examined. The results showed that at high Richardson numbers, the heat transfer rate decreased as the Hartman number increased. It was also found that the heat transfer rate increased as the Richardson number, the solid volume fraction and the channel angle increased. The maximum flow reversal was observed to occur in a vertical channel.
Masoud Kharati, Iman Jelodari,
Volume 14, Issue 3 (6-2014)
Abstract
In this research, two effective techniques to increase mixed convection heat transfer rate within an enclosure subjected to a transverse magnetic field are studied. In order to increase the heat transfer rate, the addition of Al2O3 nanoparticles is concerned as the first strategy and the change in magnetic field inclination angle is considered as the second. In this study, the left and right sides of the enclosure are kept at constant temperature while the top and bottom walls are adiabatic. In this work, the results are obtained with an in-house finite volume code. To validate the code, the results of the present code are compared to that of an existing correlation as well as those of previous works and good agreements are observed. In the present work, Richardson number varies from Ri=0.05 to Ri=50. Results show that the addition of solid particles may increase or decrease the heat transfer rate whereas the increase in magnetic field inclination angle mostly leads to increase in the heat transfer rate.
Ali Akbar Abbasian Arani, Narges Hatami Nesar, Mohammad Rezaee,
Volume 14, Issue 6 (9-2014)
Abstract
In this work, mixed convection of Cu-water nanofluid in a trapezoidal enclosure with heat source on lateral walls has been numerically investigated. Vertical walls of the enclosure are kept at constant temperatures of Th and Tc, while horizontal walls are insulated. The mixed convection flow has been generated by passing the fluid through the enclosure and natural convection has been, also, investigated by holding the left wall at a temperature higher than the right wall. In order to examine the effect of the ports position, two cases were considered. Comparison between the results indicates that the rate of heat transfer is higher when the inlet port is near the cold wall than the hot wall. The results have been presented for various volume fractions, Richardson and Reynolds numbers. It was observed that for the considered Reynolds numbers and Richardson number, at a given Reynolds number and solid volume fraction, the Nusselt number increases with increasing the Richardson number. Moreover, at a given Richardson number and solid volume fraction, increasing the Reynolds number results in an increase in the Nusselt number. For the higher Richardson and Reynolds numbers, the nanofluid has more effect on the increase of the heat transfer performance.
Farzad Bazdidi-Tehrani, Mohammad Sedaghatnejad, Naeem Ekrami, Iman Vasefi,
Volume 14, Issue 13 (3-2015)
Abstract
In the present paper, mixed convection of TiO2-water nanofluid in a laminar flow within a vertical rectangular duct is investigated numerically. A single phase and a two phase method is applied to simulate nanoparticles dispersion in the base fluid. An Euler-Lagrange approach is employed to track particles individually. In this approach, the base fluid is assumed to be a continuous phase while the particles are dispersed through it. The presence of particles in the base fluid is modeled as a source term in the momentum and energy equations. Governing equations is discretized using Control Volume based Finite Element Method (CVFEM). Effects of nanoparticles concentration, particles size, aspect ratio of cross section, asymmetrical boundary condition and buoyancy on the hydrodynamics and thermal parameters are presented and discussed. It is observed that increasing nanoparticles concentration enhances heat transfer rate and this enhancement is more considerable in higher aspect ratios. Also, at smaller values of Richardson number (Ri) where the effect of forced convection is more than natural convection, dispersion of nanoparticles in the base fluid improves heat transfer rate more considerably. Whilst an improvement in convective heat transfer is shown to be more than 6.5% at Ri=0.05, it does not exceed 4% at Ri=0.5.
Masoud Ziaei-Rad, Abbas Kasaeipoor,
Volume 14, Issue 14 (3-2015)
Abstract
This paper concerns with a similarity solution for mixed-convection boundary layer copper-water nanofluid flow over a horizontal flat plate. Appropriate similarity variables are used to convert the Governing PDEs to ODEs and the resultant equations with the nanofluid properties relations are discretized and solved simultaneously using finite-difference Keller-Box method. The effects of change in plate temperature, the volume fraction of nanoparticles, and the mixed-convection parameter, on friction coefficient, Nusselt number and velocity and temperature profiles are investigated. The results show that, the Nusselt number increases as the mixed-convection parameter and the volume fraction of nanoparticles increases. This enhancement is about 10 percent for the nanofluid with 4% volume fraction of nanoparticles, compared with the pure water. In this range, moreover, the friction coefficient parameter increases about 20 percent. However, the lower the mixed-convection parameter is, the effect of nanoparticles on the friction coefficient increment is more. The results also illustrate that the effect of the surface temperature on the increment of Nusselt number and on the reduction of friction coefficient is more considerable in higher mixed-convection parameter and volume fraction of nanoparticles. Also by increasing surface temperature, the temperature of nanofluid decreases at any surface distance.
Ali Shakiba, Mofid Gorji,
Volume 15, Issue 2 (4-2015)
Abstract
This study attempts to numerically investigate the hydro-thermal characteristics of a ferrofluid (water and 4 vol% ) in a counter-current horizontal double pipe heat exchanger, which is exposed to a non-uniform transverse magnetic field with different intensities. The magnetic field is generated by an electric current going through a wire parallelly located close to the inner tube and between two pipes. The single phase model and the control volume technique have been used to study the flow. The effects of magnetic field has been added to momentum equation by applying C++ codes in Ansys Fluent 14. The results show that applying this kind of magnetic field causes to produce kelvin force perpendicular to the ferrofluid flow changing axial velocity profile and creating a pair of vortices leads to increase the Nusselt number, friction factor and pressure drop. Comparing the enhancement percentage of Nusselt number, friction factor and pressure drop demonstrate that the optimum value of magnetic number for Re_ff=50 is between Mn=1.33*10^6 and Mn=2.37*10^6 So applying non-uniform transverse magnetic field can control the flow of ferrofluid and improve heat transfer process of double pipe heat exchanger.
Kamel Milani, Mojtaba Mamourian,
Volume 15, Issue 8 (10-2015)
Abstract
Taguchi method since 1980 is used as an effective way to optimize the design process engineering tests. In this paper by using of taguchi method optimal conditions of the mixed convection and entropy generation in a square cavity filled with Cu-water nanofluid is analyzed. For this purpose a L16 (43) orthogonal taguchi array is used. Discretization of the governing equations were achieved through a finite volume method and solved with SIMPLE algorithm. The effect of Richardson number (0.1-100 ), the volume fraction of copper nanoparticles (0-10%) and the wavelength of the wavy surface (0- 1) as an effective parameters for analyzing in four levels are considered. This analysis was performed for fixed Grashof number 104. The results show that the mean Nusselt number decreases by increase of the Richardson number, the volume fraction of nanoparticles and the wavelength of the wavy surface. It is found that the Flat plate (for wavy surface with the wavelength 0) and the volume fraction 0% in the Richardson number 0.1 is optimal design for heat transfer while the geometry with Ф=5%, Ri=100 and λ=0.25 is optimal design for entropy generation. Finally for maximum heat transfer and minimum entropy generation the geometry with Ф=0%, Ri =1 and λ=0.25 can be considered as an optimal design.
Habib Aminfar, Mohammad Nasiri, Marzieh Khezerloo,
Volume 15, Issue 9 (11-2015)
Abstract
In this study, generated entropy of mixed convection of Al2O3–water nano fluids in a vertical channel with sinusoidal walls under a constant and uniform magnetic field was numerically investigated. The effects of various parameters such as volume fraction of nanoparticles, amplitude of sine wave, Reynolds, Grashof and Hartman numbers were studied. This study was carried out by assuming the laminar, steady state and incompressible flow. Also, the thermo physical properties of nanoparticles were assumed constant. The Boussinesq approximation was used to calculate the variations of the density caused by buoyancy force and the finite volume method and two phase mixture model were used to simulate the flow. The results showed that the entropy generation due to heat transfer and viscous effects increase by adding nanoparticles to the base fluid. Also, the results showed that the entropy generation due to heat transfer increases by increasing the Grashof number and decreasing the Reynolds number, while a reverse trend is observed for entropy generation due to viscous effects. By increasing the Hartman number, the entropy generation due to heat transfer increases at first and then decreases and entropy generation due to viscous effects reduces. For all studied intensities of magnetic fields, the entropy generation decreases using corrugated channels.
Maryam Moeinaddini, Seyed Abdolreza Ganjalikhan Nasab,
Volume 16, Issue 3 (5-2016)
Abstract
This study presents a numerical investigation for laminar mixed convection flow of radiating gases in an inclined lid-driven cavity. The fluid is treated as a gray, absorbing, emitting and scattering medium. The governing differential equations consisting the continuity, momentum and energy are solved numerically by the computational fluid dynamics (CFD) techniques to obtain the velocity and temperature fields. Discretized forms of these equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, besides convection and conduction, radiative heat transfer also takes place in the gas flow. For computation of the radiative term in the gas energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinate method (DOM). The effect of lid driven speed, on the thermohydrodynamic behavior of two-dimensional cavity is carried out. Results are shown as contours of isotherms, streamlines and distributions of convective and total Nusselt numbers along the bottom wall of cavity. It is revealed that increasing in Reynolds number causes almost uniform temperature distribution in cavity, especially for 30° and 60° inclination angles.
S. Alikhani, N. Ganjbakhsh, A. Behzadmehr,
Volume 19, Issue 6 (6-2019)
Abstract
Thermal and hydrodynamic behavior of a laminar flow of water within a horizontal curved Vipertex tube with mixed convection heat transfer, in the range of low Grashof numbers, has been numerically studied. The curved horizontal Vipertex tube has geometry of 180o, fixed radius of centerline curvature of 2R/D=6.62, roughness height e/D=0.1, and a constant heat flux is exerted on the walls. The three-dimensional governing equations were using a finite volume method. To solve the problem, the computational fluid dynamics of ANSYS Fluent The results reveal that not only Grashof number and the buoyancy forces arising from it, but the mutual effects of the centrifugal and the buoyancy forces affect the thermal and hydrodynamic characteristics such as axial velocity contours, secondary flow vectors, temperature contours, heat transfer coefficient, and skin friction coefficient. So that, for a given Reynolds number, increasing due to more interaction between buoyancy and centrifugal forces, results in the Vipertex tube. Therefore, the buoyancy forces decrease and lead to the lower heat transfer coefficient, but in smooth curved Grashof number leads to the higher heat transfer coefficient. Nevertheless, the Vipertex curved tube in of Grashof and Reynolds, in each Grashof and Reynolds equally, has a higher heat transfer than a smooth curved pipe. The results also indicated that the skin friction coefficient in these types of tubes can be up to 3.5 times higher than that of smooth one with a Grashof increase.
