Showing 8 results for Heat Transfer
A. Nouri, and M. Nili-Ahmadabadi,
Volume 26, Issue 1 (7-2007)
Abstract
In this article, turbulent flow heat transfer in the air gap between rotor and stator of a generator under nonhomogeneous heat flux is studied experimentally. The rotor consists of four symmetrical triangular grooves. The stator surface is smooth and does not include any grooves. The relative heat flux between the rotor and the stator is 1 to 3. Temperature and heat flux are measured locally at three axial and two angular positions of inner and outer surface. The pressure drop of air flow through the air gap is also measured. In this work, the axial Reynolds number and rotational velocity of the rotor ranges are 4000
M. Kahrom, A. Farahbode, and D. Khodadadzadeh,
Volume 27, Issue 1 (7-2008)
Abstract
A rectangular rod is placed in a flow field flowing parallel to a flat plate. Effect of chord-thickness ratio of rectangular rod on developing vortex shedding downstream to the rod is studied. Then, for each one of the aspect ratios, the distance of the rod from the neighboring flat plate is reduced until the rod sticks to the flat plate. In each case, the effect of the flat plate boundary layer on Strouhal number and the contrary effect of the boundary layer on vortex shedding from the rectangular rod are studied. Results show that as the rectangular rod enters into the flat plate boundary layer, vortex generation from the closest side of the rod reduces, thereby reducing the Strouhal number as well. Finally, when the rectangular rod sticks to the flat plate, a stationary wake forms downstream the rod and sticks to the flat plate. Meanwhile, the boundary layer over the flat plate is disturbed effectively and heat transfer coefficient from the flat plate is enhanced by an average of 50% and up to 200% in some places, locally.
M. Falsafi, H. Kargarsharifabad,
Volume 34, Issue 1 (7-2015)
Abstract
R. Rajabi, M. Saghafian,
Volume 35, Issue 1 (9-2016)
Abstract
In this paper, viscous dissipation and roughness effects on heat transfer and fluid flow are investigated in microchannels using perturbation method in slip flow regime. The flow is considered to be laminar, developing thermally and hydrodynamically, two-dimensional, incompressible and steady-state. The working fluid is air, flowing between two parallel plates. The equations obtained from developing Navier-Stokes and energy equations are solved numerically according to different orders of Knudsen number, with second-order velocity slip and temperature jump boundary conditions. The effects of thermal creep has been ignored. Tempreture and velocity fields are obtained and estimated for both constatnt heat flux and constant wall tempreture. The effects of roughness height, space between roughness elements, roughness elements length, Re number and Kn number on slip behavior of gas flow are investigated.The results indicate considerable effect of viscous dissipation and roughness on fluid flow and heat transfer in microchannel.
E. Ebrahimnia-Bajestan, H. Niazmand,
Volume 36, Issue 1 (9-2017)
Abstract
In this paper, numerical simulation of flow and heat transfer of Al2O3/water nanofluid has been carried out through three different geometries involving a straight pipe, a 90o curved pipe and a 180o curved pipe under constant heat flux condition. Employing singe-phase model for the nanofluid, the Navier-Stokes and energy equations for an incompressible and laminar flow have been solved in a body fitted coordinate system using a homemade code based on control-volume approach, while all thermophysical properties of the nanofluid are dependent on considered temperature. The effects of different nanoparticle concentration and centrifugal forces on the temperature and pressure field have been examined in detail. The accordance of numerical results with experimental data expresses the accuracy of the employed numerical method for simulating flow and heat transfer in the curved pipes, as well as the accuracy of the single-phase model of the nanofluid. The Presented results indicated that both the nanoparticle and curvature effects improve the heat transfer characteristics dramatically, but at the expense of considerable increase in pressure drop. Furthermore, the results showed that in order to obtain the optimum operating conditions of nanofluids, different parameters such as heat transfer enhancement and pressure drop must be considered simultaneously. Finally, a method has been proposed to indicate the proper nanofluid and flow geometry for special practical applications.
H. Bazai, A. Azari, M. Moshtagh,
Volume 38, Issue 1 (8-2019)
Abstract
The purpose of this article is the numerical study of flow and heat transfer characteristics of Nanofluids inside a cylindrical microchannel with rectangular, triangular, and circular cross-sections. The size and shape of these sections have a significant impact on the thermal and hydraulic performance of the microchannel heat exchanger. The Nanofluids used in this work include water and De-Ethylene Glycol (DEG) as the base fluids and Al2O3, Cu, SiO2 and CuO as the nanoparticles. To solve the problem and extract the required data, a 3-D simulation was performed for the microchannel using ANSYS FLUENT 15.0 software and the effect of the cross-sectional shape of the fluid flow and the type of nanoparticles on the thermal transfer and fluid flow parameters was studied. From the obtained results, it can be observed that the addition of nanoparticles to the base fluid increases the heat transfer and pressure drop. The results also show that rectangular channels have the best performance among the three geometries examined as its heat transfer coefficient was 19.26% higher than the triangular cross section which had the worst performance.
A. R. Rahmati , E. Kashai,
Volume 40, Issue 2 (1-2022)
Abstract
A two-phase lattice Boltzmann model considering the interaction forces of nanofluid has been developed in this paper. It is applied to investigate the flow and natural convection heat transfer of Al2O3–H2O nanofluid in an enclosure containing internal heat generation. To understand the heat transfer enhancement mechanism of the nanofluid flow from the particle level, the lattice Boltzmann method is used because of its mesoscopic feature and numerical advantages. By using a two-component lattice Boltzmann model, the heat transfer enhancement of the nanofluid is analyzed through incorporating the different forces acting on the nanoparticles and the base fluid . The effects of interaction forces, nanoparticle volume fractions (0.0-0.05), and internal and external Rayleigh numbers (103-106) on the nanoparticle distributions and heat transfer characteristics are investigated. The average Nusselt number increases with the increase of nanoparticle volume fraction and Rayleigh number. We also compared and analyzed adding internal heat generation on the nanoparticles and the base fluid separately, and it was found that by considering heat generation on the base fluid, it mostly affects the temperature field, and by considering that on nanoparticles, it mostly affects the stream field.
S. Torfeh, Ramin Kouhikamali,
Volume 41, Issue 1 (9-2022)
Abstract
Accurate modeling of fluidization and heat transfer phenomena in gas-solid fluidized beds is not solely dependent on the particular selected numerical model and involved algorithms. In fact, choosing the right model for each specific operating condition, the correct implementation of each model, and the right choice of parameters and boundary conditions, determine the accuracy of the results in the evaluation of the performance of fluidized beds. In this research, in order to accurately simulate heat transfer in fluidized beds, important and effective parameters on two-fluid Eulerian model that incorporate the kinetic theory of granular flow were investigated. For this purpose, effects of particle-particle and particle-wall restitution coefficient, specularity coefficient, granular temperature and effective thermal conductivity coefficients determination methods on the numerical solution were evaluated. These investigations were first carried out on heat transfer from hot air to solid particles in an adiabatic fluidized bed, and then on a fluidized bed with constant temperature walls for bubbling and turbulent regimes. Results showed that specularity coefficient and effective thermal conductivity are important parameters in heat transfer process from wall to bed. In this case, the zero value of the specularity coefficient causes the air temperature to increase by about 7 degrees in the bubbling regime and about 5 degrees in the turbulent regime, and its unit value gives the same results with the no-slip condition. In addition, considering the solid and gas material thermal conductivities causes the outlet air temperature to be about 26 degrees higher than the temperature that is obtained by considering the effective thermal conductivity coefficients with standard approach. The partial differential and algebraic form of the conservation equation for the particles kinetic energy show identical results in dense fluidized beds, although considering a constant granular temperature can cause computational errors.
