Showing papers on "Nusselt number published in 2003"
TL;DR: In this article, a model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersion, where the transport equations are solved numerically using the finite-volume approach along with the alternating direct implicit procedure.
2,560 citations
TL;DR: In this paper, open-cell metal foams with an average cell diameter of 2.3 mm were manufactured from 6101-T6 aluminum alloy and were compressed and fashioned into compact heat exchangers.
681 citations
TL;DR: In this paper, an experimental investigation has been performed on the laminar convective heat transfer and pressure drop of water in 13 different trapezoidal silicon microchannels, and dimensionless correlations for the Nusselt number and the apparent friction constant are obtained for the flow of water.
446 citations
TL;DR: In this paper, the size effect induced by the variation of dominant factors and phenomena in the flow and heat transfer as the device scale decreases is discussed, and the relative importance of viscous force modifies the correlation between Nu and Ra for natural convection in a microenclosure.
297 citations
TL;DR: In this article, an experimental study of low-level turbulence natural convection in an air filled vertical square cavity was conducted, where both mean and fluctuation quantities are presented, i.e., local velocity and temperature were simultaneously measured at different locations in the cavity and both mean or fluctuation quantity are presented.
260 citations
TL;DR: In this article, analytical solutions for heat and mass transfer by laminar flow of a Newtonian, viscous, electrically conducting and heat generating/absorbing fluid on a continuously moving vertical permeable surface in the presence of a magnetic field and a first-order chemical reaction are reported.
239 citations
TL;DR: In this paper, a finite volume-based computational study of steady laminar natural convection (using Boussinesq approximation) within a differentially heated square cavity due to the presence of a single thin fin is presented.
Abstract: A finite-volume-based computational study of steady laminar natural convection (using Boussinesq approximation) within a differentially heated square cavity due to the presence of a single thin fin is presented. Attachment of highly conductive thin fins with lengths equal to 20, 35 and 50 percent of the side, positioned at 7 locations on the hot left wall were examined for Ra=10 4 , 10 5 , 10 6 , and 10 7 and Pr=0.707 (total of 84 cases). Placing a fin on the hot left wall generally alters the clockwise rotating vortex that is established due to buoyancy-induced convection. Two competing mechanisms that are responsible for flow and thermal modifications are identified. One is due to the blockage effect of the fin, whereas the other is due to extra heating of the fluid that is accommodated by the fin. The degree of flow modification due to blockage is enhanced by increasing the length of the fin. Under certain conditions, smaller vortices are formed between the fin and the top insulated wall
208 citations
TL;DR: The physical mechanisms for the size effects on the micro-channel flow and heat transfer were divided into two classifications: (a) the gas rarefaction effect occurs when the characteristic length of the flow becomes comparable to the mean free path of the molecules; (b) Variations of the predominant factors influence the relative importance of various phenomena on the flow as mentioned in this paper.
188 citations
TL;DR: In this paper, the second law characteristics of heat transfer and fluid flow due to forced convection of steady-laminar flow of incompressible fluid inside channel with circular cross-section and channel made of two parallel plates is analyzed.
179 citations
TL;DR: In this article, the Nusselt number was measured at the highest Rayleigh numbers for which Boussinesq conditions hold and sidewall forcing is negligible, and the results showed that the variation in the mean flow was approximately a 1/3 power of the Rayleigh number.
Abstract: New measurements of the Nusselt number have been made in turbulent thermal convection confined in a cylindrical container of aspect ratio unity. The apparatus is essentially the same as that used by Niemela et al. (2000), except that the height was halved. The measurement techniques were also identical but the mean temperature of the flow was held fixed for all Rayleigh numbers. The highest Rayleigh number was . Together with existing data, the new measurements are analysed with the purpose of understanding the relation between the Nusselt number and the Rayleigh number, when the latter is large. In particular, the roles played by Prandtl number, aspect ratio, mean wind, boundary layers, sidewalls, and non-Boussinesq effects are discussed. Nusselt numbers, measured at the highest Rayleigh numbers for which Boussinesq conditions hold and sidewall forcing is negligible, are shown to vary approximately as a 1/3-power of the Rayleigh number. Much of the complexity in interpreting experimental data appears to arise from aspects of the mean flow, including complex coupling of its dynamics to sidewall boundary conditions of the container. Despite the obvious practical difficulties, we conclude that the next generation of experiments will be considerably more useful if they focus on large aspect ratios.
177 citations
TL;DR: In this article, a modified Graetz methodology is applied to investigate the thermal development of forced convection in a parallel plate channel filled by a saturated porous medium, with walls held at uniform temperature, and with the effects of axial conduction and viscous dissipation included.
TL;DR: In this paper, the influence of thermocapillarity on the flow and heat transfer in a thin liquid film on a horizontal stretching sheet is analyzed, and the time-dependent governing boundary layer equations for momentum and thermal energy are reduced to a set of coupled ordinary differential equations by means of an exact similarity transformation.
TL;DR: In this paper, an experimental investigation was carried out to measure module average heat transfer coefficients in uniformly heated rectangular channel with wall mounted porous baffles, where baffles were mounted alternatively on top and bottom of the walls.
TL;DR: In this paper, heat transfer by the natural convection of air layers within vertical, rectangular cavities with aspect ratios (A) of 20, 40 and 80 was investigated in relation to applications in building facade elements, such as insulating glazing units, double-skin facades, doors, etc.
TL;DR: In this paper, a fully developed, electro-osmotically generated convective transport has been analyzed for a parallel plate microchannel and circular microtube under imposed constant wall heat flux and constant wall temperature boundary conditions.
TL;DR: In this paper, the steady-state, hydromagnetic forced convective boundary-layer flow of an incompressible Newtonian, electrically-conducting and heat-generating/absorbing fluid over a non-isothermal wedge in the presence of thermal radiation effects is considered.
Abstract: This work is focused on the steady-state, hydromagnetic forced convective boundary-layer flow of an incompressible Newtonian, electrically-conducting and heat-generating/absorbing fluid over a non-isothermal wedge in the presence of thermal radiation effects. The wedge surface is assumed permeable so as to allow for possible wall suction or injection. Also included in the model are the effects of viscous dissipation, Joule heating and stress work. The governing partial differential equations for this investigation are derived and transformed using a non-similarity transformation. In deriving the governing equations, a temperature-dependent heat source or sink term is employed and the Rossland approximation for the thermal radiation term is assumed to be valid. The obtained non-similar equations are solved numerically by an implicit, iterative, tri-diagonal finite-difference method. Comparisons with previously published work on various special cases of the problem are performed and the results are found to be in excellent agreement. Numerical results for the velocity and temperature profiles for a prescribed magnetic parameter as well as the development of the local skin-friction coefficient and local Nusselt number with the magnetic parameter are presented graphically and discussed. This is done in order to elucidate the influence of the various parameters involved in the problem on the solution.
TL;DR: In this article, experiments were performed to determine forced convection heat transfer coefficients and friction factor for air flowing in a corrugated channel employed in plate heat exchangers, and two different values of channel height 5 and 10 mm for a single corrugation angle of 20°.
TL;DR: In this article, a theoretical analysis of thermal instability driven by buoyancy forces is conducted in an initially quiescent, horizontal porous layer saturated by viscoelastic fluids, and the linear stability theory is employed to find the critical condition of the onset of convective motion.
TL;DR: In this article, a one-dimensional two-phase model is used to derive an analytical light-off criterion for a straight channeled catalytic monolith with washcoat, in which the flow is laminar.
TL;DR: In this article, experiments were performed to characterize the heat transfer enhancement produced by adding arrays of triangular tabs to the exit of turbulent round impinging jets issuing from a long pipe, and the largest increase in the average Nusselt number occurred for a nozzle-to-plate distance of approximately 4 diameter.
TL;DR: In this article, the authors presented the numerical predictions on the turbulent fluid flow and heat transfer characteristics for rectangular channel with porous baffles which are arranged on the bottom and top channel walls in a periodically staggered way.
TL;DR: In this article, the integral forms of the governing equations are solved numerically using Finite Volume method and computational domains are divided into finite numbers of body fitted control volumes with collocated variable arrangement.
TL;DR: In this paper, a simple power-law fluid model, with the power law index n and the consistency coefficient K, is adopted to study transient buoyant convection in a square enclosure of a non-Newtonian fluid.
TL;DR: In this paper, a numerical study of mixed convection heat and mass transfer along a vertical wavy surface has been carried out numerically, including the developments of skin-friction coefficient, velocity, temperature, concentration, Nusselt number as well as Sherwood number.
TL;DR: In this article, the authors presented the heat transfer and friction characteristics and performance analysis of convective heat transfer through a rectangular channel with square cross-section pin fins attached over a flat surface.
TL;DR: In this paper, an analysis was developed to study the unsteady mixed convection flow over a vertical cone rotating in an ambient fluid with a time-dependent angular velocity in the presence of a magnetic field, and the coupled nonlinear partial differential equations governing the flow were solved numerically using an implicit finite-difference scheme.
Abstract: An analysis is developed to study the unsteady mixed convection flow over a vertical cone rotating in an ambient fluid with a time-dependent angular velocity in the presence of a magnetic field. The coupled nonlinear partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. The local skin friction coefficients in the tangential and azimuthal directions and the local Nusselt number increase with the time when the angular velocity of the cone increases, but the reverse trend is observed for decreasing angular velocity. However, these are not mirror reflection of each other. The magnetic field reduces the skin friction coefficient in the tangential direction and also the Nusselt number, but it increases the skin friction coefficient in the azimuthal direction. The skin friction coefficients and the Nusselt number increase with the buoyancy force.
TL;DR: In this paper, the authors measured on a dimpled teat surface placed on one wall of a channel, were given for a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94, and Reynolds numbers R eH from 12,000 to 70,000.
Abstract: Experimental results, measured on a dimpled teat surface placed on one wall of a channel, are given for a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94, and Reynolds numbers R eH from 12,000 to 70,000. These data include friction factors, local Nusselt numbers, spatially-resolved local Nusselt numbers, and globally-averaged Nusselt numbers. The ratio of dimple depth to dimple print diameter δ/D is 0.3, and the ratio of channel height to dimple print diameter is 1.00. These results are compared to measurements from other investigations with different ratios of dimple depth to dimple print diameter δ/D to provide information on the influences of dimple depth. At all Reynolds numbers considered, local and spatially-resolved Nusselt number augmentations increase as dimple depth increases (and all other experimental and geometric parameters are held approximately constant). These are attributed to: (i) increases in the strengths and intensity of vortices and associated secondary flows ejected from the dimples, as well as (ii) increases in the magnitudes of three-dimensional turbulence production and turbulence transport
TL;DR: In this paper, an anode duct of medium temperature solid oxide fuel cell (SOFC) has been simulated and analyzed by a fully three-dimensional calculation method and the results from this study can be applied in fuel cell overall modeling methods, such as those considering unit/stack level modeling.
TL;DR: In this paper, the authors investigate numerically the heat transfer and fluid flow characteristics inside a wavy walled enclosure and apply second law of thermodynamics to predict the nature of irreversibility in terms of entropy generation.
TL;DR: In this paper, the effect of surface mass flux on mixed convective flow past a heated vertical flat permeable plate with thermophoresis has been considered, and the governing equations, reduced to local nonsimilarity boundary layer equations using suitable transformations, have been integrated employing an implicit finite difference method together with the Keller-box technique.