Showing papers on "Nusselt number published in 2009"
TL;DR: In this article, the Nusselt number and the Reynolds number depend on the Rayleigh number Ra and the Prandtl number Pr, and the thicknesses of the thermal and the kinetic boundary layers scale with Ra and Pr.
Abstract: The progress in our understanding of several aspects of turbulent Rayleigh-Benard convection is reviewed. The focus is on the question of how the Nusselt number and the Reynolds number depend on the Rayleigh number Ra and the Prandtl number Pr, and on how the thicknesses of the thermal and the kinetic boundary layers scale with Ra and Pr. Non-Oberbeck-Boussinesq effects and the dynamics of the large scale convection roll are addressed as well. The review ends with a list of challenges for future research on the turbulent Rayleigh-Benard system.
1,372 citations
TL;DR: In this article, the Cheng-Minkowycz problem of natural convection past a vertical plate, in a porous medium saturated by a nanofluid, is studied analytically.
760 citations
TL;DR: In this paper, it is shown that a similarity solution is possible if the convective heat transfer associated with the hot fluid on the lower surface of the plate is proportional to x−1/2.
583 citations
TL;DR: In this article, the authors measured the pressure drop and convective heat transfer coefficient of water-based Al2O3 nanofluids flowing through a uniformly heated circular tube in the fully developed laminar flow regime.
573 citations
TL;DR: In this article, the effect of nanofluids on convective heat transfer was investigated through a circular straight tube with a constant heat flux condition in the laminar and turbulent flow regime.
474 citations
TL;DR: In this article, the effect of inclination angle on convection heat transfer and fluid flow in a two-dimensional enclosure filled with Cu-nanofluid has been analyzed numerically.
460 citations
TL;DR: In this article, the Nusselt number prediction for nanofluids has been validated with existing well established correlations, and it is found that smaller diameter nanoparticles have higher viscosity.
379 citations
TL;DR: In this paper, different viscosity and thermal conductivity models are used to evaluate heat transfer enhancement in horizontal annuli using variable properties of Al2O3-water nanofluid.
377 citations
TL;DR: In this article, an integrated microsystem consisting of a single microchannel on one side, and two localized heaters and five polysilicon temperature sensors along the channel on the other side were fabricated.
352 citations
TL;DR: In this article, the authors investigated the natural convection heat transfer of water-based nanofluids in an inclined square enclosure where the left vertical side is heated with a constant heat flux, the right side is cooled, and the other sides are kept adiabatic.
294 citations
TL;DR: In this article, experimental and computational fluid dynamics (CFD) investigations on the friction factor, Nusselt number and thermal-hydraulic performance of a tube equipped with the classic and three modified twisted tape inserts were conducted.
Abstract: This paper reports experimental and Computational Fluid Dynamics (CFD) investigations on the friction factor, Nusselt number and thermal–hydraulic performance of a tube equipped with the classic and three modified twisted tape inserts. The results showed that the Nusselt number and performance of the jagged insert were higher than other ones. Maximum increase of 31% and 22% were observed in the calculated Nusselt and performance of the jagged insert as compared with those obtained for the classic one. The higher turbulence intensity of the fluid close to the tube wall has been expressed as the main reason for the experimental observations.
TL;DR: An improved version of the authors's published correlation (Shah 1979), extended to a wider range of parameters, is presented in this article, which is shown to be in good agreement with data ranging from highly turbulent flows to the laminar flow conditions of Nusselt's analytical solutions.
Abstract: An improved version of the authors's published correlation (Shah 1979), extended to a wider range of parameters, is presented. The new correlation has been shown to be in good agreement with data ranging from highly turbulent flows to the laminar flow conditions of Nusselt's analytical solutions. The data used for the correlation's validation includes 22 fluids (water, halocarbon refrigerants, hydrocarbon refrigerants, and organics) condensing in horizontal, vertical, and downward-inclined tubes. The range of parameters includes tube diameters from 2 to 49 mm, reduced pressure from 0.0008 to 0.9, flow rates from 4 to 820 kg/m2·s, all liquid Reynolds numbers from 68 to 85,000, and liquid Prandtl numbers from 1 to 18. A total of 1189 data points from 39 sources are predicted with a mean deviation of 14.4%. Comparisons are also made with some other well-known correlations.
TL;DR: In this article, the authors present an experimental study on the mean Nusselt number, friction factor and enhancement efficiency characteristics in a round tube with short-length twisted tape insert under uniform wall heat flux boundary conditions.
TL;DR: In this paper, a regression equation is developed to estimate the Nusselt number valid for both water and nanofluid flowing in the transition flow Reynolds number range in circular plain tube and with tape inserts.
TL;DR: In this article, an experimental and numerical study of the steady state convective losses occurring from a downward facing cylindrical cavity receiver of length 0.5m, internal diameter of 0.3m and a wind skirt diameter of0.5mm is carried out.
TL;DR: In this paper, it was shown that for a given inclination angle (φ), as the value of Hartmann number (Ha) increases, the convection heat transfer reduces.
TL;DR: In this article, a 3D numerical analysis of the porous disc line receiver for solar parabolic trough collector is presented based on renormalization-group k-e turbulent model by using Therminol-VP1 as working fluid.
TL;DR: In this paper, a numerical investigation of the steady magnetohydrodynamics free convection in a rectangular cavity filled with a fluid-saturated porous medium and with internal heat generation has been performed.
01 Jan 2009
TL;DR: In this paper, the effects of variable thermal conductivity and heat source/sink on flow of a viscous incompressible electrically conducting fluid in the presence of uniform transverse magnetic field and variable free stream near a stagnation point on a nonconducting stretching sheet are investigated.
Abstract: Aim of the paper is to investigate effects of variable thermal conductivity and heat source/sink on flow of a viscous incompressible electrically conducting fluid in the presence of uniform transverse magnetic field and variable free stream near a stagnation point on a non-conducting stretching sheet. The equations of continuity, momentum and energy are transformed into ordinary differential equations and solved numerically using shooting method. The velocity and temperature distributions are discussed numerically and presented through graphs. Skin-friction coefficient and the Nusselt number at the sheet are derived, discussed numerically and their numerical values for various values of physical parameter are presented through Tables.
TL;DR: In this article, an experimental investigation of heat transfer and friction factor characteristics of thermosyphon solar water heater system with full-length twist, twist fitted with rod and spacer fitted at the trailing edge for lengths of 100, 200 and 300 mm for twist ratio 3 and 5 has been carried out and compared with plain tube collector for the same operating conditions.
TL;DR: In this paper, an experimental investigation of heat transfer enhancement capabilities of coolants with suspended nanoparticles (Al2O3 dispersed in water) inside a radial flow cooling device is presented.
TL;DR: In this paper, the heat transfer coefficient (HTC) and Nusselt numbers were derived from the inner wall temperature converted by using the outer wall temperature measured by adhesive K-type thermocouples and a direct (tube) or indirect (annular channel) electric heating power.
TL;DR: In this article, the combined effects of Soret and Dufour diffusion and porous impedance on laminar magnetohydrodynamic mixed convection heat and mass transfer of an electricallyconducting, Newtonian, Boussinesq fluid from a vertical stretching surface in a Darcian porous medium under uniform transverse magnetic field were examined.
TL;DR: It is suggested that the small-Pr behavior is due to the breakdown of the heat-transfer-enhancing Ekman pumping because of larger thermal diffusion.
Abstract: For given aspect ratio and given geometry, the nature of Rayleigh Benard convection (RBC) is determined by the Rayleigh number Ra = bg DL3 / (kn)Ra=gL3() and by the Prandtl number Pr = n/ kPr= is the thermal expansion coefficient, g the gravitational acceleration D = Tb - Tt=Tb−Tt the difference between the imposed temperatures Tb and Tt at the bottom and the top of the sample, respectively, and v and k the kinematic viscosity and the thermal diffusivity, respectively. The rotation rate Ω (given in rad/s) is used in the form of the Rossby number Ro = O{bg D/ L / (2 W)}Ro=gL(2)
TL;DR: In this paper, the effects of different baffle tip angles on heat transfer and pressure loss in a two dimensional horizontal channel with isothermal walls and with staggered diamond-shaped baffles are investigated numerically.
TL;DR: In this article, an experimental investigation has been carried out to study the heat transfer coefficient and friction factor by using artificial roughness in the form of specially prepared inverted U-shaped turbulators on the absorber surface of an air heater duct.
TL;DR: In this article, the authors report the results of their numerical studies on laminar mixed convection heat transfer in a circular curved tube with a nanofluid consisting of water and 1 ǫvol% Al 2 O 3.
TL;DR: In this article, the authors investigated the effects of the combined effects of mechanically driven lid and the buoyancy force within rectangular enclosures, where the fluid filled enclosures are heated and lid-driven either on the upper or on the lower horizontal wall, thermally isolated on the right vertical wall, and cooled on the other walls.
TL;DR: In this paper, a 3D numerical simulation of a whole heat exchanger with middle-overlapped helical baffles is carried out by using commercial codes of GAMBIT 2.3 and FLEUNT 6.3.
TL;DR: In this article, a penalty finite element analysis with bi-quadratic elements is performed to investigate the influence of uniform and non-uniform heating of bottom wall on mixed convection lid driven flows in a square cavity.