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Showing papers on "Nusselt number published in 2007"


Journal ArticleDOI
TL;DR: In this paper, a laminar flow forced convection heat transfer of Al2O3/water nanofluid inside a circular tube with constant wall temperature was investigated experimentally.

766 citations


Journal ArticleDOI
TL;DR: In this article, a detailed parametric investigation is performed for melting in spherical shells of 40, 60, and 80mm in diameter, when the wall-temperature is uniform and varies from 2 ÂC to 20 Â C above the mean melting temperature of the PCM.

400 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of the buoyancy force, the centrifugal force and the nanoparticles volume fraction on the secondary flow, axial velocity and the skin friction coefficient were investigated.

261 citations


Journal ArticleDOI
TL;DR: In this article, the effects of inclination of the cavity on the flow and thermal fields are investigated for inclination angles ranging from 0° to 30°, and the average Nusselt number is found to increase with cavity inclination.

244 citations


Journal ArticleDOI
TL;DR: In this article, the conical-ring turbulators and twisted-tape swirl generators were used for heat transfer, friction factor and enhancement efficiency in a circular tube fitted with conical ring turbulators.

243 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented an original experimental study on compound heat transfer enhancement in a tube fitted with serrated twisted tape and found that the heat transfer augmentation attributed to the twisted tape falls in the range of 250-480% of the plain-tube level.

220 citations


Journal ArticleDOI
TL;DR: The steady laminar flow and heat transfer of a second grade fluid over a radially stretching sheet is considered in this article, where axisymmetric flow is induced due to linear stretching of a sheet.

214 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids, where the authors estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number.
Abstract: This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al 2 O 3 -H 2 O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2 ≤ O≤2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction O>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nu o as a function of O and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

207 citations


Journal ArticleDOI
TL;DR: In this article, the heat and mass transfer characteristics of natural convection about a vertical surface embedded in a saturated porous medium subjected to a chemical reaction are numerically analyzed, by taking into account the diffusion-thermo (Dufour) and thermal-diffusion (Soret) effects.
Abstract: The heat and mass transfer characteristics of natural convection about a vertical surface embedded in a saturated porous medium subjected to a chemical reaction is numerically analyzed, by taking into account the diffusion-thermo (Dufour) and thermal-diffusion (Soret) effects. The transformed governing equations are solved by a very efficient numerical method, namely, a modified version of the Keller-box method for ordinary differential equations. The parameters of the problem are Lewis, Dufour and Soret numbers, sustentation parameter, the order of the chemical reaction n and the chemical reaction parameter γ. Local Nusselt number and local Sherwood number variations and dimensionless concentration profiles in the boundary layer are presented graphically and in tables for various values of problem parameters and it is concluded that γ and n play a crucial role in the solution.

204 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental study measuring the axial heat transfer distributions and the pressure drop coefficients of the tube fitted with a broken twisted tape of twist ratio 1, 1.5, 2, 2.5 or ∞ is performed in the Re range of 1000-40,000.

198 citations


Journal ArticleDOI
TL;DR: In this article, the effect of grit geometry on the heat transfer coefficient and friction factor in a rectilinear rectangular duct of an aspect ratio 10:1 was investigated, where the top wall surface is made rough with metal ribs of circular cross section in staggered manner to form defined grid.

Journal ArticleDOI
TL;DR: In this paper, the authors used a finite volume method (FVM) implemented on a Cartesian grid system in the range as 10 ≤ Re ≤ 45 and 0.7 ≤ Pr ≤ 400.
Abstract: Forced convection heat transfer from an unconfined circular cylinder in the steady cross-flow regime has been studied using a finite volume method (FVM) implemented on a Cartesian grid system in the range as 10 ≤ Re ≤ 45 and 0.7 ≤ Pr ≤ 400. The numerical results are used to develop simple correlations for Nusselt number as a function of the pertinent dimensionless variables. In addition to average Nusselt number, the effects of Re, Pr and thermal boundary conditions on the temperature field near the cylinder and on the local Nusselt number distributions have also been presented to provide further physical insights into the nature of the flow. The rate of heat transfer increases with an increase in the Reynolds and/or Prandtl numbers. The uniform heat flux condition always shows higher value of heat transfer coefficient than the constant wall temperature at the surface of the cylinder for the same Reynolds and Prandtl numbers. The maximum difference between the two values is around 15–20%.

Journal ArticleDOI
TL;DR: In this paper, a numerical study was conducted to analyze mixed convection heat transfer in a lid-driven cavity with a sinusoidal wavy bottom surface, where the cavity vertical walls were insulated while the bottom surface was maintained at a uniform temperature higher than the top lid.

Journal ArticleDOI
TL;DR: In this article, a numerical investigation of unsteady laminar mixed convection heat transfer in a lid driven cavity is executed, where the forced convective flow inside the cavity is attained by a mechanically induced sliding lid, which is set to oscillate horizontally in a sinusoidal fashion.
Abstract: A numerical investigation of unsteady laminar mixed convection heat transfer in a lid driven cavity is executed. The forced convective flow inside the cavity is attained by a mechanically induced sliding lid, which is set to oscillate horizontally in a sinusoidal fashion. The natural convection effect is sustained by subjecting the bottom wall to a higher temperature than its top counterpart. In addition, the two vertical walls of the enclosure are kept insulated. Discretization of the governing equations is achieved through a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previously reported investigations are performed and the results show excellent agreement. Temporal variations of streamlines, isotherms, and dimensionless drag force, and Nusselt number are presented in this investigation for various pertinent dimensionless groups. Fluid flow and heat transfer characteristics are examined in the domain of the Reynolds number, Grashof number and the dimensionless lid oscillation frequency such that: 10 2 ⩽ Re ⩽ 10 3 , 10 2 ⩽ Gr ⩽ 10 5 and 0.1 ⩽ ϖ ⩽ 5 . The working fluid is assigned a Prandtl number of 0.71 throughout this investigation. The obtained results reveal that the Reynolds number and Grashof number would either enhance or retard the energy transport process and drag force behavior depending on the conduct of the velocity cycle. Moreover, relatively small lid oscillation values are found to constrain the lid associated motion to a shallow depth from the sliding lid plane.

Journal ArticleDOI
TL;DR: Forced convection heat transfer to incompressible power-law fluids from a heated circular cylinder in the steady cross-flow regime has been investigated numerically by solving the momentum and thermal energy equations using a finite volume method and the QUICK scheme on a non-uniform Cartesian grid as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the effect of spacer length on heat transfer augmentation and friction factor was investigated with full-length helical screw element of different twist ratio, and helical twist inserts with spacer lengths 100, 200, 300, and 400 mm.

Journal ArticleDOI
TL;DR: In this article, the thermal and hydraulic performances of silicon-based, low aspect ratio micropin-fin cold plates under cross flow conditions are reported, and the experiments were conducted using water, over a Reynolds number (Re) ranging from 40 to 1000, where Re is the Reynolds number based on maximum velocity and the fin diameter.
Abstract: Experimental results of the thermal and hydraulic performances of silicon-based, low aspect ratio micropin-fin cold plates under cross flow conditions are reported. The pins were both circular and square in shape with dimensions (diameter for circular and sides for square) ranging from 50 μm to 150 μm. The test chip contained 20 integral 75 X 75 μm temperature sensors which were used to determine the thermal resistance (K W -1 ) of the cold plates. The experiments were conducted using water, over a Reynolds number (Re) ranging from 40 to 1000. The data show that the average Nusselt number (Nu) based on the fin diameter varies as Re 0.84 for Re 100, where Re is the Reynolds number based on maximum velocity and the fin diameter. Analysis of the Fanning friction factor (f) data shows that f varies as Re -1.35 for Re 100.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the 2D Rayleigh-Benard convection from the threshold of the primary instability with a theoretical value of critical Rayleigh number Ra c = 1707 to the regime near the flow bifurcation to the secondary instability.

Journal ArticleDOI
Mostafa Mahmoud1
TL;DR: In this paper, the effects of variable thermal conductivity and radiation on the flow and heat transfer of an electrically conducting micropolar fluid over a continuously stretching surface with varying temperature in the presence of a magnetic field are considered.
Abstract: In this paper, the effects of variable thermal conductivity and radiation on the flow and heat transfer of an electrically conducting micropolar fluid over a continuously stretching surface with varying temperature in the presence of a magnetic field are considered. The surface temperature is assumed to vary as a power-law temperature. The governing conservation equations of mass, momentum, angular momentum and energy are converted into a system of non-linear ordinary differential equations by means of similarity transformation. The resulting system of coupled non-linear ordinary differential equations is solved numerically. The numerical results show that the thermal boundary thickness increases as the thermal conductivity parameter S increases, while it decreases as the radiation parameter F increases. Also, it was found that the Nusselt number increases as F increases and decreases as S increases.

Journal ArticleDOI
TL;DR: In this paper, both the smooth fused silica and rough stainless steel microtubes were used with the hydraulic diameters of 50-100μm and 373-1570μm, respectively, to reveal the flow and heat transfer characteristics of liquid laminar flow in micro-tubes.

Journal ArticleDOI
TL;DR: In this paper, the effects of insertion of a helical screw-tape with or without core-rod in a concentric double tube heat exchanger on heat transfer and flow friction characteristics are experimentally investigated.

Journal ArticleDOI
TL;DR: In this article, a numerical study has been carried out in rectangular enclosures, which have a vertical active wall with all the other walls insulated, and the equally divided active sidewall is heated and cooled with sinusoidal temperature profiles.

Journal ArticleDOI
TL;DR: In this paper, the effect of baffle size and orientation on heat transfer enhancement was studied in detail, and three different baffle arrangements were considered, and the results showed that an increase in the baffle height causes a substantial increase in Nusselt number but the pressure loss is also very significant.

Journal ArticleDOI
TL;DR: The effect of radiation heat transfer on the natural convection heat transfer from a porous fin attached to a vertical isothermal surface has been investigated in this paper, where the governing equations are reduced to a single nonlinear ordinary differential equation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the thermal non-equilibrium model of convection, conduction and radiation in a saturated porous medium enclosed in a square cavity using the finite element method.

Journal ArticleDOI
TL;DR: In this article, a 2D model is used to investigate the approximate estimation of the natural convection heat loss from an actual geometry of the modified cavity receiver (hemisphere with aperture plate) of fuzzy focal solar dish concentrator.

Journal ArticleDOI
TL;DR: In this article, the authors focused on the numerical study of steady, laminar, conjugate natural convection in a square enclosure with an inclined thin fin of arbitrary length.

Journal ArticleDOI
TL;DR: In this paper, the authors used transient single blow technique to study the pressure drop and heat transfer of a square pin-fin array in a rectangular channel by using the transient single-blow technique.

Journal ArticleDOI
TL;DR: In this paper, the effect of viscous dissipation and thermal radiation on natural convection in a porous medium embedded within a vertical annular cylinder is investigated, where the inner surface of the cylinder was maintained at an isothermal temperature T w and the outer surface is maintained at ambient temperature T ∞.

Journal ArticleDOI
TL;DR: In this article, the authors investigated liquid water jet impingement cooling for both free-surface jet arrays and confined submerged jet arrays with straight holes of 1.0mm diameter arranged in rectangular arrays with spacings of 3, 5 and 7 jet diameters between adjacent jets.