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Nusselt number

About: Nusselt number is a(n) research topic. Over the lifetime, 28564 publication(s) have been published within this topic receiving 636431 citation(s). The topic is also known as: Nusselt number.

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Papers
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Journal ArticleDOI: 10.1080/08916159808946559
Bock Choon Pak1, Young I. Cho2Institutions (2)
Abstract: Turbulent friction and heat transfer behaviors of dispersed fluids (i.e., uttrafine metallic oxide particles suspended in water) in a circular pipe were investigated experimentally. Viscosity measurements were also conducted using a Brookfield rotating viscometer. Two different metallic oxide particles, γ-alumina (Al2O3) and titanium dioxide (TiO2), with mean diameters of 13 and 27 nm, respectively, were used as suspended particles. The Reynolds and Prandtl numbers varied in the ranges l04-I05 and 6.5-12.3, respectively. The viscosities of the dispersed fluids with γ-Al2O3 and TiO2 particles at a 10% volume concentration were approximately 200 and 3 times greater than that of water, respectively. These viscosity results were significantly larger than the predictions from the classical theory of suspension rheology. Darcy friction factors for the dispersed fluids of the volume concentration ranging from 1% to 3% coincided well with Kays' correlation for turbulent flow of a single-phase fluid. The Nusselt n...

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Topics: Viscometer (57%), Viscosity (55%), Nanofluid (55%) ...read more

3,158 Citations


Journal ArticleDOI: 10.1016/S0017-9310(03)00156-X
Abstract: Heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids is investigated for various pertinent parameters. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersion. The transport equations are solved numerically using the finite-volume approach along with the alternating direct implicit procedure. Comparisons with previously published work on the basis of special cases are performed and found to be in excellent agreement. The effect of suspended ultrafine metallic nanoparticles on the fluid flow and heat transfer processes within the enclosure is analyzed and effective thermal conductivity enhancement maps are developed for various controlling parameters. In addition, an analysis of variants based on the thermophysical properties of nanofluid is developed and presented. It is shown that the variances within different models have substantial effects on the results. Finally, a heat transfer correlation of the average Nusselt number for various Grashof numbers and volume fractions is presented.

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Topics: Heat transfer enhancement (63%), Heat transfer coefficient (62%), Nanofluid (62%) ...read more

2,285 Citations


Journal ArticleDOI: 10.1016/J.IJHEATFLUIDFLOW.2008.04.009
Hakan F. Öztop1, Eiyad Abu-Nada2Institutions (2)
Abstract: Heat transfer and fluid flow due to buoyancy forces in a partially heated enclosure using nanofluids is carried out using different types of nanoparticles. The flush mounted heater is located to the left vertical wall with a finite length. The temperature of the right vertical wall is lower than that of heater while other walls are insulated. The finite volume technique is used to solve the governing equations. Calculations were performed for Rayleigh number (103 ⩽ Ra ⩽ 5 × 105), height of heater (0.1 ⩽ h ⩽ 0.75), location of heater (0.25 ⩽ yp ⩽ 0.75), aspect ratio (0.5 ⩽ A ⩽ 2) and volume fraction of nanoparticles (0 ⩽ φ ⩽ 0.2). Different types of nanoparticles were tested. An increase in mean Nusselt number was found with the volume fraction of nanoparticles for the whole range of Rayleigh number. Heat transfer also increases with increasing of height of heater. It was found that the heater location affects the flow and temperature fields when using nanofluids. It was found that the heat transfer enhancement, using nanofluids, is more pronounced at low aspect ratio than at high aspect ratio.

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Topics: Nanofluid (60%), Nusselt number (58%), Rayleigh number (58%) ...read more

1,538 Citations


Waqar A. Khan1, Ioan PopInstitutions (1)
Abstract: The problem of laminar fluid flow which results from the stretching of a flat surface in a nanofluid has been investigated numerically. This is the first paper on stretching sheet in nanofluids. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented which depends on the Prandtl number Pr, Lewis number Le, Brownian motion number Nb and thermophoresis number Nt. The variation of the reduced Nusselt and reduced Sherwood numbers with Nb and Nt for various values of Pr and Le is presented in tabular and graphical forms. It was found that the reduced Nusselt number is a decreasing function of each dimensionless number, while the reduced Sherwood number is an increasing function of higher Pr and a decreasing function of lower Pr number for each Le, Nb and Nt numbers.

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Topics: Nusselt number (62%), Sherwood number (62%), Prandtl number (57%) ...read more

1,250 Citations


Open accessJournal ArticleDOI: 10.1103/REVMODPHYS.81.503
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.

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  • FIG. 3. Color online Phase diagram in Ra-Pr plane. a Phase diagram in the Ra-Pr plane according to Grossmann and Lohse 2000, 2001, 2002, 2004 : The upper solid line means Re=Rec; the lower nearly parallel solid line corresponds to u,BL= u,bulk; the curved solid line is ,BL= ,bulk; and along the long-dashed line u= , i.e., 2aNu= Re. The dotted line indicates where the laminar kinetic BL is expected to become turbulent, based on a critical shear Reynolds number Re s *
    FIG. 3. Color online Phase diagram in Ra-Pr plane. a Phase diagram in the Ra-Pr plane according to Grossmann and Lohse 2000, 2001, 2002, 2004 : The upper solid line means Re=Rec; the lower nearly parallel solid line corresponds to u,BL= u,bulk; the curved solid line is ,BL= ,bulk; and along the long-dashed line u= , i.e., 2aNu= Re. The dotted line indicates where the laminar kinetic BL is expected to become turbulent, based on a critical shear Reynolds number Re s *
  • FIG. 11. Deviations from the Oberbeck-Boussinesq approximation. a , b The ratio Nu/NuOB as a function of for fixed Tm. c , d Tc−Tm as a function of , also fixed Tm. a , c Water at Tm=40.0 °C, =1.0. Solid circles, L=49.7 cm. Open circles, L=24.8 cm. Solid squares, L=9.2 cm. b , d Ethane at a pressure of 55.17 bars for =0.5. Open symbols, Tm =35.0 °C below the critical isochore temperature T =38.06 °C at this pressure. Solid symbols, Tm=41.0 °C, above T .
    FIG. 11. Deviations from the Oberbeck-Boussinesq approximation. a , b The ratio Nu/NuOB as a function of for fixed Tm. c , d Tc−Tm as a function of , also fixed Tm. a , c Water at Tm=40.0 °C, =1.0. Solid circles, L=49.7 cm. Open circles, L=24.8 cm. Solid squares, L=9.2 cm. b , d Ethane at a pressure of 55.17 bars for =0.5. Open symbols, Tm =35.0 °C below the critical isochore temperature T =38.06 °C at this pressure. Solid symbols, Tm=41.0 °C, above T .
  • FIG. 12. Behavior of LSC. Left: The LSC orientation as a function of time at z=−L /4 b, dotted line , z=0 0, triangles , and z=L /4 t, solid line . Right: The probability distribution p /2 as a function of /2 . Here = t− 0 open circles and = b− 0 solid circles . Solid line, a Gaussian distribution. Adapted from Funfschilling et al., 2008.
    FIG. 12. Behavior of LSC. Left: The LSC orientation as a function of time at z=−L /4 b, dotted line , z=0 0, triangles , and z=L /4 t, solid line . Right: The probability distribution p /2 as a function of /2 . Here = t− 0 open circles and = b− 0 solid circles . Solid line, a Gaussian distribution. Adapted from Funfschilling et al., 2008.
  • FIG. 13. Time dependence of LSC orientation. Top: A time series of 0 t spanning about 11 days. Adapted from Brown and Ahlers, 2006b. Bottom left: The LSC orientation 0 t . Bottom right: The LSC azimuthal temperature amplitude t at the sidewall, during a cessation. Adapted from Brown, Nikolaenko, et al., 2005.
    FIG. 13. Time dependence of LSC orientation. Top: A time series of 0 t spanning about 11 days. Adapted from Brown and Ahlers, 2006b. Bottom left: The LSC orientation 0 t . Bottom right: The LSC azimuthal temperature amplitude t at the sidewall, during a cessation. Adapted from Brown, Nikolaenko, et al., 2005.
  • FIG. 4. Nusselt number versus Rayleigh number. Reduced Nu for =1, obtained using water Pr 4.4 and copper plates, as a function of Ra. Open symbols, uncorrected data. Solid symbols, after correction for the finite plate conductivity. Circles, Funfschilling et al. 2005 . Squares, Sun, Ren, et al. 2005 . The downwards and upwards triangles are upper and lower bounds on the actual Nusselt number at large Ra; the diamonds originate from an estimate, see the text for details. The solid line is the GL prediction Grossmann and Lohse, 2001 .
    FIG. 4. Nusselt number versus Rayleigh number. Reduced Nu for =1, obtained using water Pr 4.4 and copper plates, as a function of Ra. Open symbols, uncorrected data. Solid symbols, after correction for the finite plate conductivity. Circles, Funfschilling et al. 2005 . Squares, Sun, Ren, et al. 2005 . The downwards and upwards triangles are upper and lower bounds on the actual Nusselt number at large Ra; the diamonds originate from an estimate, see the text for details. The solid line is the GL prediction Grossmann and Lohse, 2001 .
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Topics: Rayleigh number (69%), Turbulent Prandtl number (66%), Natural convection (65%) ...read more

1,175 Citations


Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2022104
20211,911
20201,776
20191,745
20181,522
20171,884

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Topic's top 5 most impactful authors

Tasawar Hayat

389 papers, 17.9K citations

Ioan Pop

354 papers, 15.7K citations

Ali J. Chamkha

318 papers, 12.3K citations

Mohsen Sheikholeslami

148 papers, 16.6K citations

Mikhail A. Sheremet

144 papers, 4.8K citations

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