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Nusselt's number
Average Nusselt
Combined Nusselt

Input data

Geometry

Rayleigh's number

Prandtl

Output data

Average Nusselt

Description

Ratio between the conductive thermal resistance and the convective thermal resistance of the fluid.

Medium Nusselt

Given the Rayleigh number (Ra) and Prandtl (Pr), in addition to determining its geometry, it calculates the value of the number of Average Nusselt.

GeometryRange
Vertical plateEntire range
Horizontal plate (a)¹10410^4 - 101110^{11}
Horizontal plate (b)²10510^5 - 101110^{11}
Horizontal cylinderLess than 101210^{12}
Sphere³Less than 101110^{11}

¹Horizontal plate (a): Upper surface of a hot plate or lower surface of a cold plate.

²Horizontal plate (b): Lower surface of a hot plate or upper surface of a cold plate.

³Sphere: Beyond the Ra range, the Prandtl number must be equal to or greater than 0.7.

Nusselt combined

Estimates the value of the Nusselt number for natural and forced convection combined from the Nusselt values of each type of convection and the geometry involved such as fluid flow, using the formula:

Nucombined=(Nuforcedn+Nunaturaln)1/n Nu_{combined} = (Nu_{forced}^n + Nu_{natural}^n)^{1/n}

References

  • WELTY, James R.; RORRER, Gregory L.; FOSTER, David G. Fundamentos de Transferência de Momento, de Calor e de Massa, 6ª edição. Grupo GEN, 2017.