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Average Nusselt

Combined Nusselt

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

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

Geometry | Range |
---|---|

Vertical plate | Entire range |

Horizontal plate (a)¹ | $10^4$ - $10^{11}$ |

Horizontal plate (b)² | $10^5$ - $10^{11}$ |

Horizontal cylinder | Less than $10^{12}$ |

Sphere³ | Less than $10^{11}$ |

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.

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:

$Nu_{combined} = (Nu_{forced}^n + Nu_{natural}^n)^{1/n}$

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

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

Geometry | Range |
---|---|

Vertical plate | Entire range |

Horizontal plate (a)¹ | $10^4$ - $10^{11}$ |

Horizontal plate (b)² | $10^5$ - $10^{11}$ |

Horizontal cylinder | Less than $10^{12}$ |

Sphere³ | Less than $10^{11}$ |

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.

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:

$Nu_{combined} = (Nu_{forced}^n + Nu_{natural}^n)^{1/n}$

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