Free convection cylinders spheres and enclosures
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Free Convection: Cylinders, Spheres, and Enclosures. Chapter 9 Section 9.6.3 through 9.8. The Long Horizontal Cylinder. Cylinders. Boundary Layer Development and Variation of the Local Nusselt Number for a Heated Cylinder:. The Average Nusselt Number:.

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Free Convection: Cylinders, Spheres, and Enclosures

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Free convection cylinders spheres and enclosures

Free Convection:Cylinders, Spheres, and Enclosures

Chapter 9

Section 9.6.3 through 9.8


Cylinders

The Long Horizontal Cylinder

Cylinders

  • Boundary Layer Development and Variation of the Local Nusselt Number

    for a Heated Cylinder:

  • The Average Nusselt Number:

  • How do conditions change for a cooled cylinder?


Spheres

  • In the limit as how may conditions be characterized?

Spheres

Spheres

  • The Average Nusselt Number:


Enclosures

  • Horizontal Cavity

  • Vertical Cavity

Enclosures

Enclosures

  • Rectangular Cavities

  • Characterized by opposing walls of different temperatures, with the

    remaining walls well insulated.


Enclosures cont

  • Heating from Below

Enclosures (cont)

  • Horizontal Cavities

Fluid layer is thermally stable.

Thermal instability yields a regular convection pattern in the form of roll cells.

Buoyancy drive flow is turbulent


Enclosures cont1

  • Heating from Above

A primary cellular flow is established, as the core

becomes progressively more quiescent, and

secondary (corner) cells develop with increasing

Enclosures (cont)

Fluid layer is unconditionally stable.

  • Vertical Cavities


Enclosures cont2

  • Heat transfer depends on the magnitude of relative to a critical angle ,

    whose value depends on H/L (Table 9.4).

  • Heat transfer also depends on the magnitude of relative to a critical

    Rayleigh number of

  • Heat transfer correlations Eqs. (9.54) – (9.57).

Enclosures (cont)

  • Inclined Cavities

  • Relevant to flat plate solar collectors.


Enclosures cont3

Annular Cavities

Enclosures (cont)

  • Concentric Cylinders

  • Critical Rayleigh Number:


Enclosures cont4

Enclosures (cont)

  • Concentric Spheres

  • Critical Rayleigh Number:


Problem batch reactor

Problem: Batch Reactor

Problem 9.74: Use of saturated steam to heat a pharmaceutical in a batch reactor.


Problem batch reactor cont

Problem: Batch Reactor (cont)


Problem batch reactor cont1

Problem: Batch Reactor (cont)


Problem batch reactor cont2

Problem: Batch Reactor (cont)


Problem batch reactor cont3

Problem: Batch Reactor (cont)


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