HeatTransfer-I-Section-9

387 ra1 6 l 0825 8 27 1 0492 pr9 16 ral

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Unformatted text preview: Nux = L 3 Ⱥ Ⱥ1 / 4 Pr f (Pr) = Ⱥ Ⱥ Pr + 0.986 Pr1 / 2 + 0.492 Ⱥ Ⱥ GrL < 10 9 € • There are other forms, such as the one given in your text. • The Gr criteria ensures laminar flow! 8 Convec'on Heat Transfer •  Transi'on to Turbulence –  In general for gases when Ra > 109 turbulence sets in, or more appropriately for all fluids including gases, Gr > 109 9 Convec'on Heat Transfer •  Ver'cal Flat Plate (Extended) Nu0 − L Ⱥ Ⱥ 2 0.387 Ra1 / 6 L Ⱥ = Ⱥ0.825 + 8 / 27 Ⱥ [1 + (0.492 / Pr)9 /16 ] Ⱥ Ⱥ Ⱥ RaL > 0 € 10 Convec'on Heat Transfer •  Cylinder (Churchill/Chu Model) –  0 < RaD < 1012 Ⱥ Ⱥ 2 0.387 Ra1 / 6 D Ⱥ NuD = Ⱥ0.6 + 8 / 27 Ⱥ [1 + (0.559 / Pr)9 /16 ] Ⱥ Ⱥ Ⱥ € 11 Convec'on Heat Transfer •  Sphere (Churchill/Chu Model) •  Other 3D Bodies (Cuboids/Spheroids) –  A = the surface area of body 12 Convec'on Heat Transfer •  There are other models and correla'ons in your text, e.g. horizontal and inclined plates. •  You should become familiar with them in Sec'ons 9.1 – 9.6. •  Read the chapter sec'ons in the text, as there...
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This document was uploaded on 02/14/2014 for the course ENGR 6901a at Memorial University.

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