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ME 150 – Heat and Mass Transfer

Chap. 12.3: Dimensionless Parameters

Dimensionless Parameters for Convection Transport phenomena can be described qualitatively and quantitatively by using dimensionless parameters. Convective heat transfer is described by the Nusselt Number (Nu): Nu L =

Reynolds Number Re

Prandtl Number Pr

h ⋅L = f (Re, Pr ) kf

Re L =

Pr =

U ⋅L U ⋅L⋅ρ =

ν

ν µ = α α ⋅ρ

Prof. Nico Hotz

⎛ Convection ⎞ ⎜ ⎟ ⎝ Conduction ⎠

µ

⎛ Inertial Forces ⎞ ⎜⎜ ⎟⎟ ⎝ Viscous Forces ⎠

⎛ Momentum Diffusivity ⎞ ⎜⎜ ⎟⎟ ⎝ Thermal Diffusivity ⎠ 1


ME 150 – Heat and Mass Transfer

Chap. 12.3: Dimensionless Parameters

Example: For turbulent flows inside of a channel / pipe, the following emperical correlation can be used:

Nu D = 0.023 ⋅ Re 4D/ 5 ⋅ Pr n

n = 0.4 for heating of fluid, n = 0.3 for cooling of fluid

High Re Numbers: turbulent flow Low Re Numbers: laminar flow

Prof. Nico Hotz

2


ME 150 – Heat and Mass Transfer

Prof. Nico Hotz

3


dimensionless numbers