Reynolds Analogy 6vwb

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REYNOLDS ANALOGY

A B

Jayanti, Sreenivas

C

DOI: 10.1615/AtoZ.r.reynolds_analogy

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The convective transport of mass, momentum and heat normally occurs through a thin boundary layer close to the wall.

F

The equations governing the transport of these quantities are analogous and are exact [Incropera & DeWitt (1990)] for

G

laminar flow if the pressure gradient is equal to zero and the Prandtl Number (Pr) and Schmidt Number (Sc) are equal

H

to unity. Under these conditions, their nondimensional convective transport coefficients are related by

I

(1)

J K L

where f is the Fanning friction factor, Re is the Reynolds Number, Nu is the Nusselt Number representing heat transfer

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and Sh the Sherwood Number representing mass transfer. Equation (1) is known as the Reynolds analogy, and enables the calculation of, for example, the heat transfer coefficient if either the friction factor or the mass transfer coefficient is

N

known. (See also Analogy Between Heat, Mass and Momentum Transfer.)

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For turbulent flow in a pipe or over a flat plate, the exchange of momentum, heat and mass occurs mainly by turbulent

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eddies in the bulk of the flow. However, very close to the wall, the exchange must occur by molecular diffusion across the velocity, temperature and concentration boundary layers, respectively. When Pr and Sc are equal or close to unity, the

R RACKETT EQUATION RADAR

boundary layer thicknesses are roughly equal and Eq. (1) is applicable. When this is not so, which is often the case for liquids, proper must be taken of the relative thicknesses of the boundary layers. A modified Reynolds analogy, also known as the Chilton-Colburn analogy, is found to be applicable under these conditions:

RADIAL COMPRESSOR

(2)

RADIAL ENERGY FLOWS RADIAL FANS RADIAL GAP SIZE

(3)

RADIATION RADIATION ABSORPTION METHOD RADIATION BETWEEN PARALLEL

Equations (2) and (3) are applicable for both laminar and turbulent flow [Hewitt et al. (1994)].

PLATES RADIATION DIFFUSION APPROXIMATION, FOR COMBINED

References

RADIATION AND CONDUCTION

1. Hewitt, G. F., Shires, G. L., and Bott, T. R. (1994) Process Heat Transfer, McGraw-Hill.

RADIATION DOSIMETRY

2. Incropera, F. P. and DeWitt, D. P. (1990) Fundamentals of Heat and Mass Transfer, John Wiley and Sons.

RADIATION DRYING RADIATION FROM SEMI-TRANSPARENT

Numbe r of vie ws: 3592

Article a dde d: 2 Fe bruary 2011

Article la st modifie d: 8 Fe bruary 2011

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