Nahme-Griffith Number

Equation (6.245) is the well known Nahme-Griffith number... 

Note that they use the Nahme-Griffith number Na = l>Br. Na is a ratio of temperature rise due to viscous heating to the temperature change necessary to alter the viscosity. Thus since... 

The Nahme number can be considered to be the ratio of viscous dissipation to ther-mai conduction in the direction perpendicular to flow. Large values of the Nahme number (>1) indicate that the temperature non-uniformities created by the viscous dissipation have a substantiai effect on the resulting velocity profile. Thus, if the Nahme number is iarge, a non-isothermal flow analysis has to be made in order to maintain sufficient accuracy. If the Nahme number is small, an isothermal analysis can yieid reiativeiy accurate resuits. The Nahme number is also referred to as the Griffith number. 

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