Reynold number for temperature distribution

[ConvinceMePlease]

Hello guys,

 

If we have a flow with Temperature distribution. There is a hot object around which there is flow. to find if the flow is laminar or turbulent, should we consider an average viscosity or should we consider the viscosity around the object? I feel it is safer to assume the lowest viscosity because it can tell us if the flow around the object is laminar or turbulent.

 

what do you think? should this be done? does the low temperature away from the object matter? (lets say viscosity is 10^-3 away from the object and 4X10^-4 neaer the hot object)

[studiot]

There is often a temperature difference between the mean fluid temperature and the temperature of obstacles.

So for example you would be extremely uncomfortable if your jetliner was at mean atmospheric temperature at altitude.

 

In such a case you would use the viscosity at the mean fluid temperature.

 

If however your fluid was air being drawn through the fins of a heat pump exchanger, mean or average viscosity only has meaning when the air is well clear of dew or ice points.

 

Each situation must be considered on its merits.

Edited March 3, 2017 by studiot