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Thermal Conduction along a shaft

Thermal Conduction along a shaft

Thermal Conduction along a shaft

(OP)
I am trying to figure out how to calculate what temperature a bearing on a shaft will see.

I have a damper blade and shaft (2.5"OD) in an airstream at 780degree F. I have bearings mounted 5" outboard of the damper housing. Housing is 3/8 plate. shaft is 316 stainless.

How do i determine what temperature the bearings are going to see?  

RE: Thermal Conduction along a shaft

Yep. That's a fun heat transfer problem you have there.  Conduction, convection.  Fun.

Alternately, couldn't you just get a bearing that can handle 780 F?  If the cost difference isn't that large between bearings of varying temperature ratings, then you can just buy for the maximum temperature in the system.  Nothing will get hotter than that.

RE: Thermal Conduction along a shaft

(OP)
That's what we do in practice. I was looking to see if anyone knew of a simplified way to do the calcs.

The airstream is only supposed to hit that temp ocassionaly and only for a 10 minute interval. It will normally hover around 400F. It would be nice to know what temperature gradient looks like to see if it could ever be a problem for a particular bearing.

RE: Thermal Conduction along a shaft

This is a transient convection, conduction, convection system.  I don't think the calcs will ever really be simple.  

Could you maybe mount some thermocouples where you want to know the temperature and use a datalogger to get a plot you could look at later?  That may be the quickest and most accurate way to figure it out, since it records what's actually going on and not what the theoretical ideal is.

RE: Thermal Conduction along a shaft

Damper blade isn't rotating too fast or too long so a heat slinger probably won't do much other than interfere with the bearing standoff. On the other hand, it will act like a radial fin. Depending on ambient conditions it may aid radiative or convective h.t.

Seems like the most accurate way to get the temperature is measurement. Tempstick, non-contact ir thermocouple, or an actual thermocouple. It doesn't need to stay on forever.

I think that Graphalloy would be willing to stand behind their bearing in your application.

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