Temperature measurement

[MNS747]

Hi
I am trying to analyse the thermal growth in the CNC machine spindle. spindle has bearings inside that rotates the tool that get fit in between the spindle. I was measuring the temperature at the outside surface of the spindle by running the spindle at 4000rpm. after 10 minutes of running i stopped the spindle. i got the delta T as 1.2C. my ambient temp was 23.5 and after 10 minutes the temp was 24.7C. I am now trying to model this in abaqus and i am confused about the method, shall I start with applying body heat flux on the bearings?(bearings are the actual heat source) if so could any one please tell me what exactly the formula i should use to obtain the body heat flux? in Abaqus documentation it says its units are J/T.L3. Cant interprete it.
I dont want to apply temperature boundary conditions because when bearings start they start to generate heat and i dont know the bearing temperature because of no means of measuring it. I can only measure it by using a sensor at the outside surface.
Any help will be greatly appreciated
Regards

 

[corus]

Surface heat flux is measured in Watts/m^2. Body heat flux (or a heat source is W/m^3). I'd use a surface heat flux at the bearing surface and vary it until you got the same increase in temperature. On the outside you'd need to include forced convection to the air moving at a speed equivalent to the 4000 rpm.

corus

 

[MNS747]

Thanks Corus for your valuable comments. I would definetly give it a go with surface heat flux.

Regards

 

[MNS747]

hi corus
could you please shed some light on how to model forced convection equivalent to 4000rpm in Abaqus? (sorry if it sounds odd).

Would be grateful to you
Regards

 

[corus]

I'd equate it to the fluid travelling at the equivelent speed of 4000 rpm over the surface, or v = rw. Try this

http://www.cheresources.com/convection.shtml

and use flow across a cylinder.

corus

 

[MNS747]

Thanks Corus that is a great help.
Regards

 

[MNS747]

Hi
Apart for 4000rpm thing. Currently i am only applying surface heat flux. It is a 3D model with a spindle containing bearings inside (modelled only half due to symmetry). During my test on the machine i got temperature at the spindle surface of 27.2C (amb is 23.5)
when i calculated heat flux using q=kdt/L, the flux i am getting is 3368W/m2.
Steel cond=51.9W/m2C both bearing and the spindle.
L=??? (i currently took 0.057m which is from spindle middle to the spindle surface and bearing lies between it. bearing length is 20mm. Model is like this if you start from left middle wall to the right upto surface.

left to right
middle Wall 11mm/bearing 20mm/wall 27mm(surface)

1) when i am applying that surface heat flux of 3368w/m2in abaqus and simulations runs for 1 hour it gave me temperature of 33C where as when i Halved it (1500W/m2) it gave me approx 27C which almost correlates with what i got from sensors. Does anyone got any idea why is it doing like that?

2) could anyone please inform if there is any issue related to 3D calculations for surface heat flux?

Sorry for if that is complicated
i would appreciate if i get any answers to this

Regards