Heat Transfer / thermal radiation
Heat Transfer / thermal radiation
(OP)
I have designed a machine and now I need to guard it with minimum space. The motor gets to about 100 degrees C so how far away does my steel mesh guard have to be to get to a safe working temperature????
The materials etc have already been specified so can not be changed. There is a 50% air flow.
Basically all i need is an equation/graph to show the distance 40c air would be from a motor that is 100c (air = thermal conductivity of 0.024W/mk).
Can anyone help?
The materials etc have already been specified so can not be changed. There is a 50% air flow.
Basically all i need is an equation/graph to show the distance 40c air would be from a motor that is 100c (air = thermal conductivity of 0.024W/mk).
Can anyone help?





RE: Heat Transfer / thermal radiation
I saw an equation one time that had like 20 variables in it....
Why not just fire it up - let it get to temp and measure the temp at various distances.
If you find a simple answer - let me know
RE: Heat Transfer / thermal radiation
RE: Heat Transfer / thermal radiation
Your inside surface should be mirror finished to increase the reflectivity. A perfect blackbody radiates about 640 W/m^2 into a 300K ambient.
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RE: Heat Transfer / thermal radiation
Ill use 1/2 inch gap with a mirror finish steel plate to test it!
Thanks for your help
RE: Heat Transfer / thermal radiation
You're at 100 C (close to the boiling point of water!!! depending on elevation) - so your FIRST attempt should be cooling the motor, THEN shielding the not-very-often-present workers from the too hot motor!
RE: Heat Transfer / thermal radiation
However, your initial problem statement sounds like you are treating the problem like a conduction through air calculation. I don't think that's appropriate. You have air flowing around the system, so there is convection. In addition, you have radiation from the hot parts to the guard. The temperature of the guard is the point of interest, I think, not the air temperature at the guard. They are likely to be different. If this is true, then you need to be concerned about the convection to the guard and the radiation to it.
As the others have suggested, the radiation to the guard can be reduced by shielding or by making the machine reflective. The problem with that approach is it will actually raise the T of the machine by reducing its ability to reject heat.
An alternative is to make the inner faces of the guard reflective, reducing its ability to accept the radiated heat, and only mildy impacting the dumping of heat by the machine. The operator's side of the guard should be an emissive surface so it dumps heat to the surroundings as much as possible. You could also, if the situation warrants it and costs are not prohibitve, make the guard out of something other than a single layer of expanded metal. I am thinking here of a double layer of metal with an air gap or something tubular.
JK
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com