Message Board Thread - "temperature fluctuation, point heat source"

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temperature fluctuation, point heat source nikreila 3/11/2005
hi,

we are trying to identify the temperature distribution of a thermal trace left by a point heat source by a FLIR SC3000.

a solid aluminum disc is placed ahead the heat source and is still. disc is rotating. so the trace left is circular.

we are viewing the the thermal trace left at a symmetrical point (in cylindrical coordinates, having the disc center as center, they are 180° apart)

imaging freq. is 50 Hz. this makes approximately 4 images per rotation. however the images exhibit fluctuations. i.e., consecutive images depict plus minus 20° temperature difference(disk does not vibrate and balanced).

i employed time averaging for the 3 consecutive rotations. but being curious for the reasons of the fluctuations obtained SEM photos of the trace left.

with this message I have uploaded a 3D image. as clear from the SEM, the surface texture continously changed due to the heat source.

my question is time averaging (may be additional spatial averaging using extra line tools) is enough or I have to consider something else. in order to have the right temperature profile.

thanks in advance.
 
Re:temperature fluctuation, point heat source JKEngineer 3/12/2005
Could you post a sketch of the physical setup? Your description was unclear, to me at least.
Jack
Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

Bronx, NY 10463

718-884-6644
866-884-6644 toll free
212-214-0919 fax and voice mail

JKEngineer@aol.com or JKEngineer@KleinfeldTechnical.com
come see what we can do for you: http://www.KleinfeldTechnical.com
 
Re:temperature fluctuation, point heat source nikreila 3/12/2005
here is the sketch (bird's eye view)
hope it is clear now.


Erkin Kutlu
Mech. Eng., MSc

Politecnico di Milano
Via Bonardi 9 / 20133
Milan/ITALY

Tel: +39.02.23994925
Fax: +39.02.70638377
 
Re:temperature fluctuation, point heat source JKEngineer 3/15/2005
That helps some.

Questions for you:
What are the items numbered 1,2,3,4? Are the in contact with the larger, rotating disc? Is the contact of the point source reliably constant to the rotating disc? What type of trace information do you get if you measure the system with the point source removed? That will be an indication of the sources of error beyond the heating variation.

Thoughts and cautions:
Is the aluminum disc bare? If so, emissivity will be a problem and will prevent any accuracy in your measurements. Can you paint it and still achieve the purpose of your work? (What is the purpose of this, by the way?)

If you are time averaging for only three cycles, you are not going to get great statistical reliability in terms of separating error sources from functional variation.

Jack
Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

4011 Hillman Ave
Bronx, NY 10463

718-884-6644
866-884-6644 toll free
212-214-0919 fax and voice mail

JKEngineer@aol.com or JKEngineer@KleinfeldTechnical.com
come see what we can do for you: http://www.KleinfeldTechnical.com
 
Re:temperature fluctuation, point heat source raffar 3/15/2005
I think Jack's right: emissivity is the problem. The picture posted shows a varied surface morphology, which we know affects the emissivity. I believe what you're seeing is variation in emissivity, not necessarily variation in temperature (that might be there, too). The image http://www.pyrometry.com/images/ih2003_3.gif from our site shows how we modified the surface of shiny molybdenum, and the image below, http://www.pyrometry.com/images/molybdenumcomparison.gif shows the result.

Ralph Felice
FAR Associates
http://www.pyrometry.com/
 
Re:temperature fluctuation, point heat source nikreila 3/16/2005
Jack,

the items numbered 1-4 are not present on the disc, they just symbolize the 4 acquisitions in a single rotation of the disc(they are not physically present on the disc)

necessary info;

-heat source is an arc and its position is constant to the disc(arc root dynamics is
chaotic in nature).

-aluminum disk is not bare, it is roughened and then mildly weathered.

-we can not paint the disc, heat source burns the paint out.

- the purpose is to use this profile for the characterization of process parameters
(having an IR camera we are validating if this could be a method)

for ex: diminusihing the gas flow rate widens the profile or not.

having observed this continous change in the profile, i have doubts.

regarding your questions and comments I've prepared a trace information using the attached image.

the small inserts on the top left corner are IR images on the trace

number (1) is the profile from the line tools on the disc before we applied the heat

source.(disk is rotating)

number (2) is the profile obtained after the point source is removed. note that

surface is cooled down to initial temperature, the measurements for this initial

temperatures are done with the assistance of the thermocouple wrt a point that is

away from the trace.

number (3) and (4) are profiles obtained during rotation and disc is in rotation.

:::::ralph::::::::,

i do agree with you, surface morphology is altering the emissivity. i think what we see is the variation in the emissivity as a function of morphology.

i also heat treated a large area on the surface (moving the heat source in radial direction, back and forth ) in order to distribute this morphological effect over a region and then applied the heat source, the profile was much more chaotic.
 
Re:temperature fluctuation, point heat source JKEngineer 3/17/2005
If I understand, and I am certainly getting closer ;-), the profile plots in your last posting are across the heat trace. Is that also true of the 3-D plot in the orginal post?

Is the arc grounding to the aluminum? That is, is it an electrical arc from the probe to the aluminum or is it a self contained arc near the aluminum? If it is striking the aluminum, I would expect it to affect the surface properties significantly.

The IR images in your last two graphs show a circumfrential streak that is captured in the plots of 3, but is past the plots in 4. If it is not a surface artifact on the disc, then it is showing you arc irregularities, which I think is what you are seeking.

Plot 2 shows a center peak indicating that the disc did not fully cool. Am I reading this right?

A method for reducing the impact of emissivity variations would be to provide a very low temperature background for the imaging. This will reduce the reflected energy component, so that the emitted energy is a greater proportion of the energy leaving the surface. There will still be variation due to the emissivity variation, but I think it will be reduced.

Would you be interested in more direct consulting help? As valuable as this forum is, there is a limit to what I am willing to do for free.

Jack
Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

Bronx, NY 10463

718-884-6644
866-884-6644 toll free
212-214-0919 fax and voice mail

JKEngineer@aol.com or JKEngineer@KleinfeldTechnical.com
come see what we can do for you: http://www.KleinfeldTechnical.com
 
Re:temperature fluctuation, point heat source nikreila 3/19/2005
Jack,

Thanks for the comments. I appreciate the responses that came from you and Ralph.

You got closer:)As it can be deduced from the inserts on the related images, profile plots are across the heat trace. That is also true for the 3D plot.

Arc is grounding to the aluminum(from the probe to the aluminum). Definitely it strikes aluminum and it effects the surface properties significantly(observable from the SEM image).

The streaks are surface artifacts created by the arc. This was the thing that I was not sure.So it was the reason that I've posted these images here along with SEM results.

The 2nd plot indicates that the disc did not fully cool(reference point is near to the axis). you are right.

Another interesting thing is the secondary peaks are caused by the dab of the arc interacting with the aluminum. These are more flat with a brand new surface.

The camera is shielded from environment to reduce the reflected energy component. The emitted energy is a greater proportion of the energy leaving the surface.

By saying a very low temperature background what do you intend? (of course if it is not a paid answer?:)

As you said we still have the emissivity variation.

The work we do is unique and as the surveys indicate it was not done before. There are few studies on rotating discs and heat transfer(brake disc characterization is a close example but not the same thing).

For that reason it is important to characterize.

We would be interested in more direct consulting, but first of all I have to be sure that what we have in our hand and consequently define the problem with its every facet. Thermography in research is a relatively young field and needs careful attention.

Thanks for the valuable present and future comments to all.

for direct contact,

erkin kutlu

kutlu@tmhp1.mecc.polimi.it

department of mechanical eng.
politecnico di milano
 
Re:temperature fluctuation, point heat source JKEngineer 3/20/2005
OK, one more for free:

Calculate the energy leaving the surface as a function of the surface T, background T, and emissivity. Do a sensitivity analysis to the background T, and perhaps to the variations in emissivity. Determine what background T (a low value) reduces your error to an acceptable level. The emissivity variation will cause problems, however.
Jack
Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

Bronx, NY 10463

718-884-6644
866-884-6644 toll free
212-214-0919 fax and voice mail

JKEngineer@aol.com or JKEngineer@KleinfeldTechnical.com
come see what we can do for you: http://www.KleinfeldTechnical.com
 


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