High Temperature Emissivity Measurement

1
High Temperature Emissivity Measurement

• Investigating the emissivity of welded stainless
  steel
• Greg Angelides Rafael Jaramillo
• Linda McLaren

2
Presentation Overview

• Importance of knowing high-temp emissivity
• Theoretical background
• Experimental Setup
• Results
• Discussion of results and errors
• Suggestions for future work

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Emissivity and Welding

• Ability to control temp. around weld
• HEF is crucial to weld properties
• Emissivity figures in heat equations

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Variable Emissivity

• Carbonization of metal surface, due to heat of
  welding process changes e
• Change in metal temperature changes e

We will attempt to make a model which can predict
changes in emissivity due to varying temperature
and surface conditions
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Carbonization in samples
sample 1
sample 2
sample 3
sample 4
sample 5
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TheoryStefan-Boltzmann Equation

• Q es(Tsample4 - Tsurrounding4)
• Q - heat radiated e - emissivity
• s - Stefan-Boltzmann constant

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Experimental Overview

• In order to calculate e, we design an experiment
  to measure all other variables in the
  Stefan-Boltzmann equation
• T of sample
• T of surroundings
• Q radiated

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Initial Experiment Cold Temperature Emissivity

• To test of our theory and equipment, we first
  conducted an experiment around room temperature
• (samples heated to 40 oC)

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Experimental Setup
hot plate
sample
IR camera
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Data Acquisition

• IR camera image is recorded on VHS and analyzed
  on computer
• Pixel level is easily converted into emission
  level

Example of infrared image
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Emittance Measurement Trick

• IR camera does not measure real Q
• Gives relative, unitless emission levels
• We use the following equation to convert emission
  levels to emittance

(target lvl.) (background lvl.)
(reference lvl.) (background lvl.)
e
(reference e)
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Reference Emittance Value

• Must calculate a reference emittance value for
  some point on the sample
• Need the actual temp. of a point, as well as the
  IR cameras indicated temp.
• IR camera emittance set to unity

eIRs ( Tcamera 4 Tsurrounding4) eactuals
(Tactual4 Tsurrounding4)
desired value
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Cold Temp Data
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High Temperature Experiment

• Must modify experimental setup to accommodate
  temperatures up to 450 oC
• Data is taken every 50 oC, from 50 oC to
• 450 oC
• In addition to testing our five welded samples,
  we will now test a clean, unwelded sample.

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Experimental Setup
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Analysis of Results

• Attempt to fit data to following mathematical
  model

etotal einitial T(temp) C(color)
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Isolating the Temperature Dependence
etotal einitial C(color) T(temp)
ecold einitial C(color)
etotal
T(temp)

ecold
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Graphing the Temperature Dependence
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Isolating the Effect of Weld-Produced Color Bands
etotal einitial T(temp)
C(color) ereference einitial T(temp)
etotal
C(color)
ereference
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Graphing the Color-Band Dependence
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Graphing the Color-Band Dependence
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Using C(color) and T(temp)

• With accurate graphs of the functions C(color)
  and T(temp), one could calculate the emissivity
  etotal with the following equation

etotal einitial T(temp) C(color)
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Sources of Error

• Camera placement
• Heating of camera condensation on lens
• Inconsistent surrounding temperature
• Direct thermocouple measurements insufficient
  contact with samples

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Sources of Error

• Further carbonization of samples

before heating
after heating
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Suggestion for Future Work

• Create a more uniform environment
• Isolate camera from heat
• Improve camera resolution
• Weld thermocouple leads to samples
• Account for further carbonization

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Welding So Hot, Its Cool !!!