# High Temperature Emissivity Measurment by 917mMF

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```									      High Temperature
Emissivity Measurement
Investigating the emissivity of
welded stainless steel

Greg Angelides
Rafael Jaramillo
Linda McLaren
Presentation Overview
 Importance of knowing high-temp
emissivity
 Theoretical background
 Experimental Setup
 Results
 Discussion of results and errors
 Suggestions for future work
Emissivity and Welding

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

sample 1   sample 2   sample 3   sample 4   sample 5
Theory:
Stefan-Boltzmann Equation

   Q = es(Tsample4 - Tsurrounding4)

 Q - heat radiated e - emissivity
 s - Stefan-Boltzmann constant
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

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)
Experimental Setup
hot plate

sample

IR camera
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
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.)
e=   (reference lvl.) – (background lvl.)
* (reference e)
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 camera’s indicated temp.
 IR camera emittance set to unity

eIRs ( Tcamera   4   –Tsurrounding4) =   eactuals (Tactual4 – Tsurrounding4)

desired value
Cold Temp Data
Em ittance Values for Different Bands

0.900

0.850

0.800

0.750
Em ittance

0.700

0.650

0.600

0.550

0.500
Reference   Caramel      Blue Avg.   Brow n     Bronze        Yellow   Black (flat)    Black
Avg.       Avg.                     Avg.       Avg.          Avg.       Avg.        (ridge)
Avg.
Color Band
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.
Experimental Setup

fans           31 cm
IR Camera
thermocouple
sample

Heating
Cylinder
Analysis of Results

   Attempt to fit data to following
mathematical model:

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

etotal = einitial * C(color) * T(temp)

ecold = einitial *
C(color)

etotal
=   T(temp)
ecold
Graphing the Temperature
Dependence
T(temp)

1.2

1
50
100
0.8
150
200
0.6
250
300
0.4
350
400
0.2

0
Brown   Blue   Yellow    Bronze   Black
Isolating the Effect of Weld-
Produced Color Bands
etotal        = einitial * T(temp) * C(color)

ereference = einitial * T(temp)

etotal
=   C(color)
ereference
Graphing the Color-Band
Dependence
Weld-Produced Color Band Dependence

1.4

1.2

1                                                         50
100
150
0.8                                                        200
250
0.6                                                        300
350
400
0.4                                                        450

0.2

0
Blue      Yellow     Brown      Bronze       Black
Graphing the Color-Band
Dependence
Weld-Produced Color Band Dependence

1.4

1.2

1

0.8
AVERAGE
0.6

0.4

0.2

0
Blue     Yellow   Brown     Bronze    Black
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)
Sources of Error

 Camera placement
 Heating of camera – condensation
on lens
 Inconsistent surrounding
temperature
 Direct thermocouple measurements
– insufficient contact with samples
Sources of Error
   Further carbonization of samples:

before heating   after heating
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
Welding: So Hot, it’S Cool !!!

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