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

     Q radiated
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
leads                 38 cm
                                  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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