Transcript Determination of Emissivity by Using Reflected Thermal

Determination of Emissivity by
Using Reflected Thermal Radiation
Frank Liebmann
Learning Objectives
• Learn about the effects of emissivity uncertainty
• Learn test methods to determine emissivity
• Help laboratory customers to determine emissivity
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Introduction
•
•
•
•
Emissivity is essential to accurate IR thermometry measurement
Lack of credible information on emissivity
Existing methods to determine emissivity
Reflective method – practical for field usage
– Yamada and Ishii (2011)
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Effects of Error in Estimating Emissivity
• Effects due to emissivity estimation error can be large
• Conditions for this graph
–
–
–
–
εSURF = 0.96
8 – 14 µm radiation thermometer
εIRT = 0.95
6
TAMB = 23 °C
5
4
error / K
3
2
1
0
-1
-2
-50
© 2014 Fluke Calibration
0
50 100 150 200 250 300 350 400 450 500 550 600 650
Surface Temperature / °C
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Methods for Determining Emissivity
• Comparison method
– Part of surface must have known emissivity
• Contact versus non-contact method
– Contact temperature may not be true surface temperature
• Blackbody method
– Destructive
• FTIR testing
– Laboratory measurement (for the most part)
• Emissivity tables
– No uncertainties
– Values vary greatly from table to table
• Reflective method
– Novel method discussed here
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Theory
• Vary TW
• Observe change in S(TRT)
• Solve for εS
Measurement Equation IR Thermometry
εIRT = 1.00
S TRT    S S TS   1   S S TW 
S(TRT): IR Thermometer Readout
S(TS): Surface temperature
S(TW): Reflected temperature
εS: Surface emissivity
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Theory
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Theory
• A portion of the reflected temperature (α) is coming from the heat
source
• For a reference measurement the source is blocked making α = 0.
S TW   S THS   1   S TAMB 
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Theory
• What is α?
1 S TRT   S TREF 
S  1
 S THS   S TAMB 
© 2014 Fluke Calibration
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Reflective Method with
Specular Surfaces
• For specular surfaces α = 1
• This is the equation Yamada used
 S  SPEC
© 2014 Fluke Calibration
S TRT   S TREF 
1
S THS   S TAMB 
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Reflective Method with
Lambertian Surfaces
• Lamberts Cosine Law
I    I 0 cos 
© 2014 Fluke Calibration
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Reflective Method with
Lambertian Surfaces
FS
I 0 sin 2  S 


 sin 2  S  
FTOT
I 0
© 2014 Fluke Calibration
1
 2d
1   HS
 DHS



2
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Reflective Method with Surfaces of
Unknown Diffusivity
• Initial measurements did were not as equation for Lambertian
surfaces predicted
• However, this equation’s shape was preserved α(dHS)
0.050
0.045
0.040
alpha
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
0
20
40
dHS / cm
FS
I 0 sin 2  S 


 sin 2  S  
FTOT
I 0
© 2014 Fluke Calibration
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80
1
 2d
1   HS
 DHS



2
Liebmann – Emissivity Determination
 APP  1 
1  S
2
1  adHS
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Process
(6)
 S  SPEC
(12)
S TRT   S TREF 
1
S THS   S TAMB 
© 2014 Fluke Calibration
1  S
 APP  1 
2
1  adHS
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Uncertainty
• Uncertainty analysis elements
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Radiation Thermometer Readout
Reference Readout
Heat source Calibration
Ambient Temperature Readout
Heat Source Distance
Heat Source Diameter
Radiation Thermometer Alignment
Repeatability
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Practical Measurements
• Heat Source
– Fluke Calibration 4181
– Generally used at 200 °C
– dHS 2.5 to 5 times that of DHS
• Radiation Thermometer
– Fluke 568
– 1.9 cm spot size
• 11 surfaces measured
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Results
Data Set
Sample Type
Comparison Value
εS
U(ε)
(k = 2)
ε
Type
1
Painted Wall
0.9466
0.0033
0.88 – 0.96
Table
2
Stainless Steel
0.2993
0.0253
0.16 – 0.79
Table
3
Cardboard
0.9436
0.0032
0.81 – 0.94
Table
4
Glass
0.8617
0.0032
0.68 – 0.95
Table
5
Aluminum
0.1530
0.0030
0.09 – 0.31
Table
6
White Board
0.9507
0.0008
0.84 – 0.95
Table
7
Flat Plate
0.9495
0.0123
0.9394
Contact v
Radiometric
8
Flat Plate
0.9505
0.0157
0.9448
Contact v
Radiometric
9
Flat Plate
0.9463
0.0081
0.9459
Contact v
Radiometric
10
Flat Plate
0.9501
0.0122
0.9459
Contact v
Radiometric
11
Flat Plate
0.9275
0.0107
0.9187
Contact v
Radiometric
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Results
0.870
0.156
0.960
0.155
0.865
0.955
0.860
εs
εs
εs
0.154
0.153
0.950
0.152
0.855
0.945
0.151
0.850
0.150
0
20
40
60
80
100
0.940
0
20
40
60
80
100
0
20
40
60
dhs / cm
dhs / cm
dhs / cm
Set 4
Glass
Set 5
Aluminum
Set 7
Flat Plate
© 2014 Fluke Calibration
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Results
0.97
0.96
emissivity
0.95
Refl
0.94
RvC
0.93
0.92
0.91
Set 7
© 2014 Fluke Calibration
Set 8
Set 9
Set 10
Liebmann – Emissivity Determination
Set 11
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
26
Conclusion
The reflective method…
• Works well on large surfaces
• Works fair on smaller surfaces
• In-situ type measurement
– Can be done in field
– Quick
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Acknowledgements
The author would like to thank the many people who have made this
research possible.
• Yoshiro Yamada
– Provided the author with details of his research
• Fluke Calibration
– Provided the author with time, laboratory space, and equipment
– Time to analyze the resulting data.
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
29
Overview
•
•
•
•
Introduction
Effects of Error in Estimating Emissivity
Methods for Determining Emissivity
Applying the Reflective Method to Diffuse Surfaces
–
–
–
–
•
•
•
•
Reflective Method with Specular Surfaces
Reflective Method with Lambertian Surfaces
Reflective Method with Surfaces of Unknown Diffusivity
Uncertainty
Practical Measurements
Conclusion
Acknowledgements
Questions
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
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Questions
?
© 2014 Fluke Calibration
Liebmann – Emissivity Determination
31