1. Determination of Emissivity by Using Reflected Thermal Radiation Frank Liebmann

2. Learning Objectives Learn about the effects of emissivity uncertainty Learn test methods to determine emissivity Help laboratory customers to determine emissivity © 2014 Fluke CalibrationLiebmann – Emissivity Determination2

3. 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 CalibrationLiebmann – Emissivity Determination3

4. 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 CalibrationLiebmann – Emissivity Determination4

5. 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 CalibrationLiebmann – Emissivity Determination5

6. 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 CalibrationLiebmann – Emissivity Determination6

7. Effects of Error in Estimating Emissivity Effects due to emissivity estimation error can be large Conditions for this graph –ε SURF = 0.96 –8 – 14 µm radiation thermometer –ε IRT = 0.95 –T AMB = 23 ° C © 2014 Fluke CalibrationLiebmann – Emissivity Determination7

8. 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 CalibrationLiebmann – Emissivity Determination8

9. 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 CalibrationLiebmann – Emissivity Determination9

10. 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 CalibrationLiebmann – Emissivity Determination10

11. Theory Vary T W Observe change in S(T RT ) Solve for ε S © 2014 Fluke CalibrationLiebmann – Emissivity Determination11 Measurement Equation IR Thermometry ε IRT = 1.00 S(T RT ): IR Thermometer Readout S(T S ): Surface temperature S(T W ): Reflected temperature ε S : Surface emissivity

12. Theory © 2014 Fluke CalibrationLiebmann – Emissivity Determination12

13. 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. © 2014 Fluke CalibrationLiebmann – Emissivity Determination13

14. Theory What is α? © 2014 Fluke CalibrationLiebmann – Emissivity Determination14

15. Reflective Method with Specular Surfaces For specular surfaces α = 1 This is the equation Yamada used © 2014 Fluke CalibrationLiebmann – Emissivity Determination15

16. Reflective Method with Lambertian Surfaces Lamberts Cosine Law © 2014 Fluke CalibrationLiebmann – Emissivity Determination16

17. Reflective Method with Lambertian Surfaces © 2014 Fluke CalibrationLiebmann – Emissivity Determination17

18. 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(d HS ) © 2014 Fluke CalibrationLiebmann – Emissivity Determination18

19. Process © 2014 Fluke CalibrationLiebmann – Emissivity Determination19 (6)(12)

20. Uncertainty Uncertainty analysis elements –Radiation Thermometer Readout –Reference Readout –Heat source Calibration –Ambient Temperature Readout –Heat Source Distance –Heat Source Diameter –Radiation Thermometer Alignment –Repeatability © 2014 Fluke CalibrationLiebmann – Emissivity Determination20

21. 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 CalibrationLiebmann – Emissivity Determination21

22. Practical Measurements Heat Source –Fluke Calibration 4181 –Generally used at 200 ° C –d HS 2.5 to 5 times that of D HS Radiation Thermometer –Fluke 568 –1.9 cm spot size 11 surfaces measured © 2014 Fluke CalibrationLiebmann – Emissivity Determination22

23. Results © 2014 Fluke CalibrationLiebmann – Emissivity Determination23 Data SetSample TypeεSεS U(ε) (k = 2) Comparison Value εType 1Painted Wall0.94660.00330.88 – 0.96Table 2Stainless Steel0.29930.02530.16 – 0.79Table 3Cardboard0.94360.00320.81 – 0.94Table 4Glass0.86170.00320.68 – 0.95Table 5Aluminum0.15300.00300.09 – 0.31Table 6White Board0.95070.00080.84 – 0.95Table 7Flat Plate0.94950.01230.9394 Contact v Radiometric 8Flat Plate0.95050.01570.9448 Contact v Radiometric 9Flat Plate0.94630.00810.9459 Contact v Radiometric 10Flat Plate0.95010.01220.9459 Contact v Radiometric 11Flat Plate0.92750.01070.9187 Contact v Radiometric

24. Results © 2014 Fluke CalibrationLiebmann – Emissivity Determination24 Set 4 Glass Set 5 Aluminum Set 7 Flat Plate

25. Results © 2014 Fluke CalibrationLiebmann – Emissivity Determination25

26. 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 CalibrationLiebmann – Emissivity Determination26

27. 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 CalibrationLiebmann – Emissivity Determination27

28. 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 CalibrationLiebmann – Emissivity Determination28

29. 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 CalibrationLiebmann – Emissivity Determination29

30. 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 CalibrationLiebmann – Emissivity Determination30

31. Questions ? © 2014 Fluke CalibrationLiebmann – Emissivity Determination31