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Characterization of an Ellipsoidal Radiometer
Annageri V Murthy1, Ingrid Wetterlund2, David P DeWitt3
1Aero-Tech, Inc., Hampton, VA 23666.
Summary
This study characterized an ellipsoidal radiometer for fire tests. Results show its signal is affected by angle, distance, and purge-gas flow, indicating areas for improvement in radiation and convection separation.
Area of Science:
- Metrology and Instrumentation
- Fire Science and Engineering
Background:
- Accurate measurement of radiative heat transfer is crucial in fire test methods.
- Distinguishing radiation from convection effects is a persistent challenge in fire calorimetry.
- Ellipsoidal radiometers offer potential for specialized thermal measurements.
Purpose of the Study:
- To characterize an ellipsoidal radiometer for its intended application in fire testing.
- To evaluate the radiometer's performance concerning angular response, responsivity, and environmental factors.
- To assess the feasibility of separating radiation from convection using this instrument.
Main Methods:
- Characterization of an ellipsoidal radiometer using a variable-temperature blackbody source.
- Measurements included angular response, responsivity relative to a transfer standard, and purge-gas flow effects.
- Utilized a 25 mm blackbody and an electrical-substitution radiometer for calibration and comparison.
Main Results:
- Observed asymmetrical reflection within the radiometer cavity, impacting angular response.
- Responsivity demonstrated a dependence on the distance between the radiometer and the blackbody source.
- Purge-gas flow linearly reduced the radiometer's signal output with increasing flow rate.
Conclusions:
- The ellipsoidal radiometer's current design requires further development to optimize angular response.
- Distance-dependent responsivity necessitates careful consideration during experimental setup.
- The linear effect of purge-gas on signal output provides a quantifiable parameter for correction or analysis.
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