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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