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  Change in metal temperature changes  We will attempt to make a model which can predict changes in emissivity due to varying temperature and surface conditions

Carbonization in samples sample 1sample 2sample 3sample 4sample 5

Theory: Stefan-Boltzmann Equation Q = (T sample 4 - T surrounding 4 ) Q - heat radiated -emissivity - Stefan-Boltzmann constant

Experimental Overview In order to calculate , 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 o C)

Experimental Setup IR camera sample hot plate

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.) (reference lvl.) – (background lvl.)  =* (reference  )

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  IR  ( T camera 4 –T surrounding 4 ) =  actual (T actual 4 – T surrounding 4 ) desired value

Cold Temp Data

High Temperature Experiment Must modify experimental setup to accommodate temperatures up to 450 o C Data is taken every 50 o C, from 50 o C to 450 o C In addition to testing our five welded samples, we will now test a clean, unwelded sample.

Experimental Setup

Analysis of Results Attempt to fit data to following mathematical model:  total  initial * T(temp) * C(color)

Isolating the Temperature Dependence  total  initial * C(color) * T(temp)  cold  initial * C(color)  cold  total = T(temp)

Graphing the Temperature Dependence

Isolating the Effect of Weld- Produced Color Bands  total  initial * T(temp) * C(color)  reference  initial * T(temp)  total  reference = C(color)

Graphing the Color-Band Dependence

Using C(color) and T(temp) With accurate graphs of the functions C(color) and T(temp), one could calculate the emissivity  total with the following equation:  total  initial * 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 heatingafter 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 !!!