Faculty of Process & Materials Engineering and AppliedPhysics of The Czestochowa University of TechnologyThe Department of Industrial Furnaces and Environmental ProtectionInfluence of changes objects temperature on the factor emissivity value Mgr in. Krystian Nowak*Dr hab. in .Lech Szecwka, Prof. PCzDr in. Henryk Radomiak*Author is a participant of a program called Plan Rozwoju Politechniki Czstochowskiej which is sponsored by European Social Found, European Union

Emissivity is one of basic bright property of matter. With temperature it characterizes radiation heat transfer, and it plays very important role in radiation-convectional, radiation-conductional and radiation-convection-conductional heat transfer.

Thermo visions technique

Each body which temperature is superior than absolute zero emits heat energy in the form of thermal radiation energy in seen as well as invisible ( infrared ) range. It strictly depends on objects temperature. Thermo vision camera taking advantage of this dependence and registering this radiation appoints researched surface temperature. Thermo visions technique

Thermo visions technique To main adwantages of thermo vision belong:

very wide temperature range,

capability appointment temperature of flame and gasses,

big accuracy of measurement

received results give information about holistic temperature arrangement on researched surface.

EmissivityPerfectly black body is an ideal source of thermal radiation ( temperature ). Quantity defining defection of radiation between perfectly black body( theoretical ) and real body we call emissivity. This quantity depends (among other) from temperature. It is possible to appoint emissivity with the aid of ration equivalent bright quantities of real and perfectly black bodies - stream of emissivityA- field of emitting surface. C- constans of radiation which value is 5,6693 W/(m2K4)T- temperatureEmissivity:

Exemplary results of industrial thermo vision measurementsThe presented exemplary thermogram comes from second heating zone of unclogging furnaces. Temperature measured in this zone with the aid of thermocouples was 1100oC. Exactly this temperature is accepted as parameter which defining closest surroundings. On thermogram there are singled out two fields: Ar1 and Ar2 , which are subject to detailed analysis.

Measuring position and software used to analyses A sample (dimension: 30x30x50 mm) has been placed in heating chamber of electric furnace (dimension 295x105x120). It has been put on isolating pads about 10 mm high, what was suppose to minimize uneven heating by participation of heat transfer on conductive way. Sample was preliminary oxidized, however, thin coat of oxidized material strictly adhere to the remainings.

Measuring position and software used to analyses Possible range of measuring temperature is between - 40oC +2000oC, at accuracy of measurement to 2%. Basic element of this camera is uncooled mikrobolometric detectors matrix. Analysis has been executed in the form of tables basing on standard software -ThermaCAM Reporter 7.0.Heating chamber was fullfiled by nitrogen, to obtain indifferent atmosphere. It has allowed to eliminate oxidizing of farthest materials. Such phenomenon could cause to rise of considerable unsimilarity on researched surface , and what goes behind it, differences in emissivity and registered temperatures. Under the surface of the researched sample two thermocouples connected to measuring card DaqLab2000 have been placed, which were a comparative fix-up for thermovision camera. To determinate surrounding temperature in heating chamber of furnace thermocouples from furnace measuring systems were taken.

Experiment The purpose of the experiment was to determine a change emissivity coefficient influenced by temperature, for sample with oxidized surface. Additional element is the verification of how erroneous introduction of emissivity coefficient effect accuracy on measurement executable at utilization of thermovision camera. For the purpose of the realization comparative method was done. Measurement of temperature was executed with pin method and lecture from thermovision camera with alternate emissivity coefficient, introduce in period of processing and analyses thermogram.

Result and analyses

Object Parameter Value Reflected Temperature 852.0 C Label Value Ar1: Average 800.1 C Ar1: Emissivity 0.88

TTResult and analyses Checked off field Ar1 has been chosen as part subjected analysis, where for presentation from this area was chosen average value of temperature. Conditionality was accommodation and depth that thermocouples have been fixed. Reflected temperature was accepted on base of lecture executed from regulating match of furnace. For each measurement two emissivity coefficient was adopted, such values of temperatures was closest from average pin measurements.

Lp.T1T2Tr1122Tot.[oC][oC][oC]1238,63251,07244,850,81243,900,82245,60370,002300,92302,56301,740,82301,890,83302,70370,003347,59349,86348,730,84348,100,85349,00421,004399,74399,07399,410,86399,700,87400,10435,005451,77452,64452,210,86452,000,87452,60500,006500,40499,06499,730,87499,700,88500,20537,007550,83550,66550,750,87550,400,88550,80585,008599,77600,64600,210,87600,200,88600,60638,009650,71650,13650,420,90650,400,91650,90689,0010700,86701,24701,050,89700,900,90701,40739,0011749,89750,01749,950,90749,600,91750,00786,0012800,09801,24800,670,88800,100,89800,70852,00

Result and analyses

Wykres1

244.85370243.9245.6

301.74370301.89302.7

348.725421348.1349

399.405435399.7400.1

452.205500452452.6

499.73537499.7500.2

550.745585550.4550.8

600.205638600.2600.6

650.42689650.4650.9

701.05739700.9701.4

749.95786749.6750

800.665852800.1800.7

Averege from thermocouple number 1 and 2

Souranding tempreture

Temperature for lower emissivity coeficient

Temperature for higher emissivity coeficient

Successive measurements

Temperature [oC]

Arkusz1

Lp.T1T2Tre1Te1e2Te2T ot.

oCoCoC

1238.63251.07244.850.81243.90.82245.6370

2300.92302.56301.740.82301.890.83302.7370

3347.59349.86348.7250.84348.10.85349421

4399.74399.07399.4050.86399.70.87400.1435

5451.77452.64452.2050.864520.87452.6500

6500.4499.06499.730.87499.70.88500.2537

7550.83550.66550.7450.87550.40.88550.8585

8599.77600.64600.2050.87600.20.88600.6638

9650.71650.13650.420.9650.40.91650.9689

10700.86701.24701.050.89700.90.9701.4739

11749.89750.01749.950.9749.60.91750786

12800.09801.24800.6650.88800.10.89800.7852

Arkusz2

Lp.1T2T

12

1238.63251.07244.850.81243.900.82245.60370.001.7

2300.92302.56301.740.82301.890.83302.70370.000.81

3347.59349.86348.730.84348.100.85349.00421.000.9

4399.74399.07399.410.86399.700.87400.10435.000.4

5451.77452.64452.210.86452.000.87452.60500.000.6

6500.40499.06499.730.87499.700.88500.20537.000.5

7550.83550.66550.750.87550.400.88550.80585.000.4

8599.77600.64600.210.87600.200.88600.60638.000.4

9650.71650.13650.420.90650.400.91650.90689.000.5

10700.86701.24701.050.89700.900.90701.40739.000.5

11749.89750.01749.950.90749.600.91750.00786.000.4

12800.09801.24800.670.88800.100.89800.70852.000.6

Arkusz2

Averege from thermocouple number 1 and 2

Souranding tempreture

Temperature for lower emissivity coeficient

Temperature for higher emissivity coeficient

Successive measurements

Temperature [oC]

Arkusz3

Changes of emissivity value for e1

Changes of emissivity value for e2

Temperature on surface of sample

Emissivity value

Successive measurements

Temperature difference [oC]

MBD000869DA.unknown

MBD000869DB.unknown

MBD000869D7.unknown

MBD000869D9.unknown

Result and analyses Error in designation emissivity at the level of 0,01 can cause inaccuracy in lecture of temperature (in showed case even 1,7oC).It was executable during farthest attempt of charge heating. Distinct, visible differences in colors on surface of sample are an effect of progressing from 800oC temperature of separate oxidize coat from the rest of researched material. Reason for this phenomenon was thermal expansibility differences between external oxidized coat and internal not oxidized.

Resume Usefulness of thermo vision measurement in steel industry in big degree depends on measuring techniques. In order to the result was to be reliable, it is required from the person carrying measurement elementary knowledge from range of heat transfer, acquaintances of objects, researched material and certain dependences. Often indispensable condition is the execution of preliminary research allowing the assignment of basic factor effecting the measurement. It is important to pay attention to such elements:

-emissivity

-surroundings temperature

-state (condition) researched surface.

Despite certain troubles in practice of thermo vision measurements, continuous perfecting of measurement technique and obtained new practical experiences can cause generalization of these investigative methods, giving full information about temperature and schedule on researched surface of the material ( object ).

Thank you for your attention