Ministry of Education and Science of Russian Federation
Federal State Budget Educational Establishment of Higher Professional Education
National Research Tomsk Polytechnic University
HEAT TRANSFER RESEARCH BY EMISSION
Lab report
Done: student
Checked:
Tomsk - 2013
Goal: obtaining skills of the experimental determination of heat radiation integral coefficient of the solid substance.
Task
1. determination integral radiation ability of the solid substance at different temperatures of radiated surface;
2. designing dependence of radiation abilityс from temperature;
3. comparison of obtained results with well-known literary sources;
4. compiling the report of the performed work.
5. answer test questions.
Calculating formulas
Stephen-Boltzmann law describes the surface of the density integral radiation of absolutely black object E0, W/m2
E0  0T 4 .
(1)
here σ0 = 5,67·10−8 W/(m2·K4)  constant Stephen-Boltzmann.
Stephen-Boltzmann law for technical calculations is being described in
such a way:
E0  C0 (T / 100)4 ,
(2)
where С0 = σ0·108 = 5,67 W/(m2·K4) is being called the radiation calculation
of absolutely black object.
The resultant equation of the radiant flow is being written in the following way:
 T1  4  T2  4 
Q12  ε red с0 F1 
 
 ,
100
100



 

(3)
where red – adduced integral coefficient heat radiation of object’s system;
1
;
(4)
ε red 
 1 F1  1

    1

 ε1 F2  ε 2
1, 2 – integral coefficient heat radiation of the researched wire and layer;
F1, F2 – surfaces of wire and layer, m. The surface square of tungsten wire is
small in comparison with the surface square of the layer (F1<<F2), so the
formula presents (3) red=1.
Flow radiation density of the wire surface is being determined as:
Е = Q/(dl),
(5)
where Q – power, for heating wire, W;
d – tungsten wire diameter, m;
l – wire length, m.
Direct current value is being determined by the calculating way due to
the drop voltage on the sample element of resistance:
I  U0 / R0 , Аmp.
(6)
Constant power proportional to the voltage drop on the work sector of
the wire:
Q  IU1 .
(7)
The tungsten wire temperature is being calculated on its electrical resistance R1 situated on the voltage and current strength:
R1  U1 / I , Оmh.
(8)
При нагреве проволоки электрическим током необходимо учитывать зависимость сопротивления металла от температуры:
R1  R12[1   R (t1  t2 )] , Оmh,
(9)
where R  temperature coefficient of the material resistance; R12  tungsten
wire resistance at the temperature of the environment t2, oC.
Using the dependence (9), the formula for determining tungsten wire
temperature has the following view:
t1 
R1  R12
 t2 , oC.
 R R12
(10)
Results
Setup data:
Tungsten wire diameter
Sample resistance
Temperature coefficient of tungsten
resistance
wire length
d = 0,15·10–3 m;
R0 = 0,1 Ohm;
R = (3,9 – 4,5)10–3 1/K;
l = 0,45 m.
Using measurement data on the work sector (pic.1) of the equation (3)
one can find the radiation coefficient of the researched object. The calculation is being done for every temperature mode and filled in table 1. The de-
pendence graph of the coefficient temperature radiation ε1 = f(t1) in the researched temperature mode is being designed
Рис. 1. Setup of the work post
1. chromel-copel thermocouple; 2 cylindrical glass balloon with double
walls, containing water between them, filled through vinyl tube; 3. heated tungsten wire.
Table 1
Results of measurements and calculations
№
t1,
C
o
1
…
5
Т1,
K
t2,
C
o
Т2,
K
U0,
V
U1,
V
I,
Amp
Q,
W
ε1
Analysis of the obtained results
It is obligatory to compare the obtained dependence of the radiation coefficient from the temperature with literary sources. Analyze the evaluation
of measurement errors.