TCi Operator Manual
102
And, use the following (
Cp) values as a guide:
Calibration
(
Cp), 10
6
J/m
3
K
Liquids and powders
0 - 4.5
Foams
0 - 0.5
Polymers
1.3 - 2.0
Ceramics
2.0 - 2.7
Metals
2.4 - 4.0
9.5
Temperature considerations in effusivity calibration
As seen above,
M
2
, M
1
and
C
are required for effusivity calibration at a given set of conditions.
How do these parameters change in temperature?
Equation (22) suggests that
M
2
and
M
1
will remain constant in temperature as long as the
denominator is constant. Since
SensorArea
R
I
G
2
(26)
It turns that
)
(
3
2
1
R
I
A
SensorArea
R
I
A
I
SensorArea
M
(27)
The
SensorArea
and
A
are constant in the temperature range of interest. Therefore, if the product
)
(
3
R
I
is kept constant,
M
2
and
M
1
will remain constant over the whole temperature range.
The same analysis applies also to
C
, since
C
has the same denominator in equation (19). The
sensor equivalent effusivity,
e
1
, may change with temperature though, as it depends on the
sensor materials and construction. Experiments show that
C
can be approximated by a 2
nd
order
polynomial in a wide range of temperature. The function
C(T)
is deducted empirically.
2
2
1
0
T
C
T
C
C
C
(28)
Note:
C(T)
and its 3 coefficients are different at different power levels. This entails that
C(T)
has
to be measured at all power levels used.
The figure below shows this relationship of one of the TCi sensors measured between -30
C and
+200
C in vacuum.
Summary of Contents for TCi
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