KANOMAX 6162 Anemomaster - Manual (Page 47)

7. Measurement Principle 41
Heat diffusion quantity can be found by;
( )
a u
T T N Q
− =
l
πλ
········ (1)
Q: Heat diffusion quantity N
u
: Nussselt number π:Circle ratio λ：Thermal conductivity
L: Length of cylinder T: Heating body temp. T
a
:Gaseous temperature
In order to obtain the property value of mixed gas, obtain the property value of each component. Based on the
mixing ratio, the property value of the mixture can be found. For instance, the specific heat of mixture, C
ｐ
, can be
found by;
M
Y M C
C
p
p 100
1 1 1
Σ
=
········ (2)
C
p
: Specific heat of mixture C
p1
: The specific heat of each component gas
M：Molecular quantity of mixture M
1
： : Molecular quantity of each component gas
Y
1
： : Volume percentage of each component gas
As each property value is temperature function and Nusselt number, N
u
, is function of flow velocity (U), heat
diffusion quantity in the mixed gas (Q
a
) can be find by obtaining the air temperature, T
a
, and the reference air
velocity, U
0
using the above equation (1). Given that the Q
a
is equivalent to the diffusion quantity in the air, the air
velocity value, U
M
, can be obtained. With U
0
and U
M
, the air velocity compensation table for the mixed gas can be
obtained.
Below is and example graph for air velocity compensation.
10
20
30
40
50
10 20 30 40 50
Air Temp. 100˚C
Air Temp. 300˚C
Air Temp. 500˚C
Component Mixing Ratio %
N
2
74.0
H
2
O 11.5
O
2
3.5
CO 11.0
V
elo
ci
ty Rea
ding
U
M
m
/3
Reference Velocity Value U
0
m/β
Figure 3 Example Graph for Air Velocity Compensation