Teledyne 2750 - Portable turbine generator gas analzyer - Manual (Page 15)

Turbine Generator Gas Analyzer Theory of Operation
Teledyne Analytical Instruments 15
Theory of Operation
The heart of the Model 2750 Turbine Generator Gas Analyzer is
the compact thermal conductivity cell. It senses differences in thermal
conductivity of the gas mixture and generates an output signal based on
the thermal characteristics of the gas. Since the sensor measures the
absolute T/C using an internal thermal reference, a reference gas is not
required.
2.1 Thermal Conductivity
Thermal conductivity is a measure of a substance’s ability to
conduct heat. It also varies with temperature and is further complicated
by the fact that this variation is not always linear. As an illustration,
Table 2-1 lists the thermal conductivity for selected gases at 2 different
temperatures. It also lists the percentage difference in thermal
conductivity (T/C) for the specified temperature range.
Table 2-1: Thermal Conductivity for Selected Gases
Gas
Thermal Conductivity
(cal/sec)/(cm 2 C/cm) x 10 -6
% Difference
26.7°C 48.9°C
CO
2
39.67 43.81 10.44%
CO 59.92 63.89 6.63%
N
2
62.4 65.71 5.30%
Air 62.2 66.04 6.17%
O
2
63.64 68.19 7.15%
He 360.36 376.07 4.36%
H
2
446.32 471.11 5.55%