Abstract
This paper presents a procedure to determine the thermal conductivity of gases by pulse injection, using a thermal conductivity detector (TCD). The measurements are taken at 323K and atmospheric pressure with a 160 omega tungsten filament sensor. Under well defined approximations the original nonlinear second order equation, which describes the sensors output, as a function of thermal conductivity and constant volume specific heat was transformed into a linear first order equation. According to this equation the time integrated, second order sensors electrical output signal, multiplied by the constant volume heat capacity is proportional to the constant volume heat capacity, divided by the thermal conductivity. The experimental results obtained with Ar, N2, O2, CH4, CO2, C2H4, C3H6 and i-C4H8 gases are in good agreement with the proposed theoretical model and the linearity correlation confirms the validity of the proposed method.
Highlights
The thermal conductivity characterizes the capability of a compound to transfer heat
If the Wheatstone bridge is perfectly balanced for a constant flow of carrier gas, the temperature of the filament related to the injected gas is proportional to the Wheatstone bridge’s signal output of the second order and the filament temperature is: Tf(t) = C2 [E(t)]2 (6)
The method proposed here is based on a set of nonlinear equations of the measured signal output in a Wheatstone bridge
Summary
The thermal conductivity characterizes the capability of a compound to transfer heat This transport, operating at the molecular level, is very variable according to the medium. Where λ is the mean free path, ĉ is the average molecular velocity of the molecules, and CV,m is the molar heat capacity at a constant volume.[11] A rigorous treatment to predict thermal conductivity of polyatomic fluids would require, a comprehensive knowledge of the separate and interactive behavior of translational, rotational and vibrational degrees of freedom of the polyatomic molecule.[12] By using pulse method, two different information namely, specific heat and thermal conductivity can be obtained within a single measurement.[13]. The signal output “E(t)” in the Wheatstone bridge is based on changes in the resistance of the sensor “R ”
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