Thermal Conductivity of Mixtures
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The determination of the thermal conductivity of gas mixtures is a central aspect of modeling
+transport phenomena, particularly in high-temperature and high-pressure processes. Among the
+most established approaches is the empirical equation introduced by Wassiljewa, which was
+subsequently refined by Mason and Saxena to improve its applicability to multicomponent systems.
+This model offers a reliable means of estimating the thermal conductivity of gas mixtures based
+on the properties of the pure components and their molar interactions.
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The thermal conductivity of a gas mixture, denoted by
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(1)
+In this equation,
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+ represents the molar fraction of component
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+ within the mixture,
+while
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+ denotes the thermal conductivity of the pure substance
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+. The denominator
+contains the interaction parameter
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+, which describes the influence of component
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+ on the transport properties of component
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The interaction parameter
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(2)
+Here,
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+ and
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+ are the molar masses of the components
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+Molar masses and thermal conductivity of the pure substances are listed in table 1.
+The structure of this expression illustrates the nonlinear dependence of the interaction term on
+both the molar mass ratio and the square root of the conductivity ratio of the involved species.
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+ Table 1: Properties of some gases
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+ Gas
+ Molar mass in g/mol
+ Thermal conductivity in W/m/K
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+ H2
+ 2.016
+ 0.1805
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+ O2
+ 32.00
+ 0.0263
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+ N2
+ 28.02
+ 0.0258
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+ CO2
+ 44.01
+ 0.0166
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+ CH4
+ 16.04
+ 0.0341
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+ Ar
+ 39.95
+ 0.0177
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+ He
+ 4.0026
+ 0.1513
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This formulation acknowledges that the transport properties of a gas mixture are not a simple
+linear combination of the individual conductivities. Rather, they are governed by intermolecular
+interactions, which affect the energy exchange and diffusion behavior of each component. These
+interactions are particularly significant at elevated pressures or in cases where the gas components
+exhibit widely differing molecular masses or transport properties.
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The equation proposed by Wassiljewa and refined by Mason and Saxena assumes that binary interactions
+dominate the behavior of the mixture, while higher-order (three-body or more) interactions are
+neglected. It also presumes that the gases approximate ideal behavior, although in practical
+applications, moderate deviations from ideality are tolerated without significant loss of accuracy.
+In figure 1 the resulting thermal conductivity of an H2/CO2-mixture is shown.
In engineering practice, the accurate determination of
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It is important to note that the calculated mixture conductivity reflects only the gas phase
+behavior. In porous systems such as carbon membranes, additional effects must be considered.
+These include the solid-phase thermal conduction through the membrane matrix, radiative transport
+in pore channels at high temperatures, and transport in the Knudsen regime for narrow pores.
+To account for these complexities, models based on effective medium theory, such as those of
+Maxwell-Eucken or Bruggeman, are frequently employed. These models combine the conductivities of
+individual phases (gas and solid) with geometrical factors that reflect the morphology of the
+porous structure.
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Expanded by more or less sensible AI jabbering; based on: doi:10.14279/depositonce-7390
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This line represents a reference to the equation 1.