Thermal conductivities of gases

Table 5.24 Thermal Conductivities of Gases as a Function of Temperature 5.148...

N. V. Tsederberg, The Thermal Conductivity of Gases andEiquids Massachusetts Institute of Technology Press, Cambridge, Mass., 1965. 

Bromley, L. A., Thermal Conductivity of Gases at Moder ate Pr essur es, University of California Radiation Laboratory, Report No. UCRL-1852, Berkeley, CA (1952). 

Table 1. Correlation Constants for Estimating Thermal Conductivity of Gases...

Tsederberg, N. V. (1965) Thermal Conductivity of Gases and Liquids (Arnold). 

The gas-phase wall heat-transfer coefficient can be evaluated by using the gas-phase Reynolds number and Prandtl number in Eq. (33). The thermal conductivities of liquids are usually two orders of magnitude larger than the thermal conductivities of gases therefore, the liquid-phase wall heat-transfer coefficient should be much larger than the gas-phase wall heat-transfer coefficient, and Eq. (34) simplifies to... 

Svehla, R. A., Estimated viscosities and thermal conductivities of gases at high temperatures, NASA Tech. Report R-132 (1962). 

The thermal conductivity of gases increases with temperature, but falls with increasing molecular weight. The dimensionless Prandtl number. 

Thermal Properties of Metallic Solids. In the preceding sections, we saw that thermal conductivities of gases, and to some extent liquids, could be related to viscosity and heat capacity. For a solid material such as an elemental metal, the link between thermal conductivity and viscosity loses its validity, since we do not normally think in terms of solid viscosities. The connection with heat capacity is still there, however. In fact, a theoretical description of thermal conductivity in solids is derived directly from the kinetic gas theory used to develop expressions in Section 4.2.1.2. 

In general, values of h for the heating or cooling of a gas (e.g., 5 -50 kcal h in - °C i for air) are much smaller than those for liquids (e.g., 1000-5000 kcal h m °C - for water) because the thermal conductivities of gases are much lower than those of liquids. 

R.A. Svehla. Estimated Viscosities and Thermal Conductivities of Gases at High Temperatures. Technical Report Technical Report R-132, NASA, 1962. 

We focus next on the thermal conductivity of gases at high pressure. At ambient pressure and temperature the thermal conductivity is in the range of 0.01 to 0.025 W/(K m), except for hydrogen and helium that can have higher values, around 0.18 W/(K m). The change of thermal conductivity around the critical state is seen on Fig 3.4-4 for carbon dioxide. Near the... 

As mentioned in Sec. 7.5.14, many gauges read an inferred pressure, not real pressure. Some vacuum gauges use the thermal conductivity of gases present in the system to infer the pressure of the system. These gauges are based on the concept that less gas will conduct less heat. Because different gases have different thermal conductivities,83 the user needs to make allowances if the gas in a system has a different thermal conductivity than the particular gas a gauge has been calibrated to use. 

Table 6.32 Thermal conductivity of gases (referring to 1 105Pa (=1.0 bar absolute) and T = 273 K)...

Equation (2.71) can be compared with Eq. (2.46) for the thermal conductivity of gases, and with Eq. (2.19) for the viscosity. For binary gas mixtures at low pressure, is inversely proportional to the pressure, increases with increasing temperature, and is almost independent of the composition for a given gas pair. For an ideal gas law P = cRT, and the Chapman-Enskog kinetic theory yields the binary diffusivity for systems at low density... 

The thermal conductivities of materials vary over a wide range, as shown in Fig. 1-27. The thermal conductivities of gases such as air vary by a factor of 10 from those of pure metals such as copper. Note that pure crystals and metals have the highest thermal conductivities, and gases and insulating materials the lowest. 

The kinetic theory of gase.s predicts and the experiments confirm that the thermal conductivity of gases is proportional to the square root of the thermodynamic temperature T, and inversely proportional to the square root of the molar mass M. Therefore, the thermal conductivity of a gas increases with increasing temperature and decreasing molar mass. So it is not surprising that the iheniial conductivity of helium (Af 4) is much higher than those of air (M = 29) and argon M = 40). 

The thermal conductivities of gases at 1 atm pressure are listed in Table A-16. However, they can also be used at pressures other than 1 atm, since the thermal coiiducUvily of gases is independent of pressure in a wide range of pressures encountered in practice. 

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