Brief Discussion on Thermal Conductivity

Just as diffusive momentum transfer depends on a transport property of the fluid called viscosity, diffusive heat transfer depends on a transport property called thermal conductivity. This section provides a brief discussion on the functional forms of thermal conductivity, with the intent of facilitating the understanding of the heat-transfer discussions in the subsequent sections on the conservation of energy. 

Comparing the reduced conductivity (Fig. 3.7) with the reduced viscosity (Fig. 3.3), it is apparent that their temperature and pressure dependencies have much in common. Tables of critical properties for common fluids are readily available see Bird et al. [35]. 

Even though there are a number of theories for estimating thermal conductivities (e.g., see Reid et al. [332]), in practice, empirical curve fits are often the best alternative. For most fluids a polynomial fit is quite accurate over the required temperature ranges 

The thermal conductivities of many common liquids have a nearly linear temperature dependence with a slight negative slope. However, some important fluids, like water, have significant curvature with both positive and negative temperature dependencies in tempera- 

For gases in the low-density limit, a kinetic-theory expression similar to that for viscosity can be used to evaluate single-component thermal conductivity. For a monatomic gas, meaning a gas with no rotational of vibrational degrees of freedom, the thermal conductivity is expressed as 

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