Flows Induced by Temperature Fields in a Rarefied Gas and their Ghost Effect on the Behavior of a Gas in the Continuum Limit

In the framework of the classical gas dynamics, no steady flow is induced in a gas without an external force, such as gravity, by the effect of a temperature field. In a rarefied gas, on the other hand, the temperature field of a gas (often in combination with a solid boundary) plays an important role in inducing a steady flow. In the present article, we introduce various kinds of flows induced by the temperature effect and discuss their physical mechanisms. These flows vanish in the continuum limit (the limit where the mean free path of the gas molecules tends to zero), but it has been found recently that they, strangely, affect the behavior of a gas in this limit. This interesting effect, called a ghost effect, is also discussed.