ABSTRACT
Floating bushings and gas labyrinths are mainly used as shaft seals for compressible media, such as, gas or steam. This chapter discusses some aspects of fluid dynamics that need to be understood to calculate the mass flow rate and the pressure drop of compressible fluids in seals having smooth, narrow gaps. Another aspect of compressible flow that can be important is the interchange of compressive energy and thermal energy. This generally causes temperature variations that change the pressure distribution and hence the flow rate. A comprehensive analysis requires the solution of an energy equation in terms of temperature simultaneously with a Reynolds equation. When sealing a hot or volatile fluid it may suffer a phase change within the seal gap; then there are both incompressible and compressible regions of fluid. Also, at the boiling interface between the phases, there is a large change of energy due to the latent heat of vaporization.
