What is the difference between a steam jet compressor and a steam jet vacuum pump?

It can be said that the principle is the same. They just serve different purposes.

A steam jet compressor consists of a nozzle, an absorption chamber, a mixing chamber, a diffuser chamber, and other components. Inside the nozzle, as the flow cross-section gradually decreases, the steam velocity increases, the pressure potential energy of the steam is gradually converted into kinetic energy, and the pressure decreases. When high-pressure steam passes through the nozzle, it reaches extremely high speeds (supersonic speeds) at the nozzle exit; most of its pressure potential energy is converted into kinetic energy, causing the steam pressure to drop below that of the low-pressure waste steam. This creates a local relative negative pressure that draws the flash vapor into the receiving chamber. Two coaxial fluid streams are thoroughly mixed and their velocities and energies are balanced within the mixing chamber. At the exit section of this chamber, a uniform velocity field and energy field are established, resulting in a stable and homogeneous high-velocity steam stream. Once this steam stream enters the diffuser chamber, its velocity decreases as the cross-sectional area increases; the kinetic energy of the steam is gradually converted into potential energy, and the pressure is restored step by step. By the time it reaches the end of the diffuser chamber, the pressure has been fully restored to the level required by the process, making it suitable for use in heat exchange equipment in industrial applications. Although the structure of the injector is simple, its internal flow is quite complex, belonging to high-Reynolds-number, highly shear turbulent jets. Using only a simple one-dimensional theory to describe the flow of real fluids in a injector results in significant limitations in accuracy.

The principle is the same! However, in conventional steam jet heat pumps, the compression is generally low, and so is the expansion ratio ； Steam ejectors, having a large expansion ratio, can generally achieve a relatively high compression ratio!