Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. They achieve pressure rise by adding energy to the continuous flow of fluid through the rotor/impeller. The following equation shows this specific energy input. A substantial portion of this energy is kinetic which is converted to increased potential energy/static pressure by slowing the flow through a diffuser. The static pressure rise in the impeller may roughly equal the rise in the diffuser. Equation-0.1 where the control volume nomenclature (illustrated in Figure-0.4) is: subscript, is the impeller inlet location, station1 subscript, is the impeller discharge/exit location, station2 is the energy input per unit mass, units=(LP/m) is the impeller's rotation speed, units=(radians/t) is the radius of specified location, units=(L) is velocity of fluid/gas velocity at specified location, units=(L/t) is the tangential vector component in polar coordinate system Components of a simple centrifugal compressor A simple centrifugal compressor stage has four components (listed in order of throughflow): inlet, impeller/rotor, diffuser, and collector. Figure 1.1 shows each of the components of the flow path, with the flow (working gas) entering the centrifugal impeller axially from left to right. This turboshaft (or turboprop) impeller is rotating counter-clockwise when looking downstream into the compressor. The flow will pass through the compressors from left to right. Inlet The simplest inlet to a centrifugal compressor is typically a simple pipe. Depending upon its use/application inlets can be very complex. They may include other components such as an inlet throttle valve, a shrouded port, an annular duct (see Figure 1.1), a bifurcated duct, stationary guide vanes/airfoils used to straight or swirl flow (see Figure 1.1), movable guide vanes (used to vary pre-swirl adjustably). Compressor inlets often include instrumentation to measure pressure and temperature in order to control compressor performance. Bernoulli's fluid dynamic principle plays an important role in understanding vaneless stationary components like an inlet. In engineering situations assuming adiatice flow, this equation can be written in the form: Equation-1.1 where: is the inlet of the compressor, station 0 is the inlet of the impeller, station 1 is the pressure is the density and indicates that it is a function of pressure is the flow speed is the ratio of the specific heats of the fluid Centrifugal impeller The identifying component of a centrifugal compressor stage is the centrifugal impeller rotor. Impellers are designed in many configurations including "open" (visible blades), "covered