A course in turbomachinery……………lecturer: Dr.Naseer Al-Janabi DEFINITION OF COMPRESSOR A compressor is a device that transfers energy to a gaseous fluid for the purpose of raising the pressure of the fluid as in the case where the compressor is the prime mover of the fluid through the process. The purpose may also include a desired temperature rise to enhance the chemical reaction in the process. Pumps are very similar to compressors but deal primarily with incompressible hydraulic fluids, whereas compressors generally deal with compressible gaseous fluids. TYPES OF COMPRESSORS The two basic types of compressors are positive displacement and dynamic. I- POSITIVE DISPLACEMENT COMPRESSOR The positive displacement compressor functions by means of entrapping a volume of gas and reducing that volume, as in the common bicycle pump, and the screw compressor shown in Figure 1. The general characteristics of the positive displacement compressor are constant flow and variable pressure ratio (for a given speed). 37 | P a g e

A course in turbomachinery……………lecturer: Dr.Naseer Al-Janabi Positive displacement compressors include:  piston compressor  screw compressor  vane compressor  lobe compressor II- DYNAMIC COMPRESSOR The dynamic compressor depends on motion to transfer energy from the compressor rotor to the process gas. The characteristics of compression vary depending on the type of dynamic compressor and on the type of gas being compressed. The flow is continuous. There are no valves and there is no "containment" of the gas, as in a positive displacement compressor. Compression depends on the dynamic interaction between the mechanism and the gas. Dynamic compressors include:  ejector  centrifugal compressor  axial compressor Ejector An ejector is a very simple device which uses a high-pressure jet stream to compress gas. The momentum of the high-pressure jet stream is transferred to the low pressure process gas. This type of compressor is commonly used for vacuum applications. Centrifugal Compressor A centrifugal compressor acts on a gas by means of blades on a rotating impeller. The rotary motion of the gas results in an outward velocity due to centrifugal forces. The tangential component of this outward velocity is then transformed to pressure by means of a diffuser. Figure 2 is typical of a single-stage centrifugal compressor. A high-pressure multi-stage compressor is shown in Figure 3. 38 | P a g e

A course in turbomachinery……………lecturer: Dr.Naseer Al-Janabi Axial Compressor An axial compressor imparts momentum to a gas by means of a cascade of airfoils. The lift and drag coefficients of the airfoil shape determine the compressor characteristics. Figure 4 shows a typical axial compressor. An axial compressor incorporated in a turbocharger is shown in Figure 5. 39 | P a g e

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