Category: Air Compressors

In axial flow compressors, the flow proceeds throughout the compressor in a direction essentially parallel to the axis of the machine. The unit consists of adjacent row of rotor blades and stator blades. One stage of the machine comprises a row of rotor blades followed by a row of stator blades. For efficient operation, the…

In these compressors the pressure rise takes place due to the continuous conversion of angular momentum imparted to the gas by a high-speed impeller into static pressure. Unlike reciprocating compressors, centrifugal compressors are steady flow devices hence they are subjected to less vibration and noise. Figure 10.9 shows the working principle of a centrifugal compressor. As shown…

In multiple vane type compressors, the axis of rotation coincides with the centre of the roller (O); however, it is eccentric with respect to the centre of the cylinder (O’) as shown in Figure 10.8. The rotor consists of a number of slots with sliding vanes. During the running of the compressor, the sliding vanes are held…

Fixed Vane Type Compressors These compressors belong to the category of positive displacement type as compression is achieved by reducing the volume of the gas. In this type of compressors, the rotating shaft of the roller has its axis of rotation that matches with the centre line of the cylinder; however, it is eccentric with…

P−V and T−S diagrams for multistage compression are shown in Figure 10.6. Figure 10.6 ρ−V and T−S Diagrams for Multistage Compressor If P1, T1 and delivery pressure P3 are fixed, the optimum value of the intermediate pressure P2 for minimum work can be obtained by setting the derivative dW/dP2 = 0. For perfect cooling,  In general, if there are N stages, the pressure ratio for each stage will be given by, Heat Rejected During…

Number of stages required depends on the pressure to be developed in compressor. Normally, following relationships are used with pressure and number of stages. Advantages of Multistage Compression Assumption in Multistage Compression: The following assumptions are usually made in calculation of work done in multistage compression:

The volumetric efficiency of a compressor is the ratio of actual free air delivered to the displacement of the compressor. Substituting the value of V4 in Eq. (10.1), we get Where ∈ is clearance ratio  and r is pressure ratio  Example 10.1: A single cylinder, single acting air compressor has a cylinder diameter of 150 mm and stroke of 300 mm. It…

Figure 10.5 Reciprocating Compressor with Clearance Volume

In isothermal compression work done is minimum and it is maximum for adiabatic compression.

Area 0−1−2−3 in Figure 10.4 represents the net work done, when the compression follows the polytropic law. Net work on air per cycle = Area 0−1−2−3 = Work done during compression (1−2) + Work done during air delivery (2−3) − Work done during suction (0−1). Similarly, for isentropic compression