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The relationship between pressure rise and mass flow rate at various speeds is shown in Fig. 15.8. At a certain speed, efficiency increases as the mass flow rate increases and reaches a maximum value after which it decreases, as shown in Fig. 15.9. The power consumed increases as mass flow increases. Figure 15.10 shows the performance and constant efficiency…

The static pressure ratio from Eq. (15.15) is, Temperature rise in rotating blades, Pressure rise in rotating blades, Pressure rise in stationary blades is, Pressure increase in stage is, The stagnation pressure ratio is, If the work done per stage is assumed to be the same, then number of stage z is given by, If pressure ratio per stage…

Flow Coefficient: It is defined as the ratio of flow (or axial) velocity at inlet to the blade velocity. Mathematically, we can write Flow coefficient,  Now u = vf1 (tan α1 + tan β1) Also, vf1 = vf2 = vf Head or Work Coefficient: It is defined as the ratio of actual work done to the kinetic energy corresponding to the mean peripheral velocity. One can write Head or…

It is the isentropic efficiency of one stage of a multistage compressor. This small-stage efficiency is constant for all stages of a compressor with infinite number of stages. Consider the compression process of a multistage compressor on a T-s diagram as shown in Fig. 15.6 from total pressure p01 to p02 in four stages of equal pressure ratio with intermediate pressure p0a, p0b, and p0c. Overall…

Consider the incompressible isentropic and steady flow through a cascade from condition 1 to condition 2. Using Bernoulli’s equation, we have Now, v f1 = v f2 = v f

The degree of reaction, Rd, is defined as the ratio of pressure rise in the rotor blades to the pressure rise in the compressor stage. Pressure rise in the rotor blades  Pressure rise in the compressor stage For 50% degree of reaction,  From Eqs (15.8) and (15.9), we have Therefore, with 50% degree of reaction, the blades are symmetrical.…

Figure 15.5 shows the velocity triangles for one stage of an axial flow compressor. All angles are measured from the axial direction. The blade velocity u is taken to be same at blade entry and exit as the air enters and leaves the blades at almost equal radii. Due to the diffusion process in the moving blades, vr2 < vr1 but va2 > va1. The…

When an object is placed within a fluid stream, a force is exerted on the object which may be inclined to the flow direction. The component of this force parallel to the direction of flow is called the drag and the normal component is called the lift, as shown in Fig. 15.2. Consider an aerofoil section…

The axial compressor is generally driven by an internal combustion engine or a turbine. The work input to the rotor shaft is transferred by the rotor moving blades to the air, thus accelerating it. The space between the moving blades form diffuser passages so that the velocity of air relative to the blades is decreased…