25-08-2017, 09:32 PM
Theory of turbo machine Effect of Blade Configuration on
Characteristics of Centrifugal machines
Theory of turbo machi.pdf (Size: 752.96 KB / Downloads: 163)
We already know from Mechanics
For a rotary machine
•Power = Angular velocity x Torque
= Mass flow rate x Head
•Torque = Rate of change of angular
momentum
= Mass x [Abs. Circum. velocity x radius
(in-out)]
Velocities:
V-Absolute fluid velocity
v-Relative fluid velocity
u-peripheral speed of blade
•Subscripts:
1-inlet
2-outlet
n-normal component
t-tangential component
•Geometry:
b-blade width
r-blade radius
α -angle between Vand uvectors
β-angle between vand uvectors
What we have learnt
•Blade angle (β) is ideally the angle between the relative velocity (Vr) and blade-tip velocity (u)vectors
•To draw the vector diagram note that the blade-tip velocity and relative velocity vector are in the same rotational (clockwise or anticlockwise) direction. The arm of the triangle is the absolute velocity vector which is in opposite direction.
•Power = [blade velocity x tangential component of absolute velocity] inlet –outlet
•Flow ~ Rotor circumference x width x Normal velocity
Characteristics of different types of blades
•Owing to the losses the actual characteristic is different from theoretical linear shape
•Power consumption varies with flow Q
•Efficiency varies with Q with highest value being in the design condition