1.
​ ompare fixed speed and variable speed centrifugal blower?
C
Ans.
Fixed Speed
Variable Speed
Motors runs at a fixed speed.
Motor speed varies according to required
flow and pressure.
Lower efficiency than variable speed
80-85% more efficient than fixed speed
blowers.
blowers.
Requires a butterfly valve to adjust load
Has sensors to detect and regulate speed
depending on pressure and flow
according to pressure and flow
requirements.
requirements.
Lower installation but higher
Higher installation but lower
maintenance costs.
maintenance costs.
1. Draw inlet and outlet velocity triangles for axial and centrifugal blower. Hence, list
out differences between the two.
Ans.
Axial Compressor
Centrifugal Compressor
Flow is unidirectional
Flow turns perpendicular to
axis of rotation
More efficient
Less efficient
Higher pressure ratio and
Lower pressure ratio and flow
flow rate
rate
2. What are fan characteristics curves? Explain with a neat sketch.
Ans. ​Fan characteristics curves are plots between several performance indicating characteristics vs a
variable for a given fan design. These curves allow us to calculate real time performance criteria for a
fan. The most commonly used fan characteristic curve is a head vs discharge curve.
3. What are various energy efficiency opportunities in centrifugal blowers?
Ans. Various ways to improve energy efficiency in centrifugal blowers:
1. Minimizing pressure through variable speed drive and sensitive pressure sensors.
2. Use as small a blower as possible for the given requirements.
3. Multi-staging by connecting blowers in series or parallel.
4. Controlling density of air used.
5. Selecting fans of proper size.