Roots blower delivery frequency In a rotary positive-displacement compressor using a three-lobed Roots rotor, the trapped air pockets are transferred to the discharge how many times per rotor revolution?

Introduction / Context:
Roots blowers are timing-gear-driven, positive-displacement machines. The number of lobes on each rotor determines the number of trapped volumes delivered per revolution, affecting pulsation frequency, pressure ripple, and noise.

Given Data / Assumptions:

• Three-lobed Roots rotor configuration.
• Idealised operation without leak-back considerations.
• One trapped chamber is discharged per lobe engagement event.

Concept / Approach:
Each lobe pair forms a pocket that moves from the inlet side to the discharge side. With three lobes, three discrete pockets are conveyed per revolution, producing three delivery pulses per rotor revolution per side (neglecting minor harmonics).

Step-by-Step Solution:
Count lobes → three lobes create three distinct pockets.Track pocket motion → each pocket is delivered once per revolution.Therefore, the delivery event occurs three times each revolution.

Verification / Alternative check:
Manufacturer literature lists discharge pulsation frequency proportional to rotor speed multiplied by lobe count.

Why Other Options Are Wrong:

• Two/four/six times: correspond to other lobe configurations or misunderstandings of pocket transfer.
• Once per revolution: would apply to single-lobe concepts, not standard Roots designs.

Common Pitfalls:
Confusing lobe count with gear teeth count; only lobe count directly sets the base pulsation order.

Final Answer:
three times