Adiabatic Compression
Fluid Mechanics · FE Reference Handbook section
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
a positive-displacement blower feeding an aeration basin Given volumetric flow (Q) = 5.4000 m^3/s; pressure rise (\Delta p) = 18,400 Pa; efficiency (\eta) = 0.5800, determine the shaft power (W) in W.
Given
Find
shaft power (W), in W
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except W is given, so isolate W symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: volumetric flow (Q) = 5.4000 m^3/s, pressure rise (\Delta p) = 18,400 Pa, efficiency (\eta) = 0.5800.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 171,310 W to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 342,621 — kept a factor of two that cancels in the correct rearrangement.
- 85,655 — dropped that same factor in the other direction.
- 188,441 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a centrifugal blower on a dust-collection duct Given shaft power (W) = 81,366 W; pressure rise (\Delta p) = 9,400 Pa; efficiency (\eta) = 0.6000, determine the volumetric flow (Q) in m^3/s.
Given
Find
volumetric flow (Q), in m^3/s
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3 — List the givens: shaft power (W) = 81,366 W, pressure rise (\Delta p) = 9,400 Pa, efficiency (\eta) = 0.6000.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 5.1936\ \text{m^3/s}Step 6 — Check: returning Q = 5.1936 m^3/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 10.3871 — kept a factor of two that cancels in the correct rearrangement.
- 2.5968 — dropped that same factor in the other direction.
- 5.7129 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a compressor supplying pneumatic construction tools Given shaft power (W) = 184,681 W; volumetric flow (Q) = 3.7000 m^3/s; pressure rise (\Delta p) = 28,400 Pa, determine the efficiency (\eta).
Given
Find
efficiency (\eta)
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except \eta is given, so isolate \eta symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for \eta:
Step 3 — List the givens: shaft power (W) = 184,681 W, volumetric flow (Q) = 3.7000 m^3/s, pressure rise (\Delta p) = 28,400 Pa.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning \eta = 0.5690 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1.1380 — kept a factor of two that cancels in the correct rearrangement.
- 0.2845 — dropped that same factor in the other direction.
- 0.6259 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a positive-displacement blower feeding an aeration basin Given volumetric flow (Q) = 7.1000 m^3/s; pressure rise (\Delta p) = 40,700 Pa; efficiency (\eta) = 0.6400, determine the shaft power (W) in W.
Given
Find
shaft power (W), in W
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except W is given, so isolate W symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: volumetric flow (Q) = 7.1000 m^3/s, pressure rise (\Delta p) = 40,700 Pa, efficiency (\eta) = 0.6400.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 451,516 W to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 903,031 — kept a factor of two that cancels in the correct rearrangement.
- 225,758 — dropped that same factor in the other direction.
- 496,667 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a centrifugal blower on a dust-collection duct Given shaft power (W) = 160,051 W; pressure rise (\Delta p) = 59,600 Pa; efficiency (\eta) = 0.7600, determine the volumetric flow (Q) in m^3/s.
Given
Find
volumetric flow (Q), in m^3/s
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3 — List the givens: shaft power (W) = 160,051 W, pressure rise (\Delta p) = 59,600 Pa, efficiency (\eta) = 0.7600.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 2.0409\ \text{m^3/s}Step 6 — Check: returning Q = 2.0409 m^3/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4.0818 — kept a factor of two that cancels in the correct rearrangement.
- 1.0205 — dropped that same factor in the other direction.
- 2.2450 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a compressor supplying pneumatic construction tools Given shaft power (W) = 24,108 W; volumetric flow (Q) = 1.4000 m^3/s; pressure rise (\Delta p) = 16,100 Pa, determine the efficiency (\eta).
Given
Find
efficiency (\eta)
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except \eta is given, so isolate \eta symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for \eta:
Step 3 — List the givens: shaft power (W) = 24,108 W, volumetric flow (Q) = 1.4000 m^3/s, pressure rise (\Delta p) = 16,100 Pa.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning \eta = 0.9350 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1.8699 — kept a factor of two that cancels in the correct rearrangement.
- 0.4675 — dropped that same factor in the other direction.
- 1.0285 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a positive-displacement blower feeding an aeration basin Given volumetric flow (Q) = 3.9000 m^3/s; pressure rise (\Delta p) = 18,400 Pa; efficiency (\eta) = 0.8500, determine the shaft power (W) in W.
Given
Find
shaft power (W), in W
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except W is given, so isolate W symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: volumetric flow (Q) = 3.9000 m^3/s, pressure rise (\Delta p) = 18,400 Pa, efficiency (\eta) = 0.8500.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 84,424 W to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 168,847 — kept a factor of two that cancels in the correct rearrangement.
- 42,212 — dropped that same factor in the other direction.
- 92,866 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a centrifugal blower on a dust-collection duct Given shaft power (W) = 20,876 W; pressure rise (\Delta p) = 37,000 Pa; efficiency (\eta) = 0.8200, determine the volumetric flow (Q) in m^3/s.
Given
Find
volumetric flow (Q), in m^3/s
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3 — List the givens: shaft power (W) = 20,876 W, pressure rise (\Delta p) = 37,000 Pa, efficiency (\eta) = 0.8200.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 0.4627\ \text{m^3/s}Step 6 — Check: returning Q = 0.4627 m^3/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 0.9253 — kept a factor of two that cancels in the correct rearrangement.
- 0.2313 — dropped that same factor in the other direction.
- 0.5089 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a compressor supplying pneumatic construction tools Given shaft power (W) = 49,868 W; volumetric flow (Q) = 4.4000 m^3/s; pressure rise (\Delta p) = 27,700 Pa, determine the efficiency (\eta).
Given
Find
efficiency (\eta)
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except \eta is given, so isolate \eta symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for \eta:
Step 3 — List the givens: shaft power (W) = 49,868 W, volumetric flow (Q) = 4.4000 m^3/s, pressure rise (\Delta p) = 27,700 Pa.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning \eta = 2.4441 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4.8881 — kept a factor of two that cancels in the correct rearrangement.
- 1.2220 — dropped that same factor in the other direction.
- 2.6885 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors
a positive-displacement blower feeding an aeration basin Given volumetric flow (Q) = 6.7000 m^3/s; pressure rise (\Delta p) = 56,300 Pa; efficiency (\eta) = 0.8200, determine the shaft power (W) in W.
Given
Find
shaft power (W), in W
Start with the thinking
- The governing relation printed in this handbook section is Blower / compressor fluid power.
- Everything except W is given, so isolate W symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- A blower raises the pressure of an air stream across an aeration basin diffuser system.
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: volumetric flow (Q) = 6.7000 m^3/s, pressure rise (\Delta p) = 56,300 Pa, efficiency (\eta) = 0.8200.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 460,012 W to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 920,024 — kept a factor of two that cancels in the correct rearrangement.
- 230,006 — dropped that same factor in the other direction.
- 506,013 — rounded an intermediate value before the final step.
Reference: FE Handbook — Fans, Blowers, and Compressors