FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesHard
A tube has an outside diameter of 0.500 inch and a wall thickness of 0.035 inch. What is the approximate cross-sectional area available for fluid flow inside the tube?
- A0.283 in²
- B0.196 in²
- C0.145 in²
- D0.0723 in²
Show answer & explanationAnswer & explanation
Correct answer: C. 0.145 in²
Inside diameter = OD − 2(wall thickness) = 0.500 − 2(0.035) = 0.430 in. Radius = 0.215 in. Area = πr² = 3.1416 × (0.215)² = 0.1452 in².
Why the other options are wrong
- A. This value results from using the wrong radius calculation.
- B. This uses the outside diameter instead of the inside diameter.
- D. This is roughly half the correct area, an arithmetic error.
Tube Flow Area
The cross-sectional area inside a tube available for fluid flow, based on the inside diameter, not the outside diameter.
- ID = OD − 2(wall thickness)
- Area = πr²
- Wall thickness reduces usable flow area
Memory trick: Subtract both walls before you square the radius.