At a 13 inch radius from the APU exhaust, what is the approximate temperature and velocity?

At a 13 inch radius from the APU exhaust, what is the approximate temperature and velocity?

• A. 300-310 degrees; 71 mph
• B. 328-350 degrees; 142 mph
• C. 259-295 degrees; 24 mph
• D. 270-290 degrees; 50 mph

Answer: (A)

Understanding how an exhaust plume behaves as it moves away from the outlet helps you predict what you’ll encounter near the hardware. Right at a short distance like 13 inches, the plume is still hot and moving, but it has begun to mix with ambient air and expand. The temperature doesn’t stay at the jet’s opening level, and the gas loses some momentum as it entrains surrounding air. So you expect a hot but not blistering temperature and a decelerating flow. The best pick reflects that balance: roughly 300–310 degrees Fahrenheit with a velocity near 71 mph. The temperature range captures the cooling that happens due to mixing, while the velocity range reflects the plume slowing down as it entrains air and spreads outward. The other options either imply excessively high temperatures or velocities not consistent with a plume at that distance, or unrealistically low speeds, which don’t align with how APU exhaust behaves just a short distance from the outlet.

Understanding how an exhaust plume behaves as it moves away from the outlet helps you predict what you’ll encounter near the hardware. Right at a short distance like 13 inches, the plume is still hot and moving, but it has begun to mix with ambient air and expand. The temperature doesn’t stay at the jet’s opening level, and the gas loses some momentum as it entrains surrounding air. So you expect a hot but not blistering temperature and a decelerating flow.

The best pick reflects that balance: roughly 300–310 degrees Fahrenheit with a velocity near 71 mph. The temperature range captures the cooling that happens due to mixing, while the velocity range reflects the plume slowing down as it entrains air and spreads outward. The other options either imply excessively high temperatures or velocities not consistent with a plume at that distance, or unrealistically low speeds, which don’t align with how APU exhaust behaves just a short distance from the outlet.