Tennessee Wastewater Operator Practice Exam

What happens to air pressure when it is expanded rapidly in a centrifugal blower?

1. Air pressure increases

2. Air pressure decreases

3. Air pressure remains stable

4. Air pressure fluctuates

The correct answer is: Air pressure decreases

In a centrifugal blower, when air is expanded rapidly, the air pressure decreases. This phenomenon is primarily due to the principles of thermodynamics and the behavior of gases under expansion. As air passes through the blower and is accelerated by the rotating impeller, it experiences a rapid increase in velocity. When this high-velocity air encounters the ambient air or moves into an area of lower pressure, a conversion from pressure energy to kinetic (velocity) energy occurs. The rapid expansion causes the density of the air to drop, which in turn reduces its pressure. This understanding correlates with the concept of stagnation pressure, where the accelerated air has less static pressure compared to what it had prior to being set into motion. Additionally, as the air expands, it moves from a confined space to a less confined one, creating a drop in pressure according to Pascal's law, which states that a change in pressure applied to an incompressible fluid will be transmitted throughout that fluid. Therefore, the correct answer aligns with the physical behavior of gases in a centrifugal blower system, highlighting the relationship between air velocity, volume, and pressure during rapid expansion.