Face Velocity is defined as

Face Velocity is defined as

• A. The velocity of air in motion
• B. The total pressure in the duct
• C. The cross-sectional area of the opening
• D. The measurement of airflow across the opening of a local exhaust capture hood

Answer: (D)

Face velocity is the air speed right at the opening of a local exhaust capture hood. It measures how fast air is moving across the hood’s face as contaminants are drawn into the hood, typically expressed in feet per minute or meters per second. This value is key for ensuring adequate capture of pollutants: if the velocity is too low, contaminants may escape; if it’s too high, it wastes energy and creates more noise and discomfort. In practice, face velocity can be found by taking the volumetric flow rate into the hood and dividing by the face opening area (Q/A), and it’s measured across the face rather than elsewhere in the system. This definition is specific to the hood opening and different from general room air velocity, duct pressure, or the opening’s area alone.

Face velocity is the air speed right at the opening of a local exhaust capture hood. It measures how fast air is moving across the hood’s face as contaminants are drawn into the hood, typically expressed in feet per minute or meters per second. This value is key for ensuring adequate capture of pollutants: if the velocity is too low, contaminants may escape; if it’s too high, it wastes energy and creates more noise and discomfort. In practice, face velocity can be found by taking the volumetric flow rate into the hood and dividing by the face opening area (Q/A), and it’s measured across the face rather than elsewhere in the system. This definition is specific to the hood opening and different from general room air velocity, duct pressure, or the opening’s area alone.