What term identifies the boundary layer between the clean agent and the air that declines as leakage occurs?

What term identifies the boundary layer between the clean agent and the air that declines as leakage occurs?

• A. Ascending boundary
• B. Descending interface
• C. Mixed boundary
• D. Stable boundary

Answer: (B)

The key idea is how the clean agent and the surrounding air separate and move relative to each other. When a clean agent is heavier than air, it tends to pool near the floor and form a distinct layer at the bottom of the space. As leakage continues, this dense layer can become thinner and its boundary with the ambient air moves downward toward the floor. That downward progression of the interface is described as a descending interface. So, the boundary layer between the clean agent and the air that declines as leakage occurs is the descending interface. If the agent were lighter than air, you’d instead describe an ascending boundary where the layer rises toward the ceiling. Mixed or stable boundary terms aren’t standard descriptors for this vertical movement of the agent–air interface.

The key idea is how the clean agent and the surrounding air separate and move relative to each other. When a clean agent is heavier than air, it tends to pool near the floor and form a distinct layer at the bottom of the space. As leakage continues, this dense layer can become thinner and its boundary with the ambient air moves downward toward the floor. That downward progression of the interface is described as a descending interface.

So, the boundary layer between the clean agent and the air that declines as leakage occurs is the descending interface. If the agent were lighter than air, you’d instead describe an ascending boundary where the layer rises toward the ceiling. Mixed or stable boundary terms aren’t standard descriptors for this vertical movement of the agent–air interface.