Question

A gradually expanding duct fitted to the outlet of an exhaust fan is known as

• A. chimney
• B. diffuser
• C. evasee
• D. equivalent orifice

Hint:

Think about the specific mining ventilation term, not the general engineering word, for a duct that flares out at a mine fan's outlet.

Answer 1

The Correct Option is C

This question checks whether you know the exact mining ventilation term for a fan outlet fitting, not just what the fitting does. Four terms are given, and only one of them is the mining specific name for a duct that flares out gradually where it joins a fan outlet.

1. Chimney: A chimney is simply a vertical passage that carries exhaust gases upward and out. It says nothing about the duct changing shape, so it does not match.
2. Diffuser: This is the everyday engineering word for any duct that widens to slow a flow, used across many industries such as HVAC and turbines. It describes the same physical idea but is not the word mining engineers use for this particular fan fitting.
3. Evasee: This is the mining ventilation name for a duct that expands gradually where it bolts onto a fan outlet. Slowing the air this way converts velocity pressure back into static pressure, so the fan loses less energy at exit and moves air more effectively through the mine.
4. Equivalent orifice: This term belongs to mine ventilation network calculations, where several airways of different resistance are replaced by one imaginary orifice of the same overall resistance. It is a calculation tool, not a physical duct shape.

Since the question asks for the mining specific term rather than the general engineering one, the answer is evasee.

Let's summarize:

• An evasee is the gradually flaring duct fitted to a mine fan outlet.
• A diffuser does the same job in general engineering language but is not the mining term asked for here.
• Chimney and equivalent orifice describe unrelated ventilation ideas.

So the correct term for a gradually expanding duct at a mine fan outlet is evasee.