Flow measurement devices – Terminology for an opening in a tank wall An opening in the side of a tank or vessel such that the tank's liquid surface is below the top edge of the opening is called a:

Introduction:
Weirs, notches, and orifices are common flow-measurement and discharge-control devices. Their definitions are tied to geometry and installation location, and exam questions often test the precise terminology distinguishing them.

Given Data / Assumptions:

• Opening is made in the side wall of a tank or vessel.
• The tank's free surface lies below the top edge of the opening.
• Free discharge over the opening is intended.

Concept / Approach:

A notch is an opening in the side of a tank or channel with the liquid surface below the top edge of the opening; it is typically used for flow measurement (e.g., V-notch, rectangular notch). A weir is similar in function but built across an open channel to raise water level and measure discharge over a crest spanning the channel. An orifice is an opening in a wall or floor where the liquid level is above the top edge, causing submerged discharge through the opening rather than free overfall.

Step-by-Step Solution:

Verification / Alternative check:

Standard hydraulics texts define notches and weirs in these terms; device drawings confirm the geometric distinctions used for classification.

Why Other Options Are Wrong:

Weir: Built across a channel; not merely an opening in a tank wall.Orifice: Requires liquid level above the opening for discharge through the plate.Sluice gate / venturi: Different devices serving control/measurement by other principles.

Common Pitfalls:

Confusing notches with orifices because both are plate openings; the key cue is the location of the liquid surface relative to the opening top edge.

Final Answer:

notch