Question

Of the various methods of measuring discharge through a pipe line, the one with the least loss of energy and direct reading is by
1. venturimeter
2. orifice meter
3. flow nozzle
4. traversing a pitot-static probe

Answer 1

Correct Answer - Option 1 : venturimeter

Explanation:

Orifice meter-

• In this, we experience a great loss of energy. This is because of the design of the orifice. When the obstruction makes a sudden change in diameter, the streamlines cannot change direction suddenly. This creates a swirl behind the orifice, and as the velocity of the flow increases, the vena contracta decreases. The smaller the vena contracta gets the greater the pressure difference, and thus the higher the energy loss.

Pitot tube, notch- 

• In both the cases there is a sudden change in the direction of flow which causes great loss of energy

Venturimeter- 

• It has a smaller energy loss than the other two flowmeters because of the structure of the Venturimeter. The system has a gradual change in diameter. The flow streamline through a Venturi does not have to drastically change direction like the orifice flowmeter

Meter	Formula	Cd = \(\frac{Q_{act}}{Q_{theo}}\)	Energy Loss	Cost
Venturimeter	\({{\rm{Q}}_{{\rm{act}}}} = \frac{{{{\rm{C}}_{\rm{d}}}{{\rm{a}}_1}{{\rm{a}}_2}\sqrt {2{\rm{gh}}} }}{{\sqrt {{\rm{a}}_1^2 - {\rm{a}}_2^2} }}\)	\(0.94 - 0.98\)	Less	Expensive
Orifacemeter	\({{\rm{Q}}_{{\rm{act}}}} = \frac{{{{\rm{C}}_{\rm{d}}}{{\rm{a}}_1}{{\rm{a}}_0}\sqrt {2{\rm{gh}}} }}{{\sqrt {{\rm{a}}_1^2 - {\rm{a}}_0^2} }}\)	0.68 – 0.72	More	Cheap

where, a0 = theoretical throat area