Test: Pressure & Its Measurement - 2 - Mechanical Engineering MCQ

Manometric fluid should have low vapour pressure and high density to have less height of piezometric tube.
Since Mercury have both the property hence this is the reason, Mercury used as Manometric fluid.

A fluid does not offer any resistance to change of shape and deformed under the action of small force.

Limitations of Piezometer:
1. Piezometers cannot be used to measure pressure which are considerably excess of atmospheric pressure use of very long glass tube would be unsafe. It being both Fragile and unmanageable.
2. Gas pressure cannot be measured as gas does not form any free surface with atmosphere.
3. Measurement of negative pressure is not possible due to flow of atmospheric air into the container through the tube.

Hot wire anemometer is used in the measurement of highly fluctuating velocities in air flow.

Where
S_g = Specific gravity of Mercury
S_o = Specific gravity of Oil
Here, Sg > S_o

Reference is always taken from atmospheric pressure which is indicated by Barometer. Barometer reads the local atmospheric pressure.
So pressure = 700-380 = 320 mm of Hg vacuum.

In a fluid at rest, pressure through out the any horizontal line is same.

We have, P_A = 50 cm Hg vaccum=-ρ_hgg50

and, P_atm -ρ_hggH = P_A for gauge pressure P_atm=0
0 - ρ_hggH = -ρ_hgg50 ...[-ve sign for vaccum Pressure]

H=50 cm