Flow Measurement - Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

FLOW MEASUREMENT

Venturimeter 

• Cone angle of convergence side (20°) is greater than cone angle of divergence side (5° to 7°). 
• Position of venturimeter does not play any role in discharge thus it is constant for horizontal, inclined or vertical position.

Q_ac = C_d Q_th
C_d = coefficient of discharge = 0.95 to 0.98
h = venturi head which is difference between pressure heads 

• Throat diameter is known as size of the venturimenter.

Orifice meter 

• It is a cheaper arrangement but has more energy loss.

C_d for orifice meter = 0.68 - 0.74

C_d for orifice meter = 0.68 - 0.74

a₁ = πd²/4

a₂ = πd_c²/4

Pitot Tube 

• It is based on principle of conversion of kinetic head into pressure head. The point at which velocity reduces zero is called stagnation point.

• For theoretical velocity, we do not multiply the equation by C.

• Velocity head is indicated by the difference in liquid level between the Pitot tube and the piezometer. The Pitot tube measures the total head and therefore known as total head tube.

Hydraulic Coefficients

• Contraction coefficient (Cc) = 
• Coefficient of velocity of (Cv) =
• Coefficient of discharge (Cd) = 
• C_d = C_v.C_c 

Flow through orifice in the tank

Time required to lower the level from H to h

Discharge through orifice when head over orifice is h

• Rectangular Weir/Notch

L = length of crest H = head above crest 

• Triangular weir

• Trapezoidal weir