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**Chapter 6**** Flow Measurement**

Device | Measurement |

Venturimeter | rate of flow (discharge) |

Flow nozzle | rate of flow |

Orifice meter | rate of flow |

Bend meter | rate of flow |

Rotameter | rate of flow |

Pitot tube | velocity |

Hot wire anemometer | air & gas velocity |

Current meter | velocity in open channels |

**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

-a_{1} = πd^{2}/4

-a_{2} = πdc^{2}/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.

-V_{ac} = C_{v} .V_{th}

-C_{v} = Coefficient of velocity = 0.99

-p_{s}/γ = stagnation head & static head.

-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 (C _{c}) =**

**- Coefficient of velocity of (Cv) =**

**- Coefficient of discharge (C _{d}) =**

**- C _{d} = C_{v} . C_{c}**

**Flow through orifice in the tank:**

Discharge through orifice when head over orifice is h

Time required to lower the level from H to h

**Rectangular Weir/Notch:**

L = length of crest

H = head above crest

**Triangular weir:**

** **

**Flow over cippoletti weir or trapezoidal weir:**

-Trapezoidal weir is also called as Cippoletti weir. This is trapezoidal in shape and is the modification of rectangular weir with slightly higher capacity for same crest strength.** -**The sides are inclined outwards with a slope 1:4 (horizontal : vertical)

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