Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE) PDF Download

Chapter 6 Flow Measurement

DeviceMeasurement
Venturimeterrate of flow (discharge)
Flow nozzlerate of flow
Orifice meterrate of flow
Bend meter rate of flow
Rotameterrate of flow
Pitot tubevelocity
Hot wire anemometerair & gas velocity
Current metervelocity 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.
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
-Qac = Cd Qth
-Cd = 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.

Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

Orifice meter:
-It is a cheaper arrangement but has more energy loss.
-Cd for orifice meter = 0.68 - 0.74

Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
-a1 = πd2/4
-a2 = πdc2/4

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.

Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
-Vac = Cv .Vth
-Cv = Coefficient of velocity = 0.99
-ps/γ = stagnation head & Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE) 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 (Cc) =
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

- Coefficient of velocity of (Cv) =
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

- Coefficient of discharge (Cd) =
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

- Cd = Cv . Cc

Flow through orifice in the tank:
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Discharge through orifice when head over orifice is h
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Time required to lower the level from H to h

 Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Rectangular Weir/Notch:

 Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

L = length of crest
H = head above crest 

Triangular weir:

 Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

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)

 Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

The document Flow Measurement | Civil Engineering SSC JE (Technical) - Civil Engineering (CE) is a part of the Civil Engineering (CE) Course Civil Engineering SSC JE (Technical).
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FAQs on Flow Measurement - Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

1. What is flow measurement in civil engineering?
Ans. Flow measurement in civil engineering refers to the process of determining the quantity of fluid (liquid or gas) that passes through a specific point in a system or structure. It is essential for designing and analyzing various hydraulic systems, such as water supply networks, irrigation systems, and stormwater management systems.
2. What are the different methods used for flow measurement in civil engineering?
Ans. There are several methods for flow measurement in civil engineering, including: 1. Venturi meter: It uses a constriction in a pipe to measure the pressure difference, which is then used to determine the flow rate. 2. Orifice plate: Similar to the Venturi meter, it uses a plate with a hole to create a pressure difference and calculate the flow rate. 3. Ultrasonic flow meter: It measures the flow rate by transmitting ultrasonic waves through the fluid and analyzing the time it takes for the waves to travel. 4. Magnetic flow meter: It utilizes the principle of electromagnetic induction to measure the flow rate of conductive fluids. 5. Doppler flow meter: It measures the flow velocity by analyzing the frequency shift of sound waves reflected by particles in the fluid.
3. Why is flow measurement important in civil engineering?
Ans. Flow measurement is crucial in civil engineering for several reasons: 1. Design and analysis: Accurate flow measurements are necessary for designing efficient hydraulic systems, such as water distribution networks, sewer systems, and drainage systems. 2. Performance evaluation: Flow measurements help assess the performance and effectiveness of existing hydraulic structures, allowing for optimization and improvement. 3. Resource management: Proper flow measurement enables effective management of water resources, ensuring their sustainable use, allocation, and conservation. 4. Safety and risk assessment: Flow measurements aid in evaluating potential risks associated with flooding, stormwater runoff, or hydraulic failures, allowing for the implementation of appropriate mitigation measures. 5. Compliance and regulation: Flow measurements are often required to comply with regulatory standards and guidelines for environmental protection, water usage, and wastewater discharge.
4. How is flow rate determined using a Venturi meter?
Ans. Flow rate using a Venturi meter is determined based on the principle of Bernoulli's equation and the pressure difference created by the constriction. The steps involved are as follows: 1. Measure the pressure difference (ΔP) between the throat and the upstream section of the Venturi meter. 2. Calculate the velocity of the fluid at the throat using the Bernoulli's equation, which relates the pressure and velocity of the fluid. 3. Determine the cross-sectional area of the throat (A) using the known dimensions of the Venturi meter. 4. Calculate the flow rate (Q) using the formula Q = A × V, where V is the velocity of the fluid at the throat.
5. What are the advantages of using ultrasonic flow meters for flow measurement in civil engineering?
Ans. Ultrasonic flow meters offer several advantages for flow measurement in civil engineering: 1. Non-intrusive measurement: Ultrasonic flow meters can measure flow rates without coming into direct contact with the fluid, minimizing the risk of contamination or obstruction. 2. Wide applicability: They can be used to measure the flow of various fluids, including liquids and gases, making them versatile for different civil engineering applications. 3. High accuracy: Ultrasonic flow meters provide accurate measurements with minimal errors, ensuring reliable data for hydraulic system design and analysis. 4. Low maintenance: These flow meters have no moving parts, reducing the need for frequent maintenance and minimizing downtime. 5. Portable and easy to install: Ultrasonic flow meters are lightweight, compact, and easy to install, making them convenient for temporary flow measurements or field applications.
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