What is Venturimeter?
Venturimeter is a mechanical device that is used to measure the rate of flow of fluid through pipes. The pressure energy of the fluid will be converted in the kinetic energy due to the construction of the Venturimeter. The fluid may be Liquid or Gaseous. Moreover, it works with the combination of the Convergent Part, Divergent Part, and Throat that help to achieve the basic working principle.
Most of the Types of Venturimeter are made up of brass, glass, bronze, stainless steel, and cast iron depends upon the requirement and application.
The basic working principle of Venturimeter depends upon the Bernoulli’s Theorem or Principle, which is derived from the Law of Conservation of Energy. The Bernoulli’s Principle states that “the speed of any fluid will be increase with the decreasing static pressure of the fluid”, the principle is only applicable for the Isentropic Flows only”.
Table of Contents
History of Venturimeter
- In the 18th – 19th Century, an Italian scientist named Giovanni Battista Venturi developed the concept of Venturimeter.
- He observed the effect of constricted channels on the fluid flow and they designed an instrument that consist a narrow throat at the middle portion in which the fluid passes and its speeds up as it enter into the throat portion.
- It is also observed that the speed of the fluid is going to be increased and pressure is constantly dropping. It means, the fluid in the Venturimeter con convert pressure energy into the kinetic energy.
Parts of a Venturimeter
The entire Venturimeter is divide into three portions or sections, which we can called as its parts too, they are
- Convergent Section
- Throat Section
- Divergent Section
1. Convergent Section
In this phase, the Venturimeter tube diameter regularly decreases. It is a short pipe that varies from a diameter d1 to a small diameter d2. While the liquid flows In Convergent Section, the rate of fluid will increase with a lower stress.
2. Throat Section
The throat is another section or part of Venturimeter that connects the Convergent and Divergent, which has constant diameter. It is the circular section in with a diameter d2. In this section, the rate is high and stress is minimal.
3. Divergent Section
Divergent Section is an outlet of the Venturimeter, which is attached to the Throat Part. In the convergent, the diameter gradually decreases but in this section, the diameter increases from d2 diameter to the d1 again. The length of a divergent part is 3 to 4 times more than Convergent Part. Due to the increase in diameter, the stress is increase once more to the authentic inlet stress.
Types of Venturimeter
The Venturimeter are three types, they are
- Horizontal Venturimeter
- Vertical Venturimeter
- Inclined Venturimeter
1. Horizontal Venturimeter
The Horizontal Venturimeter has the higher kinetic energy and lower potential energy. The dimension of inlet and throat are 200 mm and 100 mm is used to measure water flow.
2. Vertical Venturimeter
The Vertical Venturimeter has the higher potential energy and lower kinetic energy. These are normally fitted with circular pipe 30 cm and throat 15 cm diameter. Using this type we can easily find out the amount of water flowing through the pipes.
3. Inclined Venturimeter
The Inclined Venturimeter adds both kinetic and potential energy that lies in between above two mentioned types. It is inserted into the pipe in the vertical plane to measure flow of pipe.
Working of Venturimeter
- When liquid flowing through the Venturimeter, it is accelerated in the convergent part. So as a result of the acceleration, the velocity in the throat part increases.
- This increase in velocity results in decrease of the pressure in throat part.
- If the pressure head of the throat part falls below the separation head (which is 2.5 meter of the water), then there will be a tendency of separation of the liquid flow. This effect known as a Venturi Vacuum.
- To avoid this tendency of separation in the throat part there is always a fix diameter ratio for throat and pipe, (i.e d2/d1) this ratio is approximately 1/3 to ½.
- In the Venturimeter, the purpose of a diffuser is to assure the gradual and steady deceleration after the throat part.
- If the pressure is rapidly recovered in the divergent part and then there is possibility for the stream of the liquid to break away from the walls.
- So to avoid this effect, divergent part taking bigger than that of convergent part. And it also reduces the Frictional Losses.
Discharge Through Venturimeter
The expression for the theoretical flow rate is obtained by applying the continuity equation and energy equation at the inlet and throat section; assuming the fluid to be ideal is given by
P1 = pressure at section 1
V1 = velocity of water at section 1
Z1 = datum head at section 1
A1 = area of Venturimeter at section 1
P2, v2, z2, a2 = corresponding values at section 2
- 13.6 = specific gravity of mercury, and
- Ω = specific weight of the oil
By applying Bernoulli’s Equation at sections (1) and (2), we get
as the pipe is horizontal, hence z1 = z2
But p1-p2/ρg is the difference of pressure heads at sections 1 and 2 and it is equal to h; therefore, the equation becomes
p1 – p2/ρg = h
Substituting this value of p1-p2/ρg in the above equation, we get
Now, we need to apply continuity equation at sections 1 and 2
Substituting this value of v1 in the equation (8.1)
Discharge is taken as q = a2v2
Equation 8.2 gives the discharge under ideal conditions, which is called as Theoretical Discharge. Therefore, the actual discharge will be less than the theoretical discharge; it is taken as
Advantages of Venturimeter
The advantages of Venturimeter are
- The power loss is low as compared to other flow measuring devices.
- Venturimeter is used where a small head is available.
- Accuracy is higher for wide flow range.
- The co- efficient of discharge is very high in Venturimeter.
- It is easy to handle and used in both compressible and incompressible fluids.
- The Venturimeter is commonly used for high flow rate of discharge.
Disadvantages of Venturimeter
The disadvantages of Venturimeter are
- The Venturimeter is quite expensive to install and maintain.
- It required more space than the other one.
- It cannot be used where pipe diameter less than 76.2 mm.
Applications of Venturimeter
The applications of Venturimeter are
- Venturimeter is used in industries to measure flow rate of Fluids.
- It is used in industrial sector to determine the Pressure of Gases and Liquids inside the pipe.
- It is used to measure airflows in Engine Carburetors.
- The application of Venturimeter can be used to control process flow in Processing Industries and even in Waste Water Recovery Plants.
- It is used in arterial blood flow for the Medical Devices
Frequently Asked Questions
1. What are the types of Venturimeter available?
There are three types of Venturimeter available
- Horizontal Type
- Vertical Type
- Inclined Type
2. Why divergent part is bigger than the convergent part?
The divergent part is bigger than the convergent part to reduces the frictional losses.
3. What will be measured using Venturimeter?
Flow of discharge