Venturi Tube

A Venturi tube is a short pipe with a narrow and restricted inner surface. It is typically used to calculate fluid flows and as a functional pump. Giovanni Battista Venturi designed a device with a constricted throat in the centre. As fluid enters the throat, the fluid moving through the tube accelerates, and the pressure drops. The device is designed based on the effects of narrow and restricted channels of fluid movement.

Venturi Effect and Fluid Flow

The Venturi effect limits fluid pressure that occurs when a fluid moves through a constricted choke of a pipe. In the case of inviscid fluid dynamics, the velocity of an incompressible fluid must rise as it flows through a constriction in accordance with Bernoulli’s principle (the principle of mechanical energy conservation). So, any rise in kinetic energy a fluid may acquire by its increased velocity (constriction) is balanced by a decrease in pressure. The rate of flow can be determined by calculating the pressure (using flow measurement devices such as orifice plates and Venturi nozzles).

The restricting scenario of the Venturi effect is when fluids reach the choked flow condition, where the fluid velocity reaches the regional speed of sound. When fluid systems are in a choked flow state, a further reduction in the downstream pressure region will not pave the way for a boost in velocity unless the fluids are compressed.

The rate of mass flow for a compressible fluid increases with rising upstream pressure. It increases the liquid’s density through a constriction (even though the velocity remains constant). These are the fundamentals of a de Laval nozzle operation. Rising source temperature increases the sonic velocity. This allows for increasing mass flow speed. It is only relevant if the area of the nozzle is also enlarged to adjust for the resulting fall in density.

The video explains the fundamentals of Bernoulli’s principle

What is a Venturi Tube?

A Venturi tube is a tubular setup for calculating the flow of fluids. The fluid moves through a pipe of inconsistent diameter. To reduce excessive drag, Venturi tubes usually have one entry cone of thirty degrees and five degrees exit cone.

Typically, Venturi tubes are used in conditions where the permanent loss of pressure is not tolerable and where the highest accuracy is required in the case of heavily viscous liquids.

A pressure reduction, accompanied by a rise in the flow velocity, is the basis of the laws of fluid dynamics. In 1738, Daniel Bernoulli derived the relationship between velocity, pressure and other properties of a fluid. Fundamentally, his theorem is applied in the development of aircraft wings to generate lift from the airflow over the wing surface.

Applications of Venturi Tubes

Mainly, there are two implementations of Venturi tubes. By connecting manometers to three parts of the tube, the pressure reduction can be calculated, and the rate of flow through the tube’s throat can be calculated. A Venturi tube can utilise this negative pressure to attract a second fluid into the central flow. Even though the fundamental mechanism has stayed the same for the last two centuries, this phenomenon is applied in various industries.

It is also extensively used in waste treatment processes. It enables solid materials to move through because of its gradually inclined smooth structure. Thus, it is ideal for the estimation of dirty fluid.

Advantages and Disadvantages of a Venturi Metre

Advantages

• High-pressure recovery.
• It can be fixed in any orientation: inclined, horizontal, and vertical.
• Less permanent pressure reduction.
• Less cone angle and smooth construction help solid substances to move through it. So it can be employed for dirty fluids.
• High discharge coefficient.
• It is much more accurate than the flow nozzle and orifice.

Disadvantages

• Size and cost are comparatively high.
• It isn’t easy to examine because of its construction.
• For desired results, the Venturi tube should be preceded by lengthy, straight pipes.
• Maintenance is not very easy.
• It cannot be used in pipes that have small diameters.

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