Question
Bryan Stanley
Design Engineering

# What is Vena Contract in Orifice?

What is Vena Contract in Orifice?

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Dean Richards
Building control officer

Vena-contract is a section in orifice which has a minimum cross-section area and has maximum velocity. At this, all streamlines are parallel, straight, and uniform, so have laminar flow. It is calculated by the area of the orifice (Ao) and the coefficient of contraction (Cc). Area of vena contracta Ac= Ao *(Cc).

Vena contracta is a section in the flow of water where the flow has considerably narrow. Vena contracta can be found when there is a sudden change in the cross-sectional area.  The streamlines of the fluid cannot change abruptly when the CS area changes. This sudden reduction in the cross-sectional area makes the streamlines converge and form the vena contracta.

In this section, the velocity of the flow is maximum. From Vena contracta we can find the coefficient of contraction.

Further, Vena contracta has wide use in studying the blood flow and in various treatments ad diagnoses like echocardiography.

Vena contract is the point in flowing fluid at where the pressure energy is minimum and kinetic energy is maximum.

This phenomenon happens because of the fluid streamline can’t change its direction abruptly. Streamline can’t follow Sharpe angles so vena contract forms.

Veena Contra is a section where velocity distribution is uniform, and fluid streamline is parallel to each other.

The study of Vena Contra is used for actual velocity study in jet flow.

Coefficient of velocity is the ratio of actual velocity divided by the theoretical velocity

The actual velocity is equal to the velocity at vena contra.

Vena contracta is the point in a fluid stream where the diameter of the stream is the least and fluid velocity is at its maximum, such as in the case of the stream issuing out of a nozzle. It is a place where cross section area is minimum.