Question

Why there is rapid converging passage and gradual diverging passage are provided in venturi meter?

Answer 1

This ensures a rapid converging passage and a gradual diverging passage in the direction of flow to avoid the loss of energy due to separation. ... Subsequently, a decrease in the velocity and an increase in the pressure takes place in course of flow through the divergent part

Answer 2

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It is to avoid the loss of energy due to separation.

${Explanation:}$

There are two passages in Venturi meter:
-Converging passage
-Diverging passage

• When there is a flow through the converging passage, then according to the principle of continuity, there will be increase in the velocity in the direction of flow where as pressure decreases as per the Bernoulli's theorem

•At the neck of the Venturi meter, the velocity will be maximum and the pressure will be minimum

•Due to this there will be no loss of energy due to separation.

• In the same way,
At the diverging part of the Venturi meter,the velocity will be minimum and the pressure will be maximum

Therefore, there will be variation in fluid velocity and the pressure.

This avoids the loss of the Energy due to separation.