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what is the use of venturi meter ?and how is it work?

1.Venturimeter

This is a device, based on Bernoulli's theorem, for measuring the rate of flow of a liquid flowing through a pipe.

The venturimeter consists of a tube ABC with a narrow construction at B. Two vertical capillary tubes x and y are connected to it, one at the broad portion A of the tube and the other at the constriction B. The ends A and C of the venturimeter are connected to the pipe through which the liquid flows.

When the liquid in the main pipe flows through the venturimeter, velocity of flow is smaller at A and greater at B. Hence according to Bernoulli's theroem, pressure at A is greater than that at B. The difference in pressure of liquid at A and B is measured by the difference in heights (h) between the liquid levels in the vertical tubes x and y. By measuring h, the rate of flow V of the liquid can be calculated by the equation,

where a₁ and a₂ are the cross-sectional areas of the venturimeter at A and B