Explain the working principle of a venturi meter.

A venturi meter measures fluid flow rate by utilizing Bernoulli's principle. It consists of a converging section, throat (minimum area), and diverging section. As fluid enters the converging section, velocity increases and pressure decreases according to Bernoulli's equation. The pressure difference between the inlet and throat is measured using a differential pressure gauge. Flow rate is calculated as Q = Cd × A₂ × √(2ΔP/ρ(1-(A₂/A₁)²)), where Cd is the discharge coefficient (typically 0.95-0.99). Venturi meters have low permanent pressure loss compared to orifice meters.