Coanda Effect in Intake Screens: How It Works

The Coanda effect is the tendency of a fluid to follow a curved surface rather than continuing in a straight line. In a Coanda intake screen, this principle draws water through wedge wire slots without any moving parts, pumps, or external power. How it works: water flows over the top of a curved wedge wire panel. Surface tension and the Coanda effect cause the water to follow the curved wire surface. As the water adheres to the surface, it passes through the V-wire slots by gravity and surface tension alone. Debris, leaves, and aquatic organisms too large to pass through the slots continue over the screen surface and are carried away by the remaining flow. The result is a self-cleaning screen with no moving parts, no power consumption, and no operator intervention. Flow capacity depends on screen width, wire profile, slot aperture, and the head of water available. Typical installations handle 50-500 liters per second per meter of screen width. Wire tilt angle is critical. Standard tilt of 3-5 degrees (maximum 7) creates a shearing component that increases water extraction through the slots. Without tilt, a portion of the water that contacts the slot opening rides over it rather than passing through. Typical applications: small to medium hydropower intakes (run-of-river schemes), irrigation canal intakes, municipal raw water intakes from rivers and streams, and aquaculture water supply systems. Coanda screens are especially useful in remote locations where power supply and maintenance access are limited. Design parameters: screen width (determines total flow capacity), arc radius (typically 500-1500 mm), slot aperture (1-3 mm depending on debris size), wire profile and tilt angle, and available head (minimum 150-300 mm for reliable operation).