Benefits and constraints of Coanda effect screen

Benefits:

• Self-cleaning concerning debris, it can operate without any external intervention to remove debris from the screen.
• Desilting function: most of 0.5mm suspended silt particles and all 1mm particles are screened out of the flow to the turbines.
• Negligible maintenance time and costs.
• No moving parts or power requirement.
• Simple and inexpensive to install.
• Fish friendly.

Constraints:

• Head Loss: 1.2 m head loss for full height screens (0.7 m for half height screens).
• Algae: a problem of algae formation has been observed on several sites. In this case it is controlled by annual washing of the lower surfaces with soap and water.
• Particle Size: the particle removal characteristics of the screens may not be sufficient for some turbines, especially where very high heads or quartzite grains in the flow are involved.
• Screen Capacity: limited to 0.14 cumec/m (bit higher when the screen is new)
• Vulnerability to rock damage.
• Cost: costly in comparison with other screens. The price is about 185000 NOK per cumec.
• Requirement for a by-pass flow: to maintain the self-cleaning characteristics.