20 / 94
20
Department of Civil
and Environmental
Engineering
Fall 2016
Testing of Snorkel for
Coanda Intake
Supervisor:
Leif Lia
Co-supervisor:
Knut Alfredsen
Niklas Kovanen Sæten
MASTER THESIS
Background
The Coanda intake’s self-cleaning capabilities
has proven to work well, but it is prone to
blockage due to frazil ice. A snorkel has been
made, which is intended to maintain the
circulation of the water in the canal underneath
the screens, when the intake is blocked by ice.
This will prevent ice from forming in the canal,
thus leaving the system ready for operation as
soon as the water finds its way under the ice.
A snorkel has been mounted on the intake at
Dyrkorn power plant over a long time period, but
its function has never been documented.
A physical model of the snorkel was built and
tested on a full scale Coanda screen model.
The intake at Dyrkorn have been monitored
via webcam and observations done with the
webcam, as well as observations made by
several field trips.
The snorkel’s capacity has been estimated
to see if it can deliver enough water to avoid
stopping the power plant during the event of the
intake being blocked. Model tests have revealed
that the snorkel, in extreme cases, could act as
a siphon, a situation that should be avoided. As
a siphon the snorkel could drain the reservoir
and deliver a flow different from the natural flow
of the river. It is shown that the snorkel may
contribute to reduce the cooling of the water
due to surface heat exchange, and to earlier
establish surface ice on the reservoir. It’s main
contribution is assumed to be that the water on
the bottom of the reservoir is warmer than the
surface water and that it does not contain frazil
ice. This has not been proven and should be the
next step in the documentation of the snorkel.
The Coanda intake
at Dyrkorn