This is basically 15 metres of 1/2" copper tube wound into a helical heat exchanger which cold tap water is passed through.
It is Immersed into the wort at the end of the boil to rapidly chill
the wort to fermentation temperature.
Below is a picture of the chiller in a 90 litre pot based kettle.
Immersion Chiller in 91L kettle
Immersion Chiller in 50L Kettle with Clip OverWhirlpool Pipe
Whirlpooling is a technique adopted by brewers using centrifugal forces to encourage sediment or Trub in the Wort to settle towards the centre of the kettle in a conical shape away form the edge of the kettle where the pickup is.
Setting the wort spinning in the kettle spinning can be achieved with a sanitised spoon,pump via tangential entry or mechanical stirrer in the kettle.
In a separate whirlpool vessel the force of the wort entering via gravity from a tangential entry is often used.
On a homebrewing scale it is often not possible or economical to have a tangential entry welded to the side of your kettle.
My solution for thinner kettles has been to offer either a weldless tangential entry kit or the whirlpool pipe which clips over the edge of the pot and the wort pumped from the kettle outlet returning through the whirlpool pipe creates the spinning motion so desired.
Heavier kettles or keggles are heavy enough to have a whirlpool welded into the wall.
The whirlpool circulation has three benefits when used with an immersion chiller started just before the boil finishes-
Initially the pump and pipe are sanitised by the boiling wort.
Secondly the movement of the wort around the chiller when chilling improves the efficiency of the chiller.
Lastly once the chiller is removed the resulting whirlpool is very helpful in encouraging the trub to settle in the centre of the kettle away from the pickup.