The flow behavior of a fluid is described by its movement.
A vortex forward movement is called turbulent flow.
A tube with a Reynolds number higher than approximately 4000 will have this kind of flow behavior.
Because of the turbulent flow new coolant is brought to the wall of the cooling channel to take on heat.
After that it will move to the center of the cooling channel and from there back to the wall.
Due to this movement more heat can be taken by the coolant and hence the cooling is more efficient.
Therefore turbulent flow is recommended for a coolant.