Where the risk is
While the unit is running, the flow delays freezing to a large extent; the real risk is in the moments the system is stopped. Overnight stops, weekend stops, the wait after a fault. Standing water inside the tube can freeze within hours when the outside air is below zero.
The remedy and its price
The standard precaution is to use a water-glycol (brine) mixture instead of water. The mixing ratio sets the freezing temperature, and the freezing temperatures corresponding to each ratio are given in the table in the catalogue.
It is not free. As the glycol ratio rises, the viscosity of the mixture rises and its specific heat falls: carrying the same heat takes more flow, therefore more pump power, and the unit's capacity drops below its water figures. So the ratio is not a case of "the more the better"; it is chosen against the lowest temperature the site actually sees.
The selection is made knowing this
The capacity calculation is made together with the fluid. Raising the mixing ratio afterwards can leave an already selected unit undersized. When you choose a dry cooler, tell us the installation region and how many hours the plant stands still in winter; we will settle the ratio and the capacity together.
Ethylene or propylene
Both are used. Propylene glycol is preferred in plants where there is a risk of contact with food production. Whichever it is, the inhibitor content of the mixture and its periodic checking must not be neglected: a degraded mixture opens the very tube it was put in to protect to corrosion.