Drift (or windage) is the term for water droplets of the process flow allowed to escape in the cooling tower discharge. In every cooling tower there is a loss of water to the environment due to the evaporative cooling process. This evaporation is usually in the form of pure water vapor and presents no harm to the environment.
Drift, however, is the undesirable loss of liquid water to the environment via small droplets that become entrained in the leaving air stream. These water droplets carry the same concentration of chemicals and mineral impurities as are typically found in cooling towers
Drift eliminators are designed to capture large water droplets caught in the cooling tower air stream. The eliminators prevent the water droplets and mist from escaping the cooling tower. Eliminators do this by causing the droplets to change direction and lose velocity at impact on the blade walls and fall back into the tower.
There are three main types of Drift Eliminator used in a Cooling Tower, these all having the same design purpose as described above, these being:
- Cross-Flow Integrated
- Cross-Flow non-integrated
These drift configurations may be made from: Polypropylene (PP) or Polyvinyl chloride (PVC) & Galvanised / Stainless Steel.
- Specification / Testing Rig & Air Flows Standard – common to every certified Drift Eliminator product
- Common benchmark playing field of all certified products
- Provides customer confidence for worst case break through velocity (m/s)
- Provides evidence to European / geographic acceptance regulations i.e. NFE-38-424
It is very easy to make the right choice: just compare the products. But when product performance is not certified, this becomes impossible.
Certification makes it possible to compare objectively.
- The product performance is evaluated according to the same criteria, and the results are expressed in the same unit of measurement, regardless of the country where the products are manufactured or marketed.
- A certified product has its performance verified by an impartial, independent and competent accredited body.
- Certified products comply with standards.
- A product whose performance is certified will work according to the specifications stated by the manufacturer.
- The Eurovent Certified Performance (ECP) Drift Eliminator certification programme provides certified drift rate less than or equal to 0.01% and Break-through air velocities when tested according to the relevant Eurovent Rating Standard.
- Break-through air velocity. 3 stages can be observed:
- 1st: small droplets leave the DE then fall back down almost immediately;
- 2nd: the small droplets float above the DE without leaving,
- 3rd: droplets are carried away by the airflow and leave the DE.
- The breakthrough velocity corresponds to the beginning of the third stage. Velocity shall be expressed in m/s.
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