What does BLWDN stand for?

Blowdown

A coating defect consisting of a lower coating film weight on the bottom of the coated sheet caused by high velocity air in the oven. Blowback usually occurs with high solids coatings which have little solvent to evaporate and "set" the film.  OR In connection with boilers or cooling towers, the process of discharging a significant portion of the aqueous solution in order to remove accumulated salts, deposits and other impurities.