MECHANISMS AND PREVENTION OF SCALE FORMATION IN BOILERS

Nucleate boiling heat transfer coefficients may be strongly reduced by scale formation, even for conditions where the bulk foulant concentration is well below the saturation concentration. Due to the mechanism of micro-layer evaporation, the local concentration at the heat transfer surface can be considerably increased, causing the formation of scale and changes in bubble frequency and bubble departure diameter. The interaction between scale formation and bubble formation was studied with a precision pool boiling test apparatus in conjunction with a microprocessor-controlled camera and video equipment. The effects of EDTA which is commonly used as an antifouling agent in industrial boilers, on saturated pool boiling in the presence of foulants are discussed.