Investigation of protective nano-based surface coatings for dry hybrid coolers

Efficient rejection of waste heat is essential especially for thermally driven chillers, to keep up cooling capacity at demanding summer operation conditions. A suitable alternative to large surface reserves of dry coolers is to boost their performance by temporary wet mode operation by spraying water on the heat exchanger. But due to corrosion and fouling problems this is usually limited to a few hours. One approach to avoid this is to protect the dry coolers with special surface coatings. This paper presents the results of various experimental investigations of dry coolers equipped with hydrophilic and hydrophobic coatings. Long-term intermittent spray operation of small test coolers with tap water was performed in a laboratory test rig. The microscopic examinations and contact angle measurements showed that even best hydrophobic surface was rapidly turning to hydrophilic. Nevertheless, at over 600 hours of intermittent spray and dry operation some coatings showed positive results - a reliable corrosion protection and the positive effect of additional evaporative cooling with a minimum of water could be proved.