DROPWISE CONDENSATION OF STEAM ON VERTICAL AND HORIZONTAL U-TYPE TUBE CONDENSERS
The heat transfer characteristics of dropwise condensation of steam on vertical and horizontal U-type tube condensers were investigated. The 70Cu:30Ni white copper tube bundles used in the condensers were treated by magnetron sputtering ion plating with Cr, N, and C2H6. There were 7 U-type treated tubes of 16 mm outside diameter and 1 metre long in each condenser. For comparison, the same sized vertical and horizontal condensers in which the tube bundles were not treated were also manufactured. The experimental results indicated that an excellent quality of dropwise condensation of steam occurred on the treated tube bundles while filmwise condensation occurred on the untreated ones.The overall heat transfer coefficient of the vertical dropwise condenser was about 40% higher than that of the vertical filmwise one and the overall heat transfer coefficient of horizontal dropwise condenser was about 65% higher than that of the horizontal filmwise one. The reason why dropwise condensation formed on the special treated tubes was investigated and is discussed in the paper.