For a water cooled ammonia condenser find the heat extracted if con- denser surface area 3 m, steel tube thickness 3 mm, condenser temperature 25C, average water temperature 18C, overall coeffi- cient of heat transfer for ammonia 6000 and for water 4000 W/m.C, thickness of oil layer on ammonia side 0.1 mm and thickness of scale on water side 0.5 mm, thermal conductivity for oil 0.14 and for scale 2 W/m.C.