Functions of drain cooler are as follows: 1) Remove latent heat from exhaust stm and hence allowing the distilled water to be pumped back to system; 2) Create vacuum conditions assisting flow of exhaust steam and also allowing for low saturation tempo and hence increasing recoverable heat energy from the steam; 3) Deaerate. Only latent heat should be removed as this increases thermal efficiency. Even when the steam is expanded to vacuum conditions some 60% of the initial enthalpy at boiler conditions is thrown away in the condenser. Air must be removed from the condenser because: 1) it dissolves in water; 2) it destroys the vacuum; 3) poor conductor of heat and forms a thin film on pipes; 4) increases under cooling due to the following The stm quantity reduces and hence it is responsible for less of the total pressure. Hence it is at a lower pressure ,has lower saturation temperature and so is undercooled with respect to the actual pressure within the condenser ( that is to say the condensate should be at a higher temperature equal to the saturation temperature at the pressure measured in the condenser. Condensate falling through the lower cooler regions containing the high air content is further cooled and re absorbs gases. Condenser must have large surface area available for cooling . Hence large number of small diameter tubes used. Cross flow is adopted for ease of manufacture, this allied to the change of state gives a cooling efficiency approaching that of counterflow. Maximum sea water flow rate should be maintained so as to: 1) maintain a sufficient steam/ coolant tempo difference across the material along the tube length; 2) prevent silting. Circulating system should offer no undue resistance to flow and supply water equally to all tubes. The tube batches should be so arranged so as to provide no resistance to the flow of steam. There is normally a narrowing inlet space within or surrounding the bank so as the passage area remains constant as the steam condensers. Allowance in the design should be made for some expanding arrangement.