Optimum Design of a Horizontal Condenser A.M. Abdallah and Aly Karameldin Atomic Energy Authority-Nuclear Research Center Reactors Department P.O. 13759 Cairo, Egypt Abstract In this study a rigorous constrained thermal hydraulic model has been derived for calculating the economic design of a vapor surface condenser used in power plants and seawater desalination plants which use distillation methods. According to the economical data obtained in the present study, it has been shown that the total condenser cost components: steam generation, brine water pumping, and fixed charge contribution nearly as 83%, 6%, and 11% respectively according to the fuel cost. However the calculated cost is closed to the known ordinary values when the calculations are based on the minimum variable condenser cost  (About 55% for steam cost, 10% for pumping cost, and 35% for the fixed cost). As for the effect of some technical parameters, it has been shown that: (i) total condenser cost is nearly independent of the tube diameter (ii) total cost depends weakly on the brine velocity, and more strongly on the brine flow rate. The plant fouling condition is of prime importance and should not exceed the design values; otherwise it can lead to increase of 126 % of the total condenser cost if the fouling factor increased to 0.05 m C/W. From heat transfer point of view, the effect of the different tube material used in desalination, has a slack effect on the total condenser cost (0.055 – 0.02%). In short, the general model derived in this study is capable to deal with any horizontal condenser.