Abstract: Based on the stage-wise superstructure model of the heat exchanger network， three improved cooling water exchange networks are proposed. The hot and cold utilities are dispensable and the cold stream only contains cooling water， which is different from the traditional heat exchanger synthesis. The three design approaches all consider the water splitting and mixing to achieve the non-isothermal mixing of water. The second and third configuration can achieve phased water mixing. The minimum total annual cost is determined by the trade-off utility cost and capital cost. Particle swarm optimization (PSO) is demonstrated to optimize the heat load and the water mass flow rate in the water network. Two cases show that the total annual cost of the three improved structures proposed is better than the previous research results and in Case 1， configuration 3 has the lowest cost， and in Case 2， configuration 1 has the best economic performance.

Key words: cooling water network; stage-wise superstructure; non-isothermal mixing; particle swarm optimization (PSO); total annual cost