An extended node unstructured model is established, and an additional cold and hot stream is set up to match with the conventional hot and cold stream to determine the generation of cold and hot internal utilities, so as to realize independent matching of utilities at any position on the cold and hot flow unit and improve the degree of freedom of the model. A forced evolution random walk algorithm was introduced to optimize three practical engineering examples 9SP, 10SP and 15SP, which saved 5 600＄·a^-1, 848＄·a^-1 and 4 455＄·a^-1, respectively, compared with the optimal literature. It shows that application of the extended model obtains more economical heat exchange network designs, and has a stronger universality as well.

As RWCE algorithm is used to optimize heat exchanger networks, the existence of fixed investment cost makes it difficult to produce and retain heat exchanger units with small loads. It makes structures that have not yet fully evolved be eliminated too early. We established a relaxation method of fixed investment cost. The fixed investment cost and the heat exchange of heat exchange unit are processed according to their variation. With heat exchange of heat exchange unit, relaxation strength in optimization process is adjusted in real time to guide and promote the smooth generation and evolution of small load heat exchange unit, so as to enhance structural evolution ability of heat exchange network. The relaxation strategy is applied to 9SP and 15SP examples to verify that the relaxation strategy promotes structural evolution effectively and improves optimization quality. The optimal results (2 903 528 ＄ ·a^-1, 5 115 061 ＄ ·a^-1) are better than those in literatures.

In the process of optimizing heat exchange network of unstructured model with shunt nodes, heat exchange units could break the initial uniform distribution state and concentrate to the upstream region of the stream, which makes it impossible to generate new heat exchange units in the entrance region of cold and hot streams, resulting in the decrease of structural variation ability.The cause of this phenomenon and its influence on evolution are explored.And a dynamic regional taboo matching strategy is proposed.Free matching is allowed as the upstream region is empty.As the upstream node is not empty, the upstream region is cleared, which means that the generated nodes are equivalently transferred to the downstream region, so as to guarantee the matching vitality of the heat exchange unit in the upstream region, enhance competitiveness of newly generated heat exchange units in the process of structural evolution, and promote structural evolution of the heat exchange network.In the application of 15sp and 20sp examples, it is found that the strategy improves the network structure variation ability and achieves better results than existing literatures.

An evolutionary algorithm of multi-directional compulsive search strategy for dominant individuals is proposed to evaluate the health of global search of current population by examining individual difference index.When the optimization results stagnate for a long time, the health index becomes worse and the multi-direction forced search strategy of the dominant individual is started to expand the search direction of the dominant individual near the local optimal solution region, so as to ensure the global search ability of the algorithm.The strategy was applied to 15SP and 20SP calculation examples and results were compared with optimal results in the literature.They are decreased by 1.09% and 0.83%, respectively.It in dicates that the dominant individual multi-directional compulsive search strategy exerts fully the evolutionary potential of the dominant individual and improves the optimization efficiency of the algorithm.

In optimizing heat exchanger networks by random walk algorithm with compulsive evolution (RWCE), individual structures become similar, which leads to a decline in population diversity and algorithmic global search capability. It becames difficult to optimize the structure of heat exchanger networks further. To explore similarity of individual structures, two evaluation indexes were established to measure similarity level of individual structures.It was found that the number of similar heat units in individual structure increases gradually and the difference of heat load between similar heat units decreases during the optimization process which resulting the evolution of individual structures in the same direction. Therefore, taking the improvement of population diversity as guiding direction, a repulsive-evolution strategy for heat units was proposed. It changes the direction of structure evolution and reduces the scale of similar structure through increasing the heat load gap of similar heat exchange units and promoting differential evolution of similar heat exchange units.Finally, 20SP and 15SP were used to verify effectiveness of the strategy. Total annual cost of the structure saved 12 105 ＄·a^-1 and 52 535 ＄·a^-1, respectively, compared with the optimal result in literature, which indicating that the strategy enhances the algorithmic global search capability effectively.