| Heat exchangers are widely applied in high energy consumption industries and are closely related to the energy saving, conversion, recovery as well as the exploitation of new energy sources. To improve the performance of heat exchanger and reduce the irreversible loses occurring in the heat exchange process by optimizing the heat exchanger design is one of important ways to increase the energy efficiency and is of great importance under the current situation that the energy shortage and environment deterioration becomes more and more severe. In the present work, the single-or multi-objective optimization of shell-and-tube heat exchanger design is investigated.The key problem for heat exchanger optimization design is to choose an appropriate objective function. In our work, the total dimensionless entransy dissipation (called as entransy dissipation number) is taken as the objective function, some geometric parameters of the heat exchanger and the outlet temperature of cold fluid are set to the design variables, the admissible pressure drop and requirements of heat exchanger design standard are selected as the constraint conditions, thus an optimization design problem for heat exchanger is formulated. The genetic algorithm is employed to solve the related optimization problems. The comparison between the initial and optimized design plans shows that the optimization process improves the exchanger effectiveness and in the same time reduces the pumping power significantly. In comparison with other optimization approaches, such as the traditional cost-minimization method, the single-objective heat exchanger optimization design method with the entransy dissipation number as the objective function demonstrates obvious advantages on improving the heat exchanger performance and reducing the irreversible loses.However, there exists a drawback for the single-objective heat exchanger optimization design method with the total entransy dissipation number as the objective function, namely, the entransy dissipation induced by heat conduction under finite temperature difference is much larger than that caused by fluid friction in the heat exchange process with fluid as the heat transfer medium. Therefore, the single-objective heat exchanger optimization design method usually neglects the contribution of fluid friction to the entransy dissipation. In order to solve this problem, the entransy dissipation numbers related to the heat conduction and fluid frictions are set to two separate objective functions, a multi-objective optimization of heat exchanger design is proposed with the help of the genetic algorithm. By the analysis of the heat exchanger performance and the comparison with the results of single-objective optimization design, it is found that the multi-objective optimization of heat exchanger design is more advantageous. |
