The Application Of Entransy Dissipation Theory In Multi-Objective Optimization Design Of Plate-Fin Heat Exchanger

Plate-fin exchangers are drawing more and more attentions due to its light and compact structures as well as its high heat transfer efficiency. As the awareness and demands of saving energy arise, it is of great value to improve the plate-fin exchanger performance through reducing the irreversible dissipation with optimizing its shape structure. Based on the entransy dissipation theory and the genetic algorithm, a single-objective and multi-objective optimization design method for plate-fin exchangers is formulated.In this thesis, with the entransy dissipation numbers as the objective functions and the admissible pressure drop as well as the requirements of heat exchanger design as constraint conditions, a computer code for optimization design of plate-fin exchangers with offset-strip fin is programmed with the help of the genetic algorithm provided by Matlab genetic algorithm toolbox. The single-objective and NSGA-II multi-objective genetic algorithms are employed to optimize the geometric structures of plate-fin heat exchangers. The comparison of the results obtained by the two approaches shows that the multi-objective optimization design can significantly improve the heat exchanger performance.The heat exchanger optimization design problem consists of three parts:the design variables, constraint conditions and objective functions. We take the geometric structure parameters which have relatively great impact on the plate-fin exchanger performance as design variables. The admissible pressure drop and requirements of plate-fin heat exchanger design are selected as the constraint conditions. Firstly with the dimensionless entransy dissipation and entropy generation respectively taken as the objective function, a single-objective optimization model for plate-fin heat exchangers is formulated. Then the genetic algorithm is applied to solve the optimization problem. By analyzing the single-objective optimization design results we find that when the heat transfer load is fixed, two approaches with different objective function lead to almost the same result. Further study shows that 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. In order to fully account for the impact of flow friction on heat exchanger performance the entransy dissipation numbers related to the heat conduction and fluid friction are taken as two separate objective functions, the same design variables and constraint conditions as the single-objective optimization design are adopted, thus a multi-objective optimization design method for plate-fin heat exchangers is established by NSGA-II genetic algorithm. The comparison with the result obtained by the single-objective optimization design shows that the multi-objective optimization of heat exchanger design is more advantageous. It provides a new idea for optimizing the heat transfer exchanger design.In order for users to conveniently use the plate-fin heat exchanger optimization design program, a friendly graphical user interface is designed in the last part of my thesis. Thus users only need to input the known data of the plate-fin heat exchanger and select the proper algorithm as well as the objective function, the program will provide them the visual optimization design result. Therefore even the less non-professional users can use this program easily and conveniently.