A Novel Optimization Approach Of Passage Arrangement For Multi-stream Plate-fin Heat Exchanger Using Genetic Algorithm

With energy shortage and the requirements of the environment at present, a novel heat exchanger with energy saving, compact structure, light weight and high thermal efficiency is imminentlyneeded. Multi-stream plate-fin heat exchanger (MSPFHE), which could meet the requirements above all, is developed and widely used in cryogenics, micro-turbines, automobiles, chemical process plants, naval and aeronautical applications to exchange heat energy among more than two fluids with different supply temperatures. It has achieved significant economic benefits in utilizing heat energy, recycling waste heat, saving the raw material, reducing the cost and other specialarea. The passage arrangement, which directly influences the thermal efficiency and compact structure of the heat exchanger is the key issue of the MSPFHE design. However, it is difficult to find the optimal passage arrangement out from the huge passage arrangements using the experience method. While the number of the passage arrangement increases exponentially with the increase of fluid number in the MSPFHE. Therefore, genetic algorithm (GA) is adopted to solve the Nonlinear programming model in this work. It is an adaptive heuristic search algorithm based on the natural selection and genetic evolution concept.The main works done in this thesis are as followed:First, established the linear programming model which took mean-square deviation of passage accumulative total heat load as the objective function, and proposed GA for flexible optimization design of the passage arrangement.The uncertain factors of MSPFHE such as actual operation parameters and external condition are considered in this thesis, the flexible design is inported. Optimal passage arrangements of some main working points are obtained using GA, then these optimal passage arrangements are integrated into one passage arrangement, the final channel arrangement is achieved after fine-tuning operator is used to passage arrangement. The final passage arrangement can satisfy the MSPFHE flexible design requirements.Second, established the nonlinear programming model, which is based on heat transfer area as the objective function, proposed the use of GA to optimize the channel arranged.The differences among passage arrangements are directly relevant to the passage’s qualitative size. When the passage’s qualitative size increases, the overall heat transfer coefficient of MSPFHE will decrease and consequently the area of MSPFHE will increase, so the variable quantity of the heat-transfer equation is qualitative size. MSPFHE is used to exchange heat energy among multiple fluids. Since the temperature of inlet and outlet might be different for all the fluid, the temperature difference calculated by logarithm average method is not suitable. T-H diagram is used to simplify the calculation process.Third, proposed the solving GA which can meet the optimal design of passage arrangement. Encoding is the key in the optimization process of GA, if we use the general encoding method, the fixed number of every fluid will change while the crossover and mutation operators are applied on the passage arrangement. A novel encoding methodis developed to solve this problem, and it can make sure that the fixed passage number of every fluid maintenance while GA operation is undergoing.