Research On Leading Flow Structure Design And Heat Transfer Enhancement Technique Of Plate Fin Heat Exchanger In Large Scale Air Separation Equipment

With the development of air separation equipment to ultra large scale and low energy cost, more demands on effective usage of plate-fin heat exchanger are proposed. Achieving the heat demands effectively and swiftly, and finally, improving the production efficiency has been the important issue in the field of ultra large air separation.In this paper, by analyzing the fluid flow and heat transfer with traditional heat exchanger and traditional fins, aiming at the structure design and performance improvement of the plate-fin heat exchanger in ultra large scale air separation equipment, the leading flow and performance improvement with long channel, structure design of bionic fins, extending heat transfer surface with multi-channels and leading flow structure optimization are analyzed. Different channels and new kind of bionic fins and validate fluid flow and enhanced heat transfer in the plate-fin heat exchanger adopting numerical simulation combing with experimental method and achieve better results.Organizational structure of this thesis is as follows:In chapter 1, the components of ultra large air separation equipment and the heat transfer principle and characteristics of the plate-fin heat exchanger was introduced. The development of large air separation equipment was analyzed, besides, the fluid flow, leading flow and enhanced heat transfer principle of the plate-fin heat exchanger was brought out. The research on fluid flow and enhanced heat transfer was summarized of the exchanger and the insufficient of the present study was pointed out. Finally, the main contents of this paper and organizational structure were given.In chapter 2, the long channel design in order to improve the performance of leading flow and enhanced heat transfer in the plate-fin heat exchanger was investigated. A new kind of channel, the lateral M-style channel, was proposed by analyzing the influence of fluid flow and heat transfer in the exchanger caused by the channel structure. The new channel can change fluid flow, extend the distance of fluid flow, increase heat exchange area and finally enhance heat transfer. Comparing the new channel with the traditional channel in the exchanger and analyzing fluid flow, pressure distribution, temperature and turbulence, the heat transfer enhancement of the new channel was validated.In chapter 3, the turbulent flow in ocean by the marine organism was studied and the influence of fluid flow caused by the marine organism was analyzed. Combing with the leading flow and turbulent flow characteristics of the marine organism, a new kind of bionic fin was proposed. The model of bionic fin in the plate-fin heat exchanger was created and the calculation of fluid flow and heat transfer under the new kind of fins was deduced, meanwhile, the performance evaluation criterion of the new kind of bionic fin was given. Comparing with the traditional fin, it can be found that the new bionic fin can improve the heat transfer performance effectively.In chapter 4, the technique of leading flow and heat transfer enhancement by extending heat transfer surface with multi-channel was investigated. Aiming at fluid flow and heat transfer caused by different fin arrangements in inlet of the plate-fin heat exchanger, the fluid flow and heat transfer enhancement were deduced in inlet of the plate-fin heat exchanger. Analyzing heat transfer mechanism with different extending surface, the solution to fluid velocity, dynamic pressure drop and heat transfer surface caused by different fin arrangements was found. The grid check on mass balance and energy balance by different grid number was also given in this chapter and the criteria of heat transfer performance under different fin arrangements were also given.In chapter 5, the technique of multi-objective optimization and fluid distributed uniformly in inlet of the plate-fin heat exchanger were investigated. Due to the non-uniform distribution of the fluid flow and temperature on different layer of the exchanger along longitudinal direction, the orthogonal experiment was adopted to create non-linear objective function of the leading flow structure and the parameters of hole on the structure were optimized by the method of BP neural network combine with genetic algorithm. Finally, the optimized structure satisfying the requirement was obtained.In chapter 6, the technique of fluid flow and heat transfer enhancement in plate-fin heat exchanger proposed in this paper were applied to the ultra-large air separation equipment according to the engineering problem. The technique of fluid flow and heat transfer enhancement was compared and validated in this paper.In chapter 7, the contents of this paper and conclusions were summarized and the future work on plate-fin heat exchanger was prospected.