Study Of The Transient Characteristics Of Organic Rankine Cycle Based On Modelica

Energy is always an important issue for the development of world economic and people's life. Since the 21th-Century, energy consumption continues growing rapidly, and fossil energy still occupies large percent of the world energy consumption, resulting the increasingly serious energy crisis. At present, increasing the proportion of renewable energy utilization and energy efficiency are the main measures to ease the energy crisis. One of the most effective way is the use of low grade thermal energy, however, these energy supplies are not that stable, which makes it difficult to utilize them. In order to solve this problem, the dynamic simulation of the system using low grade heat is necessary. By researching the dynamic characteristics of the system, it is possible to keep the system in the best working conditions using appropriate control methods.This thesis begins with a brief introduction of the object-oriented programming language Modelica, meanwhile analyzing the superiority of the language, followed by simple thermal model building process which exhibits the application of Modelica language in the thermodynamic system. At last, the thesis introduces the modeling platform Dymola.For the study of the dynamic characteristics of organic Rankine cycle system, this thesis establishes a static model of the system based on the mathematical principle of the system. For the heat exchangers which need to be focused on, the static model is established by distinguished region modeling. For the expander and pump model, the experience formula method is used. After integrating the components, the static model of the system simulation results are got to determine the ideal cycle condition preparing for the dynamic simulation.Based on static model, the dynamic model of heat exchanger was established through the finite volume method. In order to ensure the robustness of the simulation models, this thesis introduces a piecewise function of the heat transfer coefficient to determine the heat transfer coefficient of different fluid states. After verifying the dynamic model, the impact of discrete degree of heat exchanger model is discussed based on the simulation results, and then though dynamic simulation, the dynamic characteristics of the heat exchanger is analyzed.Finally, this thesis sets up the simulation model of the medium, valve, expander and pump. In order to facilitate the integration of the various components of the system, the same connector model was established. After integration, the Organic Rankine cycle system simulation model is built, and based on the dynamic simulation result under different heat source condition, the transient characteristics of Organic Rankine Cycle are discussed and analyzed.