【作者】 王坤；

【导师】 贾林祥；

【作者基本信息】 哈尔滨工业大学 ， 制冷及低温工程， 2007， 硕士

【摘要】 在天然气液化装置设计过程中,对换热设备的选用大都依据流程静态计算得出的参数,而未对其动态性能及变工况的适应能力进行定量分析和评定。鉴于设备的实际运行工况并不能完全遵循设计工况,为更好地控制设备的运行,需要可靠的数学模型来预测其动态特性。本文以采用混合制冷剂液化流程的小型天然气液化装置中板翅式换热器为研究对象,对其建立动态数学模型并进行仿真研究,以达到预先判断设备的运行和控制性能的目的。首先,建立了天然气及混合制冷剂热物性计算模型。通过对多组分混合物的相平衡计算,确定不同压力、温度、成分下天然气及混合制冷剂的组成含量及相态。在此基础上,计算天然气及混合制冷剂的热力学参数及迁移性质参数,为动态建模工作提供物性计算支持,重点解决了工质在低温环境下热物性变化剧烈给模型计算精度带来的问题。随后,基于气液两相流理论及气液相平衡理论,建立了多股流、多组分、有相变情况下板翅式换热器的动态数学模型。利用质量方程、动量方程、能量方程、相平衡方程描述换热器内流体传热及流动过程。对时间项采用隐式格式、空间项采用二阶迎风格式离散上述控制方程并求解。根据模块化建模思想,采用C语言S函数将模型建立在Simulink仿真环境中。利用MATLAB软件提供的GUI功能,开发了板翅式换热器动态特性模拟软件。最后,利用上述模拟软件研究板翅式换热器的静、动态特性。通过对单台换热器降温过程的模拟,得出了在已知入口条件及换热器初始条件下,各股流体出口温度的变化及稳定后流体的压力温度分布、隔板的温度分布。通过给定制冷剂流量的阶跃扰动,获得了各股流体出口温度的响应。将上述稳定后结果与板翅式换热器模拟软件计算结果进行比较,两者一致。对两台换热器降温过程进行模拟,得出了各换热器内各股流体出口温度变化,并完成了多台板翅式换热器模型在系统级动态仿真时的软件测试。更多还原

【Abstract】 During the designing process of the natural gas liquefaction plant, parametersdescribed the static performance of the device always be used to select the heat ex-changing equipment, but the dynamic performance and the applicability to the varia-tional working conditions were not quantitatively analyzed. In view of the operationcondition can not always follow the design one, in order to control the operation bet-ter, a reliable mathematical model was needed to predict the dynamic performance ofthe device. A model was established in this paper, and it described the dynamic char-acteristics of the plate-fin heat exchanger which was used in the Mixed-RefrigerantCycle (MRC) Liquefied Natural Gas (LNG) plant, and the study was instructive toimprove the controlling performance of the device.First of all, a model was established to predict thermal properties of the natu-ral gas and mixed refrigerant, it can determine phase and percentages of the multi-component mixtures by calculating the phase equilibrium, then the thermodynamicand transport properties were acquired, and they provided support for the calculationof thermal properties in dynamic model. In other words, the property model mainlyfocused on the drastic changes of the mixture’s thermal properties in low temperature,which might reduce the accuracy of the dynamic model.Secondly, a mathematical model was established for a multi-?ow, phase-changeplate-fin heat exchanger, which was based on the theory of gas-liquid two-phase ?owand phase equilibrium. Heat transfer and ?ow characteristics in the heat exchangerwere described according to the mass equation, momentum equation, energy equa-tion and phase equilibrium equation. The governing equations were dispersed by im-plicit scheme in time dimension and second-order upwind scheme in space dimension.Based on the modularized modeling method, the model was established in Simulinkenvironment using C MEX S-function. Subsequently, using the Graphical user inter-face (GUI) which was provided by MATLAB, software was developed to simulate thedynamic performance of the plate-fin heat exchanger.Finally, static and dynamic performance of the plate-fin heat exchanger werestudied using the developed software. The cooling process of a plate-fin heat ex- changer was simulated in the case of the inlet and initial parameters were known. Atthe same time, the pressure profile and temperature profile of the ?uid, the tempera-ture profile of the parting sheet were acquired in steady state. Later, a step disturbanceof the refrigerant’s ?ow rate was given, the responses of outlet temperature was re-ceived. Results in steady state fitted the professional software well and it made themodel credible. At last, the cooling process of two plate-fin exchangers was simu-lated, and the system testing of multi-plate-fin heat exchangers in the dynamic modelwas successful completed.更多还原