基于CFD模拟的LNG空温式气化器传热特性

Heat Transfer Characteristics of Air Temperature Vaporizer Based on CFD Simulation

以LNG空温式气化器单支铝合金翅片管为研究对象,该翅片管长度为10 m,管内直径为0.02 m,管外直径为0.026 m,翅片高度为0.047 m,翅片厚度为0.002 m。管内LNG入口流速为0.01~0.10 m/s,LNG入口质量干度为0~0.8,管外空气温度为273~303 K,环境压力为101.325 kPa。采用ICEM 19.0软件建立翅片管的三维模型并划分六面体结构化网格,利用Fluent 19.0软件对管内LNG/天然气计算域、管外空气计算域以及翅片管固体计算域进行流固耦合传热模拟,研究不同LNG入口流速、LNG入口质量干度以及管外空气温度等条件对空温式气化器不同管长处的传热系数的影响。结果表明:所采用的流固耦合传热方法可以完成管内LNG流动沸腾、管外空气自然对流以及翅片管内外壁之间导热的整体传热模拟,通过分析翅片管内外的温度场和速度场的分布特性,证明该方法的合理性和可靠性。空温式气化器的传热系数沿翅片管管长方向总体呈现先增加后减小的变化趋势,传热系数曲线的变化情况主要受管内流体状态的影响,与气液两相流型的变化存在一定的关系。LNG入口流速、LNG入口质量干度以及环境空气温度对于翅片管传热系数都有显著的影响。LNG入口流速越大,则传热系数越大,但是增大LNG入口流速不能无限提高翅片管传热系数。翅片管传热系数总体上随LNG入口质量干度的增大而减小。当入口质量干度大于0.6时,传热系数沿管长方向为单调递减变化趋势。翅片管的传热系数总体上与环境空气温度呈正相关,随着环境空气温度的下降,传热系数减小的幅度越来越大。

Taking the single aluminum alloy finned tube of LNG air temperature vaporizer as the research object,the length of the finned tube is 10 m,the inner diameter of the tube is 0.02 m,the outer diameter of the tube is 0.026 m,the fin height is 0.047 m,and the finned thickness is 0.002 m.The LNG inlet velocity in the tube is 0.01 to 0.1 m/s,the inlet mass dryness is 0 to 0.8,the air temperature outside the tube is 273 to 303 K,and the ambient pressure is 101.325 kPa.The ICEM 19.0 software is used to establish a three-dimensional model of the finned tube and the hexahedral structured grid is divided.The Fluent 19.0 software is used to simulate the fluid-solid coupled heat transfer in the calculation domain of LNG/natural gas in the tube,the air calculation domain outside the tube and the solid calculation domain of finned tube.The effects of different LNG inlet velocity,LNG inlet mass dryness,and air temperature outside the tube on the heat transfer coefficients at different tube lengths of air temperature vaporizer were studied.The results show that the fluid-solid coupled heat transfer method can achieve the overall heat transfer simulation of LNG flow boiling in the tube,natural convection of air outside the tube,and heat conduction between the inner and outer walls of the finned tube.The rationality and reliability of the method are proved by analyzing the distribution characteristics of temperature field and velocity field inside and outside the finned tube.The heat transfer coefficient of air temperature vaporizer increases first and then decreases along the length of tube generally.The change of heat transfer coefficient curve is mainly affected by the state of fluid in the tube,and has a certain relationship with the change of gas-liquid two-phase flow pattern.The LNG inlet velocity,LNG inlet mass dryness and ambient air temperature all have significant impact on the heat transfer coefficients of finned tube.The higher the LNG inlet velocity is,the greater the heat transfer coefficient is.However,increasing the LNG inlet velocity cannot infinitely improve the heat transfer coefficient of finned tube.The heat transfer coefficient of finned tube generally decreases as the LNG inlet mass dryness increases.When the inlet mass dryness is greater than 0.6,the heat transfer coefficient has a monotonous decreasing trend along the tube length.The heat transfer coefficient of finned tube is generally positively correlated with the ambient air temperature,as the ambient air temperature decreases,the heat transfer coefficient decreases more and more.