摘要
为了揭示LNG空温式气化器管内流动沸腾特征,对沸腾过程中气泡行为和两相流型的分布和转换进行了研究。研究对象为竖直铝合金翅片管,并将其等效简化为竖直光管,其高度为5 m,管内直径为0.02 m,管外直径为0.026 m。管内LNG的入口流速为0.05~0.2 m/s,入口温度为111~126 K,管外表面传热系数变化范围为100~300 W/(m^2·K),环境温度为300 K,环境压力为101.325 kPa。采用ICEM 19.0软件建立竖直光管的二维模型并划分四边形结构化网格,利用Fluent 19.0软件对管内液化天然气或天然气计算域和管壁固体计算域进行传热模拟,研究不同LNG入口流速、LNG入口温度以及管外表面传热系数等条件对沸腾过程中气泡行为和两相流型分布和转换的影响。采用流体体积法对气液两相界面追踪捕捉,利用用户自定义的方式将表征沸腾过程的S.Hardt模型引入计算流程中。研究结果表明:气泡的聚合及沿热壁面的滑移是在表面张力、浮力以及气液之间剪切应力作用下的重要运动形式。LNG入口温度增加可以减小单液相流在两相流中的比例,同时增大搅拌流和雾状流区域;LNG入口流速增大时,两相流中泡状流和弹状流区域快速减少,搅拌流区域小幅增加;管外表面传热系数增大,可显著提高搅拌流的占比。与增大LNG入口温度、LNG入口流速相比,通过改善管外的表面传热强度更能够提高空温式气化器的换热效率。
In order to reveal the characteristics of flow boiling in the tube of LNG ambient air vaporizer,the bubble behavior and the two-phase flow pattern conversion was studied.The object of study is a vertical aluminum alloy finned tube,which is equivalently simplified as a vertical empty tube with a height of 5 m,an inner diameter of 0.02 m,and an outer diameter of 0.026 m.The LNG inlet flow rate in the tube is 0.05 to 0.2 m/s,the inlet temperature is 111 K to 126 K,the heat transfer coefficient of the outside surface of the tube varies from 100 to 300 W(m^2·K),the ambient temperature is 300 K,and the ambient pressure is 101.325 kPa.The ICEM 19.0 was used to establish a two-dimensional model of the vertical empty tube and the quadrilateral structured grid was divided.The Fluent 19.0 software was used to simulate the heat transfer in the computational domain of liquefied natural gas or natural gas in the tube and the computational domain of the tube wall solid.The effects of different LNG inlet velocity,inlet temperature and heat transfer coefficient of the outside surface of the tube on the bubble behavior and two-phase flow pattern distribution and conversion during boiling were studied.Fluid volume method was used to track and capture the gas-liquid two-phase interface,and the S.Hardt model characterizing boiling process was introduced into the calculation process by user-defined method.The research results show that bubble aggregation and sliding along the hot wall surface are important movement forms under the action of surface tension,buoyancy,and shear stress between gas and liquid.The increasing temperature of the LNG inlet can reduce the ratio of single liquid phase flow in two-phase flow and increase the churn flow and fog flow region;When the LNG inlet flow rate increases,the bubble and slug flow areas decrease rapidly,and the churn flow area increases slightly.The increase of heat transfer coefficient on the outside surface of the tube can significantly increase the proportion of the churn flow.Compared with increasing LNG inlet temperature and inlet flow rate,the heat transfer efficiency of the ambient air vaporizers can be improved by improving the surface heat transfer intensity outside the tube.
作者
徐少杰
高文学
严荣松
王艳
杨林
张欢
XU Shaojie;GAO Wenxue;YAN Rongsong;WANG Yan;YANG Lin;ZHANG Huan
出处
《煤气与热力》
2020年第11期I0012-I0019,I0044,I0045,共10页
Gas & Heat
基金
国家重点研发计划课题“城市燃气独立供应场站关键设施性能检测与评价技术研究”(2018YFF0215004)。
关键词
液化天然气
空温式气化器
流动沸腾
两相流型
气泡行为
表面传热系数
LNG
ambient air vaporizer
flow boiling
two-phase flow pattern
bubble behavior
surface heat transfer coefficient
