PCHE细小多通道内天然气沸腾两相流分配特性数值分析

Distribution Characteristics Analysis on Two-phase Flow of Natural Gas in PCHE Fine Multi-channels

印刷电路板式换热器具有体积小、结构紧凑、换热效率高等特点,在天然气生产工艺中应用前景极为广阔,在PCHE换热过程中,冷、热侧通道内工质往往发生沸腾相变,各子通道间普遍存在汽液两相流分配不均问题,严重降低换热效率。对此,以换热器封头和12个细小通道为建模对象,采用天然气汽液两相混合物为工质,通过Aspen Plus软件获得其物性数据,基于VOF模型追踪相界面运动位置,构建适用于预测分析PCHE内天然气两相流分配特性的三维非稳态数值模型,并开展了相关数值研究。结果表明,相比于单相液态天然气,当换热器入口混入汽相工质变为汽液两相混合物时,各子通道间工质的质量流量相对标准偏差由0.0004增加到0.036,两者相差近100倍,分配不均现象明显加剧。导致该现象的主要原因在于来流汽相工质明显倾向于进入距离换热器入口最近的若干通道,使得这些通道的汽相流量显高于其他通道,各通道汽相工质流量分配特性整体上呈现明显的“峰值分布”,但是,随着换热器入口汽相工质流速的不断增大,各通道间汽相工质的流量分配不均现象逐渐缓和,而液相工质的流量分配特性发生明显恶化。

Printed circuit plate heat exchanger has the characteristics of small size,compact structure,and high heat transfer efficiency,which has an excellent prospect for application in natural gas production technology,during the heat transfer process of PCHE,the boiling phase change of the work material often occurs in the channel of the cold and hot side,and the uneven distribution of gas-liquid two-phase flow prevails among the sub-channels,which seriously reduces the heat transfer efficiency.In this paper,numerical models are developed for the prediction and analysis on the distribution characteristics on two-phase flow of natural gas in the PCHE,using the exchanger head and 12 small channels as the modeling objects and taking the natural gas-liquid two-phase mixture as the working medium,obtaining its physical properties data by Aspen Plus software,and tracking the phase interface motion based on the VOF model.The results show that when the heat exchanger inlet is changed to a gas-liquid two-phase mixture compared to a single-phase liquid natural gas,the relative standard deviation of the mass flow rate of the work mass between the sub-channels increased from 0.0004 to 0.036,which is nearly a 100 times difference,and the uneven distribution phenomenon increased significantly.The main reason for this phenomenon is that the incoming gas phase mass flow tends to enter the nearest channels of the heat exchanger inlet,which makes the gas phase flow in these channels significantly higher than other channels,and the overall gas phase mass flow distribution characteristics of the channels show a clear“peak distribution”,however,with the increasing flow rate of the gas-phase at the inlet of the heat exchanger,the distribution unevenness of the gas-phase mass flow among the channels is gradually moderated,while the liquid-phase mass flow distribution characteristics deteriorate significantly.