超临界压力下竖直圆管内正癸烷对流换热不稳定性实验

Experiment on Flow and Convective Heat Transfer Instability of N-Decane in a Vertical Tube at Supercritical Pressures

关键词:  超临界压力流体  碳氢燃料  对流换热  不稳定性  超燃冲压发动机

Key words:  Supercritical pressure fluid  Hydrocarbon fuel  Convective heat transfer  Instability  Scramjet

摘要:

以超临界压力正癸烷为工质，在内径2mm的竖直圆管内进行了不同工况条件下的流动与换热不稳定性实验研究。实验发现两种原理的不稳定性现象。转捩型是由于流动状态由层流向湍流转变引起，多为随机的小幅震荡，约在Re=5000左右出现；物性型由准临界温度附近剧烈变化物性所致，具有较大振幅和固定周期，约8～15s。增强系统稳定性的方法主要包括提高进口流体温度、升高压力或者采用向下流动方式。实验还发现在振荡区间内存在稳定区间现象。

Abstract:

This work presents the experimental studies on the flow and heat transfer instabilities of supercritical pressure n-decane in a vertical tube with an inner diameter of 2mm at various conditions. Two types of instabilities were observed，including the transition pattern and the thermal property pattern. The transition pattern was caused by the transition of flow from laminar flow to turbulent flow with random and relatively small amplitudes when Re was about 5000，while the thermal property pattern was caused by the variation of thermal properties near pseudo critical temperature with large amplitudes and constant periods of 8 to 15 seconds. Raising the inlet bulk fluid temperature，raising the pressure or using downward direction may make the system more stable. The stable sections were also observed in the experiments.