超临界压力煤油传热不稳定实验研究

在压力2.5~4 MPa, 质量流量0.7~1.7g/s, 入口温度20~250 ℃的实验条件下, 对煤油在内径1 mm, 长度300 mm竖直上升圆管中的流动及传热不稳定现象进行了实验研究.结果表明, 当热流密度增大到一定程度后, 传热不稳定开始发生.不稳定发生的起始热流密度随压力和流量的增加而增大, 随入口油温的升高而减小, 且当入口油温升高到一定程度后无不稳定现象发生.不稳定发生的初始时刻, 出口油温迅速增加, 管道壁温明显下降, 传热系数增大; 实验段局部流速增大, 进而在管道内部形成压力脉动并产生声音.不稳定结束后, 出口油温几乎保持不变, 壁温会缓慢增加, 直至下一次不稳定发生. 

Experimental Investigation on Heat Transfer Instability of Kerosene at Supercritical Pressure

The flow and heat transfer instabilities of kerosene flowing in a vertical upward circular tube were experimentally investigated. The tube is 1mm in diameter and 300 mm in length. Pressure ranges from 2.5~4MPa, mass flow rate ranges from 0.7~1.7g/s and inlet temperature ranges from 300~520K. Results indicate that heat transfer instability appears when the applied heating power exceeds a threshold value. It is found that the instability threshold power increases with the increasing of pressure and mass flow rate while it decreases with the increasing of inlet temperature. Heat transfer instability will not happen when inlet temperature reaches a certain value. At the initial state of the instability, the outlet temperature rises rapidly while the temperature of the section wall drops rapidly. Heat transfer coefficient increases during the instability. Increasing of the local flow velocity leads to the pressure pulsation and causes sounds. After the instability, the outlet temperature keeps almost constant while the wall temperature keeps rising until the next instability happens.