厚液膜──冷凝回流中的一种特殊现象

在西安交通大学建立了模拟压水堆小破口失水事故的高温高压冷凝回流实验系统．实验表明在倒U型管的冷凝回流中主要有三种流动型式：稳态回流，不稳定回流，同向流动．在不稳定回流中作者首次发现了厚液膜，而在前人研究中均认为为液柱．本文对此现象进行了解释，并进行了计算分析．

THICK FILM-A SPECIAL PHENOMENA IN PWR REFLUX CONDENSATION

Reflux condensation is one of the natural circulation during PWR SBLOCA. In Xi'an Jiaotong University, a reflux condensation simulating test system under high pressure is conducted. The facilities are suitable for the investigation of flow and heat transfer near actual PWR conditions: pressure from 2 MPa to 10MPa, about 4m high inverted U-tube, primary side condensing and second side boiling. Through tests and analysis, the flow characteristics are investigated comprehensively and some unique phenomena about the flow are found. The flow is separated into two parts by reflux flow limit (CCFL). One, steady flow before CCFL; the other, three flow regimes after CCFL: stagnation flow, cycling wave flow,and cocurrent flow. One of the unique phenomena distinguished from previous investigations is a thick film instead of a liquid column in stagnation flow and cycling wave flow. Another is that the liquid column may occur in some U-tubes during cocurrent flow. Both of them may lower the core water level greatly to endanger nuclear safety. An explanation of the formation of the thick film is given theoretically, and the formula used to calculate the thick film is get.