Abstract:

The flow patterns of liquid inside nozzles have great effect on spray characteristics in flashing spray. A transparent nozzle was manufactured to investigate the flow characteristic inside nozzles during flashing spray and its effects on spray characteristics. The flow patterns of R134a inside the nozzle and spray outside the nozzle were recorded by a high-speed CCD camera under different injection pressure of 0.77, 0.8, 0.9 and 1.5 MPa. The relationship between the internal flow inside the nozzle and external flashing spray were analyzed. It was found that spray patterns will expand immediately around the exit of the nozzle when vaporization occurred inside the nozzle, while the further development of spray radius could be restricted in the same condition. The spray cone angle caused by internal flashing spray was smaller than that caused by external flashing spray in the same condition for the flashing spray of R134a which had high superheated degree at room temperature and atmospheric pressure. The internal flow pattern was extremely unstable under a certain scope of injection pressure, and it was helpful to form stabilized spray patterns when homogeneous bubble flow was formed inside the nozzle.

Key words: flashing spray, visualization, internal flow, spray pattern, gas-liquid flow, nucleation, phase change

摘要：

闪蒸喷雾过程中喷管内流动状态对喷雾形态及雾化效果具有重要的影响。为了观察喷管内流动状态及其对应的喷雾形态，使用高速相机对不同喷射压力条件下制冷剂R134a在石英玻璃直喷管中的流动状态及喷雾形态进行可视化研究，同时分析不同喷射压力条件下喷雾半径的动态变化情况。研究发现，喷管内的气化可以促进喷管出口处喷雾半径的迅速扩大，但同时限制了喷雾半径在喷雾过程中的进一步发展。喷管内流动状态在一定喷射压力下具有极强的不稳定性，在喷管内形成均匀的泡状流有利于形成均匀、稳定的喷雾形态。

关键词: 闪蒸喷雾, 可视化, 管内流动, 喷雾形态, 气液两相流, 成核, 相变