Abstract With the rapid deployment of large oil tank, a quick and efficient fire extinguishing foam generator becomes particularly critical to relieve the safety concerns. In this work, a cryogenic fluid/bulk fluid mixing apparatus, composed of a horizontal channel and a conical spoiler in it, is developed to generate stable and homogeneous foam flow. The flow and temperature characteristics of the mixing flow field, including flow pattern, contour of velocity and phase fraction, temperature and pressure profiles, are studied by a visualization experiment and numerical simulation. From the results, a typical flow pattern of liquid nitrogen jetting into bulk fluid (water or foam liquid) in the mixing channel is proposed. The rapid phase transition (RPT) of nitrogen liquid in bulk fluid is found to effectively enhance the mass and heat transfer between phases. Besides, the introduction of conical spoiler facilitates the flow mixing effectively. The nitrogen liquid jet is broken into small liquid blocks and vaporizes rapidly in the conical spoiler zone. A backflow zone appears at the downstream of the spoiler and further promotes the homogeneous foam flow. Moreover, compared to the liquid nitrogen/water mixing flow, the direct mixing of liquid nitrogen/foam liquid could accomplish higher foaming ability, and more homogenous and stable foam flow due to its lower surface tension, higher dispersivity, faster interphase heat and mass transfer. The study of characteristics of the mixing flow in this work could provide an important guidance for the design and optimization of foam generators in the compressed air foam systems (CAFSs).

中文翻译：

---

卧式泡沫发生器氮气泡沫流动特性研究

摘要 随着大型油罐的快速部署，一种快速高效的灭火泡沫发生器对于缓解安全问题变得尤为重要。在这项工作中，开发了一种由水平通道和锥形扰流板组成的低温流体/散装流体混合装置，以产生稳定均匀的泡沫流。通过可视化实验和数值模拟研究了混合流场的流动和温度特性，包括流型、速度和相分数的轮廓、温度和压力分布。根据结果​​，提出了液氮喷射到混合通道中的大量流体（水或泡沫液体）的典型流动模式。发现散装流体中氮液体的快速相变 (RPT) 可有效增强相间的传质和传热。此外，锥形扰流板的引入有效地促进了流动混合。氮液射流破碎成小液块，在锥形扰流区迅速汽化。回流区出现在扰流器的下游，进一步促进了均匀的泡沫流动。此外，与液氮/水混合流相比，液氮/泡沫液的直接混合具有更低的表面张力、更高的分散性、更快的相间传热和传质，可以实现更高的发泡能力和更均匀稳定的泡沫流。 .