A study on the performance of a swirling–straight composite nozzle

The nozzle is the key component of water mist fire extinguishing system. As a response to the problems of small injection angle associated with straight jet nozzles and the weak axial momentum of swirl nozzles, a swirling–straight composite nozzle is designed in this work. The comparison with a straight jet nozzle and a pressure swirl nozzle shows that the swirling–straight composite nozzle has a larger axial momentum and better injection angle. Under the same pressure, the volume flow of the swirling–straight composite nozzle is more than 27% of the pressure swirl nozzle, and the injection angle was more than 65% of straight jet nozzle. The numerical model of the swirling–straight composite nozzle is established. Meantime, the internal flow field characteristics and the influence of the straight jet aperture on the performance are studied. The results demonstrate that the straight jet fluid and swirling fluid can be mixed well in the nozzle, and a larger axial momentum and tangential momentum can be obtained. With the increase of the straight jet aperture, the swirl effect in the nozzle becomes weaker, the injection angle becomes smaller, and the axial momentum improves. When the straight jet aperture increases from 1.1 to 1.9 mm, the straight jet volume flow at the nozzle inlet increases by 127%, and the injection angle reduces by 40%.