Abstract:

To investigate the dynamic impacts of non-circular nozzle geometry and flow rate on gas dispersion, and to reveal the coupling effects of nozzle geometry and release flow rate on the axial concentration decay of horizontal jets, helium was used as a surrogate for hydrogen, and horizontal jet tests were conducted using triangular and rectangular nozzles with different hydraulic diameters and flow rates. A high-precision mass flow controller was employed to maintain constant release flow rates, and 18 high-frequency thermal conductivity gas sensors arranged along the jet centerline recorded concentration data in real time. The results show that the influence of nozzle shape exhibits a strong dependence on Re. When Re≥3 000, the sharp corners of the triangular nozzle induce vortex structures that cause significantly faster concentration decay than the rectangular nozzle, under low Re conditions, the geometric effect becomes less pronounced. Increasing nozzle size reduces exit momentum and thereby accelerates concentration decay, whereas increasing the release flow rate enhances jet momentum, suppresses ambient entrainment, and consequently slows the decay process. The measured concentration decay coefficient k ranges from 0.000 66 to 0. 001 55, indicating that the persistent influence of initial geometric conditions causes the jet to deviate from the classical self-similar decay path. Based on the test data, nozzle-geometry-specific power-law models are established. The models indicate that the decay coefficient can be characterized by the coupling of Re and D_h. The decay rate of the rectangular nozzle is more sensitive to flow rate variations, while that of the triangular nozzle is more sensitive to size variations.

Key words: nozzle geometry, horizontal jet, hydrogen leakage, concentration decay, release flow rate, Reynolds number (Re)