Effect of leakage source condition on the unignited hydrogen released issuing through a horizontal realistic pipeline geometry

An unignited gas release experiment system for the schlieren visualization and concentration quantitative measurement is designed and built to investigate the diffusion and concentration distribution features of turbulent hydrogen jets issuing from a realistic pipeline geometry. Helium is used in place of hydrogen for safety reasons. The spatial and temporal evolution of the asymmetry of turbulent helium jets was studied. The influence mechanisms of the volumetric flow rate (Q), the ratio of orifice diameter to the inner diameter of pipeline (R), and the angle between the normal of the leakage orifice and the opposite direction of gravity (θ) on the asymmetric concentration distribution are revealed. The experimental results show that the diffusion angle (α) and the inclination angle (β) of the turbulent helium jet are the largest when Q is 15 SLPM, R is 0.3, and θ is 0°, and the asymmetric feature of the turbulent helium jet is obvious. As the Q increased, the slope k of the inverse helium concentration (1/volume fraction) and a scaled distance L (L = (x/d)·(ρ_a/ρ₀)^1/2) became small. The increase of Q aggravated the concentration attenuation caused by the volumetric flow rate and the asymmetry jet. As R increased, the slope k of the inverse helium concentration and a scaled distance L first decreased and then increased. The slope k got the minimum value when R was 0.3. The downward movement of the leakage orifice position increased the turbulent intensity near the leakage orifice. This work can provide theoretical support for accident prevention and emergency treatment of hydrogen leakage accidents in long-distance pipeline low-pressure hydrogen transportation.