Experimental study on the flow characteristics during liquid nitrogen leakage

ABSTRACT

The accidental leakage from tanks and pipelines is one of the main risks in cryogenic superheated liquid storage and transportation. To investigate the effects of superheat degree and jet pressure on the leakage characteristics, the corresponding liquid nitrogen (LN₂) leakage experiments were carried out under different conditions. In this study, a rectangular nozzle ($1\mathrm{mm}\times 3\mathrm{mm}$) was applied to imitate the crack in typical release scenarios. The dynamic evolution process of jet pattern was also investigated. Three jet patterns including the mechanical breakup jet, the partially flashing jet, and the fully flashing jet were identified in the stable stage. The results indicate that the jet angle rises with the increase of superheat degree. At high superheat degree, the jet pressure presents a more significant influence on the jet angle. While the superheat degree decreases, its influence on the jet angle reduces. The leakage mass flow rate declines with the increase of superheat degree and rises with the increase of jet pressure. Furthermore, a new discharge coefficient correlation suitable for superheated LN₂ leakage is developed, and its prediction error is within±3.8%. The new correlation is a good tool to predict the mass flow rate during LN₂ leakage process.

KEYWORDS:

• Liquid nitrogen
• rectangular nozzle
• jet pattern
• mass flow rate
• Discharge coefficient

Disclosure statement

No potential conflict of interest was reported by the authors.

Nomenclature

Tj	=	Jet temperature (K)
Ts	=	Saturation temperature (K)
∆T	=	Superheat degree (K)
p	=	Jet pressure (MPa)
Cd	=	Discharge coefficient
Qact	=	Actual mass flow rate (kg/s)
A	=	Nozzle sectional area (mm2)
Δp	=	Jet pressure difference (Pa)
pcr	=	Critical pressure (Pa)
∆Tsub	=	Subcooled degree (K)
Tcr	=	Critical temperature (K)
Ao	=	Nozzle exit orifice area (mm2)
Ai	=	Nozzle inlet orifice area (mm2)
$c_{\mathrm{pl}}$	=	Specific heat capacity (J/(kg·K))
hl	=	Latent heat (J/kg)
u	=	Liquid velocity (m/s)
d	=	Nozzle diameter (m)
Greek letters	=
${\rho }_{\mathrm{l}}$	=	Liquid density (kg/m3)
${\rho }_{\mathrm{v}}$	=	Vapor density (kg/m3)
μ	=	Dynamic viscosity (N/(m2·s))

Additional information

Funding

This work was supported by the financial support of the National Natural Science Foundation of China (No. 52074237)

Notes on contributors

kang Cen

Kang Cen is a professor at the Sichuan Engineering Research Center for Gas Safety and High-Efficiency Utilization of Southwest Petroleum University. His research area of interest includes integrity evaluation of gas pipeline and station yard and gas load forecasting. He has published more than 50 research paper in various National and International journal.

yixi Wang

Yixi Wang is a postgraduate student at the Sichuan Engineering Research Center for Gas Safety and High-Efficiency Utilization of Southwest Petroleum University, dedicated to research on dangerous cryogenic liquid leakage.

wenqiang Fan

Wenqiang Fan currently works at Deyang Construction Quality and Safety Supervision Station. He has rich experience in heat and mass transfer and heat storage.

yanling Yang

Yanling Yang is a doctoral candidate at the Sichuan Engineering Research Center for Gas Safety and High-Efficiency Utilization of Southwest Petroleum University, dedicated to research on dangerous cryogenic liquid leakage.

Minxue Dai

Minxue Dai is a postgraduate student at the Sichuan Engineering Research Center for Gas Safety and High-Efficiency Utilization of Southwest Petroleum University, dedicated to research on gas load forecasting.