# Model for Cryogenic Flashing LNG Leak  
[PERSON]  
1 Sembcorp Marine, 80 Tues South Boulevard, Singapore 637051, Singapore; [PERSON]ESS]  
[PERSON]  
2 School of Mechanical and Aerospace Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Ave, Singapore 639798, Singapore 2  
fluid dynamics. However, Navier-Stokes modeling is time consuming and the integral model is used for preliminary risk assessment. Today LNG accident concern focuses on two-phase pressurized leakage through connection cracks. The specification for the bunkering of liquefied natural gas-fueled vessels (ISO 20519) lists the release of LNG through a broken instrument connection (25 mm hole) as the likely event [8]. A full-bore rupture requires a vessel or road tanker to pull away unintentionally, which is gross negligence. The United Kingdom and Singapore risk guidance regulations treat a crack leak as a major concern for risk rather than a bore rupture [9; 10]. When a pressurized cryogenic liquid leaks out into the atmosphere from a crack, it will be in two phases, liquid and vapor. The depressurization process leads to mechanical fragmentation of the liquid and forms vapor [11]. Additionally, the liquid will undergo the rapid vaporization of liquid due to the sudden pressure drop. This rapid vaporization is known as flashing. Conventionally, the non-vaporized liquid, which falls and forms a puddle on the ground, is called rainout [12]. Studies of a non-cryogenic orifice pressurized leak nature have been performed. The Center for Chemical Process Safety (CCPS) studied the release of pressurized water and trichlorofluoromethane (CFC-11) through a small orifice (6.35 mm) [13]. The CCPS study found that significant mechanical fragmentation of the liquid droplet is possible, even when the stagnant liquid temperature is above its ambient boiling temperature. In another study, [PERSON] and [PERSON] measured the droplet size and velocity distribution of liquefied propane leaks through an 8 mm orifice [14]. A Phase Doppler Particle Analyzer (PDPA) was used to measure liquid drop size and velocity. The study concluded that vaporization takes place along the jet in the flow direction. Additionally, higher pressure release is associated with more intense flashing, leading to stronger fragmentation and a higher vaporization rate. The French National Institute for Industrial Environment and Risks (INERIS) performed semi-outdoor large-scale experiments to study propane and butane release through orifices of up to 25 mm [15]. The purpose of the dispersion experiment is to develop models of flashing releases as encountered in realistic industrial environments. Both non-impinged and impinged jet releases were studied by INERIS. Rainouts were collected and measured. The study concluded that mechanical fragmentation and not flashing are the main mechanisms for vapor generation for propane and butane. For non-impinged leaks, there is hardly any rainout for propane due to its low boiling point. Up to 15% of the total mass release was recorded as rainout for the propane impinged leaks. However, the collected rainout is suspected to be a mixture of ice and propane. Hence, the exact propane rainout mass could not be determined. Recently, INERIS performed an experiment named SPARCLING, which releases subcooled LNG up to 8 bar through various orifice sizes (up to 9 mm). The study measures the size distribution and velocities of LNG droplets using a dual Phase Doppler Anemometer [16]. There are two major findings from SPARCLING. The first observation is that an orifice leak <3 mm will always be in two phases up to 9 bar. The second finding is that LNG release above 1.5 bar will not have any rainout. The work conducted thus far to model flashing leak is for non-cryogenic sources. It would be worthwhile to come up with a model specifically for cryogenic liquids such as LNG. The leak model can be used as the source term for risk assessment of accidental cryogenic liquid leakage.