A simplified model for rainout estimation for two phase releases of alternative liquified fuels

The adoption of alternative fuels in the energy and transport sectors is strategically important for achieving decarbonization goals. However, managing the risks associated with accidental leakages from storage and transfer of these fuels – such as LNG, ammonia, and methanol – is essential for their safe handling and usage. These leakages can lead to complex release dynamics due to phase changes when the fuel transitions from high-pressure storage to ambient conditions, resulting in a mixture of liquid and gas phases. Quantifying the liquid content after such leaks, referred to as rainout, is particularly challenging. This work presents an approach to estimate the rainout fraction from accidental liquid fuel releases using simplified equations for flow dynamics and two-phase physics. A relative time scale parameter is derived to determine rainout occurrence, and the resulting model is calibrated with our recent field experiments via a simple regression technique. The model is validated with historical experimental data and compared with existing models, demonstrating reliable order-of-magnitude predictions of rainout fractions across various substances and storage conditions. This simplified model provides a rapid estimation tool for rainout fraction as an input into subsequent dispersion analysis.