Methanol Pool Evaporation in Confined Spaces

The use of methanol as an alternative fuel for ships has gained momentum. Its adoption comes with various safety concerns, of which the toxic vapours due to potential hazards such as spills onboard is one. The literature on methanol spills and the associated occurring of vapours in these environments is scarce and inconclusive, highlighting a critical knowledge gap in ship safety research. Understanding the evaporation behaviour of methanol spills is crucial for the safe operation of methanol propelled vessels. To address this, this study presents a combined experimental and numerical investigation in order to examine the influence of temperature, pool size, and ventilation on methanol pool evaporation rates in closed onboard spaces, such as engine rooms. To this end, twenty evaporation experiments were conducted at TNO within a controlled climate chamber. Experiments were performed at temperatures of 18°C, 30°C, and 50°C, and at ventilation rates ranging from 15 to 60 standard litres per minute, with liquid methanol pool diameters of 86 and 135 mm. An analytical model was taken from literature and its use was validated for pool leakages in confined spaces. To gather a better understanding of the ongoing evaporation processes and fluid flows inside the experimental setup, a high-fidelity CFD model was developed for one of the experimental scenarios. The experiments confirmed that methanol evaporation rates are sensitive to temperature, ventilation speed, and pool size. The empirical model was validated and accurately predicted evaporation behaviour, with discrepancies at higher temperatures, likely due to inaccurate modelling of evaporative cooling. The CFD model was validated for the experimental case with pool diameter of 135 mm, ambient temperature of 18 ⁰C and a ventilation rate of 15 std. L/min. The model predicted the evaporation rate in agreement with experimental observations and validating the model’s accuracy. The CFD model indicated that the nitrogen flow primarily affected the upper region of the tank, with minimal mixing observed. Evaporative cooling resulted in a 5% decrease in the initial pool temperature. The findings of this study quantify the impact of methanol pool evaporation. By advancing understanding of methanol behaviour in confined shipboard-like environments, this research contributes to the establishment of safe operation protocols for the maritime industry.