Assessment and validation of evaporation models for cryogenic liquids

The unanticipated release of cryogenic liquid is a serious safety risk since the vaporization of the cryogenic fuels may result in flammable vapor cloud which can lead to an explosion and/or fire. A significant amount of work has been carried out in the past to study the boiling phenomenon of cryogenic liquids. However, the evaporation of cryogenic liquid has not been thoroughly investigated. In reality, both of these phenomena are computationally equally important since during source term modeling, these two modes of vaporization are usually interchangeable. Incorrect source term prediction in any of these two regimes will result in poor estimation of consequences and hence will undermine the safety protocols. The interest to study evaporation mode of vaporization for cryogenic liquid stems from the fact that the boiling point of cryogens is below -150 degrees C and evaporation of cryogens will further decrease the temperature of the liquid, as observed through various evaporation models. However, these evaporation models have not been validated against the cryogenic liquid data. In order to fill this gap, the present study has three primary goals in context of cryogenic liquids: (i) understand and compare the existing evaporation models; (ii) evaluate the possibility of shift between boiling and evaporation regime; and (iii) validate the existing evaporation models. Six evaporation models were selected for this study through a comprehensive literature review. The behavior of the selected evaporation models was studied through a comprehensive parameter sensitivity analysis, including pool temperature, wind speed, ambient temperature, and pool size. Also, a medium scale experiment was performed, involving the spill of liquid nitrogen over polystyrene substrate, to observe the possibility of shift in the vaporization regime, and to validate the selected evaporation models. Although the results of the sensitivity analysis reflect on the possibility of evaporation of cryogenic liquids for some models, the experimental results confirm a complete absence of evaporation regime. Hence, based on the experimental results and sensitivity analysis, it was questioned through this work that the use of evaporation models in source term modeling may not be suitable for cryogenic liquids. However, more experiments should be carried out in future, on a larger scale, before coming to a general conclusion. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.