(55j) State of the Art in Modelling Pressure Tanks Under Fire Exposure

Aims

The availability of accurate and robust models for the prediction of the behaviour of pressurized tanks under fire exposure is a key requirement to improve design of fire protection and emergency depressurization systems.

Fire tests carried out in the last 50 years have produced valuable knowledge in the field, supporting the development of numerous kinds of models.

Most of the models present in the literature and available to industry fall under the category of lumped models: they are based on the solution of integral mass and heat balance equations. Lumped models are easy to use and provide results at a very low computational cost. However, they rely to different extents on adjustable parameters and simplifying assumptions, often disregarding key phenomena such as thermal stratification. Thus, their applicability is limited to the range of experimental conditions adopted for their development.

Recently, several authors succeeded in overcoming these limitations proposing CFD-based models. However, the high computational cost represents a severe obstacle to their adoption by industry, limiting their use to the academic research.

The present contribution aims at providing an overview of the models available for the analysis of the thermo-hydraulic response of pressure vessels under fire exposure, comparing lumped and CFD-based approaches and highlighting their strengths and limitations.

Methods

A review of the main available models for the simulation of the response of pressure vessels to fire exposure is carried out. The evolution of such models and the key improvements introduced over the years are highlighted. A comparison of the strengths and limitations of lumped and CFD-based models is presented, supported by the analysis of realistic case studies.

Results

The analysis of the performance of CFD-based models shows that they are a reliable tool for the simulation of pressure tanks under fire exposure, especially when complex fire conditions are considered, when they are significantly more accurate than lumped models, which may produce non-conservative results in terms of pressurization rate. Nevertheless, the high computational time required by CFD simulations of real scale systems hinders the use of such models in industrial applications. In perspective, a solution to combine the accuracy of CFD based models with the low computational time typical of lumped ones is represented by the development of surrogate models trained on CFD simulations results.

In addition to the high computational time, it is pointed out how the main limitation of currently available CFD approaches remains their inability to adequately simulate the behaviour of tanks when the PRV is activated. This impedes their use in the analysis of depressurization systems.

Conclusions

The present contribution provides an overview of the modelling approaches available for the analysis of pressurized tanks exposed to fire. Lumped models are easy to use and provide results quickly, but suffer several limitations. Recently proposed CFD based models are more accurate, but still time consuming for industrial applications. Further research effort should be devoted to improve this aspect and to enable the simulation of PRV opening.