Dynamic calculations for relief system sizing

To achieve (b), it is necessary to use relief sizing methods that take account of the dynamics of the pressure relief, event. Pressure relief systems for runaway chemical reactions usually discharge a two-phase mixture (see 4.3). If a steady-state calculation were used to size the relief system, then it would be necessary to size it for the volumetric rate of two-phase mixture equal to the volumetric, rate, of gas/ vapour generation at a particular point (e.g. at the relief pressure for vapour systems). This leads to very large calculated relief system sizes. 

However, because the relief system is discharging a two-phase mixture, it is acting to empty the reactor. Account can be taken of this by performing a dynamic (non-steady-state) calculation, and many of the methods described later in this Workbook do this. By taking advantage of emptying, a smaller relief system size can 

An estimate of the average value of G can be provided by taking the mean of values calculated at the relief pressure and at the maximum accumulated pressure. 

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