Wildays step-wise method for vapour pressure systems

4 WILDAY S STEP-WISE METHOD FOR VAPOUR PRESSURE SYSTEMS 

The available pressure range from the relief pressure to the maximum accumulated pressure is divided into pressure steps (or the corresponding temperature range is divided into temperature steps). Average physical properties, heat release rate per unit mass (q) and relief capacity per unit area (G) need to be evaluated for each 

All parameters in equations (A5.8) to (A5.11) are evaluated at the average conditions for the time-step, except for m which is the mass remaining in the reactor at the start of the time-step. The criterion for the pressure to begin to fall during the step due to tempering is  

If the pressure-step is large, then equation (A5.8) may yield an imaginary number (i.e. 4aswcsw b2sw). When this occurs, it indicates that the pressure has turned over due to homogeneous two-phase relief within the step, so that the relief area chosen is larger than required. 

The method is quite laborious to evaluate with a pocket calculator, but is capable of obtaining a relief size in cases where other hand calculation methods are. inapplicable. Evaluation using a spreadsheet is less time consuming. 

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