Alternative version of Leungs method and associated applicability

3 Alternative version of Leung s method (and associated applicability). 

For some reacting mixtures, it is difficult to find physical property data. An alternative version of Leung s method331 makes use of the Clausius-Clapeyron thermodynamic relationship to give a formula-in which all. the data required can be measured experimentally. The Clausius-Clapeyron relationship (T(dPydT) = hfg/vfg) only holds, for ideal single-component systems, and so its use introduces the following additional conditions of applicability  

These conditions are most likely to be met at relatively low pressure (less than, say, 5 bar). If there is any doubt over the applicability of the Clausius-Clapeyron relationship, it is suggested that a different method be used (see 6.3.2 and 6.4). 

The slope of the vapour pressure versus temperature curve, dP dT, can be obtained experimentally (see nnex 2). The most accurate method is to take tangents to the pressure (corrected for the presence of pad gas) versus temperature data from a closed test, or to fit the data to the following relationship161  

The required relief flow area can be evaluated using equation (5.1) knowing the two-phase mass flow rate per unit cross-sectional area of the relief system, G. This can be evaluated using any applicable method and guidance is given in Chapter 9. 

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