modelSafetyValve

Allows the calculation of the flow or the area of a safety relief valve or disk. It uses isentropic calculation between the inlet, supposed with velocity equal to 0, and the orifice. The gas flow can be chocked or not, and all the calculations are done with the physical properties calculated by the Medium, except the possibility of manual entering of the isentropic coefficient. Correction coefficients are applied for backpressure and for viscosity, according to the API 520 methodology. It is capable for biphasic flow calculation, but the model SafetyValveFlash, that conforms to the API recommenations, is probably more adequate.

Two thermodynamic states are declared at the orifice outlet, both isentropics with the inlet. One of them at the discharge pressure of the valve, the other adjusted to obtain sonic speed at the orifice. If the discharge pressure is below the obtained critical pressure, the flow is taken from the critical calculation, if not from the discharge pressure calculation.