Step 4
Once the two-phase relieving capacity is known then we will use DIERS methodology to determine the maximum fluid flux (Gmax) using direct integration of the VdP integral for the relief nozzle based on an article by Larry Simpson, "Estimating Two-phase flow in Safety Devices", which will set the basis for the design of the relief orifice size using the equation, A = W/(Gmax), where "A", is the required orifice size, "W", is the two-phase relief rate, and "Gmax", is the maximum fluid flux that occurs at sonic (choke) conditions, or at the pipe exit.
This method will also be employed to determine the sizing of the inlet and outlet piping based on the Simpson article, " Navigating the Two-phase Maze" We can then compare the two-phase relief orifice size with the existing and single-phase size to determine if the existing relief device size is adequate for both single and two-phase relief.
Step 4-K
Two-phase Report (Integration table and graphic results)
Re run Piping program
The inlet and outlet piing program is rerun after increasing the inlet and outlet piping until the pressure drop and the fluid flowrate matches the nozzle flowrate. It is determined after running multiple pipe sizes that the inlet pipe size requires a 4" pipe and the outlet pipe requires a 10" pipe. A 10" outlet is required if the user desires to install a conventional valve and must meet the 10% of Pset requirement for the outlet pressure drop in order to meet ASME Code. The results for the inlet and outlet piping from the direct integration and the piping report are shown below.
Inlet outlet
PIpe size (in) 4" 10"
Pressure Wpipe = Wnozzle (psia) 254.3 29.27
Pressure drop (psi) 2.425 14.9
%Pset 0.945 7.44
