Far as I know, HYSYS doesn't do two-phase flow. Use Pipephase instead. If your flow goes sonic though you are SOL because Pipephase doesn't do M>1. Pete
You can try Dynamic depressurising module in HYSYS and it will do calculate. Hysys can able to two phase. If you want more details send email to HYSYS support service, they will reply in day or two.
Dynamic depressurising module in HYSYS consider a vessel with VAPOR only or VAPOR-LIQUID or VAPOR-LIQUID-AQUEOUS subject to your input stream. You can either depressure VAPOR or LIQUID (flashing) subject to your choice in HYSYS. In most cases (if not all) in a plant (per my limited experiences) , depressuring is via VAPOR depressuring. As you depressure VAPOR, it discharge to disposal system like flare which is normally design to take large vapor flow but NOT large liquid ...
Above statement is confusing. A vessel with VAPOR & LIQUID in it but only VAPOR (and/or LIQUID) depressuring, is it correct to say "HYSYS can handle two phase blowdown" ? May be.