Two-phase flow 1

[karthik13]

Hai,
I am looking for standard procedures to size a relief valve for two-phase flow.
Thanks,
karthi

 

[Montemayor]

karthik13:

Get in touch with the American Institute of Chemical Engineers (AIChE) and ask for their standards on 2-phase flow design for relief devices.

A special group, DIERS (The Design Institute for Emergency Relief Systems) was formed to study this problem. Their project manual, along with subsequent articles, computer software, and laboratory testing apparatus, have dramatically increased our understanding of the problem and provided tools to estimate the extent of liquid flow in a 2-phase vent.

If you want to obtain and study "standard" design procedures for 2-phase flow through relief devices, then this is where you should go and what you should look into. They were the first, serious group to get involved in this important phase of Chemical Engineering and they lead the field in the study and setting standards.

 

[EGT01]

As additional comment, the DIERS Project Manual (copyright 1992) is introduced as being a record of the DIERS research project. In that respect, it covers a wide range of aspects of the various methodologies that were investigated for evaluating two-phase vapor-liquid relief and will be somewhat overwhelming for a novice.

More recently, API RP-520 Part 1, 7th edition, January 2000, includes procedures for sizing relief devices for two-phase flow using the Leung "omega" method, Joseph Leung having been involved in the DIERS project and the International Symposium on Runaway Reactions. The API procedures give a step-by-step approach for sizing a relief valve for various two-phase flow conditions but do not address how to determine if two-phase flow should be considered for the required relief rate from a vessel.

Another excellent reference is the AICHE - CCPS publication "Guidelines for Pressure Relief and Effluent Handling Systems", copyright 1998. As stated in the objective of this publication, it was intended to provide a more user-friendly coverage of two-phase flow calculation technology (as compared to the DIERS Project Manual). I've only recently had a copy and have not reviewed its treatment on the subject of two-phase flow for valve sizing but I have found this to be a very useful reference in many aspects of relief system design. It also comes with a computer disc which includes programs for sizing relief devices and associated piping for either liquid, vapor or two-phase flow.

 

[MortenA]

The latest revision of API 520 (7 ed 2000) contains directions for sizing of PSV for 2 phase flow. Refe to app D.

Best regards

Morten