DIERS Two Phase Venting - PRV Sizing 3

[DITHarris]

Is some one familiarized with the DIERS Two Phase Venting PRV Sizing calculations?

I'm traying to use the coupling equation that relates flow and vent models, but I need the venting cross area. This is easy is you're rating a relief device, but if you are sizing the area, how can you determine if the calculated area is too small or too large?

 

[ChemE001]

This is a very good question. The coupling equation couples the vessel flow with the nozzle based on the flow regime model selected. You must know the orifice size of the relief valve and the cross area of the vessel. If you do not know this then you must first do a design mode calcualtion and set the flowing vapor volume fraction, "alpha model", = the vessel alpha, for homgeneous or bubbly flow and as 2*alpha for churn-turbulent flow. This will give you an appoximation of the flowing mass fraction, Xm, calculated from the coupling equation(Xe). Use the inital flowing mass fraction and the enthalpy of the liquid and vapor at relieving and aproximate choke to set up a HEM model. Use the Omega method or the rigorous Simpson integration method to determine the maximum flux rate for venting. The area is calcualted using the required flow rate perhaps from fire and divide by the Flux. So Area = W(lb/hr)/G(lb/hr-in2). With this you now can calculate a required orifice and select a standard orifice size. Then use this area in the coupling equation rating mode along with your inital relieving quality. You can then do a rating calculation and play with using different flow regime models to review the relief flow capacity. Make sure this flow meets your required flow from fire or other scenarios. Go to

http://www.digitalsolutions.org

and they have free software for you to read, view, and print single and two-phase relief design examples based on the DIERS(Design Institute of Emergency Relief Systems) benchmarks. Or go to

http://www.diers.net

and select software from the navigation bar. You can download the free Mach II Reader and Regression Tool. The Regression tool is free and allows you to regress your physical property data based on linear, polynomial or exponenital curve fitting.

 

[JAlton]

I concur, digital solutions at

http://www.nvo.com/safetyrelief

is a great resource.

J. Alton Cox
President
DeLuca Test Equipment

http://www.delucatest,com