Pressure drop calcs in low pressure steam lines
Pressure drop calcs in low pressure steam lines
(OP)
For a project, I have been involved in the pressure drop calculation of a 48 and 30 inch low pressure steam headers (98.5 quality steam). Many of the simulators I have checked use Begg-Brill & Moody for the two phase calculations. Can anyone kindly advise how well this equation handles the pressure drop calcs? Are they conservative?. To your knowledge does exist a better equation to predict the pressure drop?. For this particular case, these calcs are very sensitive because the available pressure is only 189 KPaa and every Kpa counts for the process. So every effort have to be made to be as precise as possible.





RE: Pressure drop calcs in low pressure steam lines
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: Pressure drop calcs in low pressure steam lines
Your conditions are fairly extreme in that you virtually have a gas only situation. The volume ratio for your gas to liquid is about 37000 to 1. On the usual Baker and Lockhart Martinelli charts you will find that you are off the scales.
I doubt whether you will find anything that will give you an accuracy of better than 25%. If I were doing the calculation I would assume gas only, and add 50% to the pressure drop.
I know that we all have to rely on computer packages these days to get our work done, but sometimes they can mask what is really happening. Please don't think I am knocking software (hey, I sell the stuff!) but you need to keep the calcs in perspective.
Good luck
Harvey
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com