1 reply to this topic

[dilshiva]

dear all,

iam currenly doing a mini project on LPG bullets and pipe sizing.

iam confused with sizing liquid and vapor lines.

my requirement is:

flow: (L) 1000 kg/hr; liquid density = 470kg/m3; - what will be the pipe size?

flow(V) 1000kg/hr;

Bullet pressure = 14.5kg/cm2(g

pressure at outlet of vaporiser = 1.2kg/cm2(g)

Temperature at outlet of vaporiser = 25degc


thanks & regards,
shiva

[Art Montemayor]

shiva:

That you are a confused chemical engineering student is no surprise. Many students in similar situations are. However, you don't tell us your background as to what year you are in and how many fluid mechanic classes and chemical engineering classes you have taken. We don't know your preparation, so we possibly will continue to confuse you or totally confound you unless you have an understanding of what we are talking about.

I am going to assume you have the adequate preparation – except that you have bad instructors, little guidance, or haven't done enough studying and worked enough problems. Those are all your problems and we can't help there. However, I can guide you on how an LPG line is sized in real life:

1) establish the available, allowable pressure drop in the line. You must know this or be in position to assume it. You cannot proceed without knowing what is the minimum driving force (pressure drop);

2) Always generate the Reynolds Number. For this you need to know the fluid velocity, viscosity, and density. You also have to assume a trial pipe size.

3) Establish the type of pipe proposed. With this, resolve the friction factor using the Colebrook equation or an explicit relationship like Serghides, Churchill, or Chen;

4) Use the Darcy-Weisbach equation to see if the size "fits" the diameter that you pre-selected.

You can set up a spread sheet in Excel – which I highly urge you and all other students to do – and do the calculations rather quickly. This is something that any good university should be teaching you to do. Also, obtain a copy of Crane Technical Paper #410 and read/study/work all the example problems that you find. In fact, I've already done this for you! Download the Excel Workbook that you find at the beginning of this Student Forum and start practicing how to solve fluid flow problems immediately.

Practice, practice, practice.