Steam flow through long perforated pipe

[LRLAMIT]

Hi

I am working on designing a perforated pipe meant for uniform steam distribution. The steam pressure is 7.5psig at the inlet of the pipe and flow is 150 kg/hr. The length of the pipe is 16 ft and pipe diameter is 1.5 inch. What should be the hole diameter and pitch to get the uniform steam. I appreciate all the group members for your time and advise.

 

[1503-44]

You need to specify what conditions prevail at the exterior surface of the pipe. 0 psig?, temperature, etc.

 

[LittleInch]

For any header and hole type distributor, you really need to make the main header as big as you can so that there is very little pressure drop from one end to the other.

A very simple check is that the square area of all the holes in the header should be about half or certainly no more than the square area of the header.

Think about a garden sprinkler bar, but with steam.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

If a pipe is round, what is its "square area"?

 

[TBP]

LRLAMIT - If you can find a copy of Spirax Sarco's "Hook-Ups", it has a short section on sparge steam steam systems. It's an excellent resource for all kinds of steam heating applications. I've used it for almost 40 years, and it's never let me down. I don't know if it's still published, but there has to be hundreds of thousands of copies scattered all over North America. The salesmen used to hand them out free of charge in plants.

 

[LittleInch]

OK, internal area that is "square" with the axis of the pipe. You could also say cross sectional area.

Pitch of the holes will depend on what is happening to the steam and whether there is any air movement.

If you open up a bit about what you're trying to do then you might get some better responses.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Or "cross-sectional area of flow", or pipe's "flow area". Its just that I've never seen "square area" used before, other than like for area, i.e. in[sup]2[/sup].

 

[Latexman]

LRLAMIT,

Use Search, under the thread title and between Forum and FAQs, with keywords "maldistribution" and "flow distribution" to find some related threads.

Good Luck,
Latexman

 

[georgeverghese]

If you must have the steam sparge upwards, then install at least one drip hole at the bottom of the main distributor so condensate gets to drain out, else condensate will pool and flood the distributor.

 

[IFRs]

First, you'll have to decide exactly how uniform is your "uniform". Also, what is "uniform" ? Is it the pounds of steam out of each hole, the distance the steam travels from the hole, a steam curtain with no gaps 1CM past the pipe, etc. If the tolerance is large they your solution gets easier because you can ignore smaller effects. Typically smaller holes further apart in the begining changing to larger or closer spaced holes as you go towards the far end because the supply pressure is lower at the far end. You could iteratively figure out the pressure drop in the header from a single hole, then using that source flow and pressure add a second hole, figure out the pressure drop from the second hole, etc. Then alter the hole sizes and spacing to get a feel for what the first hole's effect on the second hole's performance. For a pipe the size you have, your holes will be small and you might have throttleing issues, holes becoming clogged with impurities in the steam, perhaps even sonic velocity or thermodynamic effects that might complicate the calculations. Hopefully you can try a full size test, see if it works, then in one or two iterations have it done..

 

[georgeverghese]

Assuming a dead space of 1ft on either side of the distributor, and hole pitch of say 1 hole/ft, we have 10.7kg/hr/hole for 14 holes. I get a hole dia of 4.5mm, with a discharge coeff of 0.62 since Nre is about 68e3, and a backpressure of 100kpa abs(atmospheric discharge). Pressure drop over the distributor is 1kpa over the entire 16ft for this 150kg/hr, so pipe dia of 1.5inch is okay- maldistribution not likely for feed press of 150kpa abs. Some one care to check?

 

[IFRs]

Your solution works but suppose the OP wants more (or less) steam coming out per hour?

 

[TBP]

A quick look at "Hook-Ups" says that, at the design pressure, you can get 15 #/hr steam through a 3/32" hole, and 7 #/hr through a 1/8" hole. Assuming a horizontal sparge line, there should be 2 rows of holes, 30 degrees below the centre line of the pipe, ideally no closer than 6" apart. There should be one hole on the bottom of the sparge line to allow for drainage. I'd install it with a forward slope (3/4" from end to end over the 16' length), with the drain hole at the bottom close to the capped end.

 

[georgeverghese]

@tbp, Comparing your results with mine, and since 1/8inch > 3/32inch, I think you mean
15 lb/hr for a 1/8inch (or 4/32inch) hole
7 lb/hr for a 3/32inch hole

Extrapolating from your 1/8inch to my 4.5mm, the results match (11kg/hr from my calc cf. 13kg/hr extrapolating from yours) - okay

 

[TBP]

Thanks for catching my typo george.