16 replies to this topic

[panoska]

Hello everyone,

 

I try to calculate the size of a steam condensate line, which is the discharge line of a steam trap.

First, I calculated the flash of the steam. And then, I calculated the volume percentages of steam and water. The result showed that the steam volume percentage was about 99%. 

 

Afterwards, I used two recommendations to solve the problem:

 I can simplify the problem by considering it wet steam in the header. Also, the velocity range for wet steam is about 15-20 m/s.

 

Based on the above, I continued with the sizing of the line.

 

I used the formula Q=u*A

I assumed a steam velocity of 15 m/s

and as Q=mass of flash steam/density

(I did not take into account the mass of water.)

 

From this, I calculated the size of the line.

 

Do you agree with this shortcut calculation?

Do you have any challenging feedback?

 

Every document is more than welcome and much appreciated!

 

Thank you in advance!

[Bobby Strain]

Sounds too simple. I suggest you use a rigorous approach, then you don't have to rely on us guessing. You didn't give much information. If it's not a great flow, you may be required to use the smallest diameter pipe to hang between supports. You can use the two-phase calculator at my website. I have an old Basic program that does the flash, too, but it doesn't run on the modern platforms.

 

Bobby

Edited by Bobby Strain, 29 March 2022 - 06:59 PM.

[Pilesar]

Shortcut approaches can save a lot of time after you verify them. Your velocity criteria is conservative. I would choose 20 to 25 m/s for velocity design basis. Compare your results to the Spirax Sarco online calculations for reasonableness. 

https://www.spiraxsa...-discharge-line

[Art Montemayor]

I'm adding my post to this thread because I fully agree with Pilesar's comments and recommendation.

 

And it also is a coincidence that I have been working on the Spirax Sarco Steam Manual that they freely offer on their website, converting it to a more readable text for students and young engineers.  I am presently on module 12, but have done a quick transcription of what Pilesar identifies.

 

I am attaching the rough download that I plan to add to my full copy and I hope this helps you out.  The entire Spirax Sarco manual is very, very, voluminous - but exceedingly simple and proper for young students and engineers.

 

Again, excuse the rough copy.  You can also go to the website and download some of the material yourself.

 The condensate pipe sizing chart -Spirex Sarco.docx   280.26KB   74 downloads

[panoska]

Hi thank you all!
I am already aware of spirax sarco.I was curious to find out what is the basis of these calculations and graphs.
The calculator seems very cool.

[Pilesar]

For more info about the Spirax Sarco calculator basis, click on the blue question mark at the top of the calculator input section for a thorough explanation.

[Bobby Strain]

Well,

     I found software that will run my old Basic program on newer Windows. Any interest?

 

Bobby

[panoska]

Pilesar thanks for informing me. I will check it out.
Hi Bobby I would be interested in it, could you give the link, please?

[katmar]

Condensate lines are difficult to specify very accurately because there are so many variables that can impact on the flow and pressure drop.  During start up the flow of condensate can be 3 or more times as much as during steady state running,  Even during steady state there will be a flow controller changing the flow rate continually.  The degree of flash that you get can vary, depending on several parameters.

 

What I am getting at here is that you should not spend too much time and effort trying to get the design "right" because there isn't really a right design.  In my opinion it is better to rely on the experience of a company like Spirax Sarco and to use their charts which probably contain a fair degree of (justifiable) safety margin.  Thanks to Art for uploading just what you need.

[breizh]

Hi,

Agree with the replies .To add to the discussion 2 documents and a link :

https://www.mnteng.c...Utilization.pdf

Good luck

Breizh 

[Bobby Strain]

I used the chart to size a condensate line. The size I got was essentially the same as one using rho*V² criteria for 2-phase lines. The online sizing tool doesn't offer any guide as to sizing velocity. And there is no calculated value for pressure loss.

 

Bobby

[panoska]

Thank you so much for your reply! ????

[Bobby Strain]

Panos,

       I size two-phase lines for rho*v² =10,000 lb/ft-sec² . The program I sent calculates the mixture density and the velocity, so it's easy to check. If you can program, you can add the recommended velocity, or whatever you wish. It's old Basic.

 

     I created an account at www.SpiraxSarco.com and logged in to the sizng suite, but I can't access any calculations. Does anyone use the site to access the sizing suite?

 

Bobby

[panoska]

Is it possible to run it in your website? I have not received something!

[Bobby Strain]

Panos,

       I sent it again to the email address you supplied. It's not on my website. If you fail to get my email, send me a personal message.

There are lots of other programs included, too.

 

Bobby

[panoska]

Bobby,
Can you please send it to me in a personal message?

[Bobby Strain]

You can download it from my site. QB64 Flow.

 

Bobby