×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Steam Turbine Seal Losses
2

Steam Turbine Seal Losses

Steam Turbine Seal Losses

(OP)
Has anyone ran across a good book that states, or have a proven "rule of thumb" for estimating the average gland and labyrinth seal losses through an extraction/backpressure steam turbine.
I want to use this number in calculating the net shaft power developed by the turbine. The pressure at which the losses occur is not relevant at this time since the calculation is an estimate only.

RE: Steam Turbine Seal Losses

2
I am sorry to break the news to you that there is not a PROVEN "rule of thumb" for leakage losses.  

If you are really making "estimates", there is likely to be more error in your estimates from uncertainty of the nominal turbine efficiency than from accounting for leakage.  

Depending on steam conditions, rating (implying seal diameters), manufacturer, nominal type (reaction or impulse), etc., the HP end leakage could be 0.25% - 5% of the main flow.

The best rules of thumb will be based on measurements or calculations that make some accounting for the actual construction details of the seals on your machine.  Performance quoted by any manufacturer will account for the design-basis leakage flows.

The typical equation for these leakage flows is (simply) an orifice type of equation where:
FLOW = C1*C2*AREA * (UPSTREAM PRESSURE/UPSTR.SPEC.VOL.)^0.5

From the equation above, you can see the "the pressure at which the (leakage) occurs" IS RELEVANT.

The constants are functions of geometry and pressure ratio respectively.  I've separated them in this discussion because the magnitude of the "geometry flow coefficient" can vary by a factor of 2 or 3 for labyrinth seals alone, depending upon the seals' construction details.  The spread is greater once one includes factors such as wear and/or damage.

Actual physical areas (the annulus areas) can also vary, depending upon the turbine design.

The relationship of leakage to lost power also depends on where the leakage occurs.  The HP shaft end leakage will typically have done useful work on the first stage before leaking out.  If any of the leakage is re-entered at a downstream stage, this will reduce the lost power.

Interstage leakage - over the bucket tips and under the stationary diaphragms - is, of course, different.

RE: Steam Turbine Seal Losses

You might try KC Cottons book "Improving Power Plant Performace.

RE: Steam Turbine Seal Losses

try using Maxwell's equation, it works for me, he was just estimating the losses too!

RE: Steam Turbine Seal Losses

(OP)
bluemax; I would rather attempt to design a perpetual motion machine rather than try to apply Maxwell's equation to this problem.
I have recently reviewed a printout of a proposed steam turbine that was prepared using "steam master 5.30" software. Gland steam losses are shown on the document. Does anyone familiar with this software know if this  requires an input for these losses or whether they are auto-generated from the program?

RE: Steam Turbine Seal Losses

Hi,
I've simulated labyrinth seals windage and got an empirical formula for shaft moment losses in  labyrinth seal:
const*f(leakadge, rotation^2,radius^3,seal length)+rate*radius(outlet_swirl-inlet_swirl)
As 2nd component of equation isn't losses in itself, it helps to predict swirl in seal outlet if all other variables and inlet swirl are known.
Also I found that leakage can be calculated better by industrial codes (at least in my case - HP steam turbine, knife seals).

R,
Stanislav
----------------------------------
www.softinway.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources