5 replies to this topic

[ecas]

Hello everybody,

I'm an industrial engineer with several years of experience related with oil refineries, thermal and nuclear power plants. All these plants have some piping systems with saturated steam (dry or wet) flowing through them, as for example the Main Steam System and the Turbine Extraction Steam System.

I would like to discuss in the forum these two aspects:

1. Which must be the expansion factor Y to be used for saturated dry steam in the equation (1)?

                                               W = 1891YD²[(P₁ - P₂)/v_e1K]^0.5       (1)

This equation relates the steam flow rate W (lb/h), the piping pressure drop (P₁ - P₂) (psi), the specific volume of the steam at the beginning of the piping v_e1(ft³/lb), the internal piping diameter D (in) and the flow resistance coefficient of the piping K.

In the technical literature, for example the Crane Technical Paper No. 410 includes the graph of Y for steam and gases with k = 1.3. This value of k that is the ratio of the specific heat at constant pressure to the specific heat at constant volume, I assume that is only for reheated steam, because for example in the paper of G. S. Liao "Analysis of Power Plant Safety and Relief Valve Vent Stacks", Journal of Engineering for Power, October 1975, says that k = 1.3 for reheated steam and k = 1.13 for saturated steam.

2. When the saturated steam has wetness at the beginning of the piping, which must be the expansion factor Y?

[sgkim]

Hi Ecas,

 

Orifice meter calculation formula can be found in the Shell Flow Meter Engineering Handbook (based on ISO 5167):

http://webapps.unitn...File/246566.pdf

 

For the steam quality correction factors (Fs) the formula is given table on Sec. 14.4. as:

Fs =  1 + 0.0074*(w% H2O)  ...(1)    

Then,  Corrected Expansion Factor  = Y * Fs......(2)

 

Stefano

Edited by sgkim, 10 February 2017 - 06:08 AM.

[ecas]

Stefano, thank you for the response, but it refers to orifice flow meter calculations that are different than the flow through pipes and components, as for example the restriction orifices. Note that for restriction orifices and nozzles, the Crane Technical Paper that I quote in my post, neither includes the saturated steam.

[breizh]

hi ,

Consider the resources attached to support your work .

 

Hope this is helping you .

 

Breizh

Edited by breizh, 19 February 2017 - 04:28 AM.

[sgkim]

Stefano, thank you for the response, but it refers to orifice flow meter calculations that are different than the flow through pipes and components, as for example the restriction orifices. Note that for restriction orifices and nozzles, the Crane Technical Paper that I quote in my post, neither includes the saturated steam.

 

For the calculation of compressible flow thru orifice and the pipes, the only difference is the orifice coefficient C which can be found on various handbooks.  (All the units remain unchanged as in the first posting)

 

      W = 1891YD²[(P₁ - P₂)/v_e1K]^0.5            (1)   for pipes with diameter D  (Eq 3-22 on page 3-5 of TP 410 )

 

      W = 1891Y d ^{2 *} C * [(P₁ - P₂)/v_e1K]^0.5  (2)   for orifices with orifice diameter d (Eq 3-20 on page 3-4 of TP 410) 

 

For liquids Y= 1.00, and  'DRY' saturated steam  k = 1.3.  Crane's Technical Paper 410 provides an example for 170 psia saturated steam on page 4-13; which does not refer the 'quality" of saturated steam but simply applies k=1.3.  The net expansion factor "Y" for compressible flow  through pipe can be found from graphic chart or from talbles on p. A-22.

 

It does not seem to be reasonable to apply the fixed figure of "1.13" for saturated steam, regardless of steam quality, as quoted from the journal.

 

~ Stefano Kim

Edited by sgkim, 20 February 2017 - 08:36 PM.

[ecas]

I agree that the Crane Technical Paper No. 410 aplies k = 1.3 for saturated steam or reheated steam, but considering that the relation between the pressure and the specific volume is Pv^k = Constant and calculate with the aid of the Steam Tables different steam expansions, you will get the following results:

Reheated steam with isentropic expansions, k = 1.3

Reheated steam with isenthalpic expansions, k = 1

Saturated steam with isentropic expansions and P_s < 1000 psia, k = 1.12

Saturated steam with isenthalpic expansions and P_s < 1000 psia, k = 1

Saturated steam with isentropic expansions and P_s equal or greater than 1000 psia, average value of k = 1.04

Saturated steam with isenthalpic expansions and P_s equal or greater than 1000 psia, average value of k = 0.93

In my opinion, it's more realistic assume that the flow of steam through the pipes and components follows an intermediate expansion between the isenthalpic and the isentropic.