Dear all!

How to simulate the Slug Flow + Seismic Analysis (Combindly, Dynamically)in CaesarII?

As there is a possibility that both incidents can take place con-currently.

thanks for any reply & regards,

Arun K, New Delhi

Seismic analysis is possible in CAESAR II by response spectrum method. Slug flow analysis is possible by Force Spectrum Method/Time History method.As you are aware ,( even if you take response spectrum approach for both) first method makes a computation of max. response( displacement, accelaration, velocity ) vs time and plot the maximas vs natural frequencies where the second method takes the route of computing DLF vs time and thereby plot the DLF maximas w.r.t frequency . Essentially both the methods push the problem from Time domain to Frequency domain. However the methods are different and hence not combined.

To answer your second question:As 31.3 suggests that two occasional effects ( wind and seismic for example) need o be be considered to occur simultaneously, I think you can extend the same logic to slug and earthquake.

ARun K,
Per ASME B31.3 para. 302.3.6 Limits of Calculated Stresses due to Occasional Loads,
(a) Operation ..... "Wind and earthquake loads need not be considered as acting concurrently."
For your case of slug flow it probably is also an occasional load so it would not be included with a seismic analysis. If slug fow is the normal situation for your design, then you should include it with the other normal temperature and pressure parameters for seismic analysis.

Richard & Anindya thanks a lot for your replies.

Here the case , I have considered is "Seismic Analysis of Two phase flow lines."

So feel that para 302.3.6 of ASME B-31.3 is not applicable here, as the slug (Two Phase) flow is a continuous phenomena.

So should I treat the Slug flow as static parameter & Earthquake as occasional & Dynamic Parameter for the analysis?

thanks & regards,

Arun K,
It sounds like you need to include both your slug flow and seismic loads together in your analysis. The difficulty that I have understanding is the slug flow of a continuous phenomena, or 'steady' nature of the slug flow. Does the slug flow result from a boiler or vaporizer that is running at abnormal level? Does the process require a two phase flow, or the slug flow cannot be avoided? If the process design results in two phases, then the mechanical design could deal with two phase flows by a knockout drum, or just piping route with minimum rising slope plus no pockets - for small vapor percentages. I hesitate to design for 'continuous' slug flow, considering it to be an unstable condition difficult to characterize. Do you have a well defined interval and peak pressure of slug flow?

Richard,

Here fluid is Steam condensate and its being transferred from "Steam Condensate Flash Drum" to "BFW Deareator".

Other Process parameters are:

Design/Op. temp: 170/140 deg C
Design/Op. Pressure: 6.5/2.5 Kg/cm2 g
Fluid phase:V+L
Fluid density: 65.5 Kg/cu.m
Fluid velocity: 2.140 m/s
Vapour Frac. (Vol%):93.5

If you need any further information then pl. let me know.

regards,

Arun K,
The vapour fraction of 93.5% with the low velocity of 2.140 m/s does not seem to indicate a slug flow regime. A pipe size is not given, and I did not make any calculations. If the pipe size is large enough, there is probably high velocity vapour with slower velocity liquid flow. Flow regime might be mixed vapor + liquid at higher flows. Lower flow rates might have liquid in the bottom of horizontal pipe runs, and vertical runs of pipe might have a 'ring' of liquid on pipe wall with vapour in center of pipe. Typical BFW dearator location would be high elevation to provide adequate BFW pump NPSH. Hopefully the condensate flash drum is at low elevation or at grade. If the pipe is routed with a rising slope, or no pockets for liquid to collect to form slugs, then I don't think there would be a significant slug flow problem.

Richard,

Thanks a lot for answering my questions and clearing my doubts.

Regards,