HYSYS: Understanding Hydraulic Calculations Using Different Tools 1

[Iomcube]

@

https://www.aspentech.com/en/blog/blog/Modeling_Fluid_Flow_Hydraulics_With_Confidence

My questions relates to different tools provided in HYSYS for doing fluid flow calculations. The above recent article summarizes these tools & the pros n cons as well for each method. I need some clarifications:


1] Referring to Pipe Segment author says that Slip is not accounted for What does that mean? This is also referred [link undefined]here at page 5/5[/url] which states The pipe segment in dynamics does NOT model phase slip, so it is not suited to predict slug volumes through dynamics modeling.


2] Again for Pipe Segment author says acceleration term in the pressure drop equation ...does that mean pipe segment shouldn't be used when there is say a JT Valve (in refrigeration cycles ...too muh pressure drop means excessive density decrements & excessive velocities!)


3] Again for Pipe Segment author says Ignores the kinetic energy term of the energy balance equation for all phases ...??


4] For Compressible Gas Pipe quoting Do not use the interpolation mode ...??


So I cannot understand these x4 statements. Please clarify

 

[zdas04]

Iomcube,
Thanks for sharing the link, the author really gets it and her insights are excellent.

For you specific questions
[ol 1]
[li]The "Pipe segment" program is like virtually all useful pipeline models and does not even try to deal with the complexities of multi-phase flow. Since there is not a useful prediction model of when and where liquid accumulations might occur in a gas flow or when gas accumulation might initiate a problem in a liquid flow, all of the stand-alone pipeline models treat interfacial energy transfer as insignificant. Certainly a good choice over the thousands of arbitrary assumptions that would be required to treat slip properly in a "single-phase" line.[/li]
[li]Piping models get progressively less able to match physical world data as velocity increases. The Bernoulli equation loses all validity for flow in a pipe at about 0.1 Mach (for a moving body in a more or less static stream it is valid up to about 0.6 Mach), the empirical equations are pretty good up to 0.3 Mach, and then are progressively worse as velocity increases toward 0.6 Mach (above that they are useless). You can model the JT effects of a valve, just don't use any equation that wants length in miles or km.[/li]
[li]The kinetic energy term (1/2 mv²) is simply too small in pipe flow to be within the uncertainty of the calculation. For gas flows the mass is too small to matter and for liquid flows the velocity is too small to matter.[/li]
[li]Using the interpolation mode in this program requires that you have a deep understanding of discontinuities in the data. Few people have that understanding and without it, you are very likely to "interpolate" yourself into failing to properly treat a phase change.[/li]
[/ol]

For an excellent review of the complexities of modeling multi-phase flow, this paper by Fekete is outstanding (notice that their program also ignores KE changes).

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Iomcube]

Pardon me but are you saying that such pressure losses (image attached) are ignored in pipe segment unit operation? Btw in conjunction to ASPEN article; is this webinar from the same author you can download:

https://www.aspentech.com/Resources...en-HYSYS/?src=blog-global-web&linkId=49800366

 

[zdas04]

They absolutely are ignored. In your example (I started out working with pressurized water reactors like the example, the example was a walk down a 50 year old memory lane) the dP in the fuel channel is less than 2 kPa (about 5 oz/in^2) and no pipeline calculation will ever be able to differentiate pressure changes of that magnitude over miles (km) of pipe.

You really have to pay attention to "horses for courses", don't try to use Bernoulli for a super-sonic nozzle, don't try to use the Isothermal Gas Flow Equation for water flow, don't use the Modified Bernoulli Equation ever, if you use D'Arcy-Weisbach make damn sure that you recalculate friction factor for every segment. Use the right tool for the job.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Iomcube]

Quoting your every segment: (hopefully you are aware that HYSYS solves Pipe Segment UO by dividing them into say many finite control volumes or increments) ...if I include may many increments** in normal Pipe Segment UO (unit operation) can it be modelled as something equal to Compressible Pipe Segment UO?

**By many increments I mean count of increments such that there is always less than 5% density difference within any increment

 

[zdas04]

I am, and I expect them to recalculate friction factors every single damn step. Otherwise what is the point of breaking them up? I ran a model in another program that broke the pipe up into pretty small segments and then didn't recalculate the friction factor--the answer was exactly the same as it would have been with segment lengths of 20 miles. That program went into the trash that day.

I've used HYSYS for operations inside the plant fence, but never for pipelines, when I was doing that kind of stuff, the HYSYS pipeline module was terrible and we had Stoner and MTRAN licenses and both were excellent for pipelines.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Iomcube]

Thanks for the valuable info that extended my understanding. This statement of yours really helped

Piping models get progressively less able to match physical world data as velocity increases. The Bernoulli equation loses all validity for flow in a pipe at about 0.1 Mach (for a moving body in a more or less static stream it is valid up to about 0.6 Mach), the empirical equations are pretty good up to 0.3 Mach, and then are progressively worse as velocity increases toward 0.6 Mach (above that they are useless). You can model the JT effects of a valve, just don't use any equation that wants length in miles or km.

By the way the applications that I rely on doing Pipeline Calculations are:

1**] ABZ DesigNET (for compressible, incompressible & choke conditions)
2] Tahoe HydroFLO (for incompressible)
3] HYSYS (with PIPESYS extension

http://instruct.uwo.ca/engin-sc/cbe497/Doc/Pipesys/Pipemenu.pdf

)

** Main Stay