4 replies to this topic

[Skyline]

Dear friends

I did a simulation of a gas flow inside a pipe using HYSYS. I want to know the flow profile (pressure and velocity) of the gas inside 6, 8, and 10 inch pipe. The problem is: the solver can't solve the simulation for 6 inch pipe. But in 8 and 10 inch pipe, it worked perfectly.
I got a message: "Negative pressure calculated on increment 204 in Pipe Segment Pipa 6 inci" What is wrong with my simulation? Is it because the flow is to high for this pipe, or is there any explanation for this?

Thank you very much.

[Srikrishna Chaitanya]

Hi Skyline ,
I guess you are checking pressure drop in different pipe lines with same flow,
When you reduce the pipe size by keeping same inlet pressure & Flow, then Velocity will increase, when velocity increases your pressure drop increases because we know in Turbulent flow Delta P is proportional to velocity square. Now when you reduce the pipe size obviously your pressure drop will increase . The inlet pressure you are testing for 6 inch is not sufficient to supply the pressure drop required to converge the simulation ( Eg : your inlet P = 3 bar , your delta P = 5 bar , then simulation wont converge ) , when you increase the pipe size delta P is reducing so your simulation is converging .in order to converge six inch pipe you have to do 1) Increase inlet Pressure or 2 ) Reduce pipe length or 3) reduce flow rate .

Hope this helps

Regards ,

Satish

[demank]

absolutely agree with satish_babu,
why when simulate 6 in pipe it got errors, cause negative pressure happen.
It means, before the flow reach the end of the pipe, it have already zero pressure.

[marthin_was]

I'm not sure with the reason you reducing the pipeline size with the same flow rate? Or may be I'm missing something?

absolutely agree with satish_babu,
why when simulate 6 in pipe it got errors, cause negative pressure happen.
It means, before the flow reach the end of the pipe, it have already zero pressure.

[Skyline]

I'm not sure with the reason you reducing the pipeline size with the same flow rate? Or may be I'm missing something?

absolutely agree with satish_babu,
why when simulate 6 in pipe it got errors, cause negative pressure happen.
It means, before the flow reach the end of the pipe, it have already zero pressure.

Thank you for Satish and Demank. Now i understand the reason why it showed an error message. Once again, thank you very much.

For marthin was: I didn't mean to reduce the pipe size. As i mentioned earlier, i want to know the profile of flow in pipe to determine which pipe size could satisfy the need of flowrate without using too large pipe size. Clearly, bigger one will satisfy the feasibility aspect, but we need to consider the economic aspect too right?This is what i do. Thank you for asking.