4 replies to this topic

[manish.iitr]

Dear All

I am calculating pressure loss in Aspen Plus for a pipeline with two phase flow. The total pressure loss in pipeline is sum of static pressure loss (due to elevation), frictional loss & accelartion loss. I found an anomaly between static pressure loss calcualted by Aspen Plus & caluclated manually using standard forumla. Below is the data:

Total Mass flowrate 459156.2 Kg/hr Mass vapor fraction 5.7 % Mixture Density 128.0 kg/m3 Liquid Density 759.0 kg/m3 Vapor Density 8.6 kg/m3 Elevation Difference 21.3 m Pipe equivalent Length 40.0 m
Mass vapor fraction & liquid/vapor/mixture densities are same at inlet & outlet of pipe.

Aspen Plus caculated Static Pressure loss for above data is = 0.52 kg/cm2. In Aspen Plus, I have used Breggs Brills mehtod with 'Pipe' Model.

If we calcualte, the same with standard forumla i.e.; Static loss = (Mixture Density) X (Elevation Difference) X g; the static loss comes out to be = 0.27 kg/cm2

Could someone explain me the above anomaly!

[Technical Bard]

The difference is that the calculation method is estimating a liquid holdup in the pipe. Liquid holdup is the liquid fraction in the pipe, and is different from the flowing fraction. The liquid and vapour phases do not move at the same rate, so liquid is being "held up" in the upwards vertical flow line.

[Shivshankar]

Manish,

Is this horizontal or inclined flow ?

Regards
Shivshankar

[manish.iitr]

@Bard

In many books, I found simple correlation - Static loss = (Mixture Density) X (Elevation Difference) X g

Does it make such a huge difference when using above simple correlation instead of doing liquid holdup calculation. The two methods give very different values for static loss (0.52 kg/cm2 & 0.27 kg/cm2 respectively).

May I know what exactly liquid holdup in pipe means; and how do we caclulate it.

Is there any simplistic method for static loss calcualtion which is reasonalby correct.

@shiva

This is a vertical pipe with elevation difference of 21.3 m.

[Shivshankar]

Hello Manish,

http://www.wlv.com/p...ata/db3ch13.pdf

If you go on above link, you see example calculation of vertical tube on page 13-2 .

You can calculate for static pressure drop for homogenous fluid.

Static pressure = Homogeneous density X Elevation difference X g.

In the above book formula for Homogeneous density is given, If you know the vapor quality you can calculate homogeneous void fraction.

http://www.wlv.com/p...ata/db3ch17.pdf

http://www.cheresour...w-correlations/

http://www.tristanbr...woPhaseFlow.pdf

Regards
Shivshankar

Attached Files

•  Two Phase Flow.zip   2.67MB   65 downloads

Edited by Shivshankar, 25 June 2012 - 03:35 AM.