6 replies to this topic

[EAGLE80]

Hi,

I am facing problem to calculate accurate pressure drop for transition flow region. Fluid is fuel oil with viscosity of 680cp and density 999kg/m3. Based on NRe, flow is in transition region. Using Colebrook equation (which is truly applicable to turbulent region) for friction factor calculations, results of different programs vary significantly. Can some one help to guide how to counter this situation?

Is there other equation to calculate friction factor in transition region?

Can we rely on Colebrook equation results? If yes then shall we rely on programs like Pipesim, Stoner or in-house spread sheets?  It is noted that calculated friction losses from in-house spread sheet are lot more as compared to simulation program results.

Please share your thoughts.

 

Regards

[demank]

Refer to GPSA Section 17. 'Fluid Flow and Piping", Colebrook equation is only valid when Re no. above 4000.

WHen using spreadsheet, sometime I use Friction Factor Graph to get the friction fator value fm.

 FrictionFactorGraphGPSA.png   231.05KB   2 downloads

 

[jrtailor09]

Dear MTQ80,

 

I feel viscosity of fuel is very high 680 cp. kindly re check.

 

Regards,

[EAGLE80]

Thanks Demank.

In the traditional Moody chart, fm=64/Re is extended to transition region and this give lower fm value. While in certain programs and in spread sheets, normally average weighted value of fm is considered in transition region, which makes more conservative.

Another approach can be modified Moody graph.

 

  

 

Attached Files

•  Modified Moody Diagram.pdf   258.88KB   33 downloads

[breizh]

Consider this resource where you can find an answer to your query .(churchill's equation)

 

Breizh

Edited by breizh, 02 July 2013 - 03:00 AM.

[demank]

Also, in my spreadsheet (of course with the permission of my superrior and the client). we interpolate the laminar and turbulent friction factor by this equation:

 

f = (Re - 2000)(f_turbulen - f_laminar) / (4000 - 2000) + f_laminar

 

 TransitionFlowMoody.png   23.28KB   3 downloads

Edited by demank, 02 July 2013 - 04:31 AM.

[EAGLE80]

Thanks Breizh. Results from Churchill equation looks promising for transition flow region. I noticed that these results are in agreement with the Modified Moody chart (attached earlier). Modified Moody chart incorporated approximation by Haaland (1983) and Nikuadse (1932).