Pressure loss to double wall pipe (ventilation)

[longz]

Hi every body,

I need help to calculate the pressure drop to double wall pipe with information as below, i understand need calculate pressure loss to the straight pipe, elbows and supports but I don't know exactly how.

- Fluid : air
- Double wall pipe (stainless steel) with outer pipe OD89mm, wall thickness 3mm, inner pipe OD61mm, wall thickness 2mm. the air will blow into the void between inner and outer pipe
- Pipe distance : 7m.
- Number of 90 degree elbow : 7 pcs
- Number of plastic support to inner pipe : 9 pcs
- Air flow capacity 28 m3/h equivalent 7.8 L/s.

Some drawing for clear view:
1. Double wall pipe section

2. Double wall pipe section with support, the support is obstruction to the air flow similar to orifice.

3. Elbow

Thank every body.

 

[Chestermiller]

Which are you trying to determine, the pressure of the water or the pressure of the air?

 

[longz]

Hi Chestermiller,

I need to determine the pressure drop to the air.

Thank

 

[Chestermiller]

Hi Chestermiller,

I need to determine the pressure drop to the air.

Thank

If the air were flowing through a circular pipe, would you know how to get its pressure drop? If so, please describe.

 

[longz]

I have no idea, can you provide some instructions ?

thank

 

[Chestermiller]

I have no idea, can you provide some instructions ?

thank

See chapter 7 of Transport Phenomena by Bird, Stewart, and Lightfoot.

 

[longz]

I really sorry as I can't get this book, can you advise the specific mathematic formula ?

 

[longz]

Hi Chestermiller,

I made a study and draft a calculation to pressure drop but I not sure it is correct 100% or not, can you please have a check and correct me if i was wrong something.

thank

 

[Chestermiller]

Hi Chestermiller,

I made a study and draft a calculation to pressure drop but I not sure it is correct 100% or not, can you please have a check and correct me if i was wrong something.

thank

I didn't check your arithmetic, but I can tell you that you have done this exactly the way I would have done it. Very nice work. Kudos!

Chet

 

[longz]

Hi Chestermiller,

I found a online calculator exactly same to this matter but the result is quite different in Reynold number (509853 versus with 4988 as mine calc.) caused me confusing, can you please have a look and advise the reason? below is the link of software and information input/output.

http://www.pressure-drop.com/Online-Calculator/index.html

Input calculation

Output calculation

 

[Chestermiller]

Hi Chestermiller,

I found a online calculator exactly same to this matter but the result is quite different in Reynold number (509853 versus with 4988 as mine calc.) caused me confusing, can you please have a look and advise the reason? below is the link of software and information input/output.

http://www.pressure-drop.com/Online-Calculator/index.html

Input calculation

View attachment 213951

Output calculation

View attachment 213952

In their calculation output, the viscosity used looks too low by a factor of 100.

 

[longz]

Hi Chestermiller,

Thank for advices, you are correct. I changed the value of the viscosity and the software output similar to mine calc.

To pressure drop of inner pipe support ring, could you please advise some instructions ? I considering this is multi-hole orifices plate but the point is the holes is not same and have multi plates on the pipe route. I don't know how to start the calculation.

 

[Chestermiller]

Hi Chestermiller,

Thank for advices, you are correct. I changed the value of the viscosity and the software output similar to mine calc.

To pressure drop of inner pipe support ring, could you please advise some instructions ? I considering this is multi-hole orifices plate but the point is the holes is not same and have multi plates on the pipe route. I don't know how to start the calculation.

In a case like this, you have to use your best judgment as to whether the multi-hole is adequate. Compared to the total pressure drop, how much does the pressure drop across the plate matter?

 

[Nidum]

Simple CFD analysis using the default laminar flow model in OpenFoam .

5 m/sec uniform air velocity at inlet . Zero pressure (gauge) at outlet . Air flows from left to right .

So roughly 110 Pa pressure drop per support plate . Almost nothing really and certainly negligible .