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Pressure Losses in Air Duct
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Source：Internet Author：Unknow Pubdate：2010-06-17
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galeblanc (Aerospace)
1 Jun 10 12:09
I am currently trying to size a Pressure Blower that will be used to cool an engine. A Pipe/Hose of 40 feet will be connected at the outlet of the blower. The flow required is 660 cfm and my hose / pipe size is 5" ID.
Is there a simple way to determine pressure losses (in. H2O) in 90 deg. pipe elbows as well as flexible accordian type hoses?
Please provide some design guides / links that could help.
Thanks!!
walz (Mechanical)
1 Jun 10 15:52
i want to see how this pipe elbow looks like in elbow.
there are various types of 90 Deg Elbows in round shape which vary in different manner. Ashrae has a number of fitting database and this can be easily calculated. You can either find ASHRAE Handbook Fundamentals - Duct Design Chapter. or send me a diagram of this elbow. I'll chose the nearest or exact type of elbow & calculate for you by specialized softwares which do this
字串9
willard3 (Mechanical)
2 Jun 10 9:04
SMACNA also has data on fitting losses.
http://www.smacna.org/bookstore/pdf_toc/HVDES_T.pdf
galeblanc (Aerospace)
2 Jun 10 10:12
Hi Walz,
Would you happen to have a pdf document of the types of elbows with the equation to calculate the losses? I would also need an equation for the losses in straight galvanized sections. The elbow will be the most standard one.
Thanks!
Gabriel
walz (Mechanical)
2 Jun 10 15:45
i Tried to upload the 7 MB pdf file, but couldnt
and i cant extract the PDF aswell as it is protected.
For straight ducts it very simple, all you need to know is that friction loss rate (in of water / 100ft of duct)
But you need to give me atleast the material of pipe. I will assume it be be flexible metallic and calculate for the duct pressure loss like this. 字串5
with 5in as ID and 660 CFM, the friction rate is 15.632 in / 100 ft of duct. Muliply this value by 40/100 to get 6.2528 in of water . thats your result for the duct.
As for as 90 Deg elbow is concerned, i calculate for you at least 5 different types of elbows, and list you their Fitting number, just download the image file for your referrance of these 5 elbow types. Chose the best which suites your elbow kind as i cant chose any of them as standard.
CD3-1 : Pressure Drop = 0.24 in of water
CD3-2 : Pressure Drop = 0.45 in of water
CD3-5 : Pressure Drop = 0.75 in of water
CD3-9 : Pressure Drop = 0.535 in of water
CD3-10 : Pressure Drop = 0.20 in of water - http://files.engineering.com/getfile.aspx?folder=bdcfb4b2-af9a-42ff-b1b2-61
galeblanc (Aerospace)
2 Jun 10 18:20
Walz,
That's amazing and the values seem very good. I have found my HVAC book and there is some information in there and I will compare to your results to see if they match. Obviously the 7MB file would be great. Would it work by email instead? 字串9
Thanks very much for you helps, you're doing the work for me!!
mauricestoker (Mechanical)
3 Jun 10 8:34
The tough part would be calculating loss through accordion type hose. You might need manufacturer data and percentage hose compression estimates, assuming no sagging. ASHRAE and SMACNA are not real exact on that.
galeblanc (Aerospace)
3 Jun 10 10:05
I do have the manufacturer's curves for friction losses due to the hose, so with what I have now I should be ok to size my pressure blower!! Thanks guys!!
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