Minimum Straight Run of Pipe

What does the Manufacturer's Manual say?

Mostly it is 10D in upstream and 5D in downstream of a flow meter but I could not get the reason for the same.

There is disturbance to the flow streamlines' shape/profile when the flow passes a fitting such as an elbow, reducer, etc., and the diameters criterion is there to give the profile a chance to even-out again prior to going through the flowmeter. 5d downstream is so that the flowmeter's accuracy isn't disturbed by the next fitting downstream of it further contributing to disturbing the flow profile.

Every time a fluid goes through an elbow, a restriction, etc., a non-symmetrical flow profile is generated. Because of this, the flowmeter will not measure correctly because it was calibrated in a straight-run environment. By ten diameters downstream, the fluid profile is back to "normal".

10/5 pipe diameters upstream/downstream for the Venturi (full) tube.

Can you please tell me the reason for it to be 10/5 pipe dia.

See #5 above.

For an excellent explanation of flow development, the reason for meter run length, see the 13 page paper, An Introduction to Flow meter Installation Effects, published by Great Britain's National Measurement System. It is well illustrated with very written (no math) explanations. But you'll find that the answer they provide is

"Standards and manufacturers quote the minimum length of straight pipe required.", which has already been stated in this thread.

The site requires registration and log-in, but access is immediate upon completing the registration.

The paper is listed under the Best Practice Guides, here:
http://www.tuvnel.com/tuvnel/best_practice_guides

10D to 5D for upstream and downstream respectively, becoz flow profile of the the substance is very high for turbulent flow, thats why monimum 10 times distance required to straite the flow of upstream as per pipe size.

Just to be sure we are talking about the correct distances could you tell us exactly what type of flow meter you are asking about? What Tech is the meter using to measure the flow / velocity?

It matters....

Cheers,

Eric

What I am looking for is, any mathematical equation which can tell what should be the minimum straight run of pipe for different flow meters?

The first thing we need to know is what type of flow technology you are thinking about, as they each have different tolerances for flow steam velocity variations. The greater the flow steam velocity variation the higher the degree of accuracy degradation. So, what accuracy are you looking for and what type of meter are you thinking of using? An equation can not be developed with out very detailed data on the process. Let's start with the flow measurement equipment and take it from there.

For deciding the minimum straight run of pipe,, you have to refer the concerned standards relevant to the flowmeter type. If it is orifice meter you can refer Table (mostly 3) of ISO 5167 or AGA 3, which has various cases of installation of flow meter ( like presence of reducers, elbows,etc). For Ultrasonic meter, the recommendation is mentioned in AGA 9 and for turbine in AGA 7

Dear Mr.verma.707

The UNIFORMITY of flow in the pipe is the essential criterion. For Compressible Fluids like gas, air it is 10/5, and for Incompressible Fluids, it is 5/3 to that of the Pipe Line size, for Up-Streme and Down-Streme.

DHAYANANDHAN.S