Flow thru the Vacuum pump

[sasuan]

Hello
I need to calculate the flow through the vacuum pump which pulls air out of the condenser to keep the vacuum for the unit. Can anybody help me with this?
Right now, we are using the flow meter and taking reading inch by inch across the diameter of the pipe and the average value times area of the pipe gives us the average flow thru the pipe. But, we are getting some erroneous values recently. So, I was wondering if anybody knows of any other test that can be done online to test the flow thru the pump

Thanks in advance

 

[25362]

I understand you are averaging from inch to inch. However, one of the the most common ways to measure flow at the traversing stations is to divide the pipe into a number of equal areas taking measurements at their centroid.

The location of the measuring points, as r/D distances from center, are tabulated herebelow:

3 points/radius 0.204, 0.353, 0.457
4 points/radius 0.177, 0.306, 0.395, 0.468
5 points/radius 0.158, 0.274, 0.354, 0.418, 0.474
6 points/radius 0.144, 0.250, 0.323, 0.382, 0.433, 0.479

Taken over two perpendicular diameters.

There are other methods of locating the probes.

There are, as well, anemometers such as the hot wire, or ultrasonic.
Besides, can you measure the discharged air from the vacuum pump ?

Have a look at Fan Engineering by the Buffalo Forge Company (Buffalo, New York), for the subject of measuring air flows.

 

[Torricelli]

which size of pump / dia. of piping are we talking about ?

 

[quark]

Are your readings compensated for changes in pressure? I mean are they mass flow readings?

Regards,

 

[rmw]

You can put a block valve (like a ball valve) in the exhaust line with an appropriately sized rotameter piped to be in a bypass loop around the block valve so that when the block valve is closed, the flow is forced through the rotameter.

HEI gives some ranges of air leakage to be expected on given sizes of condensers with respect to exhaust flow rate, turbine openings, etc.

rmw

 

[sailoday28]

If the flow varies significatly with radius, then an average is only an approximation. Numerical integration of flow/area*change in area over the area of the pipe will give a better estimate of flow.