Regarding the inaccurate differential pressure orifice plate flow readings at the inlet of the diaphragm compressor
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Hello, everyone! In the project, we encountered an issue where the readings from the differential pressure orifice plate flow meter were inaccurate; please help us figure out what the problem is. Upstream of the flow meter is a gas source with periodically fluctuating flow rate → buffer tank → differential pressure orifice plate flow meter (10 before and 5 after) → diaphragm compressor. When the compressor is turned off, the flow meter readings are relatively accurate; however, once the diaphragm compressor is started, the flow meter readings are much higher than the gas flow rate upstream. What is the reason for the inaccurate traffic reading?
The main issue lies in the straight pipe sections; since the compressor’s air intake is located at the rear end, when the compressor is in operation, vibrations or a high volume of air drawn in can cause inaccuracies in the measurements taken by the orifice flow meter. Recommended solutions include: (1) increasing the length of the straight pipe sections between the flow meter and the compressor； (2) Add a (flow regulator) between the flow meter and the compressor. (3) Replace the orifice flow meter with a balanced flow meter (vibrations must not occur under any circumstances)
Orifice plates are used to measure flow rate, and they measure the flow rate of a stable fluid, that is, when the flow pattern of the fluid is stable. For fluids in a non-stable state, measurements will have large errors.
In my humble opinion, without the compressor running, the flow rate is definitely stable; however, when the compressor is operating, the medium being drawn in becomes unstable, which leads to unstable backflow pressure and flow rates. As a result, the amount of material drawn into the compressor is also unstable. Moreover, the pipelines of the flow meters are thin, which makes them even more susceptible to such effects.
It is also possible that the compressor’s displacement is insufficient, with the specifications being overstated.
A differential pressure flow meter measures steady-flowing fluids based on the Bernoulli principle. Measuring pulsating fluids can result in significant errors.
Thank you all for your replies! After conducting a simple experiment, it was found that for pipes of the same diameter, the smaller the pressure difference across them, the greater the deviation between the measured results and the theoretical calculations. It is inappropriate to set the flow rate of the orifice plate at a fixed value when the pressure difference before and after is estimated to be very close!