The positive displacement method for calibration of gas flow meters. The influence of gas compressibility

An easy technique to calibrate small gas flow meters is the positive displacement method, whose application requires a simple setup and laboratory procedure. With this methodology there is an unknown gas flow coming from a given gas source that must be known by the action of a gas flow meter. The gas flow to be measured is sent to a reservoir with rigid walls and full of water. As gas enters the reservoir water flows out and the amount of water exiting the reservoir in a given time interval can be connected with the average gas flow in that same time interval. In simple terms the volume flow rate of water leaving the reservoir is equal to the gas volume flow rate entering it. The water being incompressible, the density variation is meaningless, however the same cannot be assumed for the gas.Considerations on the simple techniques to be used to minimize the importance of gas compressibility are presented in the paper.