Total Flow Measurement by Using Auxiliary Pipe Line

Abstract

In the shunt flowmeter, an inferential meter is used as an integrator for a differential pressure flowmeter. The shunt flowmeter is based on the experimentally recognized fact that the pressure drop through a flowmeter of propeller type is approximately proportional to the square of the flow rate.
In the method, here reported, an auxiliary pipe line is used to integrate the flow rate. It may be either a separate pipe line or a bypass of the main. The flow rate of the auxiliary pipe line is so controlled that the ratio of the flow rate of the main to that of the auxiliary is kept constant all the time. The total flow of the auxiliary pipe line is measured by a positive displacement meter inserted in the line. Then the total flow of the main line is obtained from that of the auxiliary line and the ratio of the flow rates.
The advantages of this method are as follows:
(1) As the flow rate of the auxiliary line is controlled to be proportional to that of the main line, the ratio of the flow rates is always maintained exactly constant. Therefore the total flow of the main line is known with a high accuracy.
(2) If the liquid of the main flow being unsuitable to branch into the auxiliary line, the measurement is performed by using another adequate liquid flow through the auxiliary line, because the auxiliary may be equipped separately from the main.
(3) When similar differential pressure flowmeters are used in the main and auxiliary line, the discharge coefficient needs not be determined experimentally, for the discharge coefficients of the meters cancel with each other in the expression of the ratio of flow rates.