Abstract
The concentration method for flow rate measurement is substantially distinct from other methods. It is often used to measure flow rate of water through a water-turbine of power stations, but few reports of measuring gas flow rate by the concentration method have been published. Some experimental results of flow rate measurement of air by this method is herein presented. The flow rate of air is obtained by measuring both injection rate of inert gas and inert gas concentration of mixed gas, and then substituting these values into eq. (1) or (2).
The accuracy of this method depends on whether the inert gas is perfectly mixed or not. In other words, after injected inert gas is mixed with the main flow through a mixing part, the inert gas concentration must be uniform over a sampling plane normal to the direction of flow. In this work, it is examined how long distance from an elbow is required in order to attain a stable concentration profile, when an elbow is used as a mixing part and the flow rate of air is 0.5 to 1.5m3/min. in 11/2, 2, 21/2 and 3 inches standard gas pipes.
Consequently, the stable concentration profile is attained at about 80cm downstream from an elbow, and its distance does not depend on both the main flow rate of air and the pipe diameter. The accuracy of this method using an elbow is within ±1%. The dispersion of measured values is within ±2% in this work. In spite of some insufficient results, this work may be the knowledge to measure gas flow rate by the concentration method.
