Capacitance type void meter

For studies of two phase flow, it is very important to measure a void fraction; the fraction of air in water flow. Many methods for the void fraction measurement have been developed hitherto. They are, however, insufficient in respect of their accuracy, response, handling and so forth. This paper reports a void detecting method which is based on a change of the equivalent dielectric constant. By this method, the instantaneous void and the local void can be measured with a fast response. Preliminary experiments are carried out with both the simulated void in the form of glass tubes and the real void in air-water mixture. It is shown that the linearity of this device is good. The basic principle of this void measuring method is discussed, comparing the real void with equivalent circuits which consist of capacitances and resistances. Experimental results of this device applied to a thermodynamic-hydrodynamic loop which simulates the nuclear reactor are shown. (author)