Enhanced Local Void and Temperature Measurements for Highly Transient Two-Phase Flows

We introduce a novel combined temperature and conductivity needle probe measuring system for local void fraction measurements in two-phase flow experiments. The system is able to deal with direct sheathed micro thermocouples as well as open thermocouples. It consists of a thermo needle probe connected to a special electronic circuit using AC measuring technique for the conductivity measurements and a high gain instrumentation amplifier with very high common mode rejection for the amplification of the Seebeck voltage generated by the micro thermocouple. After system build up and calibration, the system has been tested in different experiments. In a dropping experiment the time constant of the temperature measurement of the needle probe system was determined as 3.6 ms. Additionally, steam-water experiments have been carried out to demonstrate the system performance.