Enhanced Local Void and Temperature Measurements for Highly Transient Multiphase Flows

We introduce a novel combined-temperature-and-conductivity needle probe measuring system for local void fraction measurements in multiphase-flow experiments. The system is able to deal with direct sheathed microthermocouples as well as open thermocouples. It consists of a thermoneedle probe connected to a special electronic circuit using an 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 microthermocouple. After system buildup 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 and gas-steam-water flow experiments have been carried out to demonstrate the system performance.