New solutions to produce a cryogenic void fraction sensor of round cross-section and its applications

•A new variant of the void fraction RF-sensor of the round cross-section is presented.•A new material, ceramic type VK-94-1, was used to make the sensitive part of the sensor.•A new meander line layout is proposed to minimize the intrinsic error.•Main characteristics of the sensor are discussed. A new variant of the void fraction RF-sensor of the round cross-section with ID=38mm is presented. Its sensitive part is made of the ceramic pipe with a meander line on the outer surface. This technique does not disturb the flow moving in the metal pipe of the same diameter. The technical solutions to provide rather high uniformity of the electric field within the sensitive volume and excellent stability of the readings are described. Irregular steps of the meander line are chosen after computer calculations and experimental checking. Some disadvantages of the previous modifications are shown as well. A new calibration procedure is discussed: it takes into account the dependence of the resonant frequency of the empty RF-sensor on the temperature of the sensor body. The method to find a mass flow rate of the two-phase helium and hydrogen flows in the range of void fractions from 0% to 100% is demonstrated with the new RF-sensor.