Design and Fabrication of Liquid Film Sensor Using Flexible Printed Circuit Board Based on Three-Ring Conductance Meter

In this study, the three-ring conductance meter is fabricated on FPCB. The FPCB can tolerate relatively high temperature (400K). And thanks to the high flexibility, it has applicability on a curved surface. This paper introduces the design procedure of liquid film sensor and calibration result in order to confirm its feasibility. Through the electrical potential analysis, liquid film sensor was designed. Two-phase flow is frequent phenomena in some industrial environments. Especially gas-liquid flow is common in nuclear industry, understanding the two-phase flow is an important part of the analysis on safety and performance of nuclear safety system. As the liquid film thickness is one of key factors, a lot of research has been conducted for measuring liquid film thickness. Recently, electrical methods have been widely applied for many years. Damsohn developed a high speed liquid film sensor that has high resolution for time and space by combining conductance method with wire-mesh signal processing unit. However, since the electric conductivity of liquid can be affected by its temperature, the conventional electrical conductance methods have limitation on applying for varying temperature conditions where a heat transfer is involved. Coney proposed three-ring conductance method that can compensate the change of conductivity of the liquid. Kim and Lee showed the feasibility of the three-ring conductance meter by fabricating it on printed circuit board (PCB) and flexible printed circuit board (FPCB) individually. Calibration procedure was conducted with the manufactured film sensor. By the result of calibration result, it was confirmed that this sensor can measure the film thickness up to 3 mm. In addition to this calibration, study on sensitivity of the sensor and optimum signal processing are needed for applying in dynamic measurement of various two-phase flow experiment