Wire-mesh sensor

Wire-mesh sensor mounted into a pipe

Wire mesh sensor allows to perform a quantitative determination of phase distribution in the pipe cross-section. This instrument can be seen as an intrusive tomograph that enables measurements of the instantaneous cross sectional void fraction distribution with a sampling frequency up to 10 kHz. Since the wire-mesh sensor also enables measuring instantaneous propagation velocities of the phase interface, it essentially allows constructing a 3D dynamic phase distribution that can be further analyzed quantitatively.

Schematic presentation of the pipe cross section with mounted sensor	Schematic presentation of the pipe side view with mounted sensor

Wire-mesh sensor consists of three parallel wire layers perpendicular to the pipe axis. Each layer is built of eight parallel thin steel wires. The wires in the external layers have the same direction, while in the intermediary layer the wires are perpendicular to those in the external layers. Therefore, the wires of any two successive layers form a rectangular mesh.

The operation principle of the wire-mesh sensor is based on the difference in conductivity of the two phases. In the current study, water has good electric conductivity, while air is an electrical insulator. The central layer serves as a transmitter, while the external layers serve as receivers. Each wire in the transmitter plane is periodically activated by a multiplexer circuit by a short voltage pulse. An additional multiplexer circuit is used to connect consecutively each one of the wires in the receiver plane during the single pulse supplied to the transmitter wire. Each output pulse depends on the local instantaneous conductivity at each crossing point of the transmitter and the receiver wires.

Local instantaneous gas fractions near each junction are calculated assuming a linear dependence of the electrical conductivity on the liquid holdup. The grid spacing limits the spatial resolution of the instrument in the pipe cross-section. The spatial resolution in the axial direction is determined by the interface propagation velocity, as well as by the sampling frequency at each junction (up to the maximum of 10 kHZ for the whole cross section of the pipe). The instantaneous phase distribution is thus obtained with high temporal resolution.