Wire-mesh sensors belong to flow imaging techniques and allow the investigation of multiphase flows with high spatial and temporal resolution. The wire-mesh sensor principle is based on a matrix-like arrangement of the measuring points. Two set of wire electrodes are stretched along a vessel or pipe having a small axial separation between them and being perpendicular to each other. This way, a mesh or a grid of electrodes is formed in the cross-section (see figure).
(left) Principle of wire-mesh sensor having 2 x 8 electrodes. (right) Wire-mesh sensor for the investiagtion of pipe flows and associated electronics.
The transmitter electrodes are sequentially activated while all receiver electrodes are parallel sampled, in such a way, that an electrical property (conductivity or permittivity) of the fluid in each crossing point is evaluated. Based on those measurements the sensor is thus able to determine instantaneous fluid distribution across the cross-section, for instance, of a pipe. The following pictures show the three-dimensional representation of a slug flow and the results of the visualization of different flow regimes of a air-water vertical flow.
Horizontal silicone oil-air slug flow in a rectangular channel measured by a capacitance wire-mesh sensor.
3D-Visualization of data acquired with a wire-mesh sensor in a vertical test section of air-water flow at the TOPFLOW test facility. By changing the air superficial velocity Jair at constant water superficial velocity Jwater = 1 m/s different flow patterns at the pipe are obtained. In the figure bubbly flow, slug flow and churn-turbulent flow can be recognized.
Types of sensors
For the investigation of liquid flows conductivity wire-mesh sensors were firstly developed. They determine the local conductivity of a liquid in the cross-section of an investigation volume. They are well suitable for the investigation of mixtures with an electrically conductive phase, as the case is with water and steam. Such sensors were employed in various applications and have been used world wide.
For further information about conductivity wire-mesh sensors.
The field of application of conductivity wire-mesh sensors is, however, limited by the fact that at least one flow phase must have an electrical conductivity of κ > 0.5 μS/cm. For this reason the principle of the wire-mesh sensor was extended to applications with non-conducting fluids. Here was crucial the development and integration of electrical capacitance (or permittivity) measurements into the principle of the wire-mesh sensor. The so-called capacitance wire-mesh sensor is thus applicable also in flow problems with oil or other organic and electrically non-conducting liquids. Therefore this sensor opens a variety of new application fields, for example in chemical engineering and in the oil & gas industry.
For further information about capacitance wire-mesh sensors.
Wire-mesh sensors can be manufactured depending on application requirements in diversity of different cross-section geometry and operating parameters. Newest wire-mesh sensors can be employed in a environmental conditions range of up to 286 °C and 7 MPa. Associated electronics for signal generation and data acquisition achieves a maximum temporal resolution of 10,000 pictures/second.
For further information about the different types of wire-mesh sensors.
Da Silva, M. J.; Schleicher, E.; Hampel, U.
Capacitance wire-mesh sensor for fast measurement of phase fraction distributions
Measurement Science and Technology 18(2007)7, 2245-2251
Pietruske, H.; Prasser, H.-M.
Wire-mesh sensors for high-resolving two-phase flow studies at high pressures and temperatures
Flow Measurement and Instrumentation 18(2007)2, 87-94
Manera, A.; Prasser, H.-M.; Lucas, D.; van der Hagen, T. H. J. J.
Three-dimensional flow pattern visualization and bubble size distributions in stationary and transient upward flashing flow
International Journal of Multiphase Flow 32(2006), 996-1016
Prasser, H.-M.; Misawa, M.; Tiseanu, I.
Comparison between wire-mesh sensor and ultra-fast X-ray tomograph for an air-water flow in a vertical pipe
Flow Measurement and Instrumentation 16(2005), 73-83
Rohde, U.; Kliem, S.; Höhne, T.; Karlsson, R.; Hemström, B.; Lillington, J.; Toppila, T.; Elter, J.; Bezrukov, Y.
Fluid mixing and flow distribution in the reactor circuit, measurement data base
Nuclear Engineering and Design, 235(2005), 421-443
Prasser, H.-M.; Beyer, M.; Böttger, A.; Carl, H.; Lucas, D.; Schaffrath, A.; Schütz, P.; Weiß, F.-P.; Zschau, J.
Influence of the pipe diameter on the structure of the gas-liquid interface in a vertical two-phase pipe flow
Nuclear Technology 152(2005)1, 3-22
Prasser, H.-M.; Scholz, D.; Zippe, C.
Bubble size measurement using wire-mesh sensors
Flow Measurement and Instrumentation 12/4 (2001) 299-312
Prasser, H.-M.; Böttger, A.; Zschau, J.
A New Electrode-Mesh Tomograph for Gas-Liquid Flows
Flow Measurement and Instrumentation 9 (1998) 111-119
Da Silva, M.J.; Schleicher, E.; Hampel, U.; Prasser, H.-M.
Grid sensor for the two-dimensional measurement of different components in the cross section of a multiphase flow
WO 2007 121708, DE 10 2006 019178
Pietruske, H.; Sühnel, T.; Prasser, H.-M.
DE 10 2004 019739, WO 2006 114081
Prasser, H.-M.; Zschau, J.; Böttger, A.
Grid sensor for determining the conductivity distribution in flow media and process for generating measurement signals.
DE 196 49 011, WO 1998 23947, EP 941472, US 6314373