Designing a high temperature high pressure mesh sensor

Abstract

Abstract State-of-the-art turbulence models are expected to accurately predict flow behavior in a wide range of geometries and flow conditions for a wide range of fluid properties. These models rely on accurate time resolved measurements of scalar and vector flow variables. One such measurement technique for obtaining a high density of flow field variables with high time resolution is in the form of electrode-mesh sensors (WMS) which measure the local instantaneous electrical conductance of a flow at a large number of positions, typically in the cross-section of a conduit at frequencies up to 10 kHz. Extensive studies on single and multiphase flows have been carried out with mesh sensor technology in the past 15 years, often focused on flows directly related to nuclear power generation. However, essentially all of these experiments have taken place at low temperatures ( A new mesh sensor construction has been designed at the ETH Zurich for operation in high temperature and pressure pipelines by implementing novel materials, assemblies and a new sealing methodology. The mesh sensor package design is scalable so as to be compatible with standard flanged pipelines of size estimated to be DN10. The new design solves the problems discussed related to prior state of the art while at the same time allowing the sensor to operate at higher temperatures and to be manufactured and assembled more easily and more cheaply. The pressure barrier is no longer guaranteed by an epoxy, as in prior state of the art developed by other researchers, but rather by a standard graphite gasket between the sensor housing flanges, the same type that would normally be sealing a bolted flange joint, and commercially available threaded sealing glands. While still maintaining space for the standard number of bolts for a given flange size, such sealing glands could conceivably allow for a very high number of electrode signals to be extracted. The ability to carry a large number of conductors through the pressure barrier, in addition to the housing flange design, enables the installation of multiple mesh sensors, three layer sensors, or other instrumentation such as thermocouples, enabling the reconstruction of additional flow properties from measured data such as velocity and interfacial area concentration. A 16-transmitter, 16-receiver prototype sensor has been constructed for a DN80 pipeline; its individual components and some assemblies thereof have been tested in an autoclave at temperatures up to 285 °C in a liquid water-vapor environment with boiling at saturation pressure. Furthermore, a test section construction has enabled the sensitivity of the sensor to temperature changes via the variable electrical conductivity of deionized water as a function of temperature to be investigated.