The figure depicts a device for measuring the electrical conductivity of a flowing liquid. Unlike prior such devices, this one does not trap gas bubbles entrained in the liquid.

A Straight Tube With a Smooth Inner Wall is formed by an assembly of electrodes and insulators in a hollow cylindrical configuration. The electrical conductivity of a liquid flowing along the tube is measured by use of the electrodes.

Usually, the electrical conductivity of a liquid is measured by use of two electrodes immersed in the liquid. A typical prior device based on this concept contains large cavities that can trap gas. Any gas present between or near the electrodes causes a significant offset in the conductivity reading and, if the gas becomes trapped, then the offset persists.

Extensive tests on two-phase (liquid/ gas) flow have shown that in the case of liquid flowing along a section of tubing, gas entrained in the liquid is not trapped in the section as long as the inner wall of the section is smooth and continuous, and the section is the narrowest tubing section along the flow path. The design of the device is based on the foregoing observation: The electrodes and the insulators separating the electrodes constitute adjacent parts of the walls of a tube. The bore of the tube is machined to make the wall smooth and to provide a straight flow path from the inlet to the outlet. The diameter of the electrode/insulator tube assembly is less than the diameter of the inlet or outlet tubing. An outer shell contains the electrodes and insulators and constitutes a leak and pressure barrier. Any gas bubble flowing through this device causes only a momentary conductivity offset that is filtered out by software used to process the conductivity readings.

This work was done by Edward W. O’Connor of Hamilton Sundstrand for Marshall Space Flight Center. For further information, contact

Chris Flynn, Hamilton Sundstrand Company New Technology Representative, at This email address is being protected from spambots. You need JavaScript enabled to view it. .

Refer to MFS-31931.