Non-invasive two phase flow measurement using soft X-ray attenuation

Some of the most difficult problems in multiphase flow measurement lie in the area of pneumatically-conveyed solids. Many examples exist, of which one of the most important is the conveyance of pulverised coal in the fuel lines feeding power station boilers. In this type of flow, pneumatic suspensions may be extremely dilute, so that radiation attenuation using common radionuclides may be less than 1%. If radiation of much lower photon energy is used, high attenuation in pipe entry and exit radiolucent windows may have to be tolerated. High intensity, soft X-ray fields are therefore required in this application. An X-ray tube operating at 25 kVp and 0.4 mA can deliver radiation intensity three orders of magnitude higher and attenuations over one order of magnitude higher than are obtainable from a 2 GBq Am-241 point source in the same geometry. The paper attempts to evaluate the potential and limitations of this approach for the particular example of dilute pneumatic suspensions of solids.