A radioactive tracer technique for particle velocity measurement in solids‐gas systems

To record the velocity history of a particle in complex problems of solid‐gas flow with greater accuracy than is possible with existing methods, a technique was developed which in essence consists of following the flight of the particle under test—which has been previously tagged with a suitable gamma‐emitting nuclide—by means of Geiger probes placed at predetermined points along the outside surface of the duct or reactor and parallel to its axis. Sharp timing pulses are thus obtained on the screen of a cathode‐ray oscilloscope, which permit the estimation of the time elapsed between probe stations to less than 1/1000 second. Complete description of the electronic aspects of the method is given, and details of the particle preparation are outlined. A brief description is given of the application of the method to the determination of the rate of mass and heat transfer from particles in accelerated motion in a turbulent co‐current gas stream and to the study of the effects of the turbulent flow parameters on the drag coefficients of particles in highly turbulent fields.