[en] Residence time measurements in the chemical industry, residence time spectrum and reactor models for a pipe reactor with stirring device, application of radio-isotopes for the investigation of the axial mixing in a rotary tube, experimental investigations on a production rotary tube furnace, intermixing studies and quantitative analysis with radioactive indicators, applicability of radio-isotopes in the aluminium industry, pneumatic homogenization, possible applications of the radionuclide technique to investigate stationary and non-stationary multiphase flows, flow investigation in the chemical industry and the determination of the flow rates in a vibrating muffle furnace for hardening and tempering of screws, are dealt with. (HK/LH)