The residence time distribution in systems with recirculation on the outlet flow

A method for the analysis of the Residence Time Distribution (RTD) in a system where a fraction of the output flow is recirculated to the inlet is presented. This method (so called direct method) utilizes Laguerre functions and appears to be very useful in radiotracer flow studies. Experimental curves with different disturbances were simulated on a digital computer to investigate the applicability of this method. The practical use of this method is demonstrated on a circular settling basin in a sewage treatment plant. (author)