This paper is concerned with the investigation of the mixing process in a pilot scale continuous powder mixer, from both experimental and modelling points of view. A Markov chain model is proposed to simulate the residence time distribution (RTD) obtained from tracer experiments and detection by image analysis. The general model consists of 10 continuous stirred tank reactors with identical exchange coefficients and may serve as a basis for other applications. A 2D chain model is also developed and applied to take into account more features of real flow, such as crosswise mixing. Agreement between the model results and experimental data is more than reasonable, and gives a clear physical meaning to the parameters introduced. The characteristics of the process are controlled by the rotational speed of the mixer, which appears to be the key scale-up variable along with stirrer design.