A Comparison of Two Experimental Methods for Measuring Axial Dispersion Coefficient

Industrial processes such as, calciners, impregnators, and cement mixers frequently use rotating drums for radial mixing of granular material. However, axial mixing can also have an impact on the mixing process. Therefore, when controlling the residence time is imperative, the axial dispersion behavior must be taken into consideration. One way of quantifying axial mixing is through the axial dispersion coefficient, which is a function of processing conditions as well as material properties. There are multiple experimental methods of calculating the axial dispersion coefficients.

A common method is to take high-resolution pictures of axial mixing in the rotating drum and create a concentration profile using image analysis via software, such as MatLab. An alternate technique is to use a spectrophotometer to create concentration profiles from samples taken from the rotating drum. This work compares the methods and accuracies of these two empirical approaches. Based on the characterization of numerous granular materials, it was found that the spectrophotometer-based method yields more precise results than the image-based method.