Abstract
It is found that the residence time of particles flowing through rotary dryers and coolers under the conditions of no air flow and air flow can be expressed by the logarithmic normal distribution, and also that the median of residence time is approximately equal to the apparent mean residence time.
As the empirical equation for the latter had been obtained by the authors, the empirical equations concerning the geometric standard deviation, which is the other parameter in the distribution function, are studied in this paper. As a result, Eq. (8) and Eq. (10), respectively, are obtained as the empirical equations of the geometric standard deviation under no air flow and air flow. These equations approximately correlate the experimental results within the accuracy of ±20%. It is also found from the both equations that the geometric standard deviation under air flow is large in comparison with that under no air flow.
