3 - Residence time of particles and its distribution

Abstract

This chapter focuses on the investigation of residence time distribution. Residence time distribution is an important behavior of particle crowds because of its complexity. Any process takes a certain amount of time and the length of the residence time often dictates the occasions when particular equipment or technology can be used. A theoretical analysis is helpful for understanding the basic characteristics of impinging stream processes and the performances of the related devices. In an impinging stream device, the residence time distribution of particles is most important in the impingement zone, because this zone is the major active region for heat and mass transfer between phases in such a device. The residence time distribution of particles is related to the properties of the particles and the gas flow, including the size distribution and the velocity of the gas flow and its profile. In practically applicable impinging stream devices, the particles being processed usually have relatively narrower size distribution. In the measurement of residence time distribution, the most convenient and widely employed input signals are the impulse and the step change. For a fluid, as continuous phase, both the signals are simple and convenient to carry out; while for solid particles, it is very difficult to input any one of the two signals usually used and the so-called frequency response is even more difficult.