Abstract

Incorporation of agitation to spouted and fluidized bed dryer result in significant increases in the drying capacity (Qs), although product retention persist, which is reduced by increasing the air flow. The physical phenomena occurring in these dryers with several liquid substrates was analyzed and the residence time distributions (RTD) were obtained by the use of dye tracers. The residence time (?) was found to be a function of the rate of agitation (n) and reaches a minimum at n = nopt, which was characteristic for each type of substrate, and where maxima also appeared for the drying capacity (Qs = Qsmax) and the heat transfer coefficient (Nup = Nupmax). The RTD can be modeled by series of consecutive dryers and a modified Vanderschuren and Delvosalle model can be employed to calculated moisture of the dry product.