THE INFLUENCE OF A SPIRAL ELEMENT ON THE LONGITUDINAL DISPERSION OF LIQUID IN THIN-LAYER EVAPORATOR

The application of a spiral element in a static thin layer evaporator (STLE) radically changes both the hydrodynamics and consequently the r ate of heat transfer. The principal objective of our work was to estab lish a relationship between the longitudinal mixing of liquid in the t hin layer evaporator (TLE) and conditions of flow down the evaporator surface. A total of 221 measurements have been performed using the STL E and the TLE equipped with spiral elements of two different pitches. The quantitative measure of the longitudinal mixing is the coefficient D which in our work changed from 280 X 10(-5) m(2) s(-1), for the TLE equipped with immovable spiral element 1, to 3159 X 10(-5) m(2) s(-1) for the STLE. The numerical values of the longitudinal dispersion coe fficients D, for all measurements, represent a logical integrity. The smaller the spiral pitch, the smaller is the coefficient D, and more p rofitable conditions occur for heat and mass transfer.