RTD studies in a falling film graphite evaporator with internal spiral fins: Influence of the geometry

A hydrodynamic study of a new graphite evaporator has been performed. In th is exchanger the fluid flows as a thin film on a spirally wound fin which f orms a spiral staircase inside a tube. The slope theta(m) of the spirally w ound Rn is modifiable. The residence time distribution (RTD) of the film wa s measured for different fin slopes theta(m) and several film flowrates m(f ). The Row pattern was then modelled thanks to the DTS software as a cascad e of perfect mixed cells and the mean residence time tau(m) was calculated. The evolution of tau(m) as a function of theta(m) and m(f) is accurately r epresented by a power law relation.