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 this exchanger the fluid flows as a thin film on a spirally wound fin which forms a spiral staircase inside a tube. The slope θ_m of the spirally wound fin is modifiable. The residence time distribution (RTD) of the film was measured for different fin slopes θ_m and several film flowrates m_f. The flow pattern was then modelled thanks to the DTS software as a cascade of perfect mixed cells and the mean residence time τ_m was calculated. The evolution of τ_m as a function of θ_m and m_f is accurately represented by a power law relation.