Effective Radial Diffusivities to Model Enhanced Mass and Heat Transfer in Laminar Flow Reactors

Abstract

-Main features of a laminar flow reactor (LFR) are streamline flow and parabolic velocity profile. Consequently, heating and cooling are difficult and there is a large spread in the residence time distribution (RTD). Enhanced heat and mass transfer can be found in coils or corrugated tubes or in the presence of wall roughness, curves, pipe fittings or mechanical vibration. Modeling these cases can be complex because of the induced secondary flow. Objective of this work is to introduce this enhanced transport in the LFR model by means of effective radial diffusivities of heat and mass. Model validation experiments were conducted in a LFR with high wall relative roughness and curves. RTD experiments were compared with model simulations of tracer dispersion to obtain the mass diffusivity. Heat transfer experiments provided the effective thermal diffusivity. Tested fluids were a glycerin/water mixture (Newtonian) and a CMC solution (pseudoplastic). Model was successfully adjusted and parameters were correlated with Reynolds number for flow.