Modeling of Non-Newtonian Reactive systems in Tubular Reactor

A vast majority of material processing in industry involves homogeneous phase reactions. These reactions are carried out in batch mode as well as continuous mode. The empty tubular reactors are widely used reactor systems for continuous processing in chemical and allied industry. The heat effects due to these reactions necessitate the use of some heat removal/addition system with these reactors. Tubular reactors for Newtonian fluids have been studied extensively experimentally as well as through modeling. A vast majority of reactions involved in polymer processing, food processing, biochemical industries etc. typically involve non-Newtonian behaviour. The modeling studies dealing with non-Newtonian fluids are very limited. The modeling and simulation study of nonNewtonian fluid reactions can lead to obvious benefits over experimental methodology. Most of the studies in non-Newtonian fluids are either based on convective models or on isothermal conditions. Novosad & Ulbrecht (1966) have modeled the reaction of power law fluids under laminar flow conditions, using residence time distribution concept to get conversions, neglecting the diffusional effects. Osborne (1975) studied convective model for non-Newtonian fluid tubular reactor under isothermal conditions. Tracer technique has been used for the systems with unknown rheological properties. For constant wall temperature conditions and adiabatic conditions, nonisothermal tubular polymerizers have been studied using finite volume method, runaway condition having been found (Kleinstreuer & Agarwal, 1986). These studies do not account for non-adiabatic operation and the radial dispersion effects. In actual systems, due to heat exchange from the reactor wall, there is existence of temperature gradients in radial direction. These gradients in temperature influence reaction rates in a given cross section, setting up concentration gradients and the effect further gets magnified due to rheological parameters. In this study, modeling of reactions of non-Newtonian fluids in tubular reactors with radial dispersion has been done. The reaction of non-Newtonian fluids has been modeled in non-isothermal non-adiabatic tubular reactor. Assuming a first order irreversible endothermic reaction of Ostwald-de-Waele power law fluids for the assumptions of constant wall temperature and axial symmetry, the 2-D model is used to generate concentration and temperature profiles in axial and radial directions.