-Enhanced heat transfer in tubes under laminar flow conditions can be found in coils or corrugated tubes or in the presence of high wall relative roughness, curves, pipe fittings or mechanical vibration. Modeling these cases can be complex because of the induced secondary flow. A modification of the Graetz problem for non-Newtonian power-law flow is proposed to take into account the augmented heat transfer by the introduction of an effective radial thermal diffusivity. The induced mixing was modeled as an increased radial heat transfer in a straight tube. Three experiments using a coiled tube and a tubular heat exchanger with high relative wall roughness are presented in order to show how this parameter can be obtained. Results were successfully correlated with Reynolds number. This approach can be useful for modeling laminar flow reactors (LFR) and tubular heat exchangers available in the chemical and food industries.

-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.