New transformation proposed for improving CFD simulation of free radical polymerization reactions in microreactors

A new yet simple transformation is proposed to significantly improve the accuracy of computational fluid dynamics (CFD) modeling and simulations of free radical polymerization (FRP) reactions carried out especially in flow microreactors. The new transformation makes the kinetic rate coefficients dimensionless in terms of concentration. To that extent, the chemical data (chemical species concentration and kinetic rate coefficients values) can be fed in original molar form instead of usual mass form to CFD software package while simulating chemical species as passive scalars. The normalization of various variables (passive scalars) helps in reducing the numerical stiffness as well as numerical errors during simulations. Another advantage of this new transformation is that the expression for transformed reaction rate equations remains unchanged thus enabling an easy coding and debugging process. The new transformation was first validated through numerical simulation against theoretical analytical solution of FRP for homogeneous batch reactor. It was then validated through CFD simulation against published experimental data for FRP in coiled tube microreactor under steady-state flow condition. It has also been demonstrated that in CFD simulations of FRP in flow microreactors, significant error arises for the prediction of number-average chain length (and thus $${\text{MW}}_{n}$$ , number-average molecular weight) from the use of chemical data in mass form instead of original molar form. This new transformation is thus found to be more suitable for CFD simulations in flow reactors compared to previous Zhu’s transformation.