CFD simulation of heat transfer and polyphenol oxidation during tea fermentation

Abstract

This paper describes a computational fluid dynamics (CFD) model developed to simulate airflow, heat transfer and enzymatic oxidation of polyphenols during black tea fermentation. The airflow through the packed bed of macerated tealeaves is modelled by the porous-medium flow equation. Spatial distribution of temperature within the packed bed of tealeaf is obtained by solving the heat transfer equation that incorporates the source heat of enzymatic oxidation and convective heat of airflow. Spatial distributions of polyphenolic compounds involved in enzymatic oxidation of tea fermentation are then predicted using species equations. The rates of depletion of reactants and formation of products of polyphenols are modelled by source/sink terms of the species equations with the rates of reactions related to the temperature. Solutions of the species equations then provide the basis for the calculation of source heat generated by the oxidative reactions. Some preliminary results are presented. The aim is to demonstrate that the CFD model provides a valuable tool to examine the effect of process conditions on the complex reaction kinetics and pathways that are responsible for the formation of polyphenolic compounds during tea fermentation.