Multiphysics Modelling of Coupled Heat-Mass-Microbial Dynamics in Natural Convection Grain Storage Systems

This study develops a multiphysics computational model that couples heat transfer, moisture migration, and microbial population dynamics in natural convection grain storage systems, advancing the theoretical foundation for optimal grain store design in tropical climates such as Nigeria's. Grain spoilage in storage is driven by the coupled interaction of heat generation from grain respiration and microbial activity, moisture migration driven by temperature gradients, and microbial growth kinetics that depend on temperature and moisture. Existing grain storage models treat these processes in isolation or with simplified coupling, limiting their ability to predict storage outcomes under dynamic ambient conditions. This study develops a coupled partial differential equation model of heat conduction, moisture diffusion, and microbial population dynamics within a grain bulk, implemented using finite element method in COMSOL Multiphysics. Constitutive relationships for maize, sorghum, and rice grain respiration, thermal conductivity, moisture diffusivity, and microbial growth kinetics are determined through systematic laboratory experiments at the National Cereal Research Institute Badeggi. Model validation uses temperature and moisture sensor array data from instrumented grain stores in Niger State and Kaduna State. Findings reveal that the coupled model predicts grain hotspot formation and mould outbreak timing with significantly higher accuracy than uncoupled models, achieving prediction of mould outbreak events within 3 days of actual onset across 18 validation storage episodes. The model identifies optimal store ventilation scheduling strategies that reduce spoilage risk by 58 percent in simulated tropical storage scenarios. The study contributes a theoretically rigorous storage simulation tool and recommends its use for national grain reserve management optimisation.

Keywords: multiphysics modelling, grain storage, heat and mass transfer, microbial dynamics, Nigeria.