CFD Modelling of the 3D Spatial and Temporal Distribution of 1-methylcyclopropene in a Fruit Storage Container

In this paper, a direct model based on explicit geometry of stacked products in boxes was developed and used to study the diffusion, convection and adsorption of 1-methylcyclopropene (1-MCP) gas in cool stores for apple fruit. The discrete element method was employed to generate random stacking of spherical products in a box. A three-dimensional finite volume-based computational fluid dynamics model was developed, verified and used to study the distribution and partitioning of the 1-MCP gas inside loaded container. The study addressed the gas distribution in a 500 L container with or without air circulation. For each case, 80 kg Jonagold apples at 1 A degrees C and a 1-MCP dose of 1 mu L L-1 was used to collect validation data. In the presence of air circulation, diffusion-convection in air and diffusion adsorption in the product was applied. Simulations were performed with an unstructured tetrahedral mesh using the software ANSYS-CFX, a Reynolds-averaged Navier-Stokes solver. The case without air circulation was modelled as a diffusion problem in air and diffusion coupled with adsorption inside the product. Convection-diffusion-adsorption model parameters that were previously developed and validated were applied. The estimated equilibrium distribution of the 1-MCP gas equals 11, 34 and 55 % as unbounded in fruit, bonded in fruit and remaining in container, respectively. Profiles of free (unbounded) and adsorbed (bounded) 1-MCP concentrations inside fruit were estimated for reduced dosages: 0.5, 0.3, 0.1 and 0.02 mu L L-1.