Multiscale coupling analysis and modeling of airflow and heat transfer for warehouse-packaging-kiwifruit under forced-air cooling

This paper develops and verifies a multiscale computational fluid dynamics (CFD) model to investigate the airflow and heat transfer in kiwifruit cold storage under forced-air cooling (FAC). The CFD model incorporates the material properties, geometry, position of kiwifruit and ventilated packaging box, and the detailed structure of the cooling unit. For the multiscale modeling, the material characteristics are described using three interconnected sub-models, focusing each on different spatial scales: the warehouse-scale, packaging-scale, and kiwifruit-scale. In the FAC experiment, the measured airflow and temperature on these three spatial scales were obtained and compared with the simulated results. The data analysis shows that the environmental fluctuations at different scales weaken significantly in a stepwise manner with the cushioning of packaging and fruit flesh, indicating coupling between the spatial scales, which is well reflected in the numerical simulation. The average kiwifruit temperature decreases from 20 to 6 °C in 14.5 h (experimental) and 15.6 h (simulated). Specifically, the average mean absolute error, mean absolute percentage error, and root mean squared error of the predicted airflow and kiwifruit temperature were 0.116 m s⁻¹, 1.26 °C; 26.8%, 14%; and 0.124 m s⁻¹, 1.54 °C, respectively. These results indicate that the multiscale CFD model accurately and efficiently simulates the airflow and spatiotemporal temperature distribution in the given kiwifruit FAC system. Finally, this study provides a reference for accurately simulating large-scale industrial FAC systems and supports optimal decision-making for the design of sustainable kiwifruit cold chains.