Air movement and temperature regime in large stacked apple bins during the initial phases of cold storage

This study presents an in-depth experimental analysis of thermal and airflow behaviour inside large bulk apple bins under typical cold storage conditions. Four instrumented bins were monitored at two vertical levels in a commercial cold room. Temperature sensors tracked fruit cooling in different regions of each bin, while embedded sensors were designed to measure interstitial slow air speeds. Cooling was characterised in two phases: an initial continuous cool-down followed by an intermittent cooling regime. A front bin directly exposed to cold airflow showed rapid cooling at the airflow-exposed face and noticeable temperature fluctuations reflecting ongoing convective cooling. In contrast, a bin located immediately behind the front bin cooled more slowly and experienced no temperature oscillations, indicating cooling dominated by natural convection and conduction. The bin centres cooled much more slowly, highlighting the limitation of cold air penetration. Airflow measurements confirmed that only the front regions of bins received significant forced-air infiltration (approximately 0.08 m s −1 ), whereas interior zones became essentially air-stagnant, with air speed nearly zero, once the fruit cooled. All bins exhibited minor vertical stratification, with top-layer fruit about 0.1 to 0.2 °C warmer than bottom-layer fruit. These findings provide direct evidence of mixed convection cooling in front bins versus purely free-convective cooling or conduction cooling in sheltered bins. The study's insights emphasise the need for improved airflow distribution in cold rooms. Practical strategies, such as improved bin design and airflow management strategies, are suggested to achieve more uniform cooling.