3.3 AIRFLOW

Airflow is an important factor in the consideration of temperature and moisture in sugar beet root storage. Rates of both heat and moisture transfer between the sugar beet roots and the air will be driven by the differential in these factors between the two phases, and the resistance of the surface to this transfer. The temperature and humidity of the air inside of the bulk of roots will depend greatly on how much of the ambient air is permitted to flow through the bulk, which in-turn will impact the differential. The resistance of the surface to transfer is proportional to the speed of airflow. There is one known study that directly measures airflow in a bulk of sugar beet roots. Tabil, Kienholz, et al. (2003) measured under controlled conditions the velocity-pressure relationship of air forced through bulks of sugar beet roots with various sizes and foreign material percentages. This has resulted in a series of data on the permeability of the bulk that can be applied in engineering studies of the fluid dynamics in sugar beet post-harvest storage. The lack of studies that directly measure airflow in sugar beet root stores is likely contributed to both the difficulty of the working environment and the more insidious nature of low and variable airflow in comparison to factors like temperature. Airflow rates in the ventilated pile systems are quoted to be between 10 and 20 cubic feet per minute (cfm) per ton of roots (Backer et al., 1979; Downie, 1950), which is equivalent to approximately 0.018 to 0.037 m3/h/t.