Resistance of sweet onions to airflow

As an aid in the selection of curing fans, an experiment was conducted to determine airflow versus static pressure gradient for sweet onions (Allium cepa. L) of the cultivar Granex 33 at different stack depths. While held in a column with static pressures measured at progressive heights, onions were tested both as a mixed composition and then as individual grades. The overall relationship of airflow versus static pressure gradient for mixed grades was found to be described by loge Q = loge –5.897 + 0.973 loge P, where Q = airflow and P = pressure gradient, with R 2 for the fit of the curve to the data being 0.96. For individual grades, there was no significant difference (P > 0.05) between the airflow versus pressure gradient curves for each grade: medium, large, and jumbo. The separate curves for individual grades were offset yet approximately parallel with the curve for mixed grades. Compared with other commodities described in ASAE Standard D272.3 (1996), the curve was found to lie between peanuts in the shell and confectionary sunflower seeds, with a slightly steeper slope than for both of these.