The harvested walnut has a relatively high moisture content of 30% compared with the safe storage moisture content of 8%. One of the common means of reducing the moisture content is by drying. For design of drying and other aeration systems for agricultural products including walnuts, the relationship between the drop in pressure and airflow velocity must be known. An airflow resistance apparatus was designed and manufatured to measure the airflow resistance of walnuts. This apparatus consisted

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... of an air compressor, a rotameter, a cylindrical bin and an inclined U-tube manometer. The pressure, drops at airflow velocities of 0.085 to 0.55 (m 3 /s)/m 2 , were measured at a constant depth of the nuts. Airflow resistance equations were fitted to the measured data. The results showed that, by increasing airflow rates, an increased drop in pressure was achieved through out walnut column. To study the effect of walnut moisture content on airflow resistance, the drop in pressure was measured at different moisture contents levels of 8.6%, 15.5%, 21.3% and 27%. Results indicated that the drop in pressure decreased with increasing moisture content , especially for high airflow rates.