Airflow resistance and pressure drop behavior in different conditions of bulk‐stored onion and its dynamic modeling

The knowledge of airflow resistance and distribution pattern in a highly porous-bed commodity like an onion is an important consideration in designing an appropriate ventilation system and for proper selection of fans. The resistance to airflow through bulk onions was determined at the airflow rates range of 0.04-1.0 m(3)/s.m(2), bed depth of 0-100 cm, and scaled and descaled condition of onion at vertical and horizontal position of the onion stock. Three models (Shedd, Hukill and Ives, and Ergun) were investigated to describe pressure drop data of onion bulbs. The pressure drop through bulk onion was increased with an increase in airflow rate and bed depth. Also, pressure drop was 43.5 and 33.3% higher in scaled condition over the descaled condition of bulbs at the vertical and horizontal position of the column, respectively. Shedd model was found to more reliable among three models to describe airflow resistance in bulk of onion bulbs. Practical Applications Onion is perishable vegetable consumed throughout the year. Being a seasonal crop and to fulfill the demand of consumers it must be stored for off seasonal use. Storage of the onion bulbs at ambient and modified environment condition is the most commonly used methods in a tropical climate. But there were huge postharvest losses mainly in the form of physiological weight loss, sprouting, and decay and considerable loss in nutritional qualities. Properly designed aeration, ventilation, and fumigation system is the only way to reduce such losses. Therefore, the understanding of dynamic behavior of applied ventilation and fumigation with its distribution pattern in a highly porous commodity like an onion is a preliminary requirement for the proper design of storage system. Different model based approach to understand flow dynamics could be used in the dimensional design of a storage system in a tropical climate.