A Generalized Model of Pressure Drop Versus Airflow for Bulk Grain
Date
1992
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Masters
Abstract
This study focused on the development of a generalized model to predict the pressure drop versus airflow for many bulk grains under different conditions.
An experimental apparatus was calibrated for the study of the resistance of bulk grain to airflow. Pressure drops through bulk wheat were investigated over an airflow range of 0.754x10-4 to about 0.9 m3/(s.m2), with the moisture content of grain varying from 10% to 26%, and fines and chaff concentration ranging from 5% to 25%. The loose fill, semi-dense fill and dense fill methods were tested. The bulk density of grain varied from 377 kg/m3 to 827 kg/m3. The effect of airflow direction on the resistance of bulk wheat to airflow was also investigated. Haque's, Hunter's and Shedd's equations were modified to predict the effect of various factors on the pressure drop of wheat.
The experimental results showed that airflow resistance of bulk wheat increased linearly with fines concentration and decreased with grain moisture content and chaff density by about 5% which resulted in an increase in airflow resistance of wheat of 39% compared to the values for the loose fill. The resistance of wheat to horizontal airflow was 0.7 times the resistance to vertical airflow.
The pressure drop versus airflow data of wheat, alfalfa seeds, Laird lentil and several other grains that are published by ASAE standard D272.2 were used to develop a generalized pressure drop versus airflow equation. The generalized equation represented pressure drop versus airflow data for different types of grains, different porosities, moisture contents and fines concentration. The effect of properties of airflow on the resistance of bulk grain to airflow was also considered in the generalized equation. A grain specific equation and a modified Leva's equation were also developed. The similarity between those two equations led to a method for estimating the shape factor for irregularly shaped particles.
Eleven pressure drop versus airflow equations were compared. Statistical analysis indicated that the generalized equation developed in this thesis has almost the same goodness of fit to the pressure drop versus airflow data as that of the modified Leva's equation. The generalized equation gives more accurate prediction results than Matthies' equation and Bakker-Arkema's equation. Hunter's equation and Hukill-Ives' equation are good models for use in fitting the pressure drop versus airflow data.
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Degree
Master of Science (M.Sc.)
Department
Agricultural and Bioresource Engineering
Program
Agricultural Engineering