Computational fluid dynamics modeling of airflow in walnut drying bins and bin modification effect on airflow

Authors: McIntyre, Joseph; Tumuluru, Jaya Shankar; FUNK, PAUL - Retired ARS Employee; Haff, Ronald; Breksa Iii, Andrew; BUTTS, CHRISTOPHER - Retired ARS Employee

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2024
Publication Date: 8/6/2024
Citation: McIntyre, J.S., Tumuluru, J., Funk, P.A., Haff, R.P., Breksa III, A.P., Butts, C.L. 2024. Computational fluid dynamics modeling of airflow in walnut drying bins and bin modification effect on airflow. Applied Engineering in Agriculture. 40(4):415-426. https://doi.org/10.13031/aea.15836.
DOI: https://doi.org/10.13031/aea.15836

Interpretive Summary: Researchers investigating how to improve walnut drying equipment need a way to quickly and easily determine airflow through walnuts drying in a bin. A computer modeling method developed for airflow through drying in-shell peanuts was tested to see if it would also work to determine airflow through drying in-shell walnuts. The computer modeling method for in-shell peanuts was found to also determine airflow through in-shell walnuts with model results comparing favorably to results of experimentally measured airflow through in-shell walnuts. The computer modeling method was then used to investigate if adding multiple air tubes to the bottom of drying bins that extended up into the drying walnuts improved airflow. The computer model results indicated that adding multiple air tubes to the bottom of a walnut drying bin did change the airflow but did not effectively improve drying batches of walnuts.

Technical Abstract: Drying walnuts in conventional drying bins can result in uneven drying reducing quality and shelf life. Improved designs for drying bins are needed, but direct testing of new configurations of drying bins is expensive and timeconsuming, so there is a need for a more rapid and less expensive method to investigate drying bin designs. An alternative method to direct testing of bins is computational fluid dynamics (CFD) modeling, which can be performed rapidly. CDF modeling could provide researchers with valuable information about airflow through drying walnuts that is impractical to obtain by direct measurement. The CFD modeling method based on permeability previously employed to model airflow through drying in-shell peanuts in a drying trailer was successfully applied to modeling airflow through drying in-shell walnuts in drying bins. The results of the CFD model were validated by finding airflow patterns from the CFD analysis that corresponded to those determined from direct measurements. After validating model results, researchers investigated modifying the design of conventional stadium-style drying bins by adding multiple vented end air tubes of various lengths that extended up into the drying walnuts from the floor of the bin. CFD modeling provided researchers with a way to visualize and quantify airflow passing up through walnuts in the modified bin design and then compare it to airflow passing up through walnuts in an unmodified bin design. Study results indicated that airflow quickly slowed in the modified bin design as air moved away from the ends of the air tubes and airflow between the air tubes was slower when compared to airflow in bins without air tubes. The addition of the air tubes to walnut drying bins while producing small areas of faster airflow did not appreciably increase the overall rate of airflow or result in a more even distribution of airflow. The CFD model analysis indicated that the addition of multiple air tubes that released air from end caps at various levels in the drying walnuts would not be expected to enhance walnut drying.