Research Paper Effects of mass compaction on airflow resistance through paddy rice grains Jeferson C. da Rocha a,* , Ricardo S. Pohndorf b , Volnei L. Meneghetti c , Maurı´cio de Oliveira a , Moacir C. Elias a a Department of Agroindustrial Science and Technology, Federal University of Pelotas, 96010-900 Pelotas, RS, Brazil b Center of Technological Development/Water Resources Engineering, Federal University of Pelotas, Campus Anglo, 96010-610 Pelotas, RS, Brazil c Federal Institute of Education Science and Technology Farroupilha, Campus Panambi, 98280-000 Panambi, RS, Brazil article info Article history: Received 23 September 2019 Received in revised form 31 January 2020 Accepted 11 March 2020 Keywords: Compaction mass Pack factor Paddy rice grain Pressure drop The effects of compaction pressures at 50, 130, and 210 kPa on airflow resistance on different classes of paddy rice (long thin, long, and short) were evaluated. The pressure drop was analysed by fitting the Shedd, Ergun, and Hukill & Ives models to the experi- mental data. The results indicated that differences in the mass compaction percentages were due to the compaction pressure rather than the distinct characteristics of the different rice classes, and compaction increased predominantly when higher pressure was applied. The applied compaction pressures produced mass compaction percentages of the paddy rice ranging from 2 to 3% for 50 kPa, 7 to 8% for 130 kPa, and 10 to 12% for 210 kPa. The three models applied to analyse the compacted grain mass showed good fit to the experimental data, with high coefficients of determination (R 2 ) for the three compaction pressures and rice classes studied. Based on the average relative errors and the high co- efficients of determination, the Ergun model is most suitable for modelling the pressure drop in rice grains. Another advantage of the Ergun model is that it consistently predicted slightly higher pressure drop values than the experimental data. Thus, there is an added safety factor if this model is used to design aeration systems since the actual pressure drop experienced in the system will be less than the design value. © 2020 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction Aeration is a technology used in grain storage in which airflow is forced through a mass of stored grain. The purpose of aeration is to reduce and standardise temperature to create favourable conditions that preserve grain quality during storage. Any bulk grain deposit will eventually undergo some degree of grain mass compaction, and consequently resulting in increased bulk density (Calderwood, 1973). Studies by Clower, Ross, and White (1973), Thompson and Ross (1983), * Corresponding author. E-mail addresses: rochajcr@gmail.com (J.C. Rocha), ricardoscherer.eng@gmail.com (R.S. Pohndorf), volnei.meneghetti@iffarroupilha. edu.br (V.L. Meneghetti), mauricio@labgraos.com.br (M. Oliveira), eliasmc@uol.com.br (M.C. Elias). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/issn/15375110 biosystems engineering 194 (2020) 28 e39 https://doi.org/10.1016/j.biosystemseng.2020.03.007 1537-5110/© 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.