Influence of self-compaction on air-flow resistance of wood chip bulks
- Publikations-Art
- Kongressbeitrag
- Autoren
- Müller, J; Karaj, S; Meissner, K
- Erscheinungsjahr
- 2012
- Tagungsname
- International Conference of Agricultural Engineering CIGR-AgEng2012
- Tagungsort
- Valencia, Spain
- Tagungsdatum
- 8. - 12. Juli 2012
Wood chip bulks are aerated by ambient ore preheated air to reduce mass losses due to respiration and to avoid toxic contamination by microorganisms. To rate the required ventilators properly, the airflow resistance of wood chip bulks have to be known. Objective of this study was to measure airflow resistance under consideration of a gradient of bulk density and hence porosity of a wood chip bulk due to self-compaction. Bulk density and self-compaction were measured via two vertical transparent tubes with 1 m and 2 m height. Air pressure drop experiments were conducted in a vertical transparent pipe with inner diameter of 480 mm and 3 m height, holding a bulk of spruce wood chips with a nominal length of 30 mm. Changes on porosity through the bulk density height were calculates based on compressibility k as the material specific physical property. Results show for average bulk density through the measured points by setting ρ0 to 162 kg/m³ and compressibility k to 9.9x10-5 Pa-1. The thermodynamic model was fitted and the pressure drop per m bulk height was higher in the bottom layer than in the top layer. This can be explained by decreasing porosity from top to bottom of a wood chip bulk due to increasing bulk density caused by self-compaction. Results demonstrated that bulk density measurements of compressible materials as commonly performed in documenting physical properties of agricultural produce are yielding an average density that is only valid for the bulk height they have been measured. Therefore, compressibility and bulk density as a function of bulk height should be included in the canon of physical properties of agricultural commodities like wood chips, hay, straw or silage.