Geometric vs. aerodynamic diameter for modelling airflow resistance of wood chip
- Publication Type
- Contribution to conference
- Authors
- Karaj, S; Meissner, K; Müller, J
- Year of publication
- 2012
- Conference name
- International Conference of Agricultural Engineering CIGR-AgEng2012
- Conference location
- Valencia, Spain
- Conference date
- 8. - 12. July 2012
Drying of biomass is an energy and cost intensive process which needs to be applied before using biomass as fuel. The problem during drying is to overcome the air pressure resistance created through the bulk material. Drying and aeration systems are designed based on airflow resistance, filling depth in storage and mathematical models for pressure drop in the bulk mass. The objective of this study was to measure the hydraulic diameter of spruce wood chip with different geometric size and fit the data obtained to the selected model in order to predict air pressure resistance during drying. Fresh Spruce wood chip materials with 30 and 50 mm nominal size were used as raw material. Air pressure drop experiments were conducted in a three meter vertical transparent pipe designed at Institute for Agrar-Technique Hohenheim, Germany. A mathematical model given from Siegel was taken into consideration in order to exactly determine the air pressure drop. Two methods were used for measuring hydraulic diameter (i) geometric hydraulic diameter (dg) and (ii) aerodynamic hydraulic diameter (da). The results of hydraulic diameter show that aerodynamic diameter method of wood chip was distinctly smaller than geometric diameter method 18.2 mm and 3.70 mm for Spruce 30 mm and 29.3 mm and 5.50 mm for Spruce 50 mm, respectively. Terminal velocity result demonstrates that Spruce 30 mm is more homogenous than Spruce 50 mm nominal size. The selected mathematical model describes the physical expression of air pressure drop and the aerodynamic hydraulic diameter was fitting better than geometric hydraulic diameter.