Pore structure and airflow resistance of bulk solids

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Bulk solids are mixtures of solid particles and pores filled with air. Many agricultural and food products are processed and stored in the form of bulk solids, such as grain, vegetables, nuts, and fruits. The knowledge of resistance to airflow through bulk solids is critical in the design and operation of processing and storage systems for these products to ensure product quality and minimal use of energy. A typical example is the drying of grain in which hot air is forced to flow through a bed of grain to lower the grain moisture for quality preservation and safe storage. The drying rate (affecting the grain quality) and energy usage are closely related to the airflow resistance of grain. Traditionally, the methods for determining airflow resistance have been empirical for agricultural applications. Theoretically, the airflow resistance of bulk solids is dictated by the nature of flow as well as the pore structure of bulk solids. My research will focus on quantifying the pore structures and their effect on airflow resistance, ultimately developing rational methods for design and operation of bulk solids systems. In the proposed research, we will first develop a numerical model to predict the pore structures in bulk solids. This pore-structure model will then be integrated with a pore-scale fluid flow model to predict airflow through bulk solids. Laboratory experiments will be conducted to quantify the pore structures in grain bulks. Pilot tests will be conducted to measure airflow resistance of grain in storage bins. The results from this research will not only contribute to the fundamental knowledge of bulk solids behaviour and flow through them, but also provide a rational tool for the agriculture and food industry to design and operate bulk solids systems, particularly grain handling and storage systems. The value of Canada's annual grain crops is about $6 billion and a large portion (70%) is exported. High quality is the key in maintaining the competitiveness of Canadian grain in global markets, whereas handling and storage is critical in maintaining the grain quality after harvest. The airflow model developed in this research will assist the grain industry in designing and managing grain storage systems to achieve the best product quality and the least energy usage.