36D-30 |
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J. LEE, K. L. McCarthy, and M. J. McCarthy. Dept. of Food Science and Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616 Porous media in food processing includes spent grains in beer processing and coffee grinds and tea leaves in brewing. Understanding the fluid drainage phenomena in porous food systems, in terms of Darcy's law, is important for maintaining food quality and process efficiency. The objective of this study was to experimentally evaluate and mathematically model fluid drainage using both model bead systems and food systems. A permeameter was constructed with a plexiglass cylinder (5 cm diameter) for flow rate and pressure drop measurements over bed heights of 9 cm. The beds were 0.5 mm glass beads, 1 mm glass beads, spent grains, and coffee grinds. Hydraulic conductivities were determined from linear regression of bulk velocity versus pressure drop curves. In addition to Darcy's law, the equation of continuity was used to describe fluid flow through the porous beds for the transient draining process. Unsteady state drainage was monitored by mass collection over the draining time for comparison to the theoretical model. Hydraulic conductivity values were 0.0031, 0.0078, 0.0135, and 0.0048 m/s for 0.5 mm beads, 1 mm beads, spent grains, and coffee grinds respectively. These values were incorporated into the unsteady state model. The agreement between the unsteady state model and experimental drainage results was good for a porous matrix that does not compress during steady state flow (e.g., the beds of glass beads). The model requires modification for structural changes (compaction) that occur with the spent grains and coffee grinds. Although Darcy's law was developed to describe steady state flows, it can be used in the study of unsteady state drainage flow. This work assists in the development of the appropriate form of the unsteady state model for food systems.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |