29E-4 |
Darcy permeability of food tissues for pressure driven flow of water |
A. K. DATTA, Dept. of Biological & Environmental Engineering, Cornell Univ., 208 Riley-Robb Hall, Ithaca, NY 14853-5701 Like the transport modes of diffusion and capillarity, pressure driven flow, also called Darcy flow, has major implications in moisture and other species transport during food processing. Source of such pressures can be significant internal evaporation as in microwave heating or it can be from shrinkage, as in roasting of meat. However, Darcy (not diffusive) permeability, the parameter characterizing this mode of transport is generally unavailable. The objectives of this study are to measure Darcy permeability of various food tissues to liquid water using a novel instrument, and interpret the data by relating permeability to food structure. A capillary flow porometer (Porous Materials Inc., Ithaca, NY) is used to measure permeability. It works by measuring the amount of water passing through a sample under certain pressure head. Potato samples in the form of cylindrical disks are cut from fresh russet potato. The samples are placed horizontally on a holder and water is pushed through the sample from the top at a number of different pressures. Permeability of fresh potato tissues ranged from 0.0265 - 0.0152 mili Darcy for different pressure values. For permeability to be constant over the entire pressure range, pressure vs. flow rate curve should be linear. Although the data obtained are close to linear, definite departures from linearity are seen signifying changes in the structure of the potato with increased pressure (perhaps compression of the tissue resulting in decreased permeability). The permeability values are also measured for other food tissues such as apple, cucumber and eggplant, and these also provide valuable insight into the fundamental porous structure of these materials. Understanding about Darcy flow would solve an important piece of the puzzle in quantitative understanding of moisture transport in food (that often determines its quality) during processing. This study would provide accurate measurement of the needed permeability data for several food tissues for the first time.
Session 29E, Food Engineering: Transport processes and kinetics
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